IWT project 000148 - KU Leuven · 2010. 11. 11. · IWT project 020209 Predictive tools for...

IWT project 020209

Predictive tools for permeability, mechanical and electro-magnetic properties of fibrous assemblies:

Modelling, simulations and experimental verification

Technical report FINAL

01/09/2003 – 30/11/2007

Leuven 2008

IWT PROJECT 020209 – FINAL TECHNICAL REPORT 2

CONTENTS

1 OVERVIEW OF THE WORK PERFORMED IN THE YEAR 3 OF THE PROJECT 4

Work Package 1. Deformability of fibrous assemblies 4 WP 1.1. Theory and predictive algorithms for internal structure of random fibre assemblies in relaxed state 4 WP 1.2. Theory and predictive algorithms for deformability of textile fabrics 6 WP 1.3. Theory and predictive algorithms for deformability of random fibre assemblies 7

WP 1.4. Experimental verification 7 WP 1.5. Development of software tools 10

Work package 2: Mechanical properties of fibre/textile reinforced composites 11 WP 2.1. Data organisation and procedures for transferring the geometrical information of the deformed reinforcement 11 WP 2.2. Solvers for the stress-strain state of a 3D shaped unit cell in a textile composite 12 WP 2.3. Parametric study and experimental validation 14 WP 2.4. Development of software tools 14

Work package 3: Permeability of fibrous assemblies 17 WP 3.1 Data organisation and procedures for transfer of geometrical information 17 WP 3.2 Predictive algorithms for permeability based on the lattice Boltzman method 17 WP 3.3 Predictive algorithms for permeability based on an incompressible Navier-Stokes PDE solver 17 WP 3.4 Parametric study and experimental validation 19 WP 3.5 Software tools 21

Work package 4: Electro-magnetic properties of conductive fibre assemblies 22 WP 4.1 Data organisation and procedures for transfer of geometrical information 22

The thin wire approximation 22

The staircase approximation 22

Practical transfer of topological data 23 WP 4.2 Theory and predictive algorithms for effective permittivity, permeability, and conductivity of conducting fibre assemblies 25 WP 4.3 Procedures for experimental determination of effective permittivity, permeability, and conductivity of conducting fibre assemblies 27 WP 4.4 Validation. 32 WP 4.5 Development of software tools 36

2 PUBLICATIONS 38

I. Book chapters 38

II. International peer-reviewed articles 38

III. International proceedings, fully published 40

IV. Theses 47

3 CONCLUSION 48


Accomplishments 48

Valorisation 49

Interaction with the User's Committee 50


1 OVERVIEW OF THE WORK PERFORMED IN THE YEAR 3 OF THE PROJECT

Work Package 1. Deformability of fibrous assemblies

WP 1.1. Theory and predictive algorithms for internal structure of random fibre assemblies in relaxed state As stated in the project description, “The model will distinguish between two cases: an assembly of short fibres, and an assembly of long randomly interlaced fibres. The former case can be addressed using an approximation of straight fibres. The latter asks for a more complex treatment of randomly placed fibre paths”.

A. Work on random assembly of short fibres – reinforcement of a composite material, with the geometry is defined by random distribution, governed by the injection flow – has been finished in the reporting period.

The use of glass fibre reinforced polypropylene composites in engineering applications increases more and more these last years. Especially, long glass fibre polypropylene (LGFPP) composites offer specific advantages over classical laminates such as higher production rates at lower costs, improved thermal and mechanical properties. However during injection molding of the part fibre breakage occurs, leading to a distribution of fibre lengths inside the material. Moreover a change in orientation of the fibres also takes place during injection process, leading to micro-structural variations that affect the overall mechanical properties of the composite. Hence, the final properties of LGFPP composite are highly dependent on the processing conditions of the part. Therefore the effect of fibre length on the mechanical properties of injection molded LGFPP composites must be combined with the effect of fibre orientation changes because the two effects would determine the final mechanical properties of these composite materials

Microstructural characterization of LGFPP was performed, using the resin burnout technique to get the fibre length distribution and optical microscopy method (applied to a polished cross-section) to obtain the fibre orientation distribution. Fibre and matrix properties and experimental data on fibre length and orientation distributions (Figure 1) were used as input in a software based on Mori and Tanaka method. This was coupled with a Monte-Carlo simulation, which was developed to predict local mechanical properties of LGFPP composites, taking into account the real microstructure in the part.

Figure 1 Measured fibre length and orientation distribution for LGFPP composite

B. Assembly of long randomly interlaced fibres – non-woven materials: the work has started in the year 2 of the project.

The geometrical description of the internal structure of non-woven material is based on the following data:

1. Fibre volume fraction of the material. For a bulk material this value is given, for a non-woven fabric the fibre volume fraction is calculated using the fabric areal density and thickness.

2. Fibre geometrical (diameter, linear density) and mechanical properties 3. Distribution of the fibre length


4. Fibre orientation distribution, given as 2nd order orientation tensor 5. Fibre waviness, represented by a combination of random harmonic functions:

1 1 2 2 2( ) sin sins ss A n nL L

π πψ ψ⎛ ⎞⎛ ⎞ ⎛= + +⎜ ⎟⎜ ⎟ ⎜⎝ ⎠ ⎝⎝ ⎠

1r r r ⎞+ ⎟⎠

The geometrical model realise these parameters of the individual fibres and the assembly via a hierarchy of modelled objects:

1. Straight fibre (a “stick”), characterised by fibre properties, length and orientation

2. Curved fibre, modelled as consisting of several straight intervals, and characterised by fibre properties, total length, averaged orientation of the intervals and shape of the fibre, generated using the given waviness parameters

3. Random realisation of an assembly of a given number of (curved or straight) fibres. The boundaries of the unit cell of the material (where all the centres of gravity of the fibres are randomly palced) are calculated based on the given fibre volume fraction and thickness of the non-woven fabric. The given number of fibres is randomly generated by the model according to the given distributions of length, orientation and waviness of the fibres. In the case of non-woven fabric (as opposed to bulk material) the orientation is corrected to fit all the fibres inside the given thickness of the fabric. The random realisation of non-woven assembly is considered periodic; the degree of stochastisity included in the description is regulated by the number of the fibres in the assembly.

4. A set of given number of random realisations, allowing Monte-Carlo calculations of the average values and scatter of parameters of the material (number of contacts, pore size, mechanical properties, permeability…)

Figure 2 Modelled and real fibrous structure of DryWeb17; calculated nodes-links model

The geometrical model, implemented in the software NoWoTex, generates random realisation of the fibre assembly based on the given statistical parameters of the material. The assembly can be mono-fibrous, or a blend of two or more fibre types.

The following structural properties are then calculated for the random realisation (Figure 2):

1. Contacts between the fibres are analysed. The calculations are based on a simple geometry of intersection of two straight fibres, which is applied to the intervals of the curved fibres. The data on the intersections is processed into a structure of contacts. The contacts are classified according to their physical nature (friction contact or thermo-welded contact), and the mechanical parameters of the contact are stored correspondingly (friction coefficient or stiffness of the welded material).

2. Based on the contacts structure, the network model, consisting of nodes (contacts) and straight links is created. The straight links retain mechanical properties of the curved


fibres forming them. The nodes-links model will be used for modelling of the mechanical behaviour of the non-woven material.

Visualisation of the assembly realisation is built using OpenGL algorithms. The visualisation accounts for the contacts, deviating the fibre accordingly.

On the request from Libeltex the dust creation when cutting a non-woven fabric has been evaluated. The algorithm, implemented in NoWoTex (new modeule has been developed), calculates the mass fraction of loose fibres (fibres without thermal bonds with others) in a non-woven fabric. The typical values for the fabrics of Libeltex give the mass fraction of loose fibres about 0.08%. When applied to the problem of loosening the dust from a cut of the fabric, this results in a value of about 1 g of dust per 1 m of the cut, which corresponds to the experimantal observations of Libeltex.

WP 1.2. Theory and predictive algorithms for deformability of textile fabrics

In the reporting period the work went on in the following directions (Figure 5):

− Deformability of woven fabrics

− Numerical experiments: Parametric study of glass reinforcements

The model of shear of woven fabrics accounts for different sources of the fabric resistance to shear: friction, compression of the yarns, yarns (un)bending, Possible simultaneous action of shear and (pre)tension is taken into account. The model predicts the typical features of a shear diagram: initial frictional resistance, low initial modulus, jamming of the yarns and dramatic increase of the resistance for higher shear angles. Input data for the simulation requires KES-F characterization of the yarns in bending, tension, compression and friction. The model produces internal geometry of the sheared fabric as well, which can be used in local micromechanical and permeability calculation for a deformed preform. The model is implemented in “virtual textile” software WiseTex.

Forming simulations of textile preforms require description of the shear resistance of the preform plies. Experimental determination of the shear diagrams is time consuming, costly and require highly qualified personnel. Typical glass rovings exhibit quite consistent behaviour; it is possible to derive “master curves” for bending, compression and tensile behaviour of them, in function of linear density of the rovings. Based on these master curves, parametrical study of the shear resistance of glass preforms has been carried out. Shear diagrams were calculated using the WiseTex model for plain, twill and 5-harness satin square fabrics. The diagrams were then

processed to create analytical expressions of the shear diagrams: 0tan

tan *

a

T T γγ

⎛ ⎞= + ⎜

⎝ ⎠⎟ , where T

is the shear force, γ is the shear angle, T0, a and γ* are parameters, tabulated as functions of yarn linear density, fabric tightness and pretension. The resulting family of shear diagrams was verified against experimental data.

X

Y

X0

Y0

Fx

Fy

T

O

Qθ1 θ2

T1 T2

RR2

00.10.20.30.40.50.6

0 20 40

gamma,°

T, N

/mm

Figure 3 Force components used in the model of shear of woven fabrics; shear diagrams:

comparison of the calculations (lines) and measurements (points)


WP 1.3. Theory and predictive algorithms for deformability of random fibre assemblies

A simple micro-mechanical model has been developed to predict the anisotropy in the tensile properties of thermal bonded nonwoven structures. The model is based on orientation averaging of tensile resistance of straight elements of the fibres between the bonds that neglects the crimp of the fibres, changes in the fibre orientation during the deformation, compliance of the bonds and bending deformation of the fibres. The model uses on the averaging schemes of the bond distribution and fibre orientation. The calculations correlate well with the observed behaviour and with the directional anisotropy and with the peculiarities of the structural characteristics (different fineness of the fibres and observed porosity).

α

αbb

1=αA

MachineDirection

b

θ

ϕ

α

X

Y

Z

Bond

θsinb

)sin(sinb αϕθ −

)cos(sinb αϕθ −

Fiber

β

'fl

fl

βsinfl

βcosfl

βε cosfl

O A

B

CB'A'

A

Figure 4 Calculation of the initial tensile modulus: (a) volume of the fabric sample having a unit

cross-sectional area; (b) projections of the fibre element between two bonds; (c) scheme for the fibre extension.

WP 1.4. Experimental verification

Experimental work has been performed in studying:

− Deformability of non-crimp fabrics

− Experimental techniques: KES-F vs Picture frame vs Biaxial tester

− Deformability of non-woven fabrics

Experimental program (Figure 5) has been carried out on glass, glass/PP and carbon woven and non-cripm fabrics – typical reinforcement for composites. Three experimental techniques were used: KES-F for low shear, picture frame and shear under controlled transversal tension of biaxial tester. Full field strain registration used to control uniformity of the shear in the sample. The results show good correspondence between different methods. Possible errors in the picture frame tests due to difference between average strain of the fabric and frame shear angle are demonstrated; the errors can be eliminated using full field strain registration. Biaxial tester provides unique possibility to study shear under a given tension of the sample. Experimental results compare well with the theoretical predictions.


a) b) c) Figure 5 Carbon-non-crimp fabric (a) and glass woven fabric (b) on the picture frame; (c) shear

angle field

Experimental program on non-woven fabrics was performed for two types of fabrics, provided by Libeltex: Dry Web T17 and Dry Web T18 (in the scope of Master thesis of Thanh Ngo, KULeuven).

The experimental program consisted of the following tests:

1. Orientation of the fibres in a non-woven fabric. These tests were performed in KULeuven using the technique of cross-sectioning the stabilised fabric in different directions and measuring ellipsoidal cross-sections of the fibres using image processing software (Figure 6). The parallel tests were performed (by an order of Libeltex) in Alassio Industries, USA, using automated inspection of shadow photographs of the fabrics. The comparison of the results revealed important drawbacks of the automated inspection.

2. Length and crimp of the fibres. These tests were performed by Centexbel – sub-contractor of the project

Tension for different orientations of the applied load. The tests have revealed a pronounced anisotropy of the fabrics, corresponding to the observed orientation distribution of the fibres (Figure 7).

( )( )

( )

( )( )

int

1

;cos

, 1...cos

ii

i

ii

is

k

k ds i N

−

Π

Ψ ΠΨ =

⋅

⎛ ⎞Ψ Π⎜ ⎟= =⎜ ⎟⋅⎝ ⎠∫

ff

f

INTf

ff n

ff n

Figure 6 Measurements of the orientation of the fibres


0

90

45

67.5°

22.5° Tension Test DryWeb T17

-0.0001

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0 0.2 0.4 0.6 0.8

Strain

Stre

ss (N

/mm

) 0 degree22,5 degree45 degree67,5 degree90 degree

Picture Frame DryWebT17

-0.02

-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0 5 10 15 20 25

Displacement(mm)

Forc

e(kN

)

1st2st3st

Figure 7 Tension and shear tests on non-woven fabrics

Shear (picture frame tests – Figure 7). The first cycle of the shear test corresponds to the process of “conditioning” the fabric, which accommodates itself to the (not ideal) clamping in the frame; the second and the third cycles give true measurement of the shear resistance.

The tensile behaviour of through-air bonded structure of basis weight 31 g/m2 has been investigated using environmental scanning electron microscope (ESEM) by identifying the regions of deformation. Since, ESEM offers the possibility of performing in situ mechanical testing along with the visual observations. The stress-strain curve of through-air bonded structure has been related to visual observations obtained from ESEM. The mechanism of load transfer is dependent upon the initial orientation of the fibres in the through-air bonded structure. It was found that the reorientation of the fibres during the load transfer can cause a delay in bearing the load that can lead to non-linear behaviour in the stress-strain curve. The anisotropy in the through-air bonded structure has been analysed quantitatively based on the ESEM images.

Figure 8 SEM images of a non-vowen fabric deformed at tension at strains of a) 2.5% b) 6.4% c)

8.1% d) 9.4% e) 12.1 % f) 14 %.


WP 1.5. Development of software tools

A new versions of the WiseTex package has been released:

WiseTex 2.4: Modifications in the model of shear of multilayered stitched preforms; export to FE package ANSYS (Tool: FETex); export to virtual reality (Tool: VRTex) (Figure 9)

WiseTex 2.5: Added: description of fibre distribution inside yarns and fibrous plies; improved model of three-axial braids. FETex: added manual for modification of volumes of the yarns to avoid interpenetrations (manual operations with intermediate FE problem)

and NoWoTex software has been developed (Figure 10)

a) b) Figure 9 FE model of pores in non-crimp fabric, FETex (a) virtual reality world, VRTex (b)

Figure 10 GUI of NoWoTex software


Work package 2: Mechanical properties of fibre/textile reinforced composites

WP 2.1. Data organisation and procedures for transferring the geometrical information of the deformed reinforcement

A. WiseTex models

The geometrical and mechanical model of textiles, implemented in the software package WiseTex, provides full description of the internal geometry of a fabric: 2D and 3D woven, two- and three-axial braided, knitted, multi-axial multi-ply stitched (non-crimp fabric). The geometry in the relaxed state of the fabric is constructed using principle of minimum energy, calculating the equilibrium of yarn interaction. For NCF the geometrical description includes fibrous plies as well as the stitching yarn. Input data include: (1) Yarn properties: geometry of the cross-section, compression, bending, frictional and tensile behaviour, fibrous content; (2) Yarn interlacing pattern; (3) Yarn spacing within the fabric repeat.

Models of the internal structure of the fabric in the relaxed state, fabric compression, bi- and uniaxial tension and shear are also based on energy balance and calculate internal structure of the fabric, as well as load-deformation relation, producing paths of midlines of the yarns and (changing along the yarn) dimensions of the cross-sections.

When used in numerical calculations, the yarn description given as arrays of values for a set of cross-sections along the yarn midline. The following parameters of each cross-section are given (Figure 11):

− Co-ordinates of the cross-section centre point O=(x,y,z) − Tangent, normal and bi-normal to the yarn heart-line t, n, b − Vectors of (orthogonal) axis of the contour a1, a2 − Dimensions in the directions of the axis d1, d2

O

r(s)

X Y

Z

α

a

t

a1

a2

Od2 d1

b

P f

Vf

c

Figure 11 Set of cross-sections defining a yarn shape in a unit cell (a), parameters of a cross-section (b) and properties of fibres in the vicinity of point P (c).

B. NoWoTex models

The same approach was used for creating voxel data arrays for non-crimp fabrics. For a random realisation of a non-woven fibre assembly, consisting of crimped fibres, comprised of straight cylindrical intervals, the algorithms of Figure 11 were used, resulting in binary voxel description of the unit cell volume. The voxel description is further transferred into permeability models or can be used for visualisation. Figure 12 illustrates the data flow from NoWoTex to Lattice Boltzmann/FE solver, and to a freeware MayaVi* for 3D visualisation via the specially developed programe ParseTex, which parses the text file with description of the voxels and creates VTK format file, readable by MayaVi (and other 3D visualisers).

An alternative approach is used for calculation of mechanical properties of composites using inclusion method. In this case each of the intervals of crimped fibres (or each straight fibre) is

* http://mayavi.sourceforge.net/


represented by an inclusion in the matrix. The data on the array of these inclusions is transferred to the inclusion model solver.

NoWoTexNoWoTex ParseTexvoxel

MayaViFlowTex

VTK

Figure 12 Data flow for voxel descripton of geometry of non-woven fabric

WP 2.2. Solvers for the stress-strain state of a 3D shaped unit cell in a textile composite

A. Short fibre reinforced composites

A software programme based on the Mori and Tanaka model was developed to predict local mechanical properties of LGFPP. The fibres in the unit cell are modeled by inclusions of an ellipsoid shape. The length and orientation of each inclusion is determined individually by sampling the experimental distribution for length, in-plane and out of plane orientations respectively, using a Monte Carlo simulation. In this way, each inclusion is assigned a unique, independent value for length, in plane orientation and out of plane orientation. Knowing the materials properties, the elastic micro-mechanical calculation can then be performed giving the total stiffness tensor of the composite material (Figure 13).

Figure 13 Longitudinal modulus obtained from different models: Mori and Tanaka (M-T),

selfconsistent (S-C), Tsai-Halpin (T-H), Cox, Finite Element Analysis (FEA) with l = 3 mm; results of calculations accounting for the fibre debonding

The model of damage considers several types of damage (matrix failure, fibre breakage, interfacial degradation…), which can occur in composite materials leading to a degradation of its overall mechanical properties. Fibre breakage has to be considered since it reduces the efficiency of the fibre-matrix load transfer. Moreover, in case of discontinuous long fibre composites, the interface between the matrix and the fibre is a critical zone for damage accumulation.

Consequently, to model correctly the mechanical behaviour of the composite material, the fibre-matrix debonding as well as the fibre breakage must be taken into account. The Coulomb criterion is used to describe the debonding. If the Coulomb criterion is satisfied in one location along the fibre or in one surface section on the cross-section of the fibre, then the fibre is considered partially debonded. Once debonded the isotropic fibre is replaced by isotropic matrix decreasing hence the total volume fraction of fibres in the unit cell (which is adjusted in the further calculations), and consequently reducing the overall stiffness of the composite. The analysis is then continued in a similar way for the remaining non-debonded fibres (Figure 13).


B. FE modelling of non-orthogonal (sheared) unit cell of textile composites

Consider a typical problem of meso modelling of a unit cell of a textile composite under loading conditions representing its actual loading in a composite part. The following tasks can be performed:

⎯ For the given applied loading (which may include also thermal and cure stresses) calculate stress-strain fields inside the unit cell;

⎯ Assess stress-strain concentrations and identify damage sites; ⎯ When damage occurs, recalculate local mechanical properties of the impregnated yarns

and matrix and recalculate homogenised properties of the damaged composite. These calculations may proceed for increasing loading (along a certain loading path) to calculate non-linear behaviour of damaged composite.

⎯ Calculate the homogenised properties of the composite material in undamaged or damaged state;

The output of meso-FE modeling may be:

⎯ Details of the stress-strain fields in the unit cell ⎯ Influence of details of the textile architecture on meso-scale: voids; uneven distribution

of fibres inside yarns/plies; non-ideal local geometry of compacted yarns etc. ⎯ Stress-strain concentrations, hence thresholds of the damage initiation ⎯ Damage development on meso-scale and deterioration of the homogenised mechanical

properties

⎯ Material models (homogenised) for elastic regime and non-linear behaviour of composite, for undeformed and deformed (compression, shear, biaxial tension) state, to be used in macro-calculations.

3

2

1

4 X1

X2

A’

A A’’

A A’’

b1

b2

B

B’’

B B

B’

b1 b2

b Figure 14 Assigning periodic boundary conditions to a unit cell of 3-axial braid and reducing the

size of the FE model

The stress-strain fields in the unit cell should have the same properties of translational symmetry as the unit cell itself. Conditions of periodicity for a given average deformation tensor (given by macro-conditions of the test or by local results of macro-simulation) are implemented in FE packages using apparatus of constrain equations, providing that the nodes on the opposite facets correspond one to another. This means that the mesh on the opposite facets should be exactly identical, which is not necessary achieved by automatic meshing engines. To reach the goal, the nodes of the boundary facets are copied and assembled into surface shell, which is meshed and “glued” to the unit cell volume. The shell is copied and “glued” also to the opposite facet of the unit cell. Then the unit cell is meshed; because of the previously meshed shells on the opposite facets, the mesh on the facets repeats the mesh on the shells, which is identical on both of them.


After meshing the shells are deleted. When the model is reduced using the symmetry of the reinforcement geometry, the systematic procedure of.Whitcomb is used for deriving boundary conditions for partial unit cells with periodic microstructure (Figure 14).

WP 2.3. Parametric study and experimental validation

A 3-axial braided carbon fabric and carbon/epoxy composite based on it has been thoroughly studied. The internal geometry of the composite and fibrous structure of the yarns was studied using micrographs of cross-sections. The mechanical behaviour of the composite was studied in tension in two directions (along and across the production direction). The strain of the samples was monitored using strain-mapping ARAMIS system, which captures strain field in the centre of the sample on the length of 50 mm. The averaged result of the strain-mapping was used to accurately characterise the strain in the middle of the sample rather then the machine readings. The accuracy of the averaged strain was controlled in comparison with the longitudinal extensometer readings (the extensometer has to be removed before fracture of the sample, but strain-mapping can continue). Acoustic emission was used to monitor the damage development; X-ray inspection and micrograph (on the cross-sections) study of the samples loaded to pre-defined strain levels provide thorough characterisation of damage, which is compared with the m-FE modelling predictions (Figure 15, Figure 17).

ε1 ε2

Figure 15 Three-axial braided fabric and the registered (X-ray) damage patterns

WP 2.4. Development of software tools

A. New version of WiseTex 2.5 package includes TexComp software for micromechanical modelling


WiseTex:un-sheared geometryof a unit cellmechanicalproperties of fibers

QUIK-FORM files:mesh definitiondirection of fibers

Results used forsimulations in SYSPLY

Data sheetsTexComp

READ NEXTCARD

READα1 & α2

CALCULATE γ& SHEARFABRIC

CALCULATES

YES

CARD ISELEMENT?

NO

CALCULATEϕ

STORERESULTS

EOF?

NO

YES

WRITERESULTS TO

FILE

*_drap3D.ps

*.WFA

MATRIXPROPERTIES

*_drap3d_KUL.txt

CALCULATE

S

Figure 16 Data flow of WiseTex/TexComp/QuikForm/SYSPLY software

A textile preform undergoes shear deformations when shaped into a 3D part. These deformations vary from point to point, changing the local properties of the composite part. The theoretical methods, implemented in software packages (WiseTex), allow calculation of the local stiffness in relation to the local deformation of performs, using meso-level description of the geometry of the unit cell of the reinforcement. The local deformation is predicted via simulation (QUIKFORM), and used together with the output of TexComp in FE packages (SYSPLY) as a material property data. The integrated model is implemented in a new version of SYSPLY software. It allows calculating for composites reinforced by woven or braided fabrics.

In the reporting period KUL-MTM has developed standalone libraries of WiseTex and TexComp modules, which are integrated in SYSPLY.

An integrated software tool WiseTex/TexComp/QUIKFORM/SYSPLY performs structural FE modelling of textile composites parts, accounting for peculiarities of the internal structure of deformed textile (woven or braided) reinforcement. This allows more accurate calculation of stresses and strains compared with traditional structural analysis tools based on laminate theory and not accounting for the reinforcement architecture.

The integrated SYSPLY version will be released by ESI in 2008.

B. Cooperation with Osaka University (Prof Zako) has led to the development of software MeshTex/SACOM for finite element simulation of woven composites, integrated with WiseTex (Figure 17).


Figure 17 FE mesh and strain field in a 3D woven fabric, calculated with (MeshTex – SACOM

software; damage in 3-axial braided composite, simulated in ANSYS

B. Macros for ANSYS package has been developed, allowing easy definition of periodic boundary conditions for non-orthogonal unit cells (Figure 17)

D. NoWoTex software includes Mori-Tanaca solver for calculation of mechanical properties of short fibre composites


Work package 3: Permeability of fibrous assemblies

WP 3.1 Data organisation and procedures for transfer of geometrical information

The fibrous structure of the yarns and mats, or, more generally, the fibrous structure of the unit cell is described as follows. Consider a point P and fibrous assembly in the vicinity of this point (Figure 11c). The fibrous assembly can be characterised by physical and mechanical parameters of the fibres near the point (which are not necessarily the same in all points of the fabric), fibre volume fraction Vf and direction f of them. If the point does not lie inside a yarn or a mat, then Vf=0 and f is not defined. For a point inside a yarn or a mat, fibrous properties are easily calculated, providing that the fibrous structure of the yarn/mat in the virgin state and its dependency of local compression of the yarn/mat, bending and twisting of the yarn are given.

Consider a point P, and s is a coordinate along the yarn midline. Searching the cross-sections of the yarns, cross-sections Si = S(si) and Si+1 = S(si+1) containing between their planes the point P, are found (binary search in the unit cell volume is employed to speed up the calculations). Then, using interpolation by s, the cross-section S(s), which plane contains the point P, is built. Using the dimensions of the cross-section S, for a given shape of it, point P is identified as lying inside or outside the yarn. In the former case, with the position of the point P inside the yarn known, using the model of the yarn microstructure, the parameters of fibrous assembly in the vicinity of the point P are calculated.

Then, the local permeability inside the yarn along (subscript l) and across (subscript t) the fibres is calculated with the formulae of Berdichevsky and Phelan:

( )(2

2

1ln 3 132l f )

f f

dK V VV V

⎛ ⎞= − − −⎜ ⎟⎜ ⎟

⎝ ⎠f

5224 1

49 2tf

dKVπ

π

⎛ ⎞= −⎜ ⎟⎜ ⎟

⎝ ⎠.

WP 3.2 Predictive algorithms for permeability based on the lattice Boltzman method

FlowTex software (see WP 3.5) has been released. The lattice Boltzmann solver is implemented in the generalised VoxFlow application for voxel description of porosity of a unit cell (which is produced by any of the geometrical software tools, see WP 1.5. Development of software tools). The voxel description is used for textiles (see below) and for non-woven materials (WP 2.1. Data organisation and procedures for transferring the geometrical information of the deformed reinforcement) WP 3.3 Predictive algorithms for permeability based on an incompressible Navier-Stokes PDE solver

A feasibility and parameter study with the parallel Navier-Stokes solver developed by the Institute for Applied Mathematics of the University of Bonn led to promising results. The code solves the Navier-Stokes equations using a finite difference discretization on a staggered grid. We have adapted the code so that it can be applied for the simulation of a flow trough a porous medium in a unit cell. Therefore, extra boundary conditions have been implemented: a) periodic boundary conditions in three dimensions for the velocity components; b) for the pressure, periodic boundary conditions in two directions and periodic boundary conditions up to a gradient in the third direction. These boundary conditions were not available in the original code.

A fast and straightforward setup of the geometry is implemented: the pixels of the geometry description are directly transferred to the calculation grid. Intra yarn flow depends on the local permeability (see WP3.1). Including this dependency into the Navier-Stokes equations leads to the Navier-Stokes-Brinkman equations. The solver has been extended to solve these equations.


A method to calculate the homogenised permeability for the representative volume element is added. The permeability is calculated according to Darcy’s law:

P

vK

∇= νρ

with v the average velocity over a (random) 2D-cut, P∇ the imposed pressure gradient, ν

the viscosity and ρ the density. Convergence of the permeability can be used as stopping criterion.

Parallel square array

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

0 10 20 30 40 50 60 70

Fiber volume fraction

Pe

rme

ab

ilit

y,

mm

2

Flow Along fibersAlong, calc LBAlong, calc FD-NSFlow Trans fibersTrans, calc LBTrans, calc FD-NS

(a)

Permeability PSA- Vf 60%

0.001

0.01

0.1

1

0.000001 0.00001 0.0001 0.001 0.01 0.1 1

Tow Permeability / Rf^2

Perm

eabi

lity

/ Rf^

2

K_along K_trans K_along_solid K_trans_solid (b)

(c) (d) Figure 18 Validation results: (a) square array of parallel impermeable cylinders with different radii; (b) permeable cylinder with varying local permeability; (c) Validation results: comparison between experimental and numerical results for two non-wovens (nonw) and two woven fabrics (PWF and MFF); (d) Streamlines of an x-flow through Natte 2115

The solver is validated on simple test cases as well as on complex geometries: For a array of parallel impermeable cylinders with different radii, the results of the solver are compared with theoretical values and results of the Lattice Boltzmann solver (WP 3.2), see Figure 18a. These results indicate that both solvers give correct results. The results for a permeable cylinder with varying local permeability is shown in Figure 18b. For this test case, no theoretical results are known, but the results of the Navier-Stokes-Brinkmann solver for vanishing local permeability converge to the solid case.

The Monofilament fabric Natte 2115 (MFF) and the Syncoglass plain woven fabric (PWF) are more realistic structures which are close to actual textile reinforcements, and for which experimental permeability results are available. Also for two non-wovens materials experimental data is compared with numerical results in Figure 18c. For these the different


textiles and different volume fractions, acceptable correspondence between the numerical and experimental values is obtained.

Although the results of the simulations are accurate, the computational cost was high. Therefore two modification to speed-up the calculations, were implemented, in close cooperation with the University of Bonn.

The basis version of the Navier-Stokes solver, uses an explicit time-stepping procedure to find the steady state solution. Explicit time-stepping has however the disadvantage of a strict time step restriction. This yields a large amount of time-steps, and thus a long computation time. Therefore, an semi-implicit time-stepping method was implemented. With this method, larger time-steps can be taken, and thus less time-steps are needed to reach the steady state. Although more computational work per time-step has to be done, the total computation time was reduced by a factor 10.

For the non-linear Navier-Stokes equations, time-stepping is one of the better options to compute the steady state solution. Numerical experiments however, showed that the non-linear convective term of the Navier-Stokes equations is negligible in comparison with the diffusive term for the kind of flows we are dealing with. If we drop the convective term, the linear Stokes equations are obtained. Linear equations can be solved with linear iterative or direct solvers instead of time-stepping. The implementation of the Stokes solver resulted in a second considerable speed-up of the permeability prediction software.

WP 3.4 Parametric study and experimental validation

The permeability can be experimentally identified by means of the PIERS (Permeability Identification using Electrical Resistance Sensors) set-up. Lots of effort has been made to optimise this set-up. It was upgraded by replacing the 30 sensor bottom plate by two sensor plates with each totally 60 sensors (Figure 19). Furthermore, the data-acquisition has been updated and the permeability identification software has been totally re-engineered. The previous software program for permeability identification, called “PMPI” (Porous Media Permeability Identification), used an analytical solution of the injection into an orthotropic medium, as was proposed by Adams & Rebenfeld (A&R). Its main limitation was that only data from sensors which are reached before the flow front reaches an edge of the reinforcement can be used because the analytical solution assumes an infinitely large reinforcement field. This shows a significant drawback when the anisotropy (ratio of the principal permeability values) of the reinforcement is high. Therefore, an inverse method, or so-called mixed numerical/experimental technique (MNET), has been developed for the identification of the full in-plane permeability tensor. Consequently, the rotation angle θ between the permeability’s principal coordinate system (x1, x2) and the set-up’s coordinate system (X, Y) is also identified. The principle of the mixed numerical/experimental technique is to compare experimental observations from a test set-up with computed values from a numerical model which simulates the experiment. In this model the permeability values will appear as parameters which will be iteratively tuned in such a way that the computed observation matches the experiment. The parameter values that were used in the last iteration are taken as the permeability values {K} of the object under study. The PIERS set-up is used for obtaining the relevant experimental data and a finite element model has been developed to simulate the experiment. The permeability values are parameters in the finite element model of the experiment and are iteratively adjusted to optimize the agreement between the experimental data and computed data. A least-squares formulation of the difference between the experimental and the numerical flow front arrival times is used, along with a Levenberg-Marquardt optimization algorithm. The full array of 120 sensors can be used in every identification process because with the finite element model, in contrast to an analytical solution, the experiment can usefully continue until all sensors are reached. The finite element model has been compared with an analytical solution for an injection into isotropic material. The simulated data converges to the analytical data if the mesh is refined. For the last sensors, the relative error decreases underneath 0,1% without significantly jeopardizing the MNET’s speed. As a direct result of using a greater number of


sensors, the data-reduction scheme is more robust: if one sensor registers a deviant measurement, this will have a smaller influence on the final outcome of the calculation, especially in the direction of smaller permeability where fewer sensors are used in the analytical approach. Furthermore, it has to be noted that effects can occur such as local turbulences at the inlet and a disturbed fiber disposal in the reinforcement at the inlet which are complementary to the inherent decrease of the relative error as the arrival times become larger. These phenomena underline once more the importance of using also the sensors which are reached after the flow front reached an edge of the reinforcement.

Figure 19 PIERS setup; the sensor plate (with 60 sensors)

The new numerical model doesn't require a constant injection pressure since the procedure allows considering different pressures at each time step. Note that experiments, where even a constant injection pressure is set, still exhibit pressure variations of roughly 5%. So, the model allows an increasing pressure during the injection trough which the time for an experiment can reduced.

A difficulty to experimentally validate numerical predictions is the scatter present in the measurement results. The latter is not surprising since the permeability is mainly dominated by the geometry of the porous medium.

Possible sources of scatter on obtained permeability values are:

• Uncontrolled nesting of layers during stacking and compression of multi-layered samples,

• deformation of the fiber texture during sample preparation (shearing),

• existence of micro-flows, also called intra-tow flows, within yarns,

• material heterogeneity due to manufacturing,

• random experimental errors (pressure, temperature and time measurements).

In practice these sources of scatter will act simultaneously, rendering clear distinction between the possible contributions difficult.

Therefore, a solid epoxy test specimen that can be used as a reference sample has recently been developed and was produced with a stereo lithography (SL) production technique (Figure 19). The additive nature of the stereo lithography process allows the production of a structure with specific and complex internal features so that a kind of “artificial” reinforcement can be created in which the propagating fluid is persistently obligated to curve. Consequently, the flow in conventional textiles can be reproduced. Moreover, this concept counters the above mentioned scatter sources so that fixed permeability values are created. Since the permeability properties of the SL specimen do not vary from test to test, an excellent repeatability of the experiments is obtained and any measured difference must be attributed to the set-up and data processing.


Consequently this SL specimen can be used as a reference sample for calibration of test rigs and for comparison of results from different test rigs. Additionally, the SL sample has a simple and geometrically correctly known unit cell, which allows a correct import of the geometry into numerical flow simulation software such as FlowTex for the numerical prediction of the permeability. Consequently, the SL specimen allows experimental validation of the flow simulation software.

The SL specimen is designed for a 2D central injection rig, called “PIERS set-up”. This specimen could be used for 1D experiments as well and the structure can also be easily adapted for through the thickness experiments and possible extra requirements of the used test rig.

Generally, we conclude that the dimensions are sufficiently accurate and the deviation on the results is acceptably small. A tolerance of 0.1mm can be easily obtained on all the dimensions. Furthermore, this accuracy was obtained on subsequent produced specimens from which can be concluded that the stereo lithography manufacturing process is sufficiently repeatable and allows a very controllable and precise geometry. The newly designed resin additionally allows a rigid structure, with a very good surface quality and a wear resistance, which can be cleaned with water.

Figure 17 The SL specimen

Moreover, a project is being set-up to perform a round-robin study between different research institutes. One SL specimen will be passed on among the participating partners such that results of permeability measurements can be compared on an objective basis.

WP 3.5 Software tools

The methods described in WP 3.3 were implemented in the software tool FlowTex. The first version of the software has been released together with WiseTex 2.5. Now the upgraded version is under development.


Work package 4: Electro-magnetic properties of conductive fibre assemblies

WP 4.1 Data organisation and procedures for transfer of geometrical information

The topology observed in woven fabrics is more complex than the ones traditionally handled in the RF community. Preserving the real topology of the woven fabric is very important. The main problem is that it is extremely difficult to use the same description procedure for the mechanical and the electromagnetic modelling. For instance in the mechanical design the description of the yarns is very accurate, like for instance in Figure 20, where the description of yarns as performed in WiseTex is shown. WiseTex is a software tool developed at MTM KU Leuven to model the mechanical properties of woven fabrics. For the electromagnetic analysis, such a description would lead to analysis times that are unfeasible with present-day computers. Therefore two approximations are used, 1. the thin-wire approximation, and 2. the staircase approximation. Implementing these two approximations allows to keep the real geometry of the yarns, as far as it is important for the electromagnetic analysis, while retaining a reasonable analysis time. The result is that woven fabrics can be described as assemblies composed of vertical and horizontal conducting strips, a topology that is indeed much easier to handle. Also, the model obtained in this way outclasses by far the very simple parallel and crossed wire models that can be found in literature [S. Tretyakov, Analytical modelling in applied electromagnetics, Artech House, 2003].

The thin wire approximation

Electric currents flow mainly on the surface of the conducting fibres. For arbitrarily oriented fibres, it is not trivial to select a suitable coordinate system to describe this surface. Only in special cases like for instance for straight cylindrical wires, there is a suitable coordinate system. The first approximation is based on the fact that the diameter of the yarns in almost all cases is much smaller than a wavelength. This means that the so-called “thin wire approximation” can be used [Tretyakov]. This approximation is based on the fact that from a macroscopic electromagnetic point of view, the exact cross section of the yarn is not important for the overall behaviour of the structure as long as the self-impedance of the conducting “wire” (the yarn) is correct. This opens the way to model the “elliptic” yarn (Figure 20) by a simpler structure, for example a strip (Figure 21) with a well chosen equivalent width.

Figure 20 Cross-section defining a yarn in a unit cell, as used in WiseTex.

The staircase approximation

Although of course it is possible to electromagnetically model currents with an arbitrary direction, in the case of currents embedded in multilayered structures, it is computationally very advantageous to consider horizontal and vertical currents only. This can be done by modelling the topology making use of a proper staircase approximation, as illustrated in Fig. 2.


a) Yarns in WiseTex b) Yarns in MAGMAS

Figure 21 Transfer of topological information between WiseTex and MAGMAS for woven fabrics.

Practical transfer of topological data

The electromagnetic analysis can be performed starting from the topological information provided by WiseTex, after a transformation procedure, composed of two steps: 1. Transfer of geometrical information with the data structure (cfl file format) used by WiseTex developed at MTM (without modifying the file formats). This is just an interfacing problem.

2. Simplification of the geometrical information into a form suited for electromagnetic analysis. This involves the implementation of the two approximations discussed before.

A special converter was developed to perform these tasks. In more detail the converter performs the following steps:

- Reading data from a cfl file, generated by WiseTex. WiseTex describes the fibres by a discrete set of neighbouring ellipses that are parametrised.

- The unit cell is meshed based on a 3D grid. The central points of the ellipses describing the fibre are projected onto the closest centres of the 3D grid cubes.

- Introduction of horizontal and vertical strips by analyzing the snapped central points.

- Meshing of strips

- Write necessary files for MAGMAS

The fact that a well-defined procedure has been established to automatically transfer topological information in between different-purpose solvers is very important. It is a necessary and crucial step towards a very universal solver that is able to predict both mechanical and electromagnetic properties of woven fabrics. Such software allows the designer to control simultaneously mechanical and electromagnetic properties of materials already in the modelling stage, something which is, as far as we know, not done at this moment. A more complex example of knitted fabrics is shown in Figure 22. In many cases the height of the fabric cell is smaller than the cell period and in this case it is possible to use the approximation with horizontal strips only as shown in Figure 23. In the section WP4.4, an example will illustrate the difference between these two approximations. All complexity of the fabrics topology can be reconstructed using simple basic elements shown in Figure 24.


Figure 22 Transfer of the topological information between WiseTex and MAGMAS for knitted

fabrics

Figure 23 Transfer of the topological information between WiseTex and MAGMAS for knitted

fabrics

a) strips b)step+bend

c) bend d) step

Figure 24 Transfer of the topological information between WiseTex and MAGMAS for knitted fabrics


WP 4.2 Theory and predictive algorithms for effective permittivity, permeability, and conductivity of conducting fibre assemblies

The analysis of fibre assemblies is performed in several steps. The first step consists in the construction of equivalent assemblies using the approach of the previous section. The next step includes the electromagnetic analysis of equivalent assemblies. Then if it is required the effective parameters are calculated via the best suited response introduced further in this section. The most time and resource consuming is the second step. The electromagnetic analysis is based on the integral equations method. The integral equations are constructed using a mixed potential formulation for electric fields in the spatial domain. This approach requires Green’s functions in the spatial domain. The direct computation of Green’s functions is time consuming. A solution consists in the pre-calculation of Green’s functions for a finite number of points within a unit cell and then using interpolation algorithms. An extensive investigation of different interpolation algorithms and special extraction techniques was performed to improve the efficiency of the Green’s function calculations. These improvements were reported at several conferences. It was worth to mention that originally MAGMAS was developed to analyse general multilayered antenna structures. The implementation of periodicity used a strong resemblance between the algorithms to calculate Green’s Functions (GFs) for a single source and a periodic array of sources. The algorithms in both cases include the following main steps: - calculation of the Green’s function in the spectral domain (same routines) - calculation of the Green’s functions in the spatial domain via the Inverse Fourier Transform (different routines) - interpolation of the Green’s functions (different routines) - calculation of the coupling matrices (slightly different routines) - calculation of electric currents (same routines) Although the steps are not exactly the same, they can sometimes be expressed in a way suited for both cases. The steps, that are different, are general routines performing specific operations with Green’s functions. The original algorithm is modified with a few adjustments in such a way that the periodicity of the sources can be implemented easily with minimum changes. In practice this means that almost all modelling steps remain unchanged. This is possible because the Green’s functions in the spectral domain are the same for a single source and a periodic array of sources and the calculation of coupling matrices uses the interpolated values of Green’s functions. The main advantage of this approach is that it is a modular analysis technique, which allows to develop new features in the global modelling scheme simultaneously for a single source and a periodic array of sources. This is possible due to the fact that in both cases (for a single source and a periodic array of source s) the GFs in the spatial domain are calculated via the Inverse Fourier Transform (IFT) from the same spectral GFs. Fundamentally, the only difference is that the IFT is expressed in terms of double infinite integrals (single source) or a double infinite series (periodic array). The main problem in the numerical evaluation of the IFT is the poor convergence of the spectral components. The extraction technique allows to solve this problem. By subtracting the asymptotes from the spectral GFs and adding them again but to the spatial GFs, the numerically calculated part of the transform becomes much easier to handle. The main idea of our asymptote extraction technique is to use the same asymptotes in both cases (for a single source and a periodic array). It is worth to briefly mention the most important techniques for periodic arrays used to improve the efficiency of the method: − asymptotic extraction technique − special asymptotic functions − acceleration of series using Shanks algorithm for oscillating functions − acceleration of series using rho-algorithm for monotone functions − use of the symmetry that allows to reduce the pre-calculated area to the quarter of a unit cell − interpolation of Green's function between the nodes of the pre-calculated grid


− special choice of auxiliary parameters (relative errors, number of terms in series, ...) to insure the stability of the whole solution procedure.

Due to the complex nature of the integral equations method and in order to check our progress during the implementation several auxiliary models were created. These models are fully functional and they are able to model specific geometries or calculate specific Green's functions. An overview of the auxiliary models is given in Table 1.

Table 1 Auxiliary models for modelling of fibre assemblies

Model Method Output

Scattering by a periodic array of horizontal strips in free space

Direct summation in the spectral domain

Scattering matrix

Scattering by a periodic array of horizontal strips located in multilayered medium

Direct summation in the spectral domain

Scattering matrix

Periodic Green's function for horizontal conductor in free space

Ewald method Green's function

Transmission through a layer in free space Solution in the spectral domain using a transmission line theory

Scattering matrix

Transmission through a layer in a rectangular waveguide

Solution in the spectral domain using a transmission line theory

Scattering matrix

Transmission through a periodic inductive grid of flat strips in free space

Equivalent lumped model Scattering matrix

Using a modular structure of our software, new features are developed simultaneously for a single source and a periodic array of sources. Dielectric volumes with the permittivities different from the host medium were implemented in this way. This problem is of interest in many applications. The implementation of dielectric volumes required a lot of work to model all Green’s functions and all possible coupling between dielectric volumes and existing elements (horizontal and vertical electric conductors). The addition of any new basic element needs not only algorithms for the self-coupling but also algorithms for the coupling with the existing elements. It is obvious that the implementation becomes more and more time consuming. Thus the modular structure is a very effective partial solution for this problem. Although dielectric volumes were mainly tested for a single volume, they are implemented simultaneously for a single volume and a periodic array of dielectric volumes.

The response of an array to an incident plane wave can be fully described in terms of scattering parameters (reflection and transmission). In some cases the description of the array in terms of effective parameters is of interest. There are several possible ways to derive these effective parameters. The first way is to average the fields in the unit cell. This way is very complex and it is better suited for bulk materials with 3D periodicity. In this project an inverse method was selected. This approach is based on the solution of the inverse problem. The idea is to find a layer with such parameters that it produces the same electromagnetic response. The benefit of this approach is that it can be used for the electromagnetic modelling and for the analysis of measurements. The model is shown in Figure 25. At first an array with metallic strips is analyzed using the integral equations method and the two main scattering parameters (reflection and transmission) are calculated. Then the array of strips is replaced by a homogeneous dielectric slab with the effective permittivity (ε) and/or the permeability (µ) and/or the conductivity (σ). The response of this slab to a plane wave is calculated using transmission line theory. A special cost function is constructed

( ) ( )( ) ( )( )22 ,,,,,, σµεσµεσµε HIEHIE TTRRF −+−= (1)

A conjugate gradient method in multiple dimensions or a golden search [Numerical Recipes in FORTRAN 77: The Art of Scientific Computing] method in one dimension is used to find the minimum


of the cost function. This minimum of the cost function corresponds to the best approximation of the periodic array by a homogeneous dielectric slab.

Incident Wave

IncidentWave

Integral Equations/ Measurements

TH(ε,µ,σ): transmission

RH(ε,µ,σ): reflection

TIE: transmission

RIE: reflection

Transmission Line Theory

Figure 25 Model for determination of effective parameters of periodic arrays

The cost function has normally an obvious minimum. This is illustrated by the actual cost function for a specific dielectric slab as shown in Figure 26. There are additional examples of cost functions and effective parameters in the previous mid-term reports.

R

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Figure 26 Model for determination of effective parameters of periodic arrays

WP 4.3 Procedures for experimental determination of effective permittivity, permeability, and conductivity of conducting fibre assemblies

Experimental determination of effective permittivity, permeability, and conductivity requires several approaches depending of the fibres concentration, the frequency of interest and so on. Each approach includes a measurement set-up and special software tools to analyse the measurement data.


During the project several measurement set-ups were used: - Transmission measurements between 2 horn antennas - Transmission measurements through an aperture between 2 horn antennas - Reflection measurements at the end of an open ended rectangular waveguide or a horn - Transmission measurements in a rectangular waveguide.

- Transmission measurements in a coaxial holder

All measurement set-ups suffer from different shortcomings. These shortcomings can be split into several groups. - frequency band limitation - unwanted RF coupling ( RF leakage/ RF diffraction/ Multiple reflections) - structure of an incident wave (polarization response, non-isotropic sample)

After a comparison study, several set-ups were selected to perform measurements in a wide frequency band from 100 MHz to 18 GHz. The selected set-ups are Set-up Frequency

Transmission measurements using a coaxial holder

100 MHz – 1.5 GHz

Transmission measurements through an aperture between 2 horn antennas

1 GHz – 8 GHz

Transmission measurements between 2 horn antennas

5 GHz – 18 GHz

A coaxial holder set-up or a so-called ASTM D4935 standard is shown in Fig. 8 and it consists of 2 specially designed coaxial adapters (ElectroMetrics, EM-2701A), two 10dB attenuators. The generator is connected via a RF cable to one of the adapter. The second adapter is connected via a RF cable to a network analyzer. All measurements were performed using the HP8510 vector network analyzer. The attenuators reduce the mismatching of the coaxial adapters. This setup allows to perform very accurate measurements of the shielding effectiveness up to 1.5 GHz.

Above this frequency higher order modes in the coaxial adapters will affect the results. The attempt to overcome this problem keeping the holder geometry leads to a smaller holder with the smaller outer diameter. For instance in [Hong YK, Lee CY, Jeong CK, Lee DE, Kim K and Joo J , “Method and apparatus to measure electromagnetic interference shielding efficiency and its shielding characteristics in broadband frequency ranges”, Review Of Scientific Instruments 74 (2): 1098-1102 FEB 2003], the outer diameter is only 7mm. Although this set-up was used up to 13 GHz, it imposes a very strict restriction on the cell's size. Namely the size of the cell should be much smaller than 1 mm.

coaxial adapter

coaxial adapter

sample

10 dB attenuator

10 dB attenuatoranalyzer

generator

Figure 27 Coaxial adapters for measurements of shielding effectiveness


Figure 28 A calibration sample for the coaxial adapters

The main benefit of this set-up is that it uses the capacitive coupling between two coaxial adapters and as a consequence the RF leakage is well controlled.

electric field

magnetic field Figure 29 Fields distribution in the coaxial waveguide

The main drawback in using this set-up for woven fabrics is the fact that this method was originally designed for homogeneous bulk materials. Textiles and woven fabrics are periodic but rather irregular structures with pronounced inhomogeneity. This means that the actual response to a plane wave depends on the polarization. This cannot be measured by the set-up. By studying the field distribution inside the holder, it is easily seen that the measured result will be an average over all polarizations. The field distribution in the coaxial holder is shown in Figure 29.

The fields behave locally as a plane wave:

- electric and magnetic field are orthogonal,

- electric and magnetic field are normal to the direction of propagation,

- the ratio between electric and magnetic field is the characteristic impedance of the medium filling the coax, in this case just air.

Observed over the whole holder aperture, the field distribution clearly is not “plane”. As a consequence, the response to non-homogeneous samples cells will be averaged in a rather complex way. This set-up is thus unable to see the difference in the response to different polarizations.

Moreover, if the unit cell is not small enough compared to the size of the holder, the measured result is even dependent on the actual mounting of the sample in the holder, something which is of course undesired.

The measurement is performed in two steps. To calibrate the set-up, the transmission without the sample or with the calibration sample (Fig. 8b) is measured (Pcal). In the case of thin samples, the difference between these 2 measurements is normally small. Hence, the calibration


can be performed without the calibration sample itself. This is very convenient for woven fabrics because the fabrication of the calibration sample is not simple due to material properties. Then the transmission through the sample is measured (Pload). The shielding effectiveness is calculated as

⎥⎦

⎤⎢⎣

⎡=

load

cal

PPSE 10log10

In some cases effective parameters (effective permittivity, permeability, and conductivity) are of interest. Then the procedure similar to explained in WP4.2 is used. However a cost function is slightly different. The set-up shown in Fig. 8a is unable to deliver the reflection coefficient used in (1) because the measured reflection is located behind the 10dB attenuator and the coaxial adapter is not well matched. As a consequence only the transmission coefficient is used in (1).

For higher frequency a set-up with 2 horns is used. One of possible configurations is shown in Figure 30.

sample

10 dB attenuator

10 dB attenuatoranalyzer

generator

wide band horn

wide band horn

Figure 30 Coaxial adapters for measurements of shielding effectiveness

For the low frequency up to 5 GHz the size of the sample should be sufficiently large to minimize the diffraction by the sample edges. The size of the sample should be at least several wavelengths. In many cases there are no samples of this size available. For this case a much smaller sample can be used. It is placed in a special adapter between 2 horns then a similar procedure (calibration and sample measurement) as in the case of the coaxial adapter is used. The set-up is constructed using 2 wide band horns antennas Dorado GH1-18N. However in contrast to the coaxial set-up, the horns set-up uses the direct coupling between 2 horns and it suffers from the RF leakage. This leakage leads to multiple reflections and the shielding effectiveness behaves like a highly oscillating function. To retrieve the correct behaviour the data is analysed and a special polyfit approximation of measured data is constructed using matlab's routines. This polifit function is considered as an estimation of the shielding effectiveness of a sample.

For higher frequency a set-up can be constructed using the direct transmission between 2 horns. For this case there are also other horns (Narda calibration horns) available. The measurement with 2 horns can be also performed in a special anechoic chamber shown in Figure 31.

An example of a sample composed from nickel-carbon fibres is shown in Figure 32. The shielding effectiveness shown in Figure 33 was measured using the coaxial holder set-up. Then the conductivity of the sample was calculated. In our model it is necessary to introduce the thickness of the sample. Although this step may look trivial, it is not always easy in practice. The problem is that some of the samples are very thin and they are not rigid. Their thickness can vary across the sample. As a consequence the calculated conductivity will be different as it illustrated in Figure 34, where several conductivities were calculated from the measured data for different thicknesses. In order to avoid the ambiguity it is necessary to calculate the surface impedance. This parameter gives a rather good estimation of the sample properties.


Figure 31 Positioner in the anechoic chamber

Figure 32 Photo of Grade 800838 Nickel Carbon

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Figure 33 Measured shielding effectiveness of the Nickel Carbon sample


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Figure 34 Conductivity and surface impedance of the Nickel Carbon sample

WP 4.4 Validation.

The validation of our software tool was performed by comparison with results available in literature and measurements. The electromagnetic analysis of fibrous assemblies reduces to the analysis of structures containing the combination of arbitrarily oriented conducting strips. Although the variety of all possible combinations is infinite, in general all this variety can be reconstructed from a rather small set of basic structures. These basis structures contain the following elements: - finite resonant and non resonant horizontal strips, including different levels (implemented) - junctions of horizontal strips, including different levels (implemented) - infinite horizontal strips (implemented) - complex strips containing vertical and horizontal parts (implemented) - dielectric volumes (testing) The environment may also contain a plain dielectric layer. In many cases there are no available results in literature for the topology of interest. In this case we use physical insight and perturbation theory. It is obvious that slight changes should have a slight impact on the results.

As an example, the transmission of a plane wave through arrays of strips with different forms is considered. These forms shown in Figure 35 cover all varieties of strips used in our models. There are 3 basic forms: straight strip, meander and 3D meander formed by strips+walls. The numerical results shown in Figure 36 confirm our assumption. It is of interest that the difference in the transmission between the meander and the 3D meander is smaller than between the meanders and the straight strips. This result is expectable because the topology of the meanders is closer to each other and the vertical segment is small in comparison with the period of the cell.

The next example shows the complete procedure of the modeling of a woven fabric. The fabric is formed by twisted metallic wires. The size of a cell is about 10 mm by 10 mm and the diameter of the wires is about 1mm. The fabric is shown in Figure 37. The topologies of this fabric in the mechanical and electromagnetic softwares are shown in Figure 38, respectively. The topology for the electromagnetic solver contains only vertical and horizontal parts. It is clear that this topology is relatively flat. It means that it can be also approximated using only horizontal strips.


Figure 35 Transmission of a plane wave through periodic arrays of strips with different form (strip,

meander, strips+walls)

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Figure 36 Transmission of a plane wave through periodic arrays of strips with different form

Figure 37 Topology of woven fabrics formed by twisted metallic wires

Figure 38 Topology for woven fabrics for modeling of electromagnetic and mechanical properties

The result of calculations and measurements is shown in Figure 39. For this type of fabrics the agreement between the calculations and the measurements is very good. Indeed, due to the fact that the diameter of the fibers is much smaller than the distance between the fibers, the thin wire


approximation will yield only very small discrepancies. Moreover, the diameter of the metal yarns is much larger than a skin depth, so that they appear almost as perfect conductors, which means that the skin effect does not affect the results any more. The difference between modeling topologies using both horizontal and vertical, or using only horizontal strips is very small. This result is expectable because the vertical parts are very small compared to the horizontal parts. Their presence is indispensable to ensure the continuity of electric currents flowing on the strips. The incident field interacts mainly with the transversal (horizontal in Figure 38) strips parallel to the field. As a consequence the induced current in both cases (with and without vertical strips) will be similar as long as the vertical parts remain small in terms of wavelengths.

The lumped component model also gives a good approximation if it is used twice, for the two decomposed polarizations, vertical and horizontal, separately. This is due to the small width of the strip in terms of wavelengths [[Cwik] T.Cwik, R.Mittra, the cascade connection of planar periodic surfaces and lossy dielectric layers to form an arbitrary periodic screen, IEEE Antennas and Propagation, Vol.35, No.12, pp. 1397-1405, 1987.; [Cwik] T.Cwik, R.Mittra, “Correction to “The cascade …”, IEEE Antennas and Propagation, Vol.36, No.9, pp. 1335, 1988]. With the increase of the frequency this structure will show a resonance behavior and the shortcoming of lumped models will be clearly visible.

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Figure 39 Calculated and measured shielding effectiveness of woven fabrics

The next example in Figure 40 shows the measured transmission of a plane wave through a grid of wires inserted in polypropylene. The size of a cell is about 5 mm and the diameter of the wires is about 0.8 mm. Each of the crossed wires is formed by twisted smaller wires. The measured results suffer clearly from diffraction effects. However the average level can be predicted using our software tools.

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ng ,

dB

Sample CTheory, w=1 mmTheory, w=1.5 mm

Figure 40 Transmission of a plane wave through a wires grid inserted in polypropylene.

The next example shows a periodic array of crosses located on a dielectric slab with the thickness h=0.3mm. The length of the cross is 6.875 mm and its width is 0.625 mm. The size of the cell is 10 mm by 10 mm. The calculated reflection and transmission coefficients through the array for different permittivities of the slab are shown in Figure 41 As a reference solution the results from [Cwik] are used. In [Cwik] the calculation was performed using the direct solution in the spectral domain. The agreement between 2 methods is very good.


0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65 0.7 0.75 0.80

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

d / λ

Ref

lect

ion

(R),

Tra

nsm

issi

on (

T)

Spectral (x−marks) and Spatial (no marks)

ε=1ε=2ε=4

TransmissionReflection

Figure 41 Transmission through a periodic array of crosses on a dielectric slab

The calculated current distribution on the cross at the resonance is shown in Figure 42.

Figure 42 Electric current distribution on the cross

The last example shows the transmission of a plane wave through a grid of finite strips with a step and without. The grid topology is shown in Figure 43. The structures with finite strips behave like frequency selective surfaces. They are normally transparent for RF waves. However there are frequencies when these structures behave like perfect conductors and reflect everything. These frequencies correspond to the resonances of the structure. The results of calculation are shown in Figure 44. There is only a slight difference between two topologies what is expectable.


Figure 43 Transmission of a plane wave through periodic arrays of finite strips with a step and

without

8 9 10 11 12 13 140

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

GHz

Tra

nsm

issi

on

ε=2 ε=1

stripstep strip

Figure 44 Transmission of a plane wave through periodic arrays of finite strips with a step and without

Other examples were reported in the previous mid-term reports.

The presented examples confirm the validity of our approach.

WP 4.5 Development of software tools

Several tools have been developed to model electromagnetic properties of fibrous materials. The main programming language is FORTRAN and the used operation system is Linux.

The developed software tools include besides our main solver (MAGMAS) several software tools: - A converter from the WiseTex cfl file to the MAGMAS input file - An effective parameter solver that is able to calculated effective parameters based on the calculated/ measured data.

During the project periodicity was implemented in our main solver (MAGMAS). It is important to emphasize that MAGMAS was developing in parallel via different branches. Now all these branches were merged together resulting in one stable powerful solver. The final software tools profits enormously from this merge.

In the last year the work was focused on the construction of a fully automated interaction between different software tools. This interaction is shown in Fig. 25. Software tools are located in the boxes in the form of an ellipse. Input/ output files are located in the boxes in the form of a rectangle. The interaction between different modules is performed semi-automatically using an


appropriated script. The final modelling can be performed automatically by executing a makefile.

The benefit of the chosen interaction scheme is that all parts can be developed and tested rather independently and similar tasks are performed by one software module. For instance the module, calculating the effective parameters, is the same for MAGMAS and measurements. The differences between the output of different modules (MAGMAS or measurements) are taken into account by introducing a selective filter during the input of the data and the use of different test functions.

Effective parameters

input filesMAGMAS

MAGMAS Measurements

S parameters (Reflection + Transmission)

Effective parameters solver

converter

cfl file

WiseTex

Figure 45 Interaction between different software tools

During the GBOU project the capability of MAGMAS has greatly increased. It is important to emphasise that due to the modular structure of the MAGMAS code it was possible to perform work in parallel by different researchers. During the last years contributions from several Ph.D students were implemented:

Ph.D.’s: G. Vandenbosch, F. Demuynck, E. Soliman, B. Van Thielen, M. Vrancken, Y. Schols,S. Mestdagh, W. Aerts

It is worth to mention the several master students (ca. 10) that contributed to the development of MAGMAS. Today MAGMAS counts ca. 350.000 lines of code. The debugging of this code and the compatibility check costs a lot of time ….


2 PUBLICATIONS

I. Book chapters

1. Lomov, S.V., I. Verpoest and F. Robitaille, Manufacturing and internal geometry of textiles, in Design and manufacture of textile composites, A. Long, Editor. 2005, Woodhead Publishing Ltd. p. 1-60.

2. Lomov, S.V. Virtual testing to establish material formability, in: Composite Forming Technologies, A. Long, Editor, 2007 Woodhead Publishing Ltd, 80-116

3. Boisse, P., Akkerman, R., Cao, J., Chen, J., Lomov, S. V., Long, A., Composites forming, Advances in material forming. Esaform 10 years on, ed Chinesta, F., Cueto, E., Springer, 2007, 61-79

4. Verleye, B., M. Klitz, R. Croce, D. Roose, S.V. Lomov, and I. Verpoest, Computation of permeability of textile reinforcements with experimental validation for monofilament and woven fabrics, in Studies in Computational Intelligence (SCI), vol 55. 2007, Springer Verlag: Berlin-Heidelberg. 93-109

II. International peer-reviewed articles

1. E.B. Belov, S.V. Lomov, I.Verpoest, T.Peters, D.Roose, R.S.Parnas, K.Hoes, H.Sol, Modelling of permeability of textile reinforcements: Lattice Boltzmann method, Composites Science and Technology, vol 64, 2004, 1069-1080

2. Summerscales, J., Russell, P.M., Lomov, S.V., Verpoest, I., Parnas, R. The fractal dimension of X-ray tomographic sections of a woven composite, Advanced Composite Letters, Vol 13, N2, 2004, 115-123

3. Hoes Kris, Sol Hugo, Dinescu Daniela, Lomov Stepan, Parnas Richard “Study of nesting induced scatter of permeability values in layered reinforcement fabrics”, Composites part A, 2004, Vol 35, N12 pp.1407-1418

4. Lomov, S.V., M. Barburski, Tz. Stoilova, I. Verpoest, R.Akkerman, R.Loendersloot, R.H.W.ten Thije, Carbon composites based on multiaxial multiply stitched preforms. Part 3: Biaxial tension, picture frame and compression tests of the performs, Composites part A, 2005, 36, 1188-1206

5. Truong Chi, T., Vettori, M., Lomov, S. V., Verpoest, I. "Carbon composites based on multiaxial multiply stitched preforms. Part 4: Mechanical properties of composites and damage observation." Composites part A, 36, 1207-1221, 2005

6. Loendersloot, R., Lomov, S.V. Akkerman, R., Verpoest, I. "Carbon composites based on multiaxial multiply stitched preforms. Part 5: Geometry of sheared biaxial fabrics" Composites part A, 37, 2006, 103-113

7. Lomov, S. V., Bernal, E., Ivanov, D. S., Kondratiev, S. V., Verpoest, I. "Homogenisation of a sheared unit cell of textile composites: FEA and approximate inclusion model." Revue européenne des éléments finis, 14, N6-7, 709-728, 2005

8. Gorbatikh, L., Lomov, S. V., Verpoest, I. "Contribution of a partially debonded circular inhomogeneity into the material overall elastic compliance and related problems." International Journal of Fracture, 131, 2005, 211-229

9. F. Desplentere, S. V. Lomov, D. L. Woerdeman, I. Verpoest, M. Wevers, A. Bogdanovich, “Micro-CT Characterization of variability in 3D Textile architecture”, Composites A, 2005, vol 65, pp. 1920-1930


10. Verpoest, I. and S.V. Lomov Virtual textile composites software Wisetex: integration with micro-mechanical, permeability and structural analysis. Composites Science and Technology, 2005; 65(15-16): 2563-2574

11. Lomov, S. V., Verpoest, I. "Model of shear of woven fabric and parametric description of shear resistance of glass woven reinforcements." Composites Science and Technology,2006; 66: 919-933

12. Lomov, S. V., Willems, A., Verpoest, I., Zhu, Y., Barburski, M., Stoilova, T., "Picture frame tests of woven fabrics with full-field strain registration." Textile Research Journal, 2006, 76(3), 243-252

13. Lomov, S.V., T.Mikolanda, M.Kosek, I.Verpoest, “Model of internal geometry of textile composite reinforcements: Data structure and virtual reality implementation”, Journal of the Textile Institute, 2007, 98(1), 1-13

14. Loendersloot, R., Lomov, S.V. Akkerman, R., Verpoest, I. "Carbon composites based on multiaxial multiply stitched preforms. Part 5: Geometry of sheared biaxial fabrics" Composites part A, 37, 2006, 103-113

15. Lomov, S. V., Verpoest, I. "Model of shear of woven fabric and parametric description of shear resistance of glass woven reinforcements." Composites Science and Technology,2006; 66: 919-933

16. Lomov, S. V., Willems, A., Verpoest, I., Zhu, Y., Barburski, M., Stoilova, T., "Picture frame of woven fabrics with full-field strain registration." Textile Research Journal, 2006, 76(3), 243-252

17. Koissin, V., Ruopp, A., Lomov, S.V., Verpoest, I., Witzel, V., Drechsler, K. On-surface fibre-free zones and irregularity of piercing pattern in structurally stitched NCF preforms, Advanced Composite Letters, 2006, 15(3), 87-94

18. Morren, G., Gu, J., Sol, H., Verleye, B., Lomov, S.V. Stereolithography specimen to calibrate permeability measurements for RTM flow simulations, Advanced Composite Letters, 2006, 15 (4): 119-125

19. S.V.Lomov, I.Verpoest, WiseTex: Virtual reality and real-world prediction of structure and properties of textile polymer composites, Tehnicheskiy Tekstil, N6, 2006, 37-41 (in Russian)

20. Kurashiki, T., Nakai, H., Hirosawa, S., Imura, M., Zako, M., Lomov, S.V., Verpoest, I. Mechanical behaviors for textile composites by FEM based on damage mechanics, Key Engineering Materials, vol 334-335 (Advances in Composite Materials and Structures), 2007, 257-260

21. Lomov, S.V., D.S. Ivanov, I. Verpoest, M. Zako, T. Kurashiki, H. Nakai and S. Hirosawa Meso-FE modelling of textile composites: Road map, data flow and algorithms. Composites Science and Technology, 67, 2007, 1870-1891.

22. Gorbatikh, L., Lomov, S. V., Verpoest, I. " On stress intensity factors of multiple cracks at small distances in 2D problems" International Journal of Fracture, 143, 2007, 377-384

23. Rawal, A., S.V. Lomov, and I. Verpoest An environmental scanning electron microscope study of a through-air bonded structure under tensile loading. Journal of the Textile Institute, 2007; 1(1): 1-7

24. Rawal, A., Lomov, S.V., Ngo, T., Verpoest, I., Vankerrebrouck, J. Mechanical characterization of through-air bonded nonwoven structure, Textile Research Journal, 2007, 77(6): 417-431

25. Vallons, K., Zong, M. Lomov, S.V., Verpoest, I. Carbon composites based on multi-axial multi-ply stitched preforms. Part 6. Fatigue behaviour at low loads: stiffness degradation and damage development, Composites A, 2007, 38: 1633-1645


26. Gorbatikh, L., D. Ivanov, S.V. Lomov, and I. Verpoest On modelling of damage evolution in textile composites on meso-level via property degradation approach. Composites Part A, 2007; 38: 2433-2442

27. Truong Chi, T., S.V. Lomov, and I. Verpoest Carbon composites based on multiaxial multiply stitched preforms. Part 8: Mechanical properties and damage observations in composite with sheared reinforcement. Composites part A, submitted

28. Lomov, S.V., D.S. Ivanov, T. Truong Chi, I. Verpoest, F. Baudry, K. Vanden Bosche, and H. Xie Experimental methodology of study of damage initiation and development in textile composites in uniaxial tensile test. Composites Science and Technology, in print

29. Lomov, S.V., D.S. Ivanov, I. Verpoest, M. Zako, T. Kurashiki, H. Nakai, J. Molimard, and A. Vautrin Full field strain measurements for validation of meso-FE analysis of textile composites. Composites part A, in print

30. Lomov, S.V., P. Boisse, E. Deluycker, F. Morestin, K. Vanclooster, D. Vandepitte, I. Verpoest, and A. Willems Full field strain measurements in textile deformability studies. Composites part A, in print

31. Willems, A., S.V. Lomov, I. Verpoest, and D. Vandepitte Optical strain fields in shear and tensile testing of textile reinforcements. Composites Science and Technology, submitted

32. Cao, J., R. Akkerman, P. Boisse, J. Chen, H.S. Cheng, E.F.d. Graaf, J.L. Gorczyca, P. Harrison, G. Hivet, J. Launay, W. Lee, L. Liu, S.V. Lomov, A. Long, E.d. Luycker, F. Morestin, J. Padvoiskis, X.Q. Peng, J. Sherwood, T. Stoilova, X.M. Tao, I. Verpoest, J. Wiggers, A. Willems, T.X. Yu, and B. Zhu Characterization of mechanical behavior of woven fabrics: experimental methods and benchmark results. Composites Part A, in print

33. Verleye, B., Morren, G. et al.: Userfriendly permeability predicting software for technical textiles., submitted to Research Journal of Textile and Apparel

34. B. Verleye, R. Croce, M. Griebel, M.Klitz, S.V. Lomov, G. Morren, H. Sol, I. Verpoest and D. Roose, Permeability of Textile Reinforcements: Simulation; Influence of Shear, Nesting and Boundary Conditions; Validation, submitted to Composites Science and Technology

35. Morren, G., Bossuyt, S., Sol, H., 2D Permeability Tensor Identification of Fibrous Reinforcements for RTM Using an Inverse Method, submitted to Composites Part A

III. International proceedings, fully published

1. Mikolanda, T., Lomov, S.V., Kosek, M., Verpoest, I. Simple use of virtual reality for effective visualization of textile material structures, CODATA Prague Workshop Information Visualization, Presentation, and Design, 29-31 March 2004, CD edition

2. Lomov, S.V., Stoilova, Tz., Verpoest, I. Shear of woven fabrics: Theoretical model, numerical experiments and full field strain measurements, Proceedings of the 7th Esaform Conference on Material Forming, Trondheim, Norway, 2004, 345-348

3. Van den Broucke, B., Tumer, F., Lomov, S.V., Verpoest, I., De Luka, P., Dufort, L. Micro-macro structural analysis of textile composite parts: Case study, Proceedings of the 25th International SAMPE Europe Conference, Paris, March 30th – April 1st, 2004, 194-199

4. Desplentere, F., Lomov, S.V., Verpoest, I., Influence of the scatter of perform permeability on the mould filling: Numerical simulations Proceedings of the 25th International SAMPE Europe Conference, Paris, March 30th – April 1st, 2004, 331-336


5. Lomov, S.V., Peeter, T., Roose, D., Verpoest, I. Modelling of permeability of textile reinforcements: Lattice Boltzmann method, Proceedings of the 25th International SAMPE Europe Conference, Paris, March 30th – April 1st, 2004, 367-392

6. Desplentere, F., Lomov, S.V., Verpoest, I. Mold filling simulations for RTM: Influence of the scatter of perform permeability, The 7th International Conference on Flow Processes in Composite Materials, Newark, Delaware, USA, 7-9 July 2004, s.p.

7. Carvelli, V., Truong Chi, T., Larosa, M., Lomov, S. V., Poggi, C., Ranz Angulo, D., Verpoest, I. "Experimental and numerical determination of the mechanical properties of multi-axial multi-ply composites", Proceedings ECCM-11. Rodos, 2004, p.CD edition.

8. Kurashiki, T., Zako, M., Hirosawa , S., Lomov, S. V., Verpoest, I. "Estimation of a mechanical characterization for woven fabric composites by fem based on damage mechanics", Proceedings ECCM-11. Rodos, 2004, p.CD edition.

9. Loendersloot, R., ten Thije, R. H. W., Akkerman, R., Lomov, S. V. "Permeability prediction of non-crimp fabrics based on a geometric model", Proceedings ECCM-11. Rodos, 2004, p.CD Edition.

10. Lomov, S. V., Van den Broucke, B., Tumer, F., Verpoest, I., De Luka, P., Dufort, L. "Micro-macro structural analysis of textile composite parts", Proceedings ECCM-11. Rodos, 2004, p.CD Edition.

11. Vettori, M., Truong Chi, T., Lomov, S. V., Verpoest, I. "Progressive damage characterization of stitched, biaxial, multi-ply carbon fabrics composites", Proceedings ECCM-11. Rodos, 2004, p.CD edition.

12. Desplentere, F., S.V. Lomov, and I. Verpoest, Influence of the scatter of preform permeability on the mould filling: Numerical simulations, in Proceedings of the 7th International Conference on Textile Composites (TexComp-7). 2004: Yonezawa. (Textile 9)1-4

13. Kurashiki, T., S. Hirosawa , M. Zako, S.V. Lomov, and I. Verpoest, On a numerical simulation of the mechanical behaviour for laminated woven fabric composites under tensile loading, in Proceedings of the 7th International Conference on Textile Composites (TexComp-7). 2004: Yonezawa. (Textile 13)1-4

14. Ivanov, D.S., S.V. Lomov, and I. Verpoest, Zero and first order homogenisation schemes: Comparison with a full FE model, in Proceedings of the 7th International Conference on Textile Composites (TexComp-7). 2004: Yonezawa. (Textile 15)1-4

15. Lomov, S.V., I. Verpoest, and T. Stoilova, Shear of woven fabrics: theoretical model and parametric study, in Proceedings of the 7th International Conference on Textile Composites (TexComp-7). 2004: Yonezawa. (Textile 16)1-4

16. Truong Chi, T., S.V. Lomov, I. Verpoest, M. Vettori, and D. Ranz Angulo, Mechanical properties and initial damage in carbon non-crimp fabric reinforced epoxy composites, in Proceedings of the 7th International Conference on Textile Composites (TexComp-7). 2004: Yonezawa. (Textile 18)1-4

17. Lomov, S.V., T. Stoilova, and I. Verpoest, Strain fields in the picture frame test, in Proceedings of the Composite Testing and Identification Conference (CompTest-2). 2004: Bristol. CD edition

18. Vettori, M., T. Truong Chi, S.V. Lomov, and I. Verpoest, Progressive damage characterisation of stitched bi-axial multi-ply carbon fabric composites, in Proceedings of the Composite Testing and Identification Conference (CompTest-2). 2004: Bristol. CD edition

19. Kyosev,Y., Lomov,S., Stoilova, Tz. (2004) Investigation over the Thickness of Glass/Polypropylene Woven Fabrics for Composites: Compression Test, 31. Aachener


Textiltagung / 31st Aachen Textile Conference, November 24-25, poster, CD-ROM edition, in DWI Reports 2004/128, editor: Brigitte Kueppers, ISSN 0942-301X, DWI-Aachen, Germany

20. S.V.Lomov, X. Ding, S.Hirosawa, S.V.Kondratiev, J.Molimard, H.Nakai, A.Vautrin, I.Verpoest, M.Zako, FE simulations of textile composites on unit cell level: validation with full-field strain measurements, Proceedings 26th SAMPE-Europe Conference, Paris, 5th-7th April 2005, 28-33

21. Thanh Truong Chi, Ho Chiew Jie, Stepan V. Lomov, Ignaas Verpoest, Sheared biaxial multi-ply carbon fabrics reinforced epoxy composites: the mechanical properties and damage initiation, Proceedings 26th SAMPE-Europe Conference, Paris, 5th-7th April 2005, 252-257

22. Laine, B., Hivet, G., Boisse, P., Boust, F., Lomov, S.V. Permeability of the woven fabrics: A parametric study, Procedings of the 8th ESAFORM Conference on Material Forming, Cluj-Napoca, 27th -29th April 2005, 995-998

23. Willems, A., Vanderpitte, D., Lomov, S.V., Verpoest, I. Biaxial tensile tests on a woven glass/PP fabric under optical strain measurement, Procedings of the 8th ESAFORM Conference on Material Forming, Cluj-Napoca, 27th -29th April 2005, 1007-1010

24. Lomov, S.V., Willems, A., Barburski, M., Stoilova, Tz., Verpoest, I. Strain field in the picture frame test: Large and small scale optical measurements, Procedings of the 8th ESAFORM Conference on Material Forming, Cluj-Napoca, 27th -29th April 2005, 935-938

25. Lomov, S.V., Verpoest, I., Bernal, E., Boust, F., Carvelli, V., Delerue, J.-F., De Luca, P., Dufort, L., Hirosawa, S., Huysmans, G., Kondratiev, S., Laine, B., Mikolanda, T., Nakai, H., Poggi, C., Roose, D., Tumer, F., van den Broucke, B., Verleye, B., Zako, M. Virtual textile composites software wisetex: integration with micro-mechanical, permeability and structural analysis, Proceedings of the 15th International Conference on Composite Materials, Durban 27th June – 1st July 2005, CD edition

26. Kurashiki, T., Zako, M., Hirosawa, S., Imura, M., Lomov, S.V., Verpoest, I. A numerical simulation of woven fabric composites by fem based on damage mechanics, Proceedings of the 15th International Conference on Composite Materials, Durban 27th June – 1st July 2005, CD edition

27. Jao Jules, E., Lomov, S. V., Verpoest, I., Naughton, P., Beekman A.W., Van Daele R. Prediction of non-linear behaviour of discontinuous long glass fibres polypropylene composites, Proceedings of the 15th International Conference on Composite Materials, Durban 27th June – 1st July 2005, CD edition

28. Verleye, B., Klitz, M., Croce, R., Roose, D., Lomov, S.V., Verpoest, I., Computation of permeability of textile reinforcements, 17th IMACS World Congress, Paris, 2005, CD Edition

29. V. Volski and G.A.E. Vandenbosch, "Electromagnetic Modeling of Fibrous Materials for EMC and Antenna Applications", Proc. International Conference Fibrous Materials XXI Century, St. Petersburg, Russia, 23-28 May 2005

30. S.V. Lomov, F. Baudry, D.S. Ivanov, T.C. Truong, I. Verpoest, M.Vettory, H. Xie, Experimental methodology of study of damage initiation and development in textile composites, 27th International SAMPE-Europe Conference, Paris, 27-29 March 2006, 21-26

31. Verleye, B., D. Roose, S.V. Lomov, I. Verpoest, G. Morren, and H. Sol, Computation of permeability of textile reinforcements, in The 9th International Conference on Material Forming ESAFORM, April 26-28, 2006, N. Juster and A. Rosochowski, Editors. 2006: Glasgow. 735-738


32. Willems, A., S.V. Lomov, D. Vandepitte, and I. Verpoest, Double dome forming simulations of woven textile composites, in The 9th International Conference on Material Forming ESAFORM, April 26-28, 2006, N. Juster and A. Rosochowski, Editors. 2006: Glasgow. 747-750

33. Lomov, S.V., A. Willems, D. Vandepitte, and I. Verpoest, Simulations of shear and tension of glass/PP woven fabrics, in The 9th International Conference on Material Forming ESAFORM, April 26-28, 2006, N. Juster and A. Rosochowski, Editors. 2006: Glasgow. 783-786

34. D.S.Ivanov, S.V.Lomov, I.Verpoest, A.Zisman, Noise reduction of strain mapping data and identification of damage initiation of carbon-epoxy triaxial braided composite, Composites Testing and Model Identification (CompTest-2006), Porto, 2006, CD Edition

35. Gerd Morren, Jun Gu, Hugo Sol, Bart Verleye, Stepan Lomov, Full-field measurements for permeability identification by inverse methods, SEM Annual Conference & Exposition on Experimental and Applied Mechanics, St. Louis, Missouri, USA, June 2006, CD edition

36. B. Van Den Broucke, Ch. Eisenhauer, P. Middendorf, S.V. Lomov, I. Verpoest, Modelling of damage in textile reinforced composites: micro-meso approach, Proceedings CDCM06, Stuttgart, 18-19 September 2006.

37. Laine, B., Hivet, G., Boisse, Ph., Boust, F., Lomov, S.V., Badel, P. Permeability of the woven fabrics, The 8th International Conference on Flow Processes in Composite Materials (FPCM8), Douai, FRANCE - 11 – 13 July 2006, CD edition

38. Lomov, S.V., Verpoest, I., Verleye, B., Laine, B., Boust, F., WiseTex-based models of permeability of textiles, The 8th International Conference on Flow Processes in Composite Materials (FPCM8), Douai, FRANCE - 11 – 13 July 2006, CD edition

39. Verleye, B., Klitz, K., Croce, R., Griebel, M., Lomov, S.V., Roose, D., Verpoest, I., Predicting the permeability of textile reinforcements via a hybrid Navier-Stokes/Brinkman solver, The 8th International Conference on Flow Processes in Composite Materials (FPCM8), Douai, FRANCE - 11 – 13 July 2006, CD edition

40. Desplentere, F., Lomov, S.V., Verpoest, I., Correlated permeability distribution: mould filling simulations versus experimental results, The 8th International Conference on Flow Processes in Composite Materials (FPCM8), Douai, FRANCE - 11 – 13 July 2006, CD edition

41. Ivanov, D., Lomov, S.V., Verpoest, I., Baudry, F., Xie, H. Damage initiation and development in triaxial braid and fine structure of damage, Proceedings of the European Conference on Composite Materials (ECCM-12), Biarritz, 29th August – 1st September 2006, CD Edition

42. Lomov, S.V., Prodromou, A. Verpoest, I., Verleye, B., Roose, D., Peeters, T., Laine, B. Voxel representation of the unit cell of textile reinforcement: Mechanical properties and permeability, Proceedings of the European Conference on Composite Materials (ECCM-12), Biarritz, 29th August – 1st September 2006, CD Edition

43. Koissin, V., Ruopp, A., Lomov, S.V., Verpoest, I., Witzel, V., Drechsler, K. Internal structure of structurally stitched preform, Proceedings of the European Conference on Composite Materials (ECCM-12), Biarritz, 29th August – 1st September 2006, CD Edition

44. Kurashiki, T., Zako, M., Nakai, H., Hirosawa, S., Imura, M., Lomov, S.V., Verpoest, I. A practical numerical simulation system of mechanical behaviour of composites, Proceedings of the European Conference on Composite Materials (ECCM-12), Biarritz, 29th August – 1st September 2006, CD Edition


45. Willems, A., Lomov, S.V., Yingbo, Z., Verpoest, I., Vandepitte, D. Deformability characterisation of fabrics using large and small scale full field optical strain measurements, Proceedings of the European Conference on Composite Materials (ECCM-12), Biarritz, 29th August – 1st September 2006, CD Edition

46. Vallons, K., Zong, M., Lomov, S.V., Verpoest, I. Carbon composites based on multi-axial multi-ply stitched preforms: Stiffness degradation and tensile strength evolution during fatigue, Proceedings of the European Conference on Composite Materials (ECCM-12), Biarritz, 29th August – 1st September 2006, CD Edition

47. Zisman, A.A., Ivanov, D.S., Lomov, S.V., Verpoest, I. Processing discrete data by gradient matrix: Application to strain-mapping of textile composites, Proceedings of the European Conference on Composite Materials (ECCM-12), Biarritz, 29th August – 1st September 2006, CD Edition

48. Koissin, V., Ivanov, D.S., Lomov, S.V., Verpoest, I., Fibre distribution inside yarns of textile composite: geometrical and FE modelling, Proceedings of the 8th International Conference on Textile Composites (TexComp-8), Nottingham, 2006, CD edition

49. Klimshin, D.V. Shanina, A.S. Borovkov, A.I. Lomov, S.V. Verpoest, I. Macro-criterion and multi-level analysis of damage in fibre reinforced composites under complex 3D loading conditions, Proceedings of the 8th International Conference on Textile Composites (TexComp-8), Nottingham, 2006, CD edition

50. Ivanov, D.S., Lomov, S.V., Verpoest, I., Error of classical homogenisation for the problem with high macro strain gradients, Proceedings of the 8th International Conference on Textile Composites (TexComp-8), Nottingham, 2006, CD edition

51. Desplentere, F., Lomov, S.V., Verpoest, I., Validation of stochastic mould filling simulations with correlated permeability fields, Proceedings of the 8th International Conference on Textile Composites (TexComp-8), Nottingham, 2006, CD edition

52. Ivanov, D.S., Lomov, S.V., Verpoest, I., Zako, M., Nakai, Kurashiki, T., Hirosawa, S, Meso-FE modelling of 3-axial braided composites, Proceedings of the 8th International Conference on Textile Composites (TexComp-8), Nottingham, 2006, CD edition

53. Morren Gerd, Gu, Jun, Sol Hugo, Verleyen Bart, Lomov Stepan “Permeability identification of textile structures by inverse methods”, , Proceedings of the 7th congres on theoretical and applied mechanics, Mons, Belgium, May 2006

54. V. Volski, W. Aerts, A. Vasylchenko and G.A.E. Vandenbosch, "Composite Textiles Filled with Arbitrarily Oriented Conducting Fibres using a Periodic Model for Crossed Strips", Proc. International Conference on Mathematical Methods in Electromagnetic Theory 2006, Kharkiv , Ukraine, 26 June-1 July 2006

55. V. Volski, Y. Schols and G. Vandenbosch, "Efficient Calculation of Green's Functions For Periodic Arrays Using a New Asymptotic Extraction Technique", Proc. of the European Conference on Antennas and Propagation 2006, Nice, France, 6-10 November 2006

56. P. Baccarelli, A. Galli, S. Paulotto, G. Valerio, V. Volski and G. Vandenbosch, "Methods For The Accelerated Computation Of Green's Functions With 2-D Periodicity In Layered Media", Proc. of the European Conference on Antennas and Propagation 2006, Nice, France, 6-10 November 2006

57. Tolosana, N., S.V. Lomov, J. Stuve, and A. Miravete, Development of a simulation tool for 3D braiding architectures, in Proceedings of the 10th ESAFORM Conference. 2007, American Institute of Physics: Zaragoza, 1005-1010 http://proceedings.aip.org/proceedings/

58. Vanclooster, K., S.V. Lomov, A. Willems, and I. Verpoest, Measurement of local deformations on thermoformed composite parts under different process conditions, in

http://proceedings.aip.org/proceedings/


Proceedings of the 10th ESAFORM Conference. 2007, American Institute of Physics: Zaragoza, 1058-1063 http://proceedings.aip.org/proceedings/

59. Verleye, B., R. Croce, M. Griebel, M. Klitz, S.V. Lomov, I. Verpoest, and D. Roose, Finite difference computation of the permeability of textile reinforcements with a fast Stokes solver and new validation examples, in Proceedings of the 10th ESAFORM Conference. 2007, American Institute of Physics: Zaragoza, 945-950 http://proceedings.aip.org/proceedings/

60. Willems, A., S.V. Lomov, I. Verpoest, and D. Vandepitte, Picture frame shear tests on woven textile composite reinforcements with controlled pretension, in Proceedings of the 10th ESAFORM Conference. 2007, American Institute of Physics: Zaragoza, 999-1004 http://proceedings.aip.org/proceedings/

61. Van Den Broucke, B., K. Drechsler, V. Hanisch, D. Hartung, D.S. Ivanov, V.E. Koissin, S.V. Lomov, P. Middendorf, A. Miravete, M. Schouten, et al., Multilevel modelling of mechanical properties of textile composites: ITOOL project, in Proceedings of the 28th International Conference of SAMPE Europe. 2007: Paris. 175-180

62. Lomov, S.V., L. Dufort, P. De Luca, and I. Verpoest, Meso-macro integration of modelling of stiffness of textile composites, in Proceedings of the 28th International Conference of SAMPE Europe. 2007: Paris. 403-408

63. Vallons, K., S.V. Lomov, and I. Verpoest, Mechanical properties and damage evolution during static and fatigue loading of carbon-epoxy NCF composites, in Proceedings of the 28th International Conference of SAMPE Europe. 2007: Paris. 670-675

64. Verleye, B., G. Morren, S.V. Lomov, H. Sol, and D. Roose, Userfriendly permeability predicting software for technical textiles, in Industrial Simulation Conference 2007, J. Ottjes and H. Veeke, Editors. 2007: Delft. 455-458

65. M. Moesen, S.V. Lomov, I. Verpoest 'The condualistic approach for modelling the geometry of heterogeneous materials' Proceedings of the Conference on Modelling of Heterogeneous Materials(MHM2007), Prague, Czech Republic, 25-27 June 2007, pp. 224-225

66. Verleye, B., S.V. Lomov, A. Long, D. Roose, and C.C. Wong, Permeability of textile reinforcements: efficient prediction and validation, in 16th International Conference On Composite Materials (ICCM-16). 2007: Kyoto. CD edition

67. Koissin, V., S.V. Lomov, and I. Verpoest, Internal geometry of structurally stitched NCF preforms, in 16th International Conference On Composite Materials (ICCM-16). 2007: Kyoto. CD edition

68. Vallons, K., S.V. Lomov, and I. Verpoest, Fatigue and post-fatigue behaviour of carbon/epoxy non-crimp fabric composites, in 16th International Conference On Composite Materials (ICCM-16). 2007: Kyoto. CD edition

69. Lomov, S.V., D.S. Ivanov, I. Verpoest, M. Zako, T. Kurashiki, H. Nakai, and T. Kurashiki, Meso-FE modelling of textile composites: road map, data flow and algorithms, in 16th International Conference On Composite Materials (ICCM-16). 2007: Kyoto. CD edition

70. Lomov, S.V., D.S. Ivanov, K. Vallons, I. Verpoest, D.V. Klimshin, and T. Truong Chi, Peculiarities of damage behaviour of ncf carbon/epoxy laminates under tension, in 16th International Conference On Composite Materials (ICCM-16). 2007: Kyoto. CD edition

71. Moesen, M., S.V. Lomov, and I. Verpoest, The Condualistic Approach for Modelling the Geometry of Heterogeneous Materials, in MHM2007: Modelling of Heterogeneous Materials with Applications in Construction and Biomedical Engineering, M. Jirasek, Z. Bittnar, and H. Mang, Editors. 2007: Prague. 252-253

72. Moesen, M., S.V. Lomov, and I. Verpoest, Parametric modelling and finite element mesh generation for porous bone scaffolds, in Proceedings of the 2007 Summer Workshop of the European Society of Biomechanics (ESB2007). 2007: Dublin. 96-97





73. Lomov, S.V., D.S. Ivanov, B. Van Den Broucke, I. Verpoest, M. Zako, T. Kurashiki, H. Nakai, and S. Hirosawa, Meso-FE modelling of textile composites: road map, data flow and algorithms, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

74. Lomov, S.V., S. Ivanov, D.S. Ivanov, and I. Verpoest, Modelling of mechanical behaviour of textile glass-polypropylene composite, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

75. Prodromou, A., S.V. Lomov, and I. Verpoest, Mechanical properties of textile composites: analytical vs. numerical models, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

76. Koissin, V., S.V. Lomov, and I. Verpoest, Meso-scale modelling of structurally stitched preform, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

77. Hanaki, S., S.V. Lomov, I. Verpoest, M. Zako, and T. Uchida, Estimation of fatigue life for textile composites based on fatigue test for unidirectional materials, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

78. Van den Broucke, B., P. Middendorf, S.V. Lomov, and I. Verpoest, Modelling of damage in textile reinforced composites: micro-meso approach, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

79. Ivanov, D.S., L. Gorbatikh, S.V. Lomov, and I. Verpoest, Criterion of damage zone propagation in damage mechanics of textile composites, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

80. Tolosana, N., S.V. Lomov, and A. Miravete, Development of a geometrical model for a 3D braiding unit cell based on braiding machine emulation, in Proceedings of symposium "Finite element modelling of textiles and textile composites". 2007: St.-Petersburg. CD edition

81. Vallons, K., S.V. Lomov, and I. Verpoest, Damage evolution in static and fatigue tensile loading of carbon/epoxy NCF composites, in ECCOMAS Thematic Conference on Mechanical Response of Composites, P.P. Camanho, Editor. 2007: Porto. CD Edition

82. Morren, G., Sol, H., Verleye, B., Lomov, S., Permeability Identification of a Stereolithography Specimen Using an Inverse Method, ICEM13, Greece, 2007

83. Morren, G., Sol, H., Verleye, B., Lomov, S., Permeability Identification of a Reference Specimen Using an Inverse Method, SEM Annual Conference & Exposition, Springfield, Massachusetts, USA, June 2007

84. V. Volski and G.A.E. Vandenbosch, "Electromagnetic Modeling of Fibrous Materials for EMC and Antenna Applications", Proc. International Conference Fibrous Materials XXI Century, St. Peterburg, Russia, 23-28 May 2005

85. V. Volski, W. Aerts, A. Vasylchenko and G.A.E. Vandenbosch, "Composite Textiles Filled with Arbitrarily Oriented Conducting Fibres using a Periodic Model for Crossed Strips", Proc. International Conference on Mathematical Methods in Electromagnetic Theory 2006, Kharkiv , Ukraine, 26 June-1 July 2006

86. V. Volski, Y. Schols and G. Vandenbosch, "Efficient Calculation of Green's Functions For Periodic Arrays Using a New Asymptotic Extraction Technique", Proc. of the European Conference on Antennas and Propagation 2006, Nice, France, 6-10 November 2006


87. P. Baccarelli, A. Galli, S. Paulotto, G. Valerio, V. Volski and G. Vandenbosch, "Methods For The Accelerated Computation Of Green's Functions With 2-D Periodicity In Layered Media", Proc. of the European Conference on Antennas and Propagation 2006, Nice, France, 6-10 November 2006

88. V. Volski, Y. Schols and G. Vandenbosch, “Modelling of a periodic quasi-3D array using an asymptotic extraction technique”, Proc. of the European Conference on Antennas and Propagation 2007, Edinburgh, UK, 11 - 16 November 2007

89. V. Volski, G. A. E. Vandenbosch, P. Bacarelli, F. Frezza, A. Galli, S. Paulotto and G. Valerio, “Interpolation of Green’s function with 2D periodicity in layered media”, Proc. of the European Conference on Antennas and Propagation 2007, Edinburgh, UK, 11 - 16 November 2007

IV. Theses

PhD

1. Prodromou, A., Mechanical modelling of textile composites utilising a cell method, PhD thesis, Department MTM. 2004, Katholieke Universiteit Leuven

2. Truong, T.C., The mechanical performance and damage of multi-axial milti-ply carbon fabric reinforced composites, PhD thesis, Department MTM. 2005, Katholieke Universiteit Leuven

3. Frederik Desplentere. Meso-macro modelling of stochastic effects in mould filling simulations for thermoplastic composites. PhD Thesis, Department MTM K.U. Leuven, 2006

4. Bart Verleye. Computation of the permeability of multi-scale porous media with application to technical textiles. PhD Thesis, Department of Computer Science 2008, Katholieke Universiteit Leuven.

Master

1. Moesen, M. Modellering en numerike bepaling van de doorlaatbaarheid van textiel, Master thesis, Department Computerwetenschappen, 2004, Katholieke Universiteit Leuven

2. Ding, X.R. Strain distribution in woven glass fibre polypropylene composites under tensile and shear loading, Master thesis, Department MTM. 2004, Katholieke Universiteit Leuven

3. Fransens, F. Biaxial tension of glass/polypropylene reinforcements, Master thesis, Department MTM. 2004, Katholieke Universiteit Leuven

4. Ho, Ch.J. The mechanical performance and initial damage of sheared non-crimp fabrics reinforced epoxy composites, Master thesis, Department MTM. 2004, Katholieke Universiteit Leuven

5. Boudry, F. Damage characterisation of three-axial braided textile composites, Master thesis, Department MTM. 2004, Katholieke Universiteit Leuven

6. Xie, H. Micro-structural and damage analysis of braided composites, Master thesis, Department MTM, 2005, Katholieke Universiteit Leuven

7. Zong, M. Fatigue in non-crimp fabric composites, Master thesis, Department MTM. 2005, Katholieke Universiteit Leuven

8. Vo Ke Thanh NGO, Investigation of internal geometry and mechanical properties of non-woven textiles, Master Thesis, Department MTM K.U. Leuven, 2006


3 CONCLUSION

Accomplishments

The work has been performed according to planning. All the tasks were accomplished. The work done is summarised as follows

WP Title Developments 1.1 Theory and predictive

algorithms for internal structure of random fibre assemblies in relaxed state

Model for random short fibre composites low Vf) developed Model for non-woven fabrics developed “Dust” model for non-wovens

1.2 Theory and predictive algorithms for deformability of textile fabrics

Model for woven fabrics developed Parametric study of glass woven reinforcements performed

1.3 Theory and predictive algorithms for deformability of random fibre assemblies

Model for the deformability input data (nodes-links structure) in connection with the model of the internal geometry Principles of modelling of deformability defined Algorithms for calculation of resistance of non-woven materials to tension

1.4 Experimental verification Picture frame tests on woven and non-crimp fabrics Major improvements in the biaxial-tester of KULeuven Development and application of techniques of full-field measurement of textile deformation Experimental program on non-woven fabrics (orientation, fibre length and crimp, tension and shear) Experimental validation of the tension model for non-wovens. SEM registration of internal structure of non-wovens under tension

1.5 Development of software tools

Versions 2.4, 2.5 of WiseTex package NoWoTex software

2.1 Data organisation and

procedures for transferring the geometrical information of the deformed reinforcement

Algorithms for textile fabrics developed and implemented in software Algorithms for non-wovens developed and implemented in software

2.2 Solvers for the stress-strain state of a 3D shaped unit cell in a textile composite

Inclusion model (Mori-Tanaka) with damage solver developed and implemented in software Boundary conditions and reduction of mesh (symmetrical transformation) for meso-FE analysis of non-orthogonal unit cell

2.3 Parametric study and experimental validation

Mechanical properties and damage initiation and development in 3-axial braided composite studied experimentally


WP Title Developments 2.4 Development of software

tools TexComp software released MeshTex/SACOM software developed in Osaka University in collaboration with KULeuven Macros’ in ANSYS for meso-FE analysis NoWoTex software Integrated software WiseTex/TexComp/QuikForm/SYSPLY


procedures for transfer of geometrical information

Algorithms developed and implemented in software for textile and non-woven fabrics

3.2 Predictive algorithms for permeability based on the lattice Boltzman method

lattice Boltzmann algorithm implemented for general voxel models

3.3 Predictive algorithms for permeability based on an incompressible Navier-Stokes PDE solver

A fast permeability simulator based on the Navier-Stokes-Brinkmann partial differential equations implemented

3.4 Parametric study and experimental validation

Upgraded PIERS setup, reference stéréolithographic test specimens manufactured


FlowTex software with finite difference Navier-Stokes-Brinkman solver has been developed and released


procedures for transfer of geometrical information

Algorithms developed to simplify the geometrical information into a form suited for electromagnetic analysis. This algorithm is implemented in a special converter that allows to read information directly from WiseTex files describing topology.

4.2 Theory and predictive algorithms for effective permittivity, permeability, and conductivity of conducting fibre assemblies

Theory developed to analyze arrays of horizontal and vertical strips Theory developed to predict the effective parameters from calculated/ measured data.

4.3 Procedures for experimental determination of effective permittivity, permeability, and conductivity of conducting fibre assemblies

Measurement of shielding effectiveness was performed using several set-ups: - Coaxial holder set-up - Horn antennas

4.4 Validation Comparison with results available in literature and with experiments


Software tool developed

Valorisation

A web site (restricted access for the partners and the members of the user’s committee)

http://sirius.mtm.kuleuven.ac.be/Research/C2/poly/gbou/

has been set up, with presentations, reports, publications, software and other materials available on line.

The software, developed by partners, is commercialised. See Valorisation Report for more details.

http://sirius.mtm.kuleuven.ac.be/Research/C2/poly/gbou/


Interaction with the User's Committee

The interaction with the User's Committee went on in the following forms:

– Half-yearly project meetings with participation of the members of the Users Committee were organised. During its many meetings, the User’s Committee has shown an interest in the research project. Many valuable comments were made, many of which have been incorporated into the research at the universities.

– New demo versions of the software in the course of the development are put on the web-site for evaluation by the members of the User's Committee.

– Possibilities of further bi- and multilateral collaboration have been explored.

– Visit of Picanol R&D team to K.U.Leuven

– Extensive collaboration with Libeltex: (1) two types of non-woven fabrics has been provided to KULeuven (DryWeb T17 and DryWeb T28) for mechanical characterisation and study of internal structure; (2) fibre orientation study at Alasso Industries, USA organised; (3) an experimental program organised at Centexbel: length distribution and crimp in non-woven fabrics; (4) exchange of scientific and technical information; (5) two samples have been provided to KULeuven (Grade 8000836 Nickel Carbon and Grade 8000838 Nickel Carbon) for measurement of the electromagnetic shielding. (6) development of “dust” algorithm in NoWoTex; (7) joint publication in Textile Research Journal; (8) samples for electromagnetic measurements @ ESAT

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