Mohamed LOUKIL 1,2, Janis VARNA 2 , Zoubir AYADI1 Institut...
Transcript of Mohamed LOUKIL 1,2, Janis VARNA 2 , Zoubir AYADI1 Institut...
PARAMETER DETERMINATION IN DAMAGED LAMINATE MODEL B Y OPTICAL FULL-FIELD MEASUREMENT OF THE DISPLACEMENT USING ES PI
1Institut Jean Lamour, SI2M, Nancy-Université, EEIGM 6 Rue Bastien Lepage, F-54010, Nancy, France2Division of Polymer Engineering, Lulea University o f Technology, SE-97187 Lulea, Sweden
Mohamed LOUKIL1,2 , Janis VARNA2 , Zoubir AYADI1
5th International Conference on Composites Testing and Model IdentificationEPFL, Lausanne, 2011
Where is Luleå?
Luleå
Where is Nancy?
Nancy
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Outline
�Introduction : Laminate Damage
�Potential of ESPI for characterizing damaged laminates
�Damage development in a glass fiber/epoxy laminate
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
�Damage development in a glass fiber/epoxy laminate
�Conclusion and perspectives
3
Damage in composite
debonding
0° Layer
90° Layer
0° Layer
Initiation (micro-scale)
Propagation (ply-scale)
Transverse cracks
Interface problem:
6/27
Direction
of propagation
0° layer
90° layer
0° layer
Delamination
Transverse
crack
Transverse crack continues to propagate
Delamination
Interface problem:
Fiber/matrix
Transverse crack Delamination
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-70°70°
70°
0°
0°
σσσσxσσσσx
X
Z
y
Crack surface
Crack surface
y
σσσσxσσσσx
x→Laminate length (Tensile axis)y→Laminate widthz→Laminate thickness
COD : Crack Opening DisplacementCSD : Crack Sliding Displacement
CSD
x
y
z.
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Why we want to measure COD and CSD?
2
2112
012
0290
0
1
121
1
−−
+
=
νννν xy
x
x
x
E
E
h
tCOD
E
E
“Glob-Loc” approach (Janis VARNA)
COD(opening) and CSD(sliding) govern
the stiffness reduction
�These parameters are calculated for 90° layer using linear
Which technique we are going to use?
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�These parameters are calculated for 90° layer using linear elastic models: Shear lag, Hashins and FEM
�To prove that these results are correct
Basic Principles of ESPIFull Field Method: Interferometry of SpeckleESPI (Electronic Speckle Pattern Interferometry)
LaserWavelength = 0.6328 µmPower = 30 mW
The area of study is lit by two beams coming for the same laser
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Before displacement
Speckle before displacement
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
x
y
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After displacement
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
x
y
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Speckle after displacement Speckle before displacement
-Subtraction
=
Results Filtering Demodulating
=
1 542 3Steps:
Speckle after
displacement
Speckle before
displacement
Fringes
map
Filtered fringes
map
Displacement
map
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Displacement map
Measurement field: about 1 cm
x
z
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x
y
Z
.
about 1 cm
Advantages of ESPI� Full field imaging of displacement with a resolution of 10 nanometers.
�Measurements can be done on a variety of materials and the displacements undermechanical and thermal loads can be measured along three perpendicular axis withoutcontact with the sample.
�ESPI offers the unique possibility to measure both, the in-plane and out-of-planedisplacement without surface preparation.
Drawbacks of ESPIDrawbacks of ESPI� Complexity, high costs of optical setups, difficulties in aligning of the opticalelements.
�There are problems in working outside the laboratory especially due to high sensitivity ofESPI devices against environmental vibrations and daylight.
� Range of the measurable displacement: about a few micrometers
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E1= 44.7 GPa
E2
= E3
= 12.7 GPa
G12
= G13
= 5.8 GPa
G23
= 4.885 GPa
ν12
= ν13
= 0.297
ν23
= 0.3
The [0,704,-708,704,0] laminate was made ofglass fiber/epoxy.Specimen of 19.5 mm width, the thickness is2.75 mm and reinforced with GF/EP end tabs inthe gripping area.
Materials1.3751.222
0.611
0
-0.611
0°
+70°
+70°
-70°
Z (mm)
X
Damage evolution by increasing the stress σσσσ
13/27
-1.222-1.375
+70°
0°
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Crack surface
Crack surface
y
σσσσxσσσσx
In plane displacement measurement
CSD
RDx
yz.
Measurement directionθθ cossin ×+×= CSDCODRD x
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
Symmetric illuminations: themeasurement is along a direction(x) of the studied surface
Bisector
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Relative Displacement in (-70 °) layer
0.18
9 µm
196
µm
RD1n=0.380 µm/MPa
Crack 1 Crack 2R
elat
ive
Dis
plac
emen
t(µ
m)
0.18
9 µm
196
µm
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
0.19
6 RD1n=0.380 µm/MPa
RD2n=0.394 µm/MPa
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xz
Rel
ativ
e D
ispl
acem
ent
Pixels
Profile of the X-direction relative displacement along the mid-plane (on the specimen edge) corresponding to a variation of the relative average stress (∆σ = 0.497MPa).
0.19
6
Relative Displacement in (70 °) layersR
elat
ive
Dis
plac
emen
t(µ
m)
Relative displacement profile along the X-axis in the midplane of the 70°ply. ( ∆σ = 0.497 MPa)
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
0°70°
70°0°
-70°
Rel
ativ
e D
ispl
acem
ent
Pixels
16
xz
Relative Displacement in (0°) layersR
elat
ive
Dis
plac
emen
t(µ
m)
Relative displacement profile along the X-axis in the midplane of the 0°ply. ( ∆σ = 0.497 MPa)
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
0°70°
70°0°
-70°
Rel
ativ
e D
ispl
acem
ent
Pixels
17
xz
Out of plane displacement measurement
CSD
Crack surface
Crack surface
RD
y
z.
σσσσxσσσσx
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
Non Symmetric illuminations:the measurement is perpendicular to the fiber direction
RDx.
Measurement direction
Bisector
We are measuring COD directly
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Crack 1 Crack 2
CODn1= 0.300 µm/MPa
166
µm
0.16
0 µm
Rel
ativ
e D
ispl
acem
ent
(µm
)
COD measurement
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
Profile of the X-direction COD along the mid-plane (on the specimen edge) corresponding to a variation of the relative average stress (∆σ = 0.533MPa).
CODn2=0.311 µm/MPa0.16
6
Rel
ativ
e D
ispl
acem
ent
Pixels
19
xz
RDn CODn CSDn COD/CSD
Crack 1 0.380 0.300 0.286 1.049
Crack 2 0.394 0.311 0.297 1.047
Comparison of COD and CSDFor (-70°) layer
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
θθ cossin ×+×= CSDCODRD
θθ
cos
sinCODDRCSD
−=
20
Interactive cracks
RD1n = 0.200 µm/MPa
RD2n = 0.299 µm/MPa
RD3n = 0.313 µm/MPa
RD = 0.257 µm/MPa
Crack 1
Crack 2
Crack 3
Crack 4
Rel
ativ
e D
ispl
acem
ent
(µm
)
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
RD4n = 0.257 µm/MPa
Profile of the X-direction COD along the mid-plane (on the specimen edge) corresponding to a variation of the relative average stress (∆σ = 0.569MPa).
Rel
ativ
e D
ispl
acem
ent
Pixels
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0,010
0,015
0,020
CO
D (
mm
)
[0 , +704 , -704]S
Crack Opening Displacement in (-70°) layer by FEM[0, 704, -704]s
0.25 Experimental points
Elliptical model (fitted)
0,000
0,005
0,010
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7
CO
D (
mm
)
Z Coordinate (mm)
Actual Crack Profile
Elliptical Profile
Actual Crack Profile = Elliptical Profile
Good relation with the results found by Farge et al . [1]
[1] Farge. L, Ayadi. Z, Varna. J. Optically measured full-field displacements on the edge of a cracked composite laminate. Science direct composites 2008; Part A 39, 1245-1252
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0
0.05
0.1
0.15
0.2
0 5 10 15 20 25z (pixels)
CO
D (
µm
)
Elliptical model(interpolated)
2)(1)0()(a
zCODzCOD −=
Elliptical model
Conclusion
ESPI Potential for characterizing damage in laminat es
�Displacement field on the edge of a cracked laminate
�Typical profile the displacement for each ply
�Displacement jumps (cracks) can be measured,
Loukil Mohamed 5th International Conference on Composites Testing 14th February 2011
�By changing the directions of laser beams, the COD is directlymeasured; the comparison between COD and CSD is done in thiswork.
�The ratio COD/CSD depends on the material and on the plyorientation.
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Perspectives
� Comparison with micromechanics models.
� Investigate the effect of interaction between cracks
� Delamination effect on COD
� Cracking in fatigue
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Thank you for your attention!your attention!
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Camera
θθθθ
θθθθ
2
Δxδ2
M’
M∆x
λ
)(πδ
λ
πδ
λ
π θφ sin42221 =+=∆
θθθθ
1
1’
M’