How to create a VCS 3D model step by step

VISUAL CRASH STUDIO (VCS) is an all-in-one environment for early design, virtual testing and optimization of complex crashworthy structures. It includes the functionalities of the 2D environment for analyzing and design of thin walled prismatic members as well as a complex 3D virtual design space for modeling and testing of individual beams, subassemblies and complete structures. This presentation illustrates the basic VCS workflow and modelling procedures. The presented example shows the creation of a VCS beam model based on an imported FE structure. You will also find basic information about cross sectional design, handling of VCS materials and usage of rigid bodies.

Visual Crash Studio – all-in-one environment

2D + 3D environment

VCS – main view

Solution Explorer

On the top of the screen you can find the MAIN TOOLBAR where you have easy access to most of the VCS main features. On the left hand side of the screen you will find 3D VIEW TOOLS dedicated for the edition of the 3D view. This icons will enable you to control appearance of the main 3D view

In the Solution Explorer window located on the right hand side of the screen you will find folders containing each and every object created in the Solution.

Properties

The Properties window on the right hand side gives the possibility to edit an object. In the properties window you will find the properties and results for the currently selected object

Output & Dynamic Engineering

Assistant

In the Output window on the bottom of the screen you will find additional information about the current status of any selected tool. This window also includes basic help information for the selected tool Dynamic Engineering Assistant provides a list of errors, warning and useful messages detected in the VCS solution.

Cross Section Editor

Material Editor

Macro Element simplified models – 2D environment

Cross Section Editor

Material Editor

All Materials used in the VCS Solution can by defined by means of the Material Editor window. The Material is described by five groups of data in the Properties window:

Material Constants

Stress Strain Characteristic

Strain Rate Characteristic

Hardening Factor

Fracture Indicator

The Cross Section Editor is used to design, calculate and optimize Thin Walled Cross Sections. Cross Sections processed by the Cross Section Editor are then used to build 3D prismatic and tapered Super Beams. All Cross Sections created in VCS consist of:

Points

Plates – created by connecting two Points

Segments – build of Plates

Super Folding Elements

Connections

Finite Element Model

Macro Element Model – VCS

Macro Element simplified models – 3D environment

The Node is used as a spatial reference point for all VCS objects

The Node encompasses number of data necessary for dynamic simulation

Nodes

Super Beam - Defined by 2 Thin Walled Cross Sections

Solid Beam - Defined by a singe Solid Cross

Section User Defined Beam - The mechanical response of the

Beam defined by 2D Characteristics

Rigid bodies: sphere, cone, cylinder and box (cube) are created as objects attached to a Node.

Beams

Rigid Bodies

Barriers

VCS implements three deformable barriers according to the following specifications: MDB FMVSS 214; MDB 96/27/EC; ODB IIHS/EEVC

3. 2D Structure – Cross Sections 2. Material definition 1. mesh/initial geometry import

4. Cross Section analysis 5. 3D Structure – Super Beams 6. 3D – additional elements

ME method work scheme – general information

12. Results – Chart Wizard

7. Mass distribution 8. Initial & Boundary conditions 9. Contact settings

10. Solution Settings 11. Calculations and animation

ME method work scheme – general information

Import base model – VCS import procedures

In VCS you can find several import possibilities:

• Import Objects from other VCS Solution

• Import Data from FE Parts (Ls Dyna, Radioss)

• Multiple File Import from STL

• Import from Nastran

• Import Cross Sections from HYPERBEAM

VCS gives the possibility to import data from FE parts model. A Macro Element model based on Super Beams can then be created basing on the imported mesh geometry.

All imported elements can be easily found in the Solution Explorer Window, in the Imported Objects folder. They will be also displayed in the 3D view window. Note that along with the geometry, all information about material of the FE elements as well as shell thickness data will be automatically imported into VCS.

VCS Import procedures – Managing FE parts geometry

A VCS model can be created basing on an original FE geometry which can be easily imported from a mesh – based software. Among several import options, VCS offers the possibility to import geometry from Ls-Dyna which is used in the presented example.

Note that along with the geometry, all information about the Material of the FE elements as well shell thickness data will be automatically imported into VCS. Moreover the import tool creates simultaneously VCS Material basing on FE data.

The first step to be taken after FE geometry is imported into a VCS Solution is creating groups of FE parts. Placing specific assemblies (for example bumper, s-frame, A pillar etc.) into separate groups is very useful during the later work and beam modelling.

All imported elements can be easily found in the Solution Explorer Window, in the Imported Objects folder.

Imported Materials All Materials used in the VCS Solution can by defined by means of the Material Editor window. The Material is described by five groups of data in the Properties window: • Material Constants • Stress Strain Characteristic • Strain Rate Characteristic • Hardening Factor • Fracture Indicator

IMPORTANT NOTICE: In case of material import from available FE models material properties have to be verified. Improperly defined Material is a common mistake that causes distortion of the simulation results!

All imported Materials can be easily found in the Solution Explorer Window

The Material Properties such as Material Constants, Stress – Strain - Characteristics and the Strain – Rate Effects parameters are visible in material definition.

VCS Materials

Material Properties such as Material Constants, Stress – Strain - Characteristics and the Strain – Rate Effects parameters will be visible in the material’s Properties window. Note that VCS allows importing both 2D Array and 3D Array. The 2D Array is used to define the Stress-Strain property of the Material. VCS imports also characteristics based on original FE file of curves definitions that describe the Stress-Strain relation including Strain Rate Effect. The VCS counterpart of this material property is the 3D array.

(*) For more information about material definition in VCS please see: - VCS Manual – Material Editor (available for download on www,impactdesign.pl)

The quasi-static (plastic) stress-strain relation and dynamic response of the defined Material can be displayed by selecting appropriate tabs (Stress - Strain or Rate Effect) on the Material Editor window.

STRESS - STRAIN

RATE EFFECT

Super Beam structure – discretization and modelling procedures

Macro Element Method is based on simplified modeling. The concept of Super Folding Element at the cross sectional level and Super Beam Element in case of a 3D structure, enable creation of simplified models of variety of design concepts.

A proper discretization should be not too dense and resemble the initial geometry as much as possible. Changes of the cross sectional geometry should be taken under consideration. It is recommended to create a group of Super Beams for each assembly of the structure separately. Proper preparation of the original FE elements will guaranty a faster and correct discretization and modelling process.

A Macro Element Model is a SIMPLIFIED MODEL!

FE structure Super Beam structure

The simplicity of cross section modeling by means of macro elements is illustrated in the picture on the right :

• on the left – a Macro Element simplified model

• on the right – the original FE geometry

Macro Element 3D Structure - SUPER BEAM ELEMENT

The Super Beam Element is build up from a collection of Super Folding Elements (SFE). Each SFE has the length of the plastic folding wave 2H and models crushing response of single corner line of a prismatic or tapered segment of thin walled cross section. Therefore, the smallest size of Super Beam Element in any VCS model should not be smaller than the length of the plastic folding wave. Since each Super Beam has two deformable sections (referred to as deformable cells) the smallest recommended length of a Super Beam Element equals 4H.

The Super Beam Element models large deformations of thin walled structures Two major features of the Super Beam Element (SBE) must be kept in mind during any modeling procedure involving those elements:

The Super Beam Element models large deformations of thin walled structures, however, it follows standard definition of a beam due to Love & Kirchhoff. In particular the segment of thin-walled structure modeled by a SBE is limited by two planes perpendicular to the initially straight centroid line. During any deformation these planes remain perpendicular to the deforming centroid line. All the loadings exerted onto the SBE must be applied to the limiting surfaces referred to as SBE interfaces. These basic features of the beam formulation impose several restrictions on to the SBE response in crashworthiness calculations. For example: • Rotation (bending angle) of each interface cannot be larger than 90 deg. • Local Shell-like response of SBE in contact impact events must be modeled

separately using contact envelopes and contact characteristics

IMPORTANT NOTICE: General concept of discretization: Super Beams can bend ONLY at the ends (where deformable cells are defined). Therefore in the example of an actual beam bending model which collapse in the middle of its span at least two Super Beams are needed. In the case when potential location of plastic hinges (local collapse of the cross section) is not known in advance, the densest (the 2H criterion) discretization is justified.

Recommended discretization of the bumper assembly. The macro element bumper model will be created from 6 Super Beam elements.

Super Beam structure – discretization and modelling procedures

Bumper assembly – discretization into Super Beams (example)

S-frame assembly – discretization into Super Beams (example)

The S-frame assembly VCS model consists of 14 Super Beams. In the pictures on the right you can view the original FE geometry and recommended discretization of this structure into Super Beams FE structure Super Beam structure

FE structure

Super Beam structure

Create Super Beams from FE parts – 3D DISCRETIZATION

FE Parts

Super Beams

Since the core of a structural joint is very stiff, we can assume that in this case deformation will occur outside of the connection area (the region where number of elements coincides with each other). We can predict that deformation will take place at the joint legs (beams) instead of the joint itself - plastic hinges will occur at the narrow sections of engine cradle.

In case of the Sub-Frame assembly a significant simplification of the model can be observed. Please note two sets of pictures which illustrate how simplified the Macro Element model may be and how expendable FE parts can be neglected during the creation of Super Beams.

Sub-frame assembly – discretization into Super Beams (example)

FE structure

Super Beam structure

An interesting example of simplification typical for the macro Element method: The front part of Sub-Frame assembly consists of several elements linked together, creating a structural joint which exemplifies a very stiff structure.

1) Build Super Beams with the use of “Create Super Beam from FE parts”

tool, following the Macro Element requirements for discretization (simplified modelling)

2) Modify original Cross Sections – fine tuning the geometry

3) Calculate Cross Sections

4) Set Super Beams orientation in space

5) Merge Nodes

6) Move Nodes to appropriate position

Create Super Beams from FE parts – modeling procedures

Remember to follow the proper sequence of the modelling procedure:

1

2 3

4 5 6

Create Super Beam from FE Part A tool dedicated to enable the User to build complex Super Beam geometry from FE models

Cross Sections are created on the basis of FE model in following steps:

1) Select two FE nodes in order to define the reference axis.

2) The cross section through the FE parts is made following selection of one of the FE elements. The selected (gray) FE element marks position of the cutting plane perpendicular to the reference axis on the FE part.

3) The trace of the extracted cross section is shown on the 3D view as thick white line.

4) Press the “C” key – a new Super Beam and a new Thin Walled Cross Section will be created.

SELECTED POINTS SELECTED FE ELEMENT

2 3 1

The Thin Walled Cross Section created automatically by the Create Super Beam from FE Part tool represents the “best fit” to the expected final shape of the cross section. The initial cross section geometry needs to be modified to fulfill all Macro Element Method requirements!

In the Solution explorer three you will be able to find automatically created: • Points • Plates • Segments

Create Super Beam from FE Part – new Cross Section

Create propor cross sections

The first step in building the Super Beam Element models is the definition of Cross Sections which characterize mechanical response of a beam. The cross sections are defined, pre-calculated and optimized in the VCS module Cross Section Editor. Please note that the cross sectional geometry needs to fulfill all Macro Element Method requirements

Every cross section used in a model has to be calculated. In the early stage of the project first significant results are obtained. Information about axial response, bending and torsion are displayed in the Cross Section Editor and in the Cross Section’s properties window.

IMPORTANT NOTICE: Proper modelling and calculations of cross sections are significant for the entire, further 3D simulation. Neglecting this stage of VCS model development can lead to errors and false results in later simulations!

1. total length, C, of two arms of a SE, C = a + b,

2. central angle, Φ

3. wall thickness ta of the arm of the length a

4. wall thickness tb of the arm of the length b

The initial geometry of a Super Folding Element is defined by four parameters:

SFE is cut by set of two horizontal, parallel planes

The distance between the horizontal planes equals the length of the plastic folding

wave of a column

The vertical boundaries – planes equally distanced from the

neighboring corners

The very core of the theoretical background of Cross Section Editor is the Super Folding Element (SFE). The SFE represents the segment of a corner line off a prismatic column. One SFE is cut off from a column by a set of two parallel horizontal planes. The distance between planes, 2H, equals the length of the plastic folding wave of the column. The vertical boundaries of a SE are defined by a set of two vertical planes equally distanced from the neighboring corners and/or vertical edges of a column

Super Folding Element

Macro Element Method – simpliefied 2D modelling.

In order to guaranty the deformation transfer connections need to be added to the model. Connections force connected element to fold in compatible manner regardless of the type of physical connection.

NEGLECTING DETAILES

ADDING CONNECTIONS

A Macro Element model is a simplified model, where details of the cross sectional geometry , such as minor dents, should be neglected. The problem of radius modelling at the Cross Section level is related to the definition of Super Folding Element (see the previous slide). Please note that SFE models crushing behavior of the entire corner area in a prismatic member. Consequently, the cross-section details smaller then dimensions (a, b) of the SFE cannot be effectively modelled using this methodology. The simplicity of the model enables quick and easy modification of the geometry which can be done by changing coordinates of points. Each plate of a cross section can be defined individually which enables testing of various thicknesses of each side face of a beam. Similarly, material type can be defined as an optimization variable.

CROSS SECTION EDITOR – 2D MODELLING

In the three presented pictures you can find stages of the cross section modelling procedure. Please note that the initial geometry created by the “Create Super Beam from FE Part” tool does not correspond to the FE geometry well enough (picture 1) Several modifications were made to transform the cross section geometry. A number of Cross Section Editor tools were used to modify the cross section as well as the “Clean model” functionality. The final result of the modification process – a properly design cross section is shown in the picture 3

Bumper assembly – Cross Section – 2D modeling example

1 2

3

CROSS SECTION EDITOR – 2D MODELLING

S-Frame cross section - Example of proper Cross Section modelling

The picture presents a proper cross sectional design based on a FE geometry.

The blue and green dots represent the original FE geometry.

Grey lines represent plates of the simplified Macro Element cross section.

Additionally please note that a number of connections has been added to the design.

In the set of pictures presented on the right you can find an example of modelling the mechanical response of a plate element. Please note that in the original FE geometry plate elements are present in this section – pink and grey elements). The Super Beam closest to the S-frame assembly reflects the mechanical response of those elements. In the 2D cross sectional view presented below you can see that plate elements are taken under account following the “effective width” rule – solely the corner part of the plate element is take under account in the cross sectional modelling.

Modeling of a plate element’

Axial Response

Design Recommendations

Bending Response

Elastic Properties

Lateral Response

Denting Response

Torsion Response

Results of calculations for a cross section are grouped in 7 expandable containers in the section Results of the properties window

Each container lists characteristic parameters for a given crushing response mode such as maximal value of force or moment, energy absorption capacity, limiting value of a deformation such as total rotation in bending hinge or jamming rotation in torsion crushing.

Calculate Cross Sections

Save and share materials and cross sections – VCS Repository

It is possible to create a personal archive of Cross Sections which can be opened and used whenever working on a new Solution. You can also export any Material or Characteristic from a Project into the Repository.

In the middle of the “Repository Explorer” window you will find a list of Cross Sections together with the date of its addition to the repository and the date of the latest modification.

On the right side of the ‘repository Explorer’ window you will find the detailed ‘read – only’ properties of the selected Material or Characteristic

Set Super Beams orientation in space IMPORTANT Proper definition of the Orientation Vector property is a necessity! Neglecting definition of this parameter may cause instability of the model and in consequence may negatively affect final results!!!

In case of the bumper assembly the structure is oriented along Y axis of the global coordinate system (green axis visible in the 3D view). This is useful information for beams orientation. After selecting a Super Beam, find the “Orientation Vector” section in the Properties window. The “Y” field should be changed to “0”. Such setting of the beam’s properties will prevent possible instabilities of the more complex model. It also facilitates the procedure of beam’s orientation in 3D space. Now change the “X” and “Z” parameter in the “Orientation Vector” field of beam’s Properties window. You can observe that the beam will change its position in 3D space. As a final result you should receive a SuperBeam model which corresponds to the original FE geometry, as shown in the picture on the left.

Connect Super Beam elements

Each beam of the structure has been defined separately and in consequence following beams creating the assembly do not share common Nodes. Therefore the next step of modelling requires merging on Nodes of the neighboring beams. In the VCS main toolbar you can find the “Merge Nodes” tool.

Moreover, in case Super Beams connection offset functionality can be used in (as illustrated in the picture on the right). Offset can be defined for each beam with the use of “Modify Offset, Orientation, Position” tool available in the VCS main toolbar. Offset is visible in the 3D view as a blue line.

IMPORTANT At this stage of modelling Super Beams are not yet connected!

Additional elements – how to use VCS Rigid Bodies

It is recommended to model components like engine, wheels or radiator by means of VCS Rigid Bodies. In the picture on the right you can see the Toyota Camry model containing all Rigid Body elements. Please note that several types of Rigid Bodies have been used to model such elements like: engine, gear box, battery, radiator, wheels and barrier. Rigid bodies: sphere, cone, cylinder and box (cube) are created as objects attached to a Node. All rigid bodies share the same create and edit procedures as well as set of properties.

Elements which cannot be modeled in VCS directly as it is in reality, need to be replaced with elements which physically work as a counterpart with equivalent response.

ENGINE AND WHEELS MODELLED WITH THE USE OF RIGID BODIES

Body in white – additional elements – Rigid Bodies

Engine, gearbox, intake manifold, water pump, alternator – Rigid Bodies

Contact Bodies Barriers Wheels and suspension

Additional elements – how to use VCS Rigid Bodies

ESTIMATED NODE POSITION

The presented example illustrates modelling of the engine, gearbox, alternator, water pump and intake manifold basing on an original FE geometry . All those elements can be modelled with the use of VCS Rigid bodies. Please note that the whole “engine “ group of rigid bodies is defined on a ONE single Node located in the center of gravity of this group – marked by green circle in the picture on the right. Coordinates of the central node can be taken from the original FE model, and should be coherent with the engine group’s center of gravity.

WHEELS and SUSPENSION – Rigid Bodies and additional Beams

In VCS simplified model wheels and suspension can be modelled by means of Rigid Bodies (cylinders), additional Super Beams, and User Defined Beams. Please note that only the most relevant elements have their counterpart in the VCS model. In Macro Element simplified modelling wheels are represented by Cylinder Rigid Bodies. Please note that in VCS friction is not defined for an object. Friction coefficient settings can be done on the level of contact settings.

Comparison of the original FE geometry and the simplified macro element structure

Additional elements – how to use VCS User Defined Beams

USER DEFINED BEAM

The vehicle suspension can be modelled with the use of a User Defined Beam.

In case of this suspension assembly the user defined beam has been defined in the center of a Super Beam, and shares the same Nodes. Please note that two offsets have been used to define the correct position of the beam. You can see the User Defined Beam marked in orange in the picture on the left. Each User Defined Beam can be found in the Beam folder of the Solution Explorer tree. Its mechanical response is defined in the properties window by means of 2D Characteristics Please note that the beam is defined by a Spring Characteristic (this information can be found in the Mechanical Response section of User Defined Beam’s Properties window).

2D Spring Characteristic defined in the Characteristic Editor.

Thank you

for your kind attention

Impact Design Europe ul. 3 Maja 18 05-816 Michalowice POLAND www.impactdesign.pl

Contact: Agata Abramowicz Sokoll CEO mail: as@impactdesign.pl