connection elements for joint representation

7th European Altair Technology Conference , June 24th - 26th 2014, MunichDr. Niels Pasligh (R&A Europe AMCAE), Dr. Robert Schilling (FoE)

N. Pasligh (Presenter), R. Schilling

Crash CAE:Connection elements for joint representation exemplarily spot welds

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Motivation

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Generic b-pillar high overloading crash example

� Force displacement chart

a) Perfect world scenario without failure

b) Joint pattern #1 and failure consideration

c) Joint pattern #2 and failure consideration

d) No connection between b-pillar and side

structure

e) Sheet metal + joint failure with joint pattern #1

Joint failure need to be considered

� Reliability required

Displacement

Generic example:

� Extreme overloading

� Simple CAE model (no trim)

� Coarse mesh

� Simplified sheet metal and spot weld

� Side structure and b-pillar

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Content

� Joint requirements

� Full vehicle CAE models

� History

� Joint environment

� Physical connections

� CAE connections

� Radioss solution and model approach

� Examples

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Joint requirements

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General joint requirements

� Automatic joint creation based on push button principle for different detail levels

� Full integration into HyperMesh, HyperCrash required

� Correlation between physical and numerical characteristics� Good theoretical approach for RADIOSS solver

� Tension, compression, shear, bending, torsional and mixed behavior treatment (load level, energy consumption, …)

� 3 to 4 sheet connection treatment

� Automatic post-processing in HyperView required � e. g. percentage to failure - tension, shear, mixed,

angle of mixed loading, current loading condition, …

Pre-processing

Processing

Post-processing

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Full vehicle CAE models

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Full vehicle model history

Past Future

Past model:

� Mesh size > 50 mm

� 30,000 elements

� No/ basic joint modelling

� …

Today’s model:

� Mesh size ~ 5 mm

� 2 - 5 million elements

� Joint modeling

� Implemented joint failure

criteria

� …

Future model:

� Mesh size > 1 mm

� Multi million elements

� More detailed joint modeling

� Complex, interactive failure

criteria

� …

M o d e l c o m p l e x i t y

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Examples of physical joining methods

Others

• Thermal (Laser

welding, brazing, …)

• Mechanical (Riveting,

screwing, …)

Example:

Spot welding Bonding

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Full vehicle joint environment

Detailed FEM-model

� Time step too small

� Millions of elements for joints

�� not applicable to full car CAE

Extracted mid surfaces

� Time step as full car model

� Few additional elements

�� Applicable for full car CAE

Transfer to full vehicle

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Type of joints

Common nodes Contacts Elements

1-D 2-D 3-D

Surface to surface

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RADIOSS solution and model approach

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σσσσxx

σσσσyy

ττττyx

ττττyz

ττττxy

ττττxz

Node 1 Node 2

Node 3

Node 5

Node 7Node 8

5.0 mm

Single 3-D joint element

• Considered element strength calculated

at integration points of mid surface

• Reference plane: mid surface with 4

integration points

• Element

height “H” can be zero

• Artificial

definition possible

� Connection methodology to connect shell mid surface layer

� Most important internal forces are considered at four integration points (allows

splitting forces into momentums)

� Element formulation is time step independent

σσσσzz

ττττzx

ττττzy

σσσσzz

ττττzx

ττττzy

Node 6

Continuum solid Cohesive solidvs.

3-D joint element example

� Details of 3-D element treatment

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� Modeling approach by cohesive /MAT/LAW59/ formulation in Radioss

/MAT/LAW59/59Connection element - D U M M Y -# Init. dens.

7.65E-6# E G

10.0 123.4# Nfunc Fsmooth Fcut Y_flag

1 1 0 0# Y_Func_N Y_Func_T Strain Rate ref. Yield stress Scale

1 2 0.00001 1/FAIL/CONNECT/59# EPS_N_MAX EXP_N ALPHA_N SR_N IFAIL ISOLID ISYM

1.0 2 1 0 1 1 1# EPS_T_MAX EXP_T ALPHA_T SR_T

10.0 2 1 0# EI_MAX

0/PROP/CONNECT/59Adhesive#---1----|----2----|----3----|----4----|----5----|----6----|----7----|----8----|----9----|---10----|/FUNCT/1Tensile curve# X Y

0 1.0000 1.0 1.0000

/FUNCT/2Shear curve# X Y

0 1.000 10.0 2.000

Shape parameter

Tensile strength vs. displacement

Shear strength vs. displacement

Failure displ.

Modulus data

Tension (mode I) Shear (mode II)

Joint material card

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� *1.rad file setting for MAT/LAW59

� /ANIM/BRICK/USR - variable settings for displacement based failure criteria

/ANIM/BRICK/USR3/1

/ANIM/BRICK/USR5/1

Source: Altair Engineering GmbH, 2013

Joint post-processing

Tension (mode I) Shear (mode II)

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Joint material card modification

� Characterization of spot welds for full vehicle models

Shear load

Width = 0.5 “h”

t “h

Ftension = 2 * Fshear

Width = “h”

Ftension = Fshear

Width = 1.5 “h”

Ftension = 0.67 * Fshear

Shear load Shear load

� True thickness flag � compensation of mesh dependent momentums

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� Improvement of mixed mode treatment

Joint material card update �� MAT/LAW83

α=0.1

α=-2α=-10

Influence of alpha parameter Influence of beta parameter

Source: V. Dampuré: Altair Engineering GmbH, 2014

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Meshing of joints

� Meshing proposals CAE

5.0 mm

Source: Altair Engineering GmbH, 2011

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Examples

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CAE design development support

Physical joining Full vehicle test

Validation: ComponentCalibration: Coupon Validation: Sub-system

5.0 mm

CAE concept Product development

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� Load case

Validation component

� CAE model

� Results

� Force-displacement chart of a component test example

Adhesive

Spot weld

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Validation sub-system

� CAE model� Load case

� Results

Adhesive

Spot weld

� Force-displacement chart of a sub-system test example

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Product development: Pre-processing

� Generation of joints

Pre-processingE. g. Fiesta � single parts

Source:

A. Hänschke

Source:

U. FoxScrew

Spot weld

Automatic model assembly

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� Full vehicle load case: examples

Processing

Product development: CAE crash analysis

Post-processing

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Summary

� Efficient pre-processing tools needed

� More efficient integration and fully automatic pre-processing

� Solve 3T and 4T dependency for multi layer joints

� Stable connection solving algorithm

� Stabilize element deletion and energy release rate handling

� Mixed load handling, joint interaction and mid surface gap treatment

� Fully supported and automatic visual/ tabulated/ … inspection of joints by post-processing tools

Connection elements are for developing a reliable crash CAE design

Thanks to Altair team for support! Special thanks to M. Bulla and V. Dampuré.

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Thank you very much for your attention!

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