Die Simulation von Crash- und Impaktvorgängen auf ... · Die Simulation von Crash- und...

1 composite simulation – Ludwigsburg – Dr. André Haufe – 23. Februar 2012

Die Simulation von Crash- und Impaktvorgängen

auf Faserverbundstrukturen:

Eine Herausforderung in der Produktauslegung.

Dr. André Haufe, Dr. Stefan Hartmann, Dr. Thomas Münz

DYNAmore GmbH

Stuttgart


DYNAmore GmbH Gesellschaft für

FEM-Ingenieurdienstleistungen

Stuttgart - Karlsruhe - Ingolstadt - Langlingen - Berlin

Dresden - Linköping - Götheburg - Zürich

Industriestraße 2

D-70565 Stuttgart

Tel. 07 11 - 45 96 00 - 0

Fax 07 11 - 45 96 00 - 29

e-mail: [email protected]

Internet: www.dynamore.de


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für LS-DYNA

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Fluid-Struktur-Interaktion

Automotive

Schiffbau

Luft- und Raumfahrt

Offshore

Transportation

Biomechanik

Bauwesen

...

Crash

Insassensicherheit

Optimierung

Airbag, Dummy

Metallumformung

Impact und Falltest

Herstellungsprozesse

Glasumformung

Durchstoßprobleme

Weitere Informationen unter www.dynamore.de

Themen:

9. & 10. Oktober 2012 in Ulm

8. LS-DYNA® Forum


Composites

in technical applications


Composites: A rather broad term!

A combination of two or more materials (reinforcing elements, fillers, and

composite matrix binder), differing in form or composition on a macroscale. The

constituents retain their identities, i.e. they do not dissolve or merge completely into

one another although they act in concert. The components can be physically

identified and exhibit an interface between one another.

Definition

Concrete (cement/stone/steel)

Long fiber

reinforced polymers (glass/carbon/PA/PP/EP)

Sandwich/Laminates (alloy/polymer/..glass/PVB/…)

Short fiber

reinforced polymers (glass/PP)








Definition

Concrete (cement/stone/steel)

Long fiber

reinforced polymers (glass/carbon/PA/PP/EP)

Sandwich/Laminates (alloy/polymer/..glass/PVB/…)

Short fiber

reinforced polymers (glass/PP)

fibrous composite materials

(fibers in a matrix)

laminated composite materials

(layers of various materials)

particulate composite materials

(particles in a matrix)

short fibers long fibers








Definition

Properties that drive or limit the application in the automotive industry:

Weight & CO2 A reduction compared to steel and/or light alloys is anticipated.

Can be strongly dependent on composite setup, though!

Stiffness & strength Depending on the type or combination of fiber and matrix.

Can be higher or less that for comparable classic materials.

Production issue Usually curing of matrix material is one order of magnitude lower than

that of comparable engineering materials: Slow production cycle.

Economic issue At present, especially high performance composites are

rather expensive.

Part complexity Can be higher than for steel/alloys. May compensate higher cost.

&


Manufacturing: Predictive producibility simulation?

Short fibers:

Injection Molding (even shorter fibers)

Glass Mat Reinforced Thermoplatics (GMT)

Sheet Molding Compound (SMT) matrix usually vinylester & polyester

Bulk Molding Compound (BMT) matrix usually vinylester & polyester

Long/continuous fibers:

Pre-Pregs - pre-impregnated fibers

- available in single plies or laminates

- cooling chain necessary

- curing in forming tools or autoclave (heat&pressure)

Liquid composites molding (LCM):

- draping of “dry” fibers (not impregnated)

- injection/infusion of draped fibers in the tool

- curing in the tool


Application: Predict serviceability in crashworthiness

Length scale [ ]m [ ]mm [ ]cm

micro meso macro sub-ply

Status: Mostly shell like structures.

Stiffness and/or deformation prediction possible

IF fiber content and/or orientation is known.

Failure prediction may be possible if failure mode

can be engineered to be ductile.

Brittle failure is hard to predict, because

many different failure modes may exist

due to mechanisms on different length scales:


Application: Predict serviceability in crashworthiness

Length scale

[ ]m [ ]mm [ ]cm

micro meso macro sub-ply

Crushing/cracking/delamination/buckling on different length scales…

T/C in plane T/C out of plane

Shear

70ies

0.6k ele.

1990

12k ele.

1994

75k ele.

2004

2M ele.

smaller ele.


Modeling failure: Interlaminar vs. intralaminar

[Camanho]

Intralaminar (within one lamina):

Element: layered (thick/thin) shell

or one solid for each layer

Material: elasto(plastic) material models

with damage behavior

Interlaminar (between laminae):

Risc of delamination modeled by

cohesive elements or tiebreak

contacts

Element size in crashworthiness models is 1-2 orders of magnitude bigger, hence damage

and failure cannot be described in detail. A smeared approach is unavoidable.

stacked

coincident

layered

smeared stacked solid

hybrid stacked


Composite process chain: Producibility2Servicability

Problem: Different applications use different modeling techniques, constitutive models,

standards and validation procedures.

Producibility Serviceability

GMT, SMC, BMC

LMC or Prepreg??

Anisotropy and inhomogeneity Anisotropy and inhomogeneity

Co

nst.

mo

de

l m

ap

pin

g

Geometrical

mapping

Modeling technique


Producibility Serviceability

Geometrical

mapping C

on

st.

mo

de

l m

ap

pin

g

GMT, SMC, BMC

LMC or Prepreg??

Anisotropy and inhomogeneity Anisotropy and inhomogeneity

Composite process chain: Producibility2Servicability

? ?

Length scale?

Problem: Different applications use different modeling techniques, constitutive models,

standards and validation procedures.


Producibility


Process simulation: Motivation

Length scale

• Bundeled beam elements

• Automatic model setup

• Detailed studies

• Solid- or shell elements

• Automatic model setup

• Impact / draping simulation

• Single shell elements

• Autom. Model setup

• Draping simulation

• Smeared modeling

• Production-/Processsim.

• Draping and wrinkles

[ ]m [ ]mm [ ]cm


Process simulation: Motivation

Length scale

• Single shell elements

• Autom. Model setup

• Draping simulation

• Smeared modeling

• Production-/Processsim.

• Draping and wrinkles

[ ]mm [ ]cm

1 ply 2 plies 3 plies

membrane

homogeneous shell

layered solid/shell

stacked solid or shell


Example:

Generation of finite element model on the basis of CT data

Simulation on the μm-scale

real Piqué structure

diskretisation with

single beam

elements for each

individual thread

full model

[ITV Denkendorf, Finckh]


Example:

- Draping simulation of Piqué knitwear discretized with individual beams

- Experimental validation of simulation results via optical system

Simulation on mm-scale

[ITV Denkendorf, Finckh]

simulation experiment


Simulation on cm-scale

real structure structure of

mech. model

homogenized

structure

Smeared approach: Homogenization of local structure and constitutive properties

Validation of load bearing

properties by basic experiments

Homogenisierungsstrategie Homogenization strategy

str

ess

strain

Perpendicular

behavior

Longitudinal

behavior

Shear behavior


Modeling techniques on cm-scale: Fabric materials available for draping simulation

MAT_34 MAT_235 MAT_234


Picture Frame Test: MAT_MICROMECHANICS_DRY_FABRIC

Sensitive parameter: and lock 12

Single layer membrane element; Material parameters determined by optimization


Draping: MAT_MICROMECHANICS_DRY_FABRIC / MAT_ELASTIC incl. lay-up

Membrane formulation with coincident, elastic shell

Three element layers stacked with contact formulation


Modeling woven fabrics with beam elements:

Warp and weft direction *MAT_LINEAR_ELASTIC_DISCRETE_BEAM (MAT_066)

Diagonal behavior modeled with *MAT_CABLE_DISCRETE_BEAM (MAT_071)

Draping: Using discrete elements for strong anisotropy

This approach allows also to model positive and negative shear loading.

Optional matrix may be represented with shell elements and elastic/plastic material.


plain weave 5 harness weave

Process simulation: Draping with strong anisotropy

Some fabrics (preforms) show extreme orthotropic behavior. Here modeling with shell elements

using different constitutive models is possible:

and more…

modeling technique

single layer


Process simulation: Draping with strong anisotropy

Some fabrics (preforms) show extreme orthotropic behavior.

Here modeling with shell elements using

different constitutive models is possible.

For stacked preforms a similar approach

in finite element modeling is of course

possible: Multiple layers of shell elements.

modeling technique

three layers

y


Serviceability

(crashworthiness)


The challenge to predict failure in crashworthiness

on higher length scale

(smeared model) on same length scale

(detailed model)

Modeling complex failure modes…

Simple failure criteria

will often do!

Complex failure criteria

necessary!


The challenge to predict failure in crashworthiness

Element erosion, which is often seen as the only adequate (or available) solution to

failure modeling, leads to strong element dependency

Laminated glass:

Simple failure criteria on various meshes!

Possible solution:

Enhance discretization towards higher order modeling (and/or finer discretization)

Separate brittle failure modes (usually tensile fiber failure) from more ductile

mechanisms like compressive matrix failure.

Enhance constitutive models with orthotropic damage formulations.

Erode elements based on more complex criteria; use fading of elements.

Impact loaded composite tube:

Shock front travelling through part

…in space: …in time:


*MAT_022: (*MAT_COMPOSITE_DAMAGE)

plane stress

Chang-Chang failure criteria: fiber tension, matrix tension/compression

fiber compression is missing

“sudden” failure: E1,E2,nu12,G12 = 0.0

*MAT_054/055: (*MAT_ENHANCED_COMPOSITE_DAMAGE)

plane stress

failure criteria (54: Chang-Chang – 55: Tsai-Wu):

fiber tension/compression, matrix tension/compression

failure: stresses kept constant till failure strain reached,

then: E1,E2,nu12,G12 = 0.0

*MAT_058: (*MAT_LAMINATED_COMPOSITE_FABRIC)

plane stress

Hashin failure criteria: fiber tension/compression,

matrix tension/compression

exponential damage model

*MAT_059: (*MAT_COMPOSITE_FAILURE_Option_MODEL)

Option: SHELL/SOLID

LS-DYNA: Available models for composite structures

MAT_54 enhanced by inter-laminar shear

damage and failure model plus minimum

stress limits.

Constitutive models for composite structures


*MAT_158: (*MAT_RATE_SENSITIVE_COMPOSITE_FABRIC)

superposition of viscous stress tensor to strain rate

independent def. in *MAT_058.

*MAT_114: (*MAT_LAYERED_LINEAR_PLASTICITY)

plasticity model that DOES use laminated shell theory (LAMSHT=1)

*MAT_116: (*MAT_COMPOSITE_LAYUP)

elastic behavior (pre-integration in thickness direction for stiffness

matrix, saves CPU-cost)

requires *INTEGRATION_SHELL

resultant formulation (no stresses calculated)

*MAT_117: (*MAT_COMPOSITE_MATRIX)

elastic behavior (pre-integration in thickness direction

outside of LS-DYNA)

stiffness coefficients as material parameters given in

material coordinate system

*MAT_118: (*MAT_COMPOSITE_DIRECT)

like *MAT_117 but stiffness coefficients given in element coordinate

system (less storage required, no transformation necessary)

*MAT_161/162: (*MAT_COMPOSITE_MSC)

suitable for delamination

strain rate dependent

special license required (Material Science Corporation)

LS-DYNA: Available models for composite structures

Only available at extra cost.



*MAT_Camanho (Continuum-Damage-Model)

plane stress

coupled failure criteria

bi-linear softening law based on fracture toughness

1D-plasticity-model (mixed hardening) for in-plane shear

behavior

*MAT_Pinho (Continuum-Damage-Model)

3D-stress space

coupled failure criteria

complex 3D-fibre kinking model

linear softening law based on fracture toughness

1D-plasticity-model (mixed hardening) in in-plane shear behavior

LS-DYNA: Recent developments

*PART_Composite

Easier definition of lay-ups in part-section by just defining MATID, thickness and orientation.

*ELEMENT_(t)shell_composite

Same input scheme as in *PART_Composite but on element level.

Useful to define different lay-ups within one part (elementwise definition of lay-up).


New options for composite (part) modeling

Damage models with softening properties.

Usable for inter- and intra-laminar modeling.

Implemented in collaboration with Daimler AG.

Available in future releases.


Impacting mass of 350kg with 10m/s, triggered to fail in shear

UD carbon/epoxy composite with [90/0/-45/45]sym lay-up

MAT_54 for intra-laminar damage and failure; laminate theory invoked

Layered shell: No inter-laminar failure possible

Variation of softening behavior of neighboring

elements via parameter SOFT in MAT_54

(crashfront algorithm).

It is expected, that the failure mode becomes

more ductile, however in this example the

parameter set was chosen to be too brittle for

the model to take effect.

SOFT=0.5 SOFT=0.7 SOFT=0.9 SOFT=0.98 SOFT=0.0/1.0


4 stacked shells: Failure intra- and inter-laminar

Impacting mass of 350kg with 10m/s, triggered to fail in shear


MAT_54 for intra-laminar damage and failure modeling

Cohesive contact formulation for inter-laminar failure (debonding)



Impacting mass of 350kg with 10m/s, triggered to deform in buckling mode





Summary

Process simulation of different preforms is state-of-the-art and necessary to

transport important orthotropic properties into the world of crashworthiness.

A number of modeling techniques was presented.

Mapping of relevant data from forming/draping to the crash application is

available. However, the various modeling techniques require some adjustments.

Prediction of failure and crushing in crashworthiness applications is an ongoing

and very challenging topic. Transferring history variables is a must for more

complex part designs that one expects in the near future.

Simple failure models (stress or strain based) as used in the past will be

replaced by more sophisticated orthotropic damage evolution models. Partially

these are already available.

Rigorous testing and validation of code-procedures but also of hard-testing-

procedures is necessary to correlate models up to the needed quality.


FIN

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