affordable lightweigthing using multi-scale materials...

Anthony CHERUET / e-Xstream Engineering

Affordable Lightweigthingusing Multi-scale Materials

Modeling to address Automotive new challenges

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Overview

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Digimat for CFRP insertion into Design

1 Introduction and Automotive Challenges

Digimat for SFRP-based metal to plastic programs

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3

Digimat Technology

Case Study (Valeo): Static Failure

Case Study (Volvo Cars Corporation): Dynamic Failure

NVH applications

Conclusion

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e-Xstream engineering

• The company• Founded in 2003

• Acquired by MSC Software in Sep 2012

• The Business: • 100% focused on material modeling

• A team of 50 people • 65% PhDs

• 25% MS & BS Engineering

• 10% Marketing, Finance & Admin

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Louvain-la-Neuve

Bascharage

Munich

Belgium

Luxembourg

Germany

U.S.

http://www.e-xstream.com/en/

http://www.e-xstream.com/en/

E-Xstream Engineering

• More than 300 hundreds customers in the world: aerospace, automotive, materials suppliers and academics.

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Digimat to simulate Multiple Types of Multi-Phase material with one Single Tool

• Digimat, Unique Solution for Multi-Materials

Short Fiber Reinforced Plastics Long Fiber ThermoplasticsWoven & Braided Composites

Hybrid Composites

Carbon Nanotubes

Mucell

Unidirectional fiber

sandwich panel

DFC

CHALLENGES IN THE AUTOMOTIVE INDUSTRY

Cost-Effective

Performance

Eco-Friendly

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Plastics usage will continue to grow thanks to their inherent properties

• Main Technical Challenges: Lightweighting….but not only

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COMPOSITES IS THE ANSWER…BUT WHICH MATERIAL TO SELECT?

What are the Challenges in Modeling Short Fiber Reinforced Thermoplastic ?

Skin

Core

Part is injected, resulting in a very spread local fiber orientation

Local orientation will result in difference local material properties

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What are the Challenges in Modeling Short Fiber

Reinforced Thermoplastic ?• Inter-dependencies between the manufacturing process and the final

performance of the part

Local material properties impacts

the final performance

Manufacturing sets

local microstructure

Local microstructure sets

material properties

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Overview

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Digimat Technology



NVH applications

Conclusion

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Multi-Scale Modeling Technology

• Prediction of Non-Linear Anisotropic Macroscopic behavior from constituents properties and microstructure

Semi-Analytical method

Mean-Field homogenization

• Mori-Tanaka

• Fast model preparation/solution

• Easy coupling with FE solver

RVE Direct Analysis method

Full-Field homogenization

• Build the accurate RVE geometry

• Compute it by FEM directly

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Multi-Scale Modeling Technology

• Building the bridge between Manufacturing and Analysis

• Improve accuracy of the Finite Element Analysis with Multi-Scale Modeling

Molding Process

Draping Process

CT Scan

For any types of performance

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Overview

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Digimat Technology



NVH applications

Conclusion

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• Vehicle Engine Cooling Radiator

Chopped fiber reinforced plastic automotiveapplication

Courtesy of

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Pin break testCourtesy of

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Experimental Result

• Load 1 : top to bottom

• Average force to break = 2350N

• Load 2 : bottom to top

• Average force to break = 2080N

Break

Courtesy of

Example shown : load 1

Simulation must be able to capture the different forces at failure for load 1 and load 2

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Isotropic method : Load 1 – attempt 1Courtesy of

• Material properties from classical lab tests

• Structural FEA

Overestimated force at break : 4033N

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Adjusting Isotropic Material model for FEACourtesy of

• Factor is applied to the stress/strain curve…

• …up to find the correct force at failure

For this loadcase and after several iterations, a -40% factor needs to be applied to match correctly measured force at failure

What if we change the loadcase ?

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Load 2 – Adjusted isotropic materialCourtesy of

• Material properties : adjusted stress/strain curve

Isotropic FEA prediction : 2356N

Different from real test !

The adjusted material model is not robust

• Measured force at failure : 2080N

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Injection Molding SimulationCourtesy of

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Digimat-RP, Rheology-Structure CouplingSolution

Courtesy of

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Structural Simulation with DigimatCourtesy of

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ConclusionsCourtesy of

• Isotropic material models (even « calibrated ») should not be used whensimulating parts made of reinforced plastics

• Good experimental correlation with rheology-structure coupling approach(Digimat failure indicator) at the 1st run

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Overview

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4

3

Digimat Technology



NVH applications

Conclusion

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Short fiber reinforced plasticsCourtesy of

• Volvo Cars Corporation has used Digimat for modeling short fiber reinforced plastics

• They investigated:

• Component tests

• Quasi-static strength

• Dynamic impact bending

• Vehicle loadcase

• Pedestrian safety

• Can not be disclosed

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Calibration of elastoplastic and strain rate dependent material parameters

Courtesy of

• The selected material was tested under Static and Dynamic conditions

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Short fiber reinforced plasticsCourtesy of

• Volvo simulated the injection and used Digimat MAP to transfer the local fiberorientation onto the Structural mesh,with specific attention to the skin-coreeffect

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Quasi Static LoadcasesCourtesy of

• Two different loadcases were defined:

3-point bending

Off-center 3-point bending

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Quasi Static ResultsCourtesy of

Loadcase 2Off-center 3 point bending

Loadcase 1Center 3 point bending

Test vs LS-Dyna exp / DigimatLS-Dyna imp / Digimat

Test vs LS-Dyna exp / DigimatLS-Dyna imp / Digimat

• Very good capture of the first failure• Good post-failure behavior

• Good capture of the first failure• Good post-failure behavior (for Implicite

Solver)

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Dynamic ResultsCourtesy of

Loadcase 2Off-center 3 point bending

Loadcase 1Center 3 point bending

Test vs LS-Dyna exp / DigimatTest vs LS-Dyna exp / Digimat

• Internal Energy is correctly transferred to the structure

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Dynamic Loadcase 2Courtesy of

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ConclusionsCourtesy of

• The predictability in terms of stiffness and progressive failure in LS-

Dyna/Digimat has been demonstrated

– 2 quasi static loadcases

– 2 dynamic loadcases

• Digimat parameters for Durethan BKV30 has been determined from the

limited test data available

– A more complete testing program would yield higher confidence in parameters

• Simulation of full crash loadcase (Pedestrian)

– 3-5% increasing computational cost for replacing isotropic model with local

anisotropic Digimat in one component

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Overview

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4

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Digimat Technology



NVH applications

Conclusion

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Usual Numerical Workflow for NVH FEA

Modal AnalysisNastran SOL103

Design process evolution

Frequency Response NastranSOL111

Acoustical ResponseActran

Stiffness/Mass Stiffness/Mass/Damping Air Acoustical Property

EigenfrequenciesEigenfrequencies+peak values in terms of acceleration responses

dB at passengers ears

Body in White

Components : seats, dashboard beam,

engine mounts, cam cover, steering system…

Body in WhiteFull Vehicle

Components : seats, dashboard beam, engine

mounts, cam cover, steering system…

Full Vehicle

Possibly the component source of noise

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• Complexity increases with integration of reinforced plastics

Modeling challenges

Mechanical complexity with Reinforced plastics Effect on inaccuracy

Stiffness

Local anisotropyFiber orientation

dependency error in identification of modal basis and excited

frequenciesFrequency dependency Visco-elasticity

Damping

Local anisotropyFiber orientation

dependencyerror in identification of

noise levels

Frequency dependency Visco-elasticity

These errors can lead to overdesign AND wrong design- unexpected noises will appear in physical testings !- Additional design iterations will be required

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Digimat 2016.0 can be usedfor advanced NVH of plastics and composites

• Digimat is able to predict Stiffness and Damping taking into account

local fiber orientation

• NVH with Nastran SOL1XX inside Digimat-RP

• Harmonic analysis is now supported with Marc (or Abaqus)

– When using viscoelastic (VE) Digimat material model

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Structural Engineering : Digimat 2016 added value

Nastran+Digimat Nastran alone

Stiffness

Homogeneous anisotropy

Local anisotropy

Frequency dependency

Damping

Homogeneous anisotropy

Local anisotropy

Frequency dependency

Chopped fiber reinforced materials

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Notes : - Nastran SOL1XX & Abaqus 6.14 : complete capability shown on table above- MARC & Abaqus 6.13 : only local anisotropic stiffness with frequency dependency available

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Digimat-RP/moldex3D : Driving point case

• Roof Front Beam

Roof Front Beam in sh

ell elements

Frequency response case : driving point2 possible fiber orientations to show how local

orientation affects the harmonic response

A Digimat viscoelastic material model

Gate position 1 Gate position 2

FE model

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Resolution aspects with Digimat RP (Nastran Solver)

• The user has the choice between 2 strategies

– Strategy 1: Ask to compute the material properties for a given frequency and re-

used these properties on all the analyzed spectrum

– Strategy 2: Ask to compute the material properties at each frequency of the

analyzed spectrum

1. Execution of Nastran 103 (Modal Analysis)

– One time if strategy 1; Each frequency step if strategy 2

– Anisotropy is taken into account via Digimat to compute Stiffness K and Mass M

2. Execution of Nastran 111 (Harmonic Response)

– For 1 resolution at 1 specific frequency

• A new bdf file is generated (1 time if Strategy 1)

• Digimat is used to generate local visco-elastic material properties (thru Nastran

Material Card).

• Maximum 230 materials are used to describe properly the variation of properties

due to the Anisotropy

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Excited frequencies and peak values are now predicted ensuring frequency and local fiber orientation dependency

Digimat : - Predict the complete vibrational behavior depending on injection process

Isotropic :- No link with injection process

- Need to be conservative to ensure that targets will be respected = OVERDESIGN !

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

0 50 100 150 200 250 300

Acc

eler

atio

n (

mm

/s2

)

Frequency (Hz)

Local Aniso [K(f) - D(f)] - Gate Position 1

Local Aniso [K(f) - D(f)] - Gate Position 2

Global Iso [0.6*Axial K - Conservative D(f)] - no injection dependency

An isotropic assumption can lead to very different conclusions

Shift in FrequencyPeak Value

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Full frequency solution ensure to get the correct response whatever are the excited frequencies

1.00E+01

1.00E+02

1.00E+03

1.00E+04

1.00E+05

1.00E+06

1.00E+07

0 50 100 150 200 250 300

Acc

eler

atio

n (

mm

/s2

)

Frequency (Hz)

K(100Hz) - D(100Hz) - Gate Position 1 K(300Hz) - D(300Hz) Gate Position 1 Local Aniso [K(f) - D(f)] - Gate Position 1

Comparison of results :

- Full frequency dependency

- Local anisotropic stiffness and damping from behaviors at 100Hz and 300Hz

Full frequency response matches with response with K and D computed at 100Hz

Full frequency response matches withresponse with K and D computed at 300Hz

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Summary

Challenges for NVH simulations with reinforced plastic and composite

made parts- Isotropic homogeneous method drives to overdesign or additional design iteration loops

due to error in the final part prediction

- Regarding stiffness and damping, such materials are

- locally microstructure dependent

- frequency dependent

Last enhancements in Digimat 2016.0 provide a complete answer- Local anisotropic stiffness and damping due to local microstructure variations

- Frequency dependency can be fully or partially taken into account in FEA

Digimat latest capabilities for NVH simulations with Nastran using visco-elastic

multi-scale material models will help to improve accuracy of predictions

Design iteration loops will be executed with more confidence to get better

lightweight and NVH performances for your next reinforced plastic and

composite parts

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Summary

• Integration of SFRP into the design brings new challenges in terms of

modeling- Such materials are

- locally microstructure dependent

- frequency dependent

- Isotropic homogeneous method drives to overdesign or additional design iteration

loops due to error in the final part prediction

• New Developments in Digimat- Computation of the local anisotropic stiffness and damping accounting for the local

microstructure variations

- Frequency dependency can be fully or partially taken into account in FEA

• Benefits− Improve accuracy of predictions

− Limit the number of iterations, bring confidence to get optimal lightweight and NVH

performances

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Overview

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4

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Digimat Technology



NVH applications

Conclusion

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Insertion of CFRP into Design follows a Building Block Approach

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Deformable barrier side crash

Digimat for multi-material conception

Roof and rear roof beams

NCF: CFRP with Damage Propagation ModelingLFT: EP with failure Indicator

Layups NCF + LFT

178 473 shell elts5 506 shell elts

28 692 shell elts

Roof beams

Passenger cell

Material Assignment :

• 212 671 shell elements assigned to a Digimat material model (7% of all shell elements)

Trunck floor

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FEA run & Global Deformation History

BMW reference Digimat POC 2015

Run Successful YES YES

CPU Time 68.3 h 77.5h / R = 1.13

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Comparison with BMW’s reference

BMW and Digimat models absorbed the barrier’s kinetic energy with similar strength.

BMW’s reference

Passenger cell deformations and failure locations are similar

U2 max = 342mm

U2 max= 350mm

Digimat POC 2014

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Conclusion

• CPU Time remains in the same range of value with or without Digimat

• Quality of the stiffness, failure and post failure prediction with Digimat for

CFRP made components is comparable to the best references used today in

the automotive industry

• The Digimat technology is usable in a multi-material context

• Digimat technology is an industrial solution usable at all scales of the building

block validation process

• Times required for all the Material Calibration with Digimat was much smaller

that for Standard Material Card (ie Progressive Failure of CFRP)

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Overview

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4

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Digimat Technology



NVH applications

Conclusion

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Conclusion

• Digimat bridges the gap between Manufacturing Process and Structural Performance

• Integrated Environment

• Benefits to the user:

Reduce Weight

Reduce material usage

Reduce risk of prototyping

Increase product Performance

• Is the part producible?• Where is the best performing and cheapest material that can be

used in the design?• Does the final design perform well in its working environment?

Bring systematic answers to big questions such as:

affordable lightweigthing using multi-scale materials...

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