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Bridging the Gap between Autodesk Moldflow and Nonlinear FEA of Reinforced Plastic PartsDr. Roger A. AssakerCEO, e-Xstream engineeringChief Material Strategist, MSC Software

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Class Objectives

To learn about the latest developments in modeling nonlinear behavior

of structures made of fiber reinforced plastics, including:

Long Fibers & MuCell Materials

Injection and Compression Molding Compression

Fatigue and Creep Performance

High Performance Computing

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Class Structure

Introduction & Motivation

Compression Molding

Long Fiber Reinforced Plastics

MuCell

Fatigue

Creep

Hybrid Solution Procedure

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Introduction & Motivation

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Composites in Automotive

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Opportunities: Weight Reduction Average/Indicative Facts: 1995 2005: +17% of mass (1118 kg1310kg) +200 kg +18% of Fuel consumption (4.8 l/100km 5.7 l/100km)

Objective : -200 kg or -15 to 20 g CO2/km by 2020

Plastic parts: interior, under the hood, … Optimize using advanced CAE/Material Modeling

Optimize design: e.g. engine mount: -40% weight & -15% in cost Reduce thickness

Part consolidation

Metallic parts: Platform, Cabin Frame, Skin,… Optimal mix of materials : Plastics, Composites, …

6

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Mutli (Composite) Materials

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Chopped Fibers/Injection Molding

Fully aligned flow

Flow lines

Weld lines

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Challenges of Reinforced Plastics

Process-dependent (Local)

Moldflow (Fiber orientation)

Nonlinear

Stain-rate dependent

Anisotropic

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Process Material Structure

Material Processing• Injection molding• Compression

modling• D-LFT

Material Microsturcure• Chopped fibers• Nano, ...

Material Chracteristics• Mechanical• Thermal• Electric, ...

Structural Performance

Stiffness

Strength

Fatigue, …

…

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Material Behavior: Measured

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Source:

LKT, Prof. DrummerFriedrich-Alexander-Universität

Erlangen-Nürnberg

Skin-core effect

Source:

DatapointLabse-Xstream Users‘ Meeting 2011

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Material properties from ISO 527 specimen Average orientation

OT{Trace} = [ 0.80 | 0.15 | 0.05 ] Scaling (factor = 0.6 – 0.8)

Material properties from injection molded plate 0° properties Scaling (factor = ???)

Material properties from injection molded plate 0° / 30° / 45° / 60° / 90° properties Reverse engineering Skin-Core effect

OT = [ multi-layer RVE ]

Measured Properties FEA ?

Globalisotropic

Localanisotropic

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Local, Nonlinear, Anisotropic Material

ISO 527100%

IM 22%

2D 36%

Loading

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Local Results: Plastic Strain

14

anisotropic

isotropic

equivalent scaling

Without Moldflow & Digimat)

With Moldflow & Digimat)

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Local Results: Weldline

15

Accumulated plastic strain in material matrix

Fiber orientations

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Materials: Long Fiber Thermoplastics (LFT)

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LFT – Effect of Fiber Waviness

Tortuose

Straight

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LFT – Effect of Fiber Bundling

Without bundling

With bundling~ 2300 MPa

~ 2800 MPa

+ ~ 500 MPa

s11 [MPa]

e11

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LFT - Effect of Bundling in Digimat-MF

+ 5% fibers 5% bundling

ar = 50

ar = 5

s11 [MPa]

e11

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Materials: MuCell

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MuCell RVE Generation

Source: http://www.genesisllc.com/gpe/images/mucell_glass.gif

15 % fibers

20 % voids

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Strain Distribution in the Microstructure

TensileDirection mean

local

TensileDirection

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MuCell: Effect of Void on the Material Stiffness

aligned

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MF vs FE modeling of MuCell

7.8% voids

15% voids

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MuCell: Distribution of the VF of Air Inclusions

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MuCell: 3-Point Bending Beam

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MuCell: Armrest Vertical Load

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MuCell: Horizontal Side Impact

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MuCell: Horizontal Impact CAE Performance Curves

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Performance: Fatigue

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Chopped Fiber Reinforced Plastics: Fatigue Analysis Workflow DIGIMAT reinforces the fatigue life computation at two levels:

Computation of the unit load case (Digimat-CAE/Structural) Computation of the fatigue life prediction (Digimat-CAE/Fatigue)

DIGIMAT Fatigue software

Digimat Material File (.daf)

Orientation data

Fatigue data(SN curve)

Static tests data

DIGIMAT interface to fatigue software

Element ID, critical plane orientation, ...

S-N curve, damage accumulation, ...

Digimat to CAE

FEA result file(odb,rst, …)

FE model

Fatigue model

Fatigue loadingFatigue modeling

options

Resolution of FEA on « unit load test cases »

DIGIMAT including new fatigue modeling capabilities

Fatigue results

Including new capabilities to call DIGIMAT for material computations

Fatigue data

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Fatigue: Chopped Fiber Reinforced Plastics

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First Pseudo Grain Fatigue (FPGF) Model Ply composite

Using fatigue failure criteria (i.e. Tsai-Hill) Pros : Different « strengths » per direction, multi-axial Cons : Purely meso/macro if not coupled with multi-scale methodology

Tsai-Hill

S: Fatigue strengths depending over N (nb cycles to failure) 1/L: Fiber direction 2/T: Transverse direction

Users workflow Exp measurement: S-N curves measured for 0°, 45° 90° UD specimens Material modeling: Define the measured S-N curves and corresponding microstructure (0° vs 90°) Fatigue solution: Prediction of local S-N curves in each integration point (ply in each element) of the FE model, accounting for any

• Stress amplitude • Mean stress• Loading direction / Fiber alignment

Damage accumulation: Miner’s rule

Tensile 0°

Tensile 90°

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Fatigue of Chopped Fiber Reinforced PlasticsUnit Load: Stress S11

Fatigue life

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Creep & Relaxation

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Creep & Relaxation

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Creep: Affine vs General vs Spectral vs FE

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Thermo-ViscoElasticity

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Thermo-ViscoElastic Relaxation

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CPU Optimization: Digimat Hybrid

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Hybrid Solution Procedure

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Crush Simulation: Digimat-CAE/LS-Dyna

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2012 DIGIMAT Users’ Meeting 43

Bumper Beam impact Material definition

Digimat v4.3.1 Viso-plastic propety FPGF failure

Tsai-Hill-2D strains§ Micro: strain base§ Hybrid: stress base

Mircostructure Morphology Orientation Length: Short Fibers (AR=20) Weight Fraction of Fibers

Isotropic Use MD property from Digimat-MF result Viso-plastic property Failure : end point of MF curve

MD

TD

FP

GF

failu

re d

efin

ed

at t

his

st

rain

-ra

te

Digimat Nonlinear Micro Material Model

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Optimization Decomposition• Default decomposition

Digimat elements in 3 domains

29 domains have no Digimat elements

• Improved decomposition

Digimat elements in 22 domains

10 domains have no Digimat elements

•Optimized decomposition–Almost same as improved but all domain has Digimat elements.

Optimal Domain Decomposition

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16 cores 32 cores 64 cores

Iso(improved)

17 h 59 m 9h 17m 10h 0m

Hybrid(default)

- 42h 31m -

Hybrid(improved)

26 h 37 m 14h 16m 8 h 15 m

Hybrid(optimized)

- 12h 5m -

Micro(improved)

-152 h 51 m(6.4 days)

-

Iso

Hybrid

Iso

Hybrid

CPU Performance: Digimat vs Isotropic

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Conclusions Reinforced Plastics is a light weight alternative to metals Advanced CAE, including nonlinear multi-scale material modeling ,

enables effective & efficient design of reinforced plastic parts by Taking advantage the process simulation done with Moldflow

The latest developments in Multi-Scale Material & Structural Modeling support: Long Fiber and MuCell Fatigue and Creep Performance

Hybrid Solution Procedure and HPC make Nonlinear Multi-Scale a efficient solution procedure for accurate part and system simultion

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