1. Bridging the Gap between Autodesk Moldflow and Nonlinear FEA of Reinforced Plastic Parts
Dr. Roger A. Assaker
CEO, e-Xstream engineering
Chief Material Strategist, MSC Software

2. 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

3. Class Structure Introduction & Motivation Compression Molding
Long Fiber Reinforced Plastics
MuCell
Fatigue
Creep
Hybrid Solution Procedure

4. Introduction & Motivation

5. Composites in Automotive

6. Opportunities: Weight Reduction
Average/Indicative Facts:
1995  2005: +17% of mass (1118 kg1310kg)
+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, …

7. Mutli (Composite) Materials

8. Chopped Fibers/Injection Molding
Fully aligned flow
Flow lines
Weld lines

9. Challenges of Reinforced Plastics
Process-dependent (Local)
Moldflow (Fiber orientation)
Nonlinear
Stain-rate dependent
Anisotropic

10. 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, … …

11. Material Behavior: Measured
Source:
LKT, Prof. Drummer
Friedrich-Alexander-Universität
Erlangen-Nürnberg
Skin-core effect
Source:
DatapointLabs
e-Xstream Users‘ Meeting 2011

12. Measured Properties  FEA ?
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 = ???)
0° / 30° / 45° / 60° / 90° properties
Reverse engineering
Skin-Core effect
OT = [ multi-layer RVE ]
Global
isotropic
Local
anisotropic

13. Local, Nonlinear, Anisotropic Material
Loading
ISO 527
100%
2D 36%
IM 22%

14. Local Results: Plastic Strain
equivalent scaling
isotropic
anisotropic
With Moldflow & Digimat)
Without Moldflow & Digimat)

15. Local Results: Weldline
Fiber orientations
Accumulated plastic strain in material matrix

16. Materials: Long Fiber Thermoplastics (LFT)

17. LFT – Effect of Fiber Waviness
Tortuose
Straight

18. LFT – Effect of Fiber Bundling
s11 [MPa]
e11
Without bundling
With bundling
~ 2300 MPa
~ 2800 MPa
+ ~ 500 MPa

19. LFT - Effect of Bundling in Digimat-MF
ar = 50
ar = 5
+ 5% fibers
5% bundling
s11 [MPa]
e11

20. Materials: MuCell

21. MuCell RVE Generation 15 % fibers 20 % voids
Source:
15 % fibers
20 % voids

22. Strain Distribution in the Microstructure
Tensile
Direction
mean
local
Tensile
Direction

23. MuCell: Effect of Void on the Material Stiffness
aligned

24. MF vs FE modeling of MuCell
7.8% voids
15% voids

25. MuCell: Distribution of the VF of Air Inclusions

26. MuCell: 3-Point Bending Beam

27. MuCell: Armrest Vertical Load

28. MuCell: Horizontal Side Impact

29. MuCell: Horizontal Impact CAE Performance Curves

30. Performance: Fatigue

31. 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)

32. Fatigue: Chopped Fiber Reinforced Plastics

33. 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°

34. Fatigue of Chopped Fiber Reinforced Plastics
Unit Load: Stress S11
Fatigue life

35. Creep & Relaxation

36. Creep & Relaxation

37. Creep: Affine vs General vs Spectral vs FE

38. Thermo-ViscoElasticity

39. Thermo-ViscoElastic Relaxation

40. CPU Optimization: Digimat Hybrid

41. Hybrid Solution Procedure

42. Crush Simulation: Digimat-CAE/LS-Dyna

43. Digimat Nonlinear Micro Material Model
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
FPGF failure defined at this strain-rate TD

44. Optimal Domain Decomposition
Optimization Decomposition
Default decomposition
29 domains have no Digimat elements
Digimat elements in 3 domains
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.

45. CPU Performance: Digimat vs Isotropic
Hybrid
Hybrid
16 cores
32 cores
64 cores
Iso
(improved)
17 h 59 m
9h 17m
10h 0m
Hybrid
(default) -
42h 31m
26 h 37 m
14h 16m
8 h 15 m
(optimized)
12h 5m
Micro
152 h 51 m
(6.4 days)

46. 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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