1. Failure Analysis of Fiber Reinforced Injection Moldings Using a Composite Lamina Approach
Robert Sherman
Senior CAE Analyst, RTP Company

2. Class Summary
In this class we will present to you a reasonable approach to structural analysis of fiber reinforced injection molded designs. We will also provide some insight into important parameters in the analysis that can be utilized to improve the simulation performance of your designs.

3. Learning Objectives At the end of this class, you will be able to:
Understand the importance of anisotropic structural analysis for good design
Appreciate the need for further structural research of fiber reinforced materials
Implement the lamina failure approach in predicting injection molded strength
Better predict the strength of any fiber reinforced injection molded part design

4. Problem: Predicting Structural Integrity

5. Designing with Fiber Reinforced Materials
Quasi-isotropic analysis no longer acceptable
Everyone wants to optimize their design
Few engineers know HOW!
Validation of fiber orientation
Microscopy
Microtomography (Skyscan)
New fiber orientation parameters
Reduced Strain Closure (RSC) model
Anisotropic Rotary Diffusion (ARD) model
Fiber aspect ratio

6. How can we validate fiber orientation?
Validate orientation by micro-mechanical property predictions
If orientation is right – stiffness and strength are right
Requires thickness variations and flow/cross-flow orientation
Some already done for mechanical properties
Determine correlation parameters with selected materials
Tensile modulus correlation validates intensity of orientation
Flexural correlation validates distribution through thickness

7. Standard Test Panels

8. RSC Factor – Slow Orientation Dynamics
Standard Tucker-Folgar model
Represents orientation in fully developed steady-state flow
RSC factor introduced
Orientation requires flow history to fully develop
That rate may vary based on many factors
Polymer
Fibrous reinforcement
Reinforcement volume content
Others???

9. RSC Factor Presents an Opportunity !!!
Glass half empty (typical user’s normal attitude!)
Or, glass half full ???
Utilize new parameter to improve the orientation correlation
Still requires experimentation to establish
Possibly for all major polymer types (or classes)
% level of reinforcement
GF, CF, VLGF, VLCF

10. What a Difference a Factor Can Make !!!

11. WHAT DO I DO NOW !!!!!!!

12. Start with Molded Specimen Orientation Validation

13. Molded Tensile Modulus vs. RSC & Fiber AR

14. Flow Direction Modulus vs. RSC & Fiber AR (Spec. T1)

15. Flow Direction Modulus vs. RSC & Fiber AR (Spec. T5)

16. Flow Direction Modulus vs. RSC & Fiber AR (Spec. T3)

17. Flow Direction Modulus for RSC=0.25 & AR=40

18. Cross-flow Direction Modulus for RSC=0.25 & AR=40

19. FIBSTRS API – Nanda Santhanam

20. Composite Lamina Stress Analysis – NEi NASTRAN®
Linear material model utilizes AMI modulus predictions
Don’t rely on “back-calculated” resin properties
Utilize low % secant modulus ( %)
Delete panel geometry except tensile specimen of interest
Apply testing boundary conditions and test load or displacement
Add estimated strength allowables to material property cards
Evaluate stress distributions and failure index based on different failure criteria

21. Stress Analysis – Flow Direction Specimen T5

22. Stress Analysis – Flow Direction Specimen T5; Ply #2

23. Stress Analysis – Flow Direction Specimen T5;Ply #5

24. Summary
Micro-mechanical property predictions can assist in orientation validation
RSC factor has no “default” value
Fiber AR may now be a useful variable with RSC implementation
Composite lamina failure techniques can detect critical stress locations
Implementation of “successive ply failure” and flexural simulation should help
Much room for more research

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26. Bob Sherman rsherman@rtpcompany.com
Questions?
Bob Sherman

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