Simulation of Twisted Fiber LaminatesDept of Mechanical & Industrial Engineering, TAMUK

Graduate Student: Madhuri Lingala Faculty Mentor: Dr. Larry D Peel, P.E.

Abstract

The current work explores extreme Poisson’s ratio twisted fiber laminates. Fiber reinforced elastomer (FRE) composites show promise for use in tires, morphing wings, vibration dampers, impact resistance, solid-state actuators, inflatable aerospace structures, and various bio-mechanical applications. These are made possible because of their high impact strength, vibration damping ability, large elastic deformations, and tailorable nonlinear characteristics.

Recently, FRE laminates have been fabricated that exhibit extreme (high and negative) Poisson’s ratios. The current research includes developing finite element models of twisted fiber laminates, which will be investigated using linear and non-linear finite element analysis and verifying the simulations through fabricated specimens, if possible.

It has been observed that uni-axial fiber-reinforced elastomer laminates, where the fibers are twisted, exhibit an effective increase in axial stiffness, and may have high Poisson’s Ratios. Negative Poisson’s ratios may be produced if the fibers have a double helical path.

Background - Fiber Reinforced Elastomers

Concerns with FEA of twisted fibers

• Fibers merge into one another (need contact elements / formulation)

• Spacing of strands• Mesh size• High number of elements

Intermediate Conclusions and Planned Work

FEA results indicate that an increase in axial stiffness is possible, but better analysis is needed.

We will ensure that fibers do not merge into each other (through contact formulations). We will assess laminate Poisson’s ratios of single and double twisted fiber laminates using nonlinear FEA, and we plan to simulate several applications. We intend to fabricate twisted fiber bundle specimens using better impregnation methods than before and would try to overcome gripping issues that were faced to test the specimens due to low stiffness values of the fibers. Results from FEA will be verified through tests.

Previous Work with Twisted Fiber-Reinforced Elastomers• Fabrication and testing of twisted cotton / rubber specimens• Finite element analysis of twisted cotton laminates• Comparison of FE analysis and experimental results• FE analysis of twisted fiber bundles and Gr/elastomer

Spiral fiberglass fibers/RP6410 resin with matrix Poisson’s Ratio =.5

Spiral fiberglass fibers /RP6410 resin with matrix Poisson’s Ratio = .35

Research Objectives• Develop linear and non-linear FEA models of twisted fiber-reinforced

elastomer laminates that: a) Exhibit Stress Stiffening, b) Exhibit High Poisson’s ratios, or c) Exhibit Negative Poisson’s ratios.

• Fabricate specimens of each type, and conduct experiments.• Verify the simulations by comparing experimental and simulated

results.

Acknowledgement

I wish to express my sincere gratitude to my mentor, Dr. Larry Peel for his valuable suggestions, guidance and encouragement at every point. This work is based on Dr. Peel’s in-depth researchin the field of FREs.

Poisson’s ratio of twisted fiber laminates:

• Single twist fibers- Possible High Poisson ratio• Double twisted fibers- Possible Negative Poisson’s ratio

Non-Linear analysis required when:• Contact elements needed• Nonlinear material properties• Large and nonlinear displacements• Large geometry changes• Trying to gain better understanding of physical phenomenon

Previous work on Fiber Reinforced Elastomers (FRE)

Research areas of Peel on Fiber reinforced elastomers:• Fabrication of FRE specimens• Tensile response of FRE laminates• Nonlinear modeling• Comparison of predicted and experimental data• Fabrication of morphing wing

Finite Element Analysis

Comparison of FEA and Twisted Cotton / Elastomer Test Results

• Increase in effective axial stiffness is noticed• Increased stiffness is function of elastomer stiffness, non-linearity

Advantages Drawbacks

•High impact strength•Vibration damping•Tailaroble non-linear properties•Good in plane stiffness

•High viscosity•Short cure times•Difficulty in testing•Non-linear properties

Material @25o twist Matrix PR % E Increase Axial stiffness (psi)

Cotton Fiber – TestCotton/RP6410 - TestCotton/Silastic S-test

dna 0.499 0.499

0.00% 127.7 % 74.5 %

47,000 107,000 82,000

Cotton Fiber - FEACotton /RP6410 - FEACotton/RP6410 - FEA

dna 0.499 0.350

0.00 % 138.7 % 72.1 %

10,523 25,122 18,105

Fiberglass- FEAFiberglass/RP6410 - FEAFiberglass/RP6410 - FEAFiberglass/Epoxy - FEAFiberglass/Epoxy – FEA

dna 0.499 0.350 0.300 0.499

0.00 % 46 % 6.1 % 198.7 % 266.7 %

1,254,956 1,831,929 1,331,287 3,748,148 4,602,469