Center for Composite Materials - University of Delaware

Research Summary

Micromechanical Modeling of Unidirectional Composites: Dynamic Effects of Fiber Break

Authors: Raja Ganesh, Subramani Sockalingam, Bazle Z. (Gama) Haque, and John W. Gillespie, Jr.

Introduction

• Predictive multiscale tool for tailoring material and architecture for optimum composite performance (materials-by-design)

Dynamic Effects of Fiber Break

• Even under static tensile loading, the breaking of a fiber is a locally dynamic process
• Classical shear lag theory suggests that the dynamic stress concentration factors in the neighboring fibers around a broken fiber are higher than the corresponding static stress concentration factors
• Dynamic effects of a fiber break could play a key role in the evolution of damage under axial tensile

Micromechanical FE Model

• Fiber-level infinite element model
• Automated model generation through python scripting
• Fiber - Linear Elastic
Resign - Elastic-Plastic

Shear Lag Theory

Assumptions
- Fibers take only axial load
- Resin takes only shear load
- Poisson's ration = 0 (for both fiber and matrix)
- Matrix has negligible density

FE Model with Dynamic Break

• 2D Finite Element Model
• Plane stress elements
• Static loading until just before Axial Stress 1 Gpa
• Model transferred to Abaqus explicit and loaded at 0.1 mm/s
• Dynamic Element deletion through User-Defined Field subroutine (VUSDFLD)

Results

• FE Model is in good agreement with shear lag model if all the assumptions in the shear model are considered
• The Dynamic Stress Concentration Factor (SCF) converges to the Static SCF value
• If Axial stiffness of Resin is considered, then both Dynamic as well as static SCFs are much lower. This is because the resign shares the additional load from the fiber break, thus reducing the overload on the neighboring fiber

Evolution of Stress

Modeling Roadmap

Summary

• Classical Shear lag theory over-predicts the Dynamic as well as static SCFs
• The Dynamic SCF is about 15% Greater than the corresponding Static SCF
• This will increase the probability of failure of fibers surrounding a broken fiber in the immediate aftermath of a fiber break

Current Work

3-Dimensional Dynamic FE Model with interfacial debonding and resin plasticity

Acknowedgements

This work is supported by the Center for Composite Materials, University of Delaware

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