<p>Polymers and their composites (PMCs) are considered important structural materials in the aerospace and automotive industries. These materials are lightweight, possess good stiffness and toughness, and often cost lower than traditional metals and alloys. With recent advancements in composite manufacturing technology, polymer matrix composites are now being used in elevated temperature and dynamic mechanical loading applications. In order to ensure the safety during the life of these materials, studying the behavior under cyclic mechanical loading and non-isothermal creep is of crucial importance. In this work, we study the behavior of unidirectional glass-fiber-reinforced epoxy composite both theoretically and experimentally subjected to a combined mechanical and thermal cycle. Glass-fiber composites are widely used in high-temperature applications in the electronics and automotive markets. Our preliminary experimental studies reveal a rate-dependent nonlinear quasi-static behavior under flexural loading of these composite specimens. Additionally, we observed a fiber-orientation-dependent constitutive response within the material, characterized by DIC and microscopy. We performed the viscoelastic characterization using Dynamic Mechanical Thermal Analysis with three-point bending. &nbsp;Following this, we develop a coupled thermo-viscoelastic large deformation model to predict the rate-dependent response of the PMCs. Firstly, we consider the composite RVE as a mixture of fiber and matrix, characterized by the fiber volume fraction and fiber orientation. We develop a macroscale homogenized theory that considers the anisotropic behavior of the PMCs induced by the fiber orientation. We model the polymer matrix using Arruda-Boyce hyperelastic material and the fibers using an invariant-based approach. Subsequently, we model the failure (damage initiation) and crack propagation in the homogenized PMCs using an anisotropic phase-field fracture theory that considers the effect of fiber orientation in the gradient of the phase-field or the damage variable building upon an energy-based anisotropic failure criterion. We obtain the model parameters by fitting the experimental data from the present work. To incorporate the effect of cyclic loading-unloading behavior, the fracture energy of the composite is considered as a decreasing function after several cycles of loading. We capture this phenomenon by introducing a fatigue-loading history-dependent degradation parameter in calculating the fracture energy evolution. The proposed model is thermodynamically consistent, and we numerically implement it by writing a user-element subroutine (UEL) in ABAQUS/Standard. The numerical simulations show that the model can predict the PMC behavior under cyclic-loading, the local temperature rise due to viscous dissipation in the matrix, crack initiation, and propagation under mode-I, II, and mixed-mode loading cases in a coupled thermo-mechanical loading scenario.&nbsp;</p>

A Phase-Field Fracture Model to Predict Failure in Polymer-Matrix Composites Under Cyclic Mechanical and Thermal Loading

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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