Effects of Manufacturing-Induced Voids on Local Failure in Polymer-Based Composites

This paper presents results of a computational study focused on examining the role of manufacturing-induced voids in the initiation and growth of damage at the microstructural level in polymer matrix composites loaded in tension normal to fibers. The polymer deformation is described by an improved macromolecular constitutive model accounting for strain-rate-, pressure-, and temperature-sensitive yielding, isotropic hardening before peak yield, intrinsic postyield softening, and rapid anisotropic hardening at large strains. A new craze model that accounts for craze initiation, growth, and breakdown mechanisms is employed. An energy-based criterion is used for cavitation induced cracking that can lead to fiber/matrix debonding. The role of voids is clarified by conducting a comparative study of unit cells with and without voids. The effects of strain rate and temperature are investigated by a parametric study. The overall composite stress-strain response is also depicted to indicate manifestation of microlevel failure on macroscopic behavior.

Quantification of Environmental Stress Cracking in Polymer Blends through Eyring Modeling

ABSTRACTThe effect of blending polycarbonate (PC) with an amorphous copolyester (PCTG) and a crystallizable polyester (PBT) on the environmental stress cracking (ESC) resistance was studied. The determination of the ESC resistance for the blend was accomplished through tensile testing in a fluid environment utilizing an Eyring-type activated process to describe ESC. It was found that the miscible blend, PC/PCTG, displayed a rule of mixtures for ESC resistance to all fluids tested except ether resistance. The immiscible blend, PC/PBT, displayed a significant negative deviation from the rule of mixtures for ESC resistance, except for ether resistance, which has been attributed to the development of stress sites for craze initiation at the interface between the blend components on the surface of the test sample. The differences in ether resistance compared to the trends found for the fluid ESC resistance in this study were attributed to possible changes in crystallization for the samples tested in ether. The data suggests that strongly swelling fluids, e.g. diethyl ether in the presence of PC, may cause densification from polymer crystallization resulting in voids that facilitate in the initiation and growth of crazes.