Mechanics of Long-Term Behavior of High Temperature Polymer Composites

摘要

The general objective of the present program was to develop and assemble fundamental understandings and mechanistic mechanics and materials models needed to describe and anticipate the long-term mechanical behavior of polymer composites at high temperatures with variable time- and cycle - dependent mechanical loading. The primary points of departure of this program from previous work are the concentration on the effect of temperature on strength, as well as stiffness, and the concentration on using constituent behavior to predict the fiber-dominated strength and life of composite materials. Salient results of the effort include the development of micromechanical fiber-direction strength models for unidirectional composites that correctly predict temperature-dependent changes that are large compared to stiffness variations; the construction of a new equivalence concept between strain rate and temperature which correctly predicts instantaneous stiffness changes over seven orders of magnitude of strain rate; and postulation and initial validation of an entirely new concept for predicting instantaneous stiffness variations across primary and secondary transitions in polymers as a function of temperature, for use in robust design codes, especially for life prediction in virtual design spaces.