Shear-dominated biaxial failure analysis of polymer-matrix composites at room and elevated temperatures

This dissertation addresses the influence of shear-dominated biaxial stresses on the behavior of unidirectional and woven fabric polymer-matrix composites at room and elevated temperatures. The experimentally determined elastic-plastic properties of the various composite materials have been examined and applied to finite element analyses of shear-dominated biaxial tests: the standard Wyoming Iosipescu, biaxial Iosipescu, and off-axis tensile tests. The numerically determined internal stresses and strains have been used to study the failure behavior of the shear test specimens and the composite materials. It has been determined that while the Iosipescu test may be used to determine the shear modulus of unidirectional and woven-fabric composite and the interlaminar shear strength of woven-fabric composites, it is inadequate for the determination of intralaminar shear strength of unidirectional composites. Also, a series of off-axis tensile tests have been conducted on the unidirectional graphite/PMR-15 composite at room and various elevated temperatures. The elastic-plastic and failure properties have been determined for each temperature, and relations have been generated that describe the properties as a function of temperature.