Nonlinear analysis of laminated fibrous composites

Abstract

A computerized analysis of the nonlinear behavior of fibrous composite laminates including axial loading, thermal loading, temperature dependent properties, and edge effects is presented. Ramberg-Osgood approximations are used to represent lamina stress-strain behavior and percent retention curves are employed to model the variation of properties with temperature. Balanced, symmetric laminates comprised of either boron/epoxy, graphite/epoxy, or borsic/ aluminum are analyzed using a quasi-three-dimensional finite element analysis. An incremental loading procedure is developed where the mechanical properties of each finite element may be adjusted depending on the temperature and/or the strain level. Results are presented for the interlaminar stress distributions in cross-ply, angle-ply, and more complex laminates. Elastic results for the boundary layer effect are shown to compare favorably with existing numerical solutions. It is shown that for angle-ply laminates the fiber orientation for maximum stress due to mechanical loading is matrix material dependent whereas the fiber orientation for maximum thermal stress is not matrix material dependent. It is also shown that the combined nonlinear thermal and mechanical analysis exhibits significant differences from the linear elastic results. Nonlinear stress-strain curves for a variety of composite laminates in tension and compression are obtained and compared to other existing theories and experimental results. It is shown that excellent agreement between theory and experiment is exhibited for many, but not all, laminates. The inclusion of thermal effects is shown to give improved predictions. It is also shown that the mode of failure is laminate dependent. Whereas angle-ply laminates fail as the result of in-plane strains exceeding maximum values, other laminates fail according to either a first ply failure theory, a progressive failure theory, or they fail as a result of edge effects.