A theory for stress analysis of composite laminates

Abstract

Failures in laminated resin matrix composite materials often begin with matrix microcracking and delamination. These modes of damage are three-dimensional in nature and are controlled by interlaminar stresses. One important key to understanding and ultimately predicting the failures in composite materials is an analytical approach that provides reliable stress estimates in critical regions. Conventional laminate theories are inadequate for this purpose as they are based on global displacement assumptions. Moreover, the interlaminar stresses are often neglected in the initial formulations. Therefore, solutions based upon these theories cannot yield realistic stress distributions. Recent theoretical research shows that there are certain nonclassical influences that affect bending-related behavior. They include section warping and its concomitant nonclassical surface-parallel stress contributions and transverse normal strain. The stress prediction capability of a bending theory improves significantly if these nonclassical influences are incorporated. A comprehensive bending theory is developed for arbitrary composite laminates. Its effectiveness is demonstrated in examples for a cross-ply laminate and a quasiisotropic laminate.