Uprating and life assessment under fatigue-creep conditions

Abstract

Failure criteria are often used to assess the structural integrity of laminated composite plates subjected to multiaxial loading conditions, and to determine which laminae within a laminate may fail. Although many such criteria are successful from the point of view of the numerical results obtained, the way in which they are formulated often leads to results that are physically incorrect. Two factors that may lead to difficulty are, first, criteria are often adapted from those used for isotropic materials and, second, individual laminae are usually taken to be homogeneous. The purpose of the present paper is to discuss these two problems and to suggest the form that a physically acceptable failure criterion should adopt. Results are compared with experimental failure loads in uniaxial tension on carbonfibre-reinforced epoxy laminates having different ply lay-up configurations.