Nonlinear Response of Boron/Aluminum Angleplied Laminates Under Cyclic Tensile Loading: Contributing Mechanisms and Their Effects

The nonlinear response of boron/aluminum angleplied laminates subjected to cyclic loads was investigated. A procedure is outlined and criteria are proposed which can be used to assess the nonlinear response. The procedure consists of testing strategically selected laminate configurations and analyzing the results using composite mechanics. Results from the investigation show that the contributions to nonlinear behavior are due to: premature random fiber breaks where the ply orientation angle (POA) is small relative to the load direction, ply relative rotation (PRR) at intermediate values of the POA, and nonlinear aluminum matrix behavior at large values of the orientation angle. Premature fiber breaks result in progressively more complaint material; large PRR result in progressively suffer material; and, pronounced matrix nonlinear behavior results in no significant change in the modulus of the initial portion of the stress-strain curve.