Fatigue Resistance Criteria for Laminated Composite Structures.

摘要

This work investigated criteria for prevention of fatigue damage in metal matrix composite laminates. The approach was based on an earlier observation that, in as-fabricated unidirectional composites with elastic-brittle fibers and soft elastic-plastic matrices, fatigue failure can be prevented if the composite shakes down during cyclic loading. First, a plasticity theory was developed for axisymmetric deformation of unidirectional composites under mechanical and thermal loads. A modified self-consistent scheme was used to evaluate the elastic-plastic response of the composite. The results were applied to heat-treatment problems and to evaluation of residual microstresses in heat-treated materials. Next, a plasticity theory was developed for fibrous laminates. To construct a phenomenological constitutive relation suitable for use in numerical solutions of geometrically complex problems in laminated structures. The author concludes that fiber reinforcement strengthens the metal matrix considerably against ultimate failure, but it does not expand significantly the elastic deformation range of the matrix in the overall stress space. The advantage derived from fiber reinforcement of metal matrices can be used only in the elastic-plastic deformation range of the composite. This opens the possibility of repeated cyclic plastic straining of the matrix in dynamic loading situations, and the prospect of low-cycle fatigue failure if the loading range is not limited by the requirement that the matrix must shake down and thus resume an elastic deformation mode.