Some features of fatigue failure in metallic composite materials

Abstract

1. The process of defect accumulation in composite materials, based on a study of the reduction in natural vibration frequency of specimens under cyclic loading, is considerably different from that of quasi-isotropic materials. 2. During comparative tests under severe conditions it is possible to define “failure” as a specific reduction in the natural frequency (Δf, Hz). This, however, should be confirmed by metallographic studies. 3. The defect accumulation process in composite materials, based on the reduction in natural vibration frequency of specimens, is of a damped and nonuniform nature with periods of acceleration and retardation. Cracks form and develop until they reach the fiber-matrix interface, at which stage they stop progressing further. 4. The average parameters of specimen life for composite materials can be calculated assuming a logarithmic-normal distribution of life. 5. The life of composite material specimens has a multimodal distribution which requires an indepth study with considerable data.