Micromechanical modeling of fatigue strength of unidirectional fibrous composites

This paper deals with modeling of fatigue strength of a unidirectional fibrous composite in terms of the fatigue properties of its constituent fiber and matrix materials and the fiber volume fraction only. When the composite is subjected to any kind of fatigue load, the resulting internal stresses in the constituents are determined through a new and simple micromechanics model, the bridging model . A fatigue failure criterion similar to the maximum normal stress criterion has been established to detect failure of a constituent material. The composite fatigue strength is assumed when any constituent fails. The fatigue strengths of the constituents can be obtained through individual failure tests on the constituent materials, or can be retrieved using composite fatigue data in two different directions. In the paper, various off-axis S–N relationships of unidirectional graphite/epoxy and glass/epoxy composites have been estimated. The predicted results are in good agreement with available experimental data.