Fatigue Life Prediction of Off-Axis Unidirectional Laminate

Abstract

The prediction method of fatigue life of unidirectional laminate with the special ply fatigue life is an important support to build the prediction model of fatigue life of any lay-up laminate based on the special ply fatigue life. In this paper, the fundamental mechanical hypothesis of the fatigue failure criterion of unidirectional laminate, which is developed from the static failure criterion of laminate, has been analyzed. Based on the investigation on the fatigue failure regularities of the different unidirectional laminates, a phenomenon has been found that the location of unidirectional laminate S-N curve is monotonously decreasing with the increasing of ply orientation angle in the same coordinate. Then, a function has been proposed to describe the phenomenon. To analyze the mathematical characteristic of the function deeply, a fatigue life prediction model, which the fatigue life of unidirectional laminate can be predicted with the fatigue lives of longitudinal and transverse laminates, has been proposed by means on a special material S-N curve function. Based on the model, the fatigue life of any unidirectional laminate can be predicted by the S-N curves of two arbitrary unidirectional laminates. Twelve sets of experimental data of five kinds of laminates were employed to verify the model, and the results show that predicted fatigue life is in agreement with the experiment ones.