A relational expression between the fatigue life and stress level, temperature, humidity for composite materials

The prediction and evaluation of fatigue life for composite materials under hydrothermal environment are of importance in engineering practice. So far fatigue life in given conditions can generally be obtained by tests. In this paper, a relational expression between the fatigue life and stress level, temperature and humidity is proposed and the parameters in the formula are then determined by least square method. Verification based on a great amount of test data indicates that the expression can effectively describe the relation between the fatigue life of composite materials and the effects of loading and environmental conditions. The calculation results show that the expression reaches a satisfactory precision. As an example, resin-matrix composite laminates is utilized to show the applicability. With the proposed formula, the information of fatigue life can be obtained by limited test data. The reduction in experiment numbers will result in a great saving, which is significant for engineering practice.