A Micromechanical approach for the Prediction of Fatigue Life in Composite Laminates

Abstract

A micromechanics based fatigue life prediction of composite laminates under multi-axial loading was developed. Many mechanical tests are required to fully characterize the composite laminates made of various materials and having different layup sequences. In order to reduce number of tests, a methodology was presented in this paper to predict fatigue life of composite laminates based on fatigue life of constituents, i.e. the fiber, matrix and interface, using micromechanics of failure (MMF). For matrix, the equivalent stress model which is generally used for isotropic materials was employed to take care of multi-axial fatigue loading. For fiber, a maximum stress model considering only stress along fiber direction was used. Critical plane model was introduced for the interface of the fiber and matrix, but interface fatigue strength was presumed strong enough than that of matrix and fiber and, therefore, its failure was ignored. The modified Goodman approach was utilized to take into account the mean stress effect. In order to validate the proposed methodology, the fatigue life of three different GFRP laminates, UDT[90°], BX[±45°]S and TX[0°2/±45°]S, was examined experimentally. The predictions are compared with the experimental data, and are shown in good agreement. A comprehensive implementation example is also presented for the case of composite wind turbine rotor blade structure.