Effects of fibre and matrix properties on the tension-tension fatigue limit of unidirectional composites

A primary design challenge of composite structures is to avoid failure under cyclic loading (fatigue). It is of great importance to prevent fatigue damage in composite materials. In the present work, a parameter study is performed for the prediction of an endurance fatigue limit of unidirectional fibre composites using a micromechanical model. The fatigue limit is calculated as the maximum applied cyclic strain at which failure of one fibre does not cause failure in its nearest neighbouring fibres. Failure in neighbouring fibres is assessed by considering the stress induced to the neighbouring fibres from the debond crack tip of the broken fibre. The model is used for unidirectional composites made of glass or carbon fibres in a polymer matrix. The parameter study covers the fibre strength, described in terms of Weibull parameters (characteristic strength and Weibull modulus), the fibre radius, residual stresses and the Young’s moduli of the fibres and the matrix. These model predictions can provide important guidance to the manufacturing of future composite materials with a significantly higher fatigue limit.