Fatigue Response and Modelling of Variable Stress Amplitude and Frequency in AS-4/PEEK Composite Laminates, Part 1: Experiments

Abstract

This paper aims to investigate the tension-tension (T-T) fatigue behavior at variable fatigue loadings in AS-4/PEEK composite laminates. Three lay-ups of specimens, such as cross-ply [0/90]4s, quasi-isotropic [0/45/90/-45]2s and angle-ply [±45]4s, were tested at room temperature and moisture. The parameters involved were maximum stress (low and high), frequency (5 Hz and 25 Hz), and stress ratio (R = 0 and 0.2). We received the fatigue life and found that the maximum stress and stress ratio are the two controlling factors on lives, whilst frequency affects significantly in [±45]4s laminates. Next, stiffness and strength degradation were defined to describe the laminate damage process due to cyclic loadings and these experimental data were correlated with suitable models proposed in power function form. From the damage curves we observe that three stages of damage growth can be clearly divided and different failure mechanisms exist among three lay-ups. All these valuable data will be used to predict fatigue life under multi-block cyclic loadings in association with Cumulative Damage Theory in Part 2: Analysis and Formulation.