On static and fatigue strength determination of carbon fibre/epoxy composites Part 1: Experiments

This work seeks to investigate the static and fatigue properties and the failure mechanisms of T300/QY8911 carbon-fibre-reinforced composite laminates with different layups to optimize the stacking sequence effect. Three different layups have been studied, namely, [45/0 ₂ /-45/90 ₂ /-45/0/45/90] _s , [45/-45/0/-45/0/45/90/45/0/-45] _s and [45/0/-45/0/-45/0/45/0/90/0]s. The results for static strength and fatigue residual strength under different fatigue stress amplitudes are evaluated and compared with each other. The damage and failure mechanisms of the composite laminates are discussed. It is observed that all tension-tension fatigue damage patterns of the notched laminates are similar while the tension-tension fatigue properties vary with the laminate layup. The reduction of stress concentration caused by the tension-tension fatigue damage leads to an improvement of the residual strength of the notched specimens in contrast to their static strength properties. The damage mechanics of the notched laminates under compression-compression loading are more complex than those of the tension-tension fatigue specimens; their damage patterns are influenced by the test clamping fixture, the layup, the size of specimens and the diameter of the hole. The residual strengths are lower than those of the specimens without fatigue damage. It is verified that in a high-temperature and moisture environment, there is a decrease in static compression strength. The results of this study provide an insight into fatigue damage development in composites and constitute a fundamental basis for the development of a strain-based residual strength model.