The effects of fibre pre-stressing on the impact performance of composite laminates
This thesis has presented the results and findings of a study carried out into the effects of fibre pre-stressing on the impact performance of composite laminates. Fibre prestress has been explained as a way of mechanically altering the internal residual stress state of a composite, which typically is a result of thermal, moisture and chemical expansions. It has been suggested that pre-stressing can offer potential benefits to composites by reducing or reversing the hygro-thermal stresses in a composite. It has also been suggested that the impact performance could be improved through fibre prestressing, which has given rise to this study. In this study panels have been made with various levels of pre-stress. A special system was developed to apply pre-stress to the laminates and the produced laminates were tested under low- and high-velocity impact regimes. To apply these regimes, an instrumented falling weight and a gas gun were used respectively. A short finite element study was carried out to supplement the experimental study and offer further insight into the failure mechanics. The main findings of the study were that although pre-stressing had no discernable effect on the high-velocity impact performance of the composite laminate considered, there was a noted effect on the low-velocity impact performance. Under low-velocity impacts the laminate showed an improved impact performance for increase levels of pre-stress, except at one critical pre-stress level (60 MPa), where the laminate absorbed less energy per damage area compared with unpre-stressed laminates.