Effect of voids on interlaminar behaviour of carbon/epoxy composites

Porosity is a common manufacturing defect in composite materials. It can be induced by trapped air during lay-up, ineffective debulk or an inadequate autoclave curing cycle. It is almost impossible to completely eliminate voids during manufacturing. They can lead to development of other defects such as delamination and have a detrimental effect on matrix-dominated properties of composites. Many researchers have investigated the effect of void content on mechanical properties of composites, but size, shape and location are important parameters often not characterised. In this work destructive and non-destructive techniques were used to identify void content and their parameters. Short beam shear tests (SBS) were performed to measure interlaminar shear strength (ILSS). As expected ILSS reduced with increasing void content. However it was shown that location of the voids in a composite also influences the mechanical performance. Thus maximum void volume fraction in a ply showed the best correlation with the knockdown of ILSS. For better understating of behavior of composites with high level of porosity the void morphology was analysed.