Effects of defect sizes at different locations on compressive behaviors of 3D braided composites

This paper reports the effects of defect sizes at different locations on the compressive behaviors of 3D braided composites. A polytetrafluoroethylene (PTFE) particle was embedded into the composite to form a defect. Low-velocity impact compression tests, high-speed photographic observations and micro-computed tomography (micro-CT) analyses were performed. Finite element analysis (FEA) models were developed to reveal stress distributions. We found that the compressive strength decreases and damages deteriorate with the defect size. The size effect of the defect in the center region is more significant than that in the surface region. FEA results show that there is a stress concentration around the defect, where the stress magnitude increases with the defect size. The decrease in compressive strength is attributed to stress changes in the shear region caused by defects. We expect such an investigation could be applied to characterize compressive strength in various composites with defects in different sizes and locations.