A study of failure in carbon/foam sandwich composites with stress concentration

Abstract

Both experimental and numerical studies were performed to understand the failure mechanism of carbon/foam sandwich composite plates with stress concentration. The plates had circular holes and were subjected to bending and compressive loading. Both three-point and four-point bending tests were conducted, For the testing, the foam thickness, the size of the hole, the number of holes, and the hole location were varied. In addition, a finite element analysis was conducted to verify and understand the experimental results. It was found that four-point bending is not an effective test method to evaluate the effects of stress concentration at a hole. Compressive loading is an effective method. A sample without a hole fails at the quarter point due to foam core shear failure. With a hole at the center, the core shear stress at the quarter point increases with increasing hole size. However, the skin bending stress at the hole increases at a faster rate. When the hole size reaches a critical diameter, the failure mode changes to skin bending failure at the hole. (MM)