Microscale experimental investigation of failure mechanisms in off-axis woven laminates at elevated temperatures

Off-axis woven laminates fabricated from carbon fiber and a high glass transition temperature thermosetting resin were subjected to tensile static and fatigue loading at temperatures ranging from room temperature up to 205 °C. The damage mechanism prevalent to these specimens was investigated by post-mortem examination using a scanning electron microscope. During most of their life fatigue specimens had accumulated minimal damage which consisted of matrix cracks, transverse bundle cracks and intra-ply delamination. Just before failure fiber bundles began to straighten out and rotate towards the loading direction. This behavior led to large elongation and necking of the specimens before fracture. Overall, the matrix-dominated material behavior and fiber reorientation due to the off-axis configuration had a far greater influence on the fracture morphology than the gradual accumulation of damage due to fatigue loading. It was also found that damage formation was strongly influenced by the type of applied loading and the test temperature.