Composite Failure Surface Analysis

In this work, the features of the fracture surfaces of graphite-epoxy specimens as seen by both optical and scann ing electronic microscope (SEM) are presented. A variety of test conditions were investigated. They are: tension (quasi- static), compression (quasi-static), and tension-tension fatigue. Failure due to delamination was also studied (Mode I-Peel Testing). The sequence of events leading to failure was monitored using an X-ray technique with an opaque additive for image enhancement. After mechanical testing, specimens were sectioned and prepared for microscopic analysis. Two principal fracture surface features were identified: (1) overlapping platelets of epoxy and (2) branched microcrack structures. These fatures could be used to identify the direc tion of failure propagation and, in some cases, distinguish between failure modes.