Acoustic Emissions from Damage Mechanisms in Composites

Composite materials experience complex evolution of damage even under static loading conditions. These damage events are associated with acoustic emission signals and such events have been extensively studied in the past to identify the different types of failure modes. A set of cross-ply and quasi-isotropic coupon specimens were instrumented with a configuration of sensors that are likely to preserve the acoustic emission features. These specimens were then tested under quasi-static tensile load to failure. Damage events such as matrix cracks, delamination, and scattered fiber breaks occurred throughout the loading cycles. Typically, several tens of thousands of acoustic emission events were recorded during each of these coupon tests. Features of acoustic emission signals corresponding to different types of damage events were examined. These include features such as frequency content and duration. The features were further analyzed to relate acoustic emission signals with likely failure modes based on the stress levels in the laminates. In addition, features that are indicators of the static strength in the presence of the accumulated damage are also examined. Based on these analyses the features of critical damage events are identified.