Characterization of interfacial failure using a reflected light technique

A simple optical method of observing and tracking interface failure in transparent matrix composites is developed to extend the range of material systems that can be tested with the cruciform test for measuring the normal strength of a bi-material interface. This technique of detecting debonds using reflected light is demonstrated on two model material systems with fibers 140 and 15 μm in diameter. The reflected light technique is more reliable and provides information about the interface that cannot be obtained with previous methods of debond detection, such as photoelasticity, surface strain gages, and acoustic emission. Using this technique, debond initiation, location, length, and shape are measured as a function of applied load; thus, all the required parameters for calculating the normal strength of the interface, as well as the interfacial energy release rate are acquired.