Heat Damage Assessment of Advanced Composites Using ESPI

Advanced composites are widespread in structural components of automotive and aircraft designs due to their exceptional mechanical properties. In the specific application of Navy aircrafts, graphite-epoxy composites are being used primarily due to ther high strength and low weight. Due to the extreme environments that these materials experience, a nondestructive evaluation (NDE) technique is needed in order to evaluate the effects of exposure to high heat on the composite structures. Electronic speckle pattern interferometry (ESPI) offers a NDE method that provides a means of both qualitative and quantitative evaluation of heat damage/degradation of composite structures. This technique will utilize state of the art technology in laser diodes and fiber optics to achieve real time analysis in a compact unit. The use of fiber optics allows access to remote locations. Instantaneous qualitative analysis of the resultant interferograms provides indications of areas with cracks, delaminations and weak spots. Futher quantiataive analysis of the interferograms by the system control computer will provide strain and stress measurements of the areas of concern. This analysis will indicate the degree of thermal dmage experienced by the composite structure. The Phase I effort of this project will demonstrate the capabilties of a fiber optic ESPI system in the evaluation of heat damage.