A laser-based instrument is being developed for measuring strain at temperatures up to 4,000 F on ceramic and carbon composite materials. The method relies on reflective interference of laser light from pyramid shaped indentations or protrusions on the specimen surface. Methods are being developed for maintaining the reflectivity of the specimen surface over the active gage length. Both conventional and new ideas are being used to insure a high probability of success. Conventional approaches include indentation of the ceramic surface oxide layer, and indentation of small refractory tabs which are bonded to the sample. A more aggressive, innovative approach as using chemical vapor deposition to form pyramid shaped ceramic crystals on the specimen surface from which laser light can be reflected. Later efforts would be directed towards improved electro-optical processing of interference patterns and development of a commercially available gage. The ability to measure dynamic strains at temperatures up to 4,000 F would provide a valuable tool for understanding failure mechanisms and developing design strategies for non-metallic materials. The accurate determination of properties for ceramic and carbon composites is essential. For many advanced defense applications.
