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A novel approach to the measurement of fatigue crack growth at elevated temperatures based on digital image analysis technology is presented. An operational prototype was designed to demonstrate the feasibility of this technique to measure crack lengths at temperatures up to 1093°C (2000°F). The crack tip image transmission was accomplished using fiber-optic guides and relay lenses. The technique provides a direct (without calibration) measurement of the crack length and position with a resolution better than 0.025 mm (0.001 in.) and a capability for automation. The experimental observations of the crack tip using the digital image analysis system prototype showed that this technique can be applied to crack measurement at temperatures up to 1093°C (2000°F). The method requires further experimental work for verification of crack length accuracy under cyclic and thermal-mechanical spectrum loads, various specimen geometries, and other high temperature materials.
crack length, digital image analysis, elevated temperature, automation, image transmission, direct measurement, fatigue crack growth, fatigue testing, fracture testing
President, Strainoptic Technologies, Inc., North Wales, PA
Professor, Lehigh University, Bethlehem, PA
Aerospace engineer, USAF, Wright Research and Development Center, WRDC/FIBEC, Wright Patterson Air Force Base, OH