Measurements of crack growth in a solid at elevated temperature by holographic interferometry

Real-time holographic interferometry was used to follow the crack-opening displacement (COD) of a compact tension specimen of zirconium 2.5-percent niobium subjected to a constant tensile load at 120°C for a period of 860 h. This was made possible by a dimensionally stable invar plate placed beside the specimen as the reference for the alignment of holograms. A finite-element elasto-plastic stress-analysis code and measurements on a duplicate specimen with a clip gage were used to correlate the measured COD and the corresponding crack growth.