Measurement of crack growth and strain distribution around crack tip under elevated temperature

Through the macroscopic measurement of crack growth under the elevated temperature, the crack propagation rate has been found to be in better correlation with the J contour integral value than with other candidate parameters e.g. elastic stress intensity factor, net section stress. In order that this J value may be defined under the stationary creep condition, we must be aware of a certain singular strain field around the crack tip, which has been theoretically analyzed but the existence of which is not recognized experimentally. Using the Moire topographical method and digital processing of raw Moire grids and fringe patterns, the interesting informations have been obtained regarding the strain concentration at the crack tip.