Use of stereoscopic fractography for analyzing resistance to the development of cracks

Abstract

1. The relationship between the height and width of the stretch zone [Eq. (11)] may be considered acceptable, at least, in comparatively ductile failure. 2. With a 25 times increase in test sample thickness there is practically no change in the height of the stretch zone. 3. At low temperatures a correlation has been established between the height of the stretch zone and fracture roughness which is predicted by mathematical models of the opening at the crack tip. A linear corrlation coupling factor between 2h and K Ic 2 /Eσy equal to 0.9 corresponds to the results of this work. 4. At quite high temperatures the height of the stretch zone is less than 0.9(K Ic 2 /Eσy. This is explained, frist, by the increase in deformation strengthening with an increase in temperature and, second, by the fact that in this case the values of KIc are determined in the presence of a macroscopic increase in crack length. 5. The subcritical crack growth in the investigated steel has the character of jumps and stops. The presence of secondary stretch zones is apparently caused by delay and blunting of the crack in front of a macroscopic jump and their area is quantitatively related to the R-curve at a given temperature.