CRACK GROWTH AND DEVELOPMENT DURING CREEP OF BARRE GRANITE

Sample of Barre granite were subjected to a uniaxial stress equal to 87% of their fracture strength for various lengths of time. Crack growth and development as a function of time under load was studied with the scanning electron microscope. New stress-induced cracks appear to be continuously generated. Average crack lengths increased with time as much or more than they did upon loading, but average crack widths remained relatively unchanged, suggesting that cracks close down to an equilibrium value after the sample has been unloaded. Crack interaction with other cavities seemed to increase in time as the numbers of individual cracks increased, until near the onset of tertiary creep crack coalescence may have become more important than the slow growth of individual cracks. The tensile character of stress-induced cracks and other observatios by Tapponnier and Brace [7] were confirmed. There may be a difference in the mode of crack development between tests at constant stress and tests at constant strain rate. Differences in inelastic strain and acoustic emission generated in the two test types also suggest this. © 1979.