MIXED-MODE CRACK-GROWTH IN SM45C AND Z02-NKDT STEEL SUBJECTED TO REPEATED IMPACT AND FATIGUE

The strain energy density criterion first proposed by Sih accounts for both the rate and direction of crack extension subjected to mixed-mode loading regardless of whether it is applied statically, dynamically or cyclically. This criterion is applied to investigate the mixed mode crack growth behavior in SM45C structural steel and Z02-NKDT maraging steel specimens under repeated impact and fatigue. The specimen contains an off-axis crack whose angle of inclination can be varied with reference to the loading axis to simulate different degrees of mixed loading. A Maekawa type impact tension machine is used. The direction and rate of crack growth under repeated impact and fatigue are measured and compared well with those predicted from the strain energy density criterion.