The goal of the work presented here is to study dynamic crack initiation in ductile steels "NiÐCr steel and 293 stainless steel# at di}erent loading rates and to establish appropriate dynamic failure criteria[ A variety of infrared and visible optical methods and high!speed photography are used in this study[ Precracked steel specimens are subjected to dynamic three!point bend loading by impact...

The formation and propagation of cracks occur through irreversible dislocation movements at notches, material defects, grain boundaries. Since this process is partly thermally controlled, the resistance to low temperatures increases. This slows both fatigue initiation crack propagation. From recent experimental data, it can be seen that growth accelerated below transition temperature (FTT) corr...