Thermographic Investigation of Fatigue Crack Propagation in a High-Alloyed Steel

Crack propagation experiments under constant stress intensity conditions were performed on SEN specimen of a high-alloyed steel. The experiments were accompanied by thermo elastic stimulated lock-in thermography investigations. The experiments showed that the crack propagation rate decreases with increasing crack length. Concurrent an increase in the dissipated energy in an area beside the crack flanks as well as in front of the crack tip was observed. The size of the plastic zone was also determined by thermographic measurements and was found to be constant during the crack propagation experiment. The increase of the dissipated energy doesn't reflect in the size of the plastic zone but seems to be responsible for the decrease of the crack propagation rate.