FRACTURE BEHAVIOUR OF HIGH STRENGTH STRUCTURAL STEEL

Investigations have been directed towards understanding the microstructure and its variation, the effect of microstructural variations on the deformation behaviour, and the correlation between deformation and fracture, ultimately tracing back to correlations of fracture with microstructure. The fracture mechanics parameters used for characterizing fatigue crack growth and fracture, ranging from ductile to quasi-brittle, were found to vary in a systematic manner. The formation of the stretch zone which leave a signature of the state of deformation at the crack tip on initiation of fracture, and which is an important parameter for identification of fracture toughness, was also studied by 3-D SEM fractography. It was observed that except for relatively low toughness situations the stretch zone was unable to indicate the critical crack extension at fracture.