The role of notch tip shape and radius on deformation mechanisms of 12Cr1MoV steel under impact loading. Part 2. Influence of strain localization on fracture and numeric simulations

The fracture energy of 12Cr1MoV steel specimen with V-shaped, U-shaped and I-shaped notches under impact loading was measured and analysed. The results were described using three common approaches to ductile-brittle fracture: force-based, energy-based and strain-based. Within the stage-wise approach of physical mesomechanics of materials, the rate of increase/decrease of load at the stage of initiation and propagation of a macroscopic defect was evaluated, providing a good correlation with the work of fracture. The excitable cellular automata technique was applied to simulate the deformational behaviour of the specimens with different shape of notches. It was demonstrated that in the case of the blunted notch, the maximum impact toughness is facilitated by a more uniform distribution of the load along the notch, which hinders brittle fracture at lower testing temperature. For the specimen with the sharp I-notch, the bands of localised shear are oriented normally to the loading axis, inhibiting macroscopic localisation of strain and crack propagation. For this reason, the impact toughness of the specimen with the I-notch appeared to be higher than that of the V-notched one. Using the fractographic analysis and the size of shear lips as a quantitative fracture parameter, a physical-mechanistic scheme of fracture was suggested for the case of enhanced localised plasticity near the stress riser.