Fracture of 30CrMnSiA Steel under Mixed-Mode Loads

Notched 30CrMnSiA steel specimens were exposed to rupture load (mode I) at an angle of 90° between their fracture surface and load direction and to shear load (mode II) at an angle of 45° and 15°. For shear loading, Richard’s grips were used allowing one to vary the load from pure tension to pure shear by varying the notch orientation angle to the tensile load direction. Assessed under loading were the parameters of acoustic emission (AE) and strain fields (by the digital image correlation (DIC) method), and after failure, the damage parameters and microhardness on the polished lateral surface of the specimens, and the macro- and microreliefs of fracture surfaces. It is shown that increasing the shear component under tension changes the mechanical and the acoustic parameters of the specimens (total number of AE signals, their activity, b_AE-value), and the critical temperature of brittleness, changing the fracture surface morphology from ductile to brittle at a load orientation of 45°. Simultaneously, a nonlinear dependence of the damage parameters (relative area of microcracks S^*, their average length l_av, orientation to the loading axis) on the load angle is observed, showing a correlation with principal strains estimated by the DIC method.