Experimental and theoretical study on energy convergence characteristics of adiabatic shear fracture process in high-speed machining of hardened stainless steel

Abstract

The formation of isolated segment chip due to the occurrence of adiabatic shear fracture (ASF) in adiabatic shear band (ASB) is a significant phenomenon under the high cutting speed. In the present work, the experimental and theoretical methods were adopted to further investigate the energy convergence characteristics in ASB during ASF process in high-speed machining. A hardened stainless steel used in turbine blade was selected as the workpiece. The chip morphology transformation from serrated chip to isolated segment chip was obtained through the high-speed machining experiment. The ductile crack propagation in ASB was observed microscopically. The relations of serrated segment geometry with the cutting conditions were revealed experimentally. According to the continuum governing equations and the deformation and energy analytical models, the distributions of shear velocity, shear strain rate, shear strain, and shear energy in ASB under various cutting speeds and feeds were analyzed combining with the constitutive and stress relations. The energy convergence characteristics in ASB during ASF process with the change of cutting conditions were analyzed and discussed. The results showed that the austenite blocks in the hardened stainless steel influenced the crack propagation in ASB. The larger shear strain induced thinner ASB would accelerate the thermal softening and strain localizing effects, resulting in severer energy convergence in ASB. The energy convergence was uniformly distributed and always kept a constant limit value in the whole ASB when ASF occurred.