Thermographic study of nucleation and propagation of Portevin-Le Châtelier bands

Abstract

The Portevin-Le Châtelier (PLC) effect occurs in some materials under certain conditions of temperature and strain rate. According to physical explanation, local deformation patterns of plastic instability rely on dynamical strain aging, dislocation interaction and negative strain rate sensitivity. The purpose of this work is the investigation of the nucleation and propagation of PLC deformation bands in aluminium alloys. In particular, the morphology and kinematics of PLC bands are investigated experimentally using both mechanical and thermal measurement methods. The latter employs a high speed infrared (IR) camera which captures temperature changes resulting from mechanical dissipation and heating due to the nucleation and propagation of PLC bands. Moreover, an image correlation algorithm is utilised to calculate the plastic deformation from the contrast due to the roughness of surface. The simultaneous measurement of plastic deformation and temperature increment is a meaningful method to investigate the relationship between the local plastic deformation and heat dissipation. The measurements yield correlations between the spatiotemporal evolution of stress, strain and temperature in the specimens and PLC-band development. The dependence of band velocity and strain jump on strain and strain rate is measured. Further, the critical strain is measured as a function of strain rate.