Measurement of strain, strain rate and crack evolution in shear cutting

Abstract Shear cutting is a prominent process in the chipless separation of metallic sheet materials. The cutting surface characteristics are the basis for quality assessment. Many present investigations deal with part quality and the influence of different process parameters, i.e., cutting edge geometry, punching speed and die clearance. Material failure occurs when the material's forming limit is reached, which depends on the deformation and the stress state. Here, strain and strain rate primarily drive material behavior and interact in the shear affected zone. An overall analysis of the complex cause-effect relationships has not been possible until now. Hence, an experimental setup enabling a detailed evaluation of the shear zone is presented. First, a shear cutting tool is introduced, which allows an in situ high resolution analysis of the material deformation in the shear affected zone under plain strain conditions. Based on the recorded high speed images, strains and strain rates are derived using classical block matching, the digital image correlation, and a tailored image handling routine. Further, for the first time, crack initiation and propagation could be recorded and evaluated using a new optical flow model with total generalized variation prior.