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Direct In Situ Observation of Deformation Modes in Wedge Indentation of Metals

We study deformation patterns in wedge indentation of annealed metals (e.g., copper) using high-resolution, in situ imaging and image correlation. Based on attributes of the deformation such as velocity fields, grid distortion and strain distributions, we discriminate between two modes of deformation - a cutting mode with narrow-angle (sharp) wedges, e.g., apex angle of 30 degrees, and a radial-compression mode with wide-angle (blunt) wedges, e.g. apex angle of 120 degrees. The cutting mode is characterized by significant material flow parallel to the wedge face; and a thin region of very high strain (similar to 3), that is located immediately adjacent to the indenter face (wall-layer), and arises from friction-induced deformation. The radial-compression mode is distinguished by material flow normal to and away from the indenter face, with negligible velocity component parallel to the indenter face. The corresponding strain field is one of bulk deformation, with the highly-strained region (strain similar to 1) being of semicircular shape that extends from near the edge of indenter contact at the specimen surface, to well below the indenter tip. The observations show that indenter wall friction is likely to have a major influence on the deformation field only with narrow-angle indenters. Based on the observations of material flow, a suggestion is made (and validated) as to how the challenges faced in computational modeling of narrow-angle wedge indentation can be overcome. Implications for use of narrow-angle wedge indentation to study tribology of metalworking contacts, and ductile failure and damage in metals, are briefly discussed.