Characterization of deep drawing steels using optical strain measurements

This paper reports on an experimental investigation of hardening and anisotropy of three different steels commonly used in deep drawing (HSLA 320, IF 300 and DC06). The experiments consist of conventional tensile testing of specimens taken at different orientations with respect to the rolling direction. Strain measurements are performed by means of a mechanical transducer and an optical measurement technique. Where mechanical transducers have been proven as a reliable method for determination of strain before ultimate stress, the post diffuse necking strain data that are observed in sheet metal forming applications cannot be measured by such method. This is because uniform extension ceases and the uniaxiality of stress at the center of a tensile specimen is lost. Therefore an optical system suitable for full-field, non-contact measurement of deformations has been employed. A comparison of mechanical and optical strain measurements before diffuse necking shows that the optical technique can accurately and reliably measure strain. Therefore it is used to measure the strains beyond diffuse necking. The optically determined stress-strain curves have further been evaluated to describe the anisotropic behavior of the metals, especially after diffuse necking. An elaborate comparison of hardening and anisotropy for each material is reported