A vision-integrated tension test for use in sheet-metal formability studies

In the prediction of formability of sheet metals, it is necessary to determine the material properties which are normally evaluated based on the data obtained by performing a simple tension test. Anisotropy is width strain over thickness strain, and the change in width traditionally measured by using an extensometer is not always acceptable. Also, as it is impractical to measure the change in the thickness of the sheet metal, it is normally estimated indirectly by measuring the extension of the specimen. Generally, this measurement is unable to establish the longitudinal strain accurately since the exact portion of the specimen that actually contributes to extension is uncertain, i.e. extension is not limited to the gauge length alone. In this paper, a new vision-integrated methodology has been introduced for the estimation of material properties through a uniaxial tension test. The required experimental data can be obtained by integrating the simple tensile test with a vision-based system that offers a most direct, continuous, non-interfering and accurate way of measuring the surface strains involved. Thus, with the establishment of actual strains, it is now possible to estimate the stress accurately.