The non-proportional loading of mild steel

Abstract

Abstract. The effect of proportional loading on formability has been extensively studied. However, non-proportional loading occurs frequently in a stamping operation and its impact on formability has been studied less. Non-proportional loading occurs in two areas of stamping: continuously during the draw stage of a complex geometry and discontinuously through stamping stages. Studies on non-proportionality (eg. [1]) show that it can change the formability of a material compared to when it is loaded proportionally. This paper introduces an experimental method that allows a comparison of the deformation in mild steel subject to continuous and discontinuous loading mechanisms. A notable innovation of the method is that it can be carried out inside the chamber of a scanning electron microscope, allowing in-situ measurements of plastic deformation. The experiments show that the plastic behavior of the material under the continuous mode is distinct to when it is deformed discontinuously