Variation of Sheet Metal Formability in Biaxial Stretching Processes

Abstract

<p>The deformation of circular and elliptical steel diaphragms subjected to hydrostatic pressure is investigated and the different modes of failure of these diaphragms are analysed and compared.</p> <p>An experimental program is carried out to determine the inherent variability of the forming-limit curves where a number of samples from different grades of deep drawing quality steel are hydrostatically bulged to failure. A quantitative metallographic analysis is also performed in an effort to establish a relationship between microstructural parameters and formability.</p> <p>A hypothetical model of ductile fracture is proposed to predict the formability of a sheet which contains a population of voids and is subjected to a non-uniform biaxial straining process. A simulation process is developed for this model using the Marciniak analysis and the extreme value theory. Numerical solutions are obtained to show the influence of material defect parameters and process variables on the distribution of forming limits. Theoretical results are then compared with the experimentally determined forming limit curves.</p>