ANALYSES OF FAILURE LIMITS OF ANISOTROPIC SHEET MATERIALS

Abstract

Formability of a sheet material is a measure of its ability to undergo plastic deformation without being damaged. It is affected by both material characteristics and forming operation process variables. Formability maps are necessary for sheet materials before its usage in industry in order to have knowledge of extent of deformation to be undertaken. Aerospace and automotive industries are having great applications of formability. The present work is dedicated to study the formability of titanium, steel, dual phase steel and aluminium at room temperature with different thicknesses, hardening exponents and anisotropic coefficients. Titanium and aluminium are widely used in aerospace due to their high strength to weight ratio and high corrosion resistance. The materials were characterized in terms of mechanical properties by using uniaxial tensile test. Formability maps can be used to select material and identify deformation paths that reduce the chances of failure. A comparative analysis on estimation of forming limit has been carried out using various theoretical models. The experimental forming limit diagram (FLD) has been used by extracting data using Plot-Digitizer software. The experimental FLD has been compared with FLD predicted by theoretical models such as Hill, Swift, Keeler and Brazier etc. The effect of strain hardening exponent, anisotropic coefficient and thickness has been studied in this work. In this work, it is observed that increase in hardening exponent will increase the formability. When thickness of material increases, the formability increases. The anisotropy coefficient is having no effect on forming limit diagram in negative minor strain region but have negligible effect on positive minor strain region and the effect is to decrease the formability on increasing the normal anisotropy coefficient.