Design optimisation of biaxial tensile test specimen using finite element analysis

One of the most restricting aspects of the biaxial tensile test for sheet metal is the design of the cruciform specimen. Although specimens of the cruciform type have been investigated quite extensively previously, no standard geometry for the cruciform specimen exists. Using a specifically designed pantograph apparatus for operation in a standard tensile testing machine, various cruciform specimens machined from low-carbon cold rolled steel sheet were analysed experimentally. Finite element modelling of the specimens was conducted in parallel to the experimental test programme to establish optimum specimen geometry. Through a process of optimisation, a standard cruciform specimen was designed which can be used to accurately predict the mechanical behaviour of the mild steel when formed in multiple directions simultaneously. This paper describes the optimisation process and the results obtained from both the experimental testing and numerical modelling.