In Pursuit of an Integrated Methodology for Accurate Elevated Temperature and Superplastic Tensile Testing

Abstract

Hydro and pneumatic sheet metal forming operations are commonly carried out at warm and elevated temperature; hence for modelling the behaviours of the formed materials, testing at such temperatures is necessary. The uniaxial tensile test is the most universally-adopted mechanical testing procedure for material characterisation purposes; yet in spite of its simplicity and standardisation for room temperature testing, the test is problematic at higher than-ambient-temperatures. Perhaps that explains the disagreements between different researchers in the field on some of the most critical aspects of the test. Crucially, any inaccuracies in warm and elevated temperature tensile testing have direct impact on the accuracy of the constitutive models and finite element simulations, which we rely on in running and optimising hydro/pneumatic forming operations. This work presents a comprehensive testing methodology that aims at resolving the most critical of issues encountered in this unique type of testing. The methodology is centred about quick-mount grips that tackle the thermal issues by facilitating mounting the test specimen in a very short time. A testing procedure is devised accordingly, and preliminary testing results are presented to demonstrate the impact of the methodology on the accuracy of the results. In addition, the effect of the specimen geometry on the test outcome is investigated using a wide variety of geometries; an optimised geometry is derived based on the obtained experimental results. The methodology is validated by testing AZ31B-H24 magnesium alloy specimens at different temperatures and strain rates.