A method for estimating superplastic material parameters via free–inflation tests

In this work, a new methodology for evaluating the constitutive parameters of superplastic materials is presented. The proposed methodology provides the characterization of the material by means of a variable called apparent viscosity. This variable is calculated for three different materials through data collected by free inflation tests made at different temperatures and pressure values. The apparent viscosity was then used to calculate some material parameters by which the experimental tests were reproduced numerically in a finite element commercial code. The results obtained by numerical simulations were compared both with the experimental ones and with ones deriving by simulations run with material parameters calculated by a commonly used methodology. The proposed approach revealed to have a good prediction capability with deviations lower than the one found by the approach taken as reference. A second validation step was then performed by comparing the stress and strain-rate values found through the proposed methodology with the curves constructed by applying uniaxial tests results from literature. This latter comparison showed that results fit well with the behaviour shown using the standardised uniaxial tests.