Inverse calibration of the AA5754-H22 constitutive equation at high temperature

The numerical modelling of sheet metal forming processes requires an accurate preliminary characterization of the material behaviour under operating conditions close to the real forming process. Data from experimental tests are generally used to calibrate the material constants, initially unknown, belonging to constitutive equations that relate the equivalent state stress state to the equivalent strain, or strain rate. In the present work, the behavior at hot temperature (400°C) of the AA5754-H22 aluminium alloy is investigated by means of free inflation test, that are based on the deformation of circular blank clamped at its periphery by means of a pressurized gas. Data from the free inflation tests, carried out at different pressure levels, are used to inversely calibrate the unknown material constants belonging to the Backofen equation (σ=Cε ̇^m) [1]. The proposed method, differently from the analytical approach available in literature [2][3], integrates a Finite Element (FE) model – replicating the experimental inflation tests – within an automated optimization procedure driven by the MOGA-II genetic algorithm. The procedure allows to iteratively change the material constants and identify the optimal set able to minimize the error function calculated as the difference between the experimental and numerical data. The procedure is replicated at each pressure level, providing a set of material constants for each loading condition.