Characterisation and modelling of thermomechanical behaviour of AA6082 sheet under heterogeneous temperature and strain fields

High-temperature testing using Gleeble thermal-mechanical simulator has been widely adopted to characterise the thermomechanical behaviour of metallic materials. However, the inherent non-uniform temperature distribution along the specimen length in these high-temperature tests often compromises the ability to maintain a constant strain rate, thereby limiting the reliability of the experimental data for material characterisation. This study investigates the high-temperature mechanical response of AA6082 through Gleeble uniaxial tests with digital image correlation (DIC), focusing on strain localisation and strain rate evolution. The experimental results reveal non-uniform strain distribution and significant strain localisation at elevated temperatures, with higher temperatures leading to earlier strain localisation and deviations from the target strain rates. The stress-strain curves extracted from uniaxial test data demonstrate a reduction in flow stress with increasing temperature and decreasing strain rate. A new fitting technique considering varying strain rates has been proposed to refine constitutive modelling, improving the accuracy of calibration. A near-perfect plasticity behaviour is revealed for AA6082 under constant strain rates at high temperatures. Finite element (FE) simulations, implemented with the calibrated material model, successfully captured the non-uniform strain distributions observed in experiments. This study provides a new calibration strategy for non-uniform strain distribution and non-liner strain evolution encountered in Gleeble high-temperature testing and new insights into the thermomechanical behaviour of AA6082.