Phenomenological model for prediction of localised necking in multi-step sheet metal forming processes

Prediction of localised necking is crucial for cost, time and material efficient production of sheet metal components. Especially in multi-step forming operations, nonlinear strain paths occur due to complex part and tool geometry as well as changing loading conditions during the forming process. Today, prediction of localised necking for such components is often based on empirical knowledge of experienced forming specialists or specialised damage models particularly related to sheet metal materials. It is well known, that calibration of such damage models can be difficult, particularly for industrial applications. The model presented in this paper is a phenomenological approach for prediction of localised necking under varying loading conditions which is easy to calibrate. For the calibration procedure only 36 uniaxial tensile tests are needed. The model calibration and failure prediction was carried out for DP600 material with sheet thickness of 0.98 mm. An experimental forming component manufactured in three forming operations was used for validation of the model presented. Mathematical setup of the model, simulation approach as well as a comparison between numerical and experimental results will be given.