Integrated design in welding and incremental forming: Material model calibration for friction stir welded blanks

Typically, the development of new forming products is performed using numerical tools such as finite element analysis software. However, the precision of these tools is dependent on the input data, particularly the one related to constitutive models and material parameters. These parameters are generally used to calibrate the model for each specific material, knowing a priori that the material behavior and properties are constant within the part/specimen. However, in welded blanks, the material behavior and properties drastically change with the proximity to the welded zone and, therefore, new challenges arise with the calibration of constitutive models for such heterogenous materials. The present study is part of a larger project that deals with the incremental forming of welded aluminum blanks. These are initially joined by Friction Stir Welding (FSW), and tensile tests were carried out both on the base material and on the welded material, transversely to the weld, using a Digital Image Correlation (DIC) device to capture the strain field. Moreover, hardness measurements were carried out. Results show the evolution of change on the material behavior and properties throughout three well distinct areas, namely: the nugget zone at the center of the weld; the thermo-mechanically affected zone (TMAZ); and the heat affected zone (HAZ), making it possible to create a suitable elastoplastic model with multi-linear piecewise function parameters, properly calibrated for the friction stir welded material. A finite element model updating scheme was applied using a smooth interpolation scheme for the DIC data with outliers and gap control. The calibration process resulted in a model with quite good accuracy in comparison to experimental results.