Calibration of kinematic hardening parameters on sheet metal with a Computer Numerical Control machine

This article investigates the relevance, for material parameter identification, of substituting a set of 3 experiments (uniaxial tension, monotonous shear and reverse shear tests) by a test performed by a Computer Numerical Control (CNC) machine, where a spherical tool replacing the cutting tool performs a simple path on a fixed square sheet. This tool path is defined by one indent, one go linear path, one further indent and one return linear path. This so called line test is a simple version of Single Point Incremental Forming (SPIF) process where the depth of the produced part is however usually smaller. Completed by a uniaxial tensile test, this line test allows identifying the parameters of both kinematic and isotropic hardening models. This CNC test provides an easy alternative to tensile-compression test or reverse shear test. It generates non uniform cyclic loadings in sheets which are necessary to accurately identify kinematic hardening laws. This identification method of isotropic and kinematic hardening is applied on a brass CuZn37 sheet of 1 mm thick. It uses only the experimental measured force during the line test and a classical tensile test. The Levenberg-Marquardt algorithm is used to determine the optimal hardening material set of parameters, through inverse modelling based on finite element (FE) simulations. The sensitivity of the identification method is evaluated and the approach is validated by the capacity of the identified hardening material data set to simulate an experimental reverse shear test and a second “SPIF like test” having a more complex shape.