Constitutive model calibration for railway wheel steel through tension-torsion tests

The identification of the parameters contained in an elastic-plastic material model, apt to simulate steady-state ratchetting, is studied herein with reference to cyclic biaxial tests on cylindrical compact specimens. The material considered is steel employed for high-speed train wheels. In order to generate strain states close to those expected in severe service conditions due to wheel-rail rolling-sliding contact, out-of-phase tension-torsion unsymmetric cycles are applied in laboratory tests. The experiments are simulated by conventional finite elements and Chaboche model with nonlinear kinematic hardening. The material parameters are identified through a deterministic, batch (non-sequential) inverse analysis in two stages (genetic and first-order algorithms) in view of the peculiar constraints in the minimization problem. This study leads to the following conclusions of practical use: multiaxial ratchetting tests are desirable to characterize cyclic material behavior in the industrial context considered; compact (instead of thin-walled tubular) specimen tests, combined with parameter identification by inverse analysis, exhibit the advantages of cost effectiveness and of small size needed to assess material properties locally.