Extension of the Rusinek–Klepaczko Model for Materials with Saturated or Moderate Strain Hardening: Application to 2024 Aluminum Alloy

Abstract The model presented in this work is a modified version of the Rusinek–Klepaczko (RK) constitutive relation, aiming to account not only for strain rate and temperature effects, but also for stress saturation occurring for large strains or moderate hardening. This extension introduces a saturation mechanism into the flow stress description while preserving the physical foundation of the original RK model. A key advantage of the approach is that it requires only a limited number of mechanical tests to calibrate all model parameters. Moreover, some constants are directly derived from physical aspects, enhancing robustness and interpretability. Unlike the original RK model, the present version explicitly incorporates the saturation of strain hardening. For simplicity, the hardening coefficient is assumed constant in this study, but can be extended to depend on strain rate and temperature, as in the original formulation. The model is applied to 2024 aluminum alloy. In addition, this model is compared with the classical Johnson–Cook model formulation that includes non-stress saturation and non-linear sensitivity to strain rate. The analysis of the uniaxial traction using the new version of the RK model implemented as the VUHARD subroutine is presented.