Mechanical Characterization and Constitutive Modeling of AA2014-T6 and AA5059 Alloys at Intermediate Temperatures and High Strain Rates

Capturing the thermoviscoelastic behavior of materials at high strain rates and varying temperatures is crucial for understanding their complete dynamic behavior. The Johnson–Cook constitutive model incorporates thermal softening, strain-rate sensitivity, and hardening. However, the saturation of the flow stress at large plastic strains was not considered in the JC model. This study presents a detailed investigation of the mechanical behaviors of AA2014-T6 and AA5059 aluminum alloys at high strain rates under varying initial temperatures. Split Hopkinson pressure bar (SHPB) coupled with a custom furnace is used to gather experimental data such as strength of the alloy, strength, ductility, strain hardening, and temperature sensitivity. The results demonstrated distinct hardening behaviors and thermal responses linked to their chemical compositions, with AA2014-T6 exhibiting higher strength owing to precipitation hardening and AA5059 exhibiting enhanced ductility and multiplicative temperature sensitivity. A modified Johnson–Cook constitutive model incorporating strain hardening saturation, nonlinear strain rate sensitivity, and thermal softening was developed and calibrated using a differential evolution algorithm. The model accurately reproduces the experimental observations, including the thermal effects under adiabatic conditions, and highlights the necessity of multiple strain rates and temperatures for robust parameter identification. The thermal softening coefficients of 1.1450 for AA5059 and 1.2578 for AA2014-T6 indicated a comparable decrease in the mechanical strength with increasing temperature. Based on the experimental data, a comparative analysis of their performances was conducted, and a constitutive relation was proposed for both alloys, accounting for the temperature and strain-rate sensitivity.