Indentation Behavior of CoCrFeNiMn High-Entropy Alloys under Dynamic Loads

To address the challenge of evaluating the internal stress of materials or structures in service environments, a method combining finite element analysis and micro-indentation testing is proposed. Taking the CoCrFeNiMn high-entropy alloy as the research object, compression, shear and micro-indentation tests were carried out at various loading speeds respectively. Based on an asymmetric initial yield function, Swift hardening and the associated flow rule, an elastoplastic constitutive model for this material was established. The constitutive model was programmed by using the stress integration algorithm and interfaced with the ABAQUS finite element software. Furthermore, by comparing the finite element simulation results with the experimental results from the split Hopkinson pressure bar (SHPB) tests and the indentation model, the reliability of the model was verified. Using the SHPB model, the numerical simulation of the dynamic compression experiment was carried out, and the stress fields at different dynamic deformation moments were imported into the indentation model as the initial stress (internal stress) fields for indentation simulation analysis. The results indicated that the initial stress field in the loading stage significantly reduces the indentation load at the same indentation depth, and the reduction amplitude increases with the increase of stress. In addition, the existence of the initial stress field will further weaken the stress concentration during the indentation process. Through the quantitative analysis of the load-indentation displacement curves under different compression amounts, the indentation response laws of the materials under different initial stress conditions were revealed. The research results provide a reference for the evaluation of the internal stress of materials or structures under service conditions.