Investigation of the mechanical properties of steel using instrumented indentation test with simulated annealing particle swarm optimization.

• An optimization was used to determine the material mechanical properties. • Mechanical properties were directly extracted from multiple loading–unloading data. • The uniqueness and adequately precision can be assured with the proposed method. A methodology is proposed to obtain mechanical properties of bulk materials from multiple loading-unloading curves of an instrumented indentation test (IIT). The mechanical properties, including strain-hardening exponent (n) and strain-hardening rate (K), were extracted from IIT data using iterative finite element simulation coupled with a simulated annealing swarm particle optimization. A systematical study was carried out to discuss the uniqueness of the identified properties. Results showed that the mechanical properties obtained in this way are unique and accurate adequately. It was found that the maximum errors of K and n generated from the macro indentation tests are 8.2% and 6.3% respectively. The identified mechanical properties from ten loading-unloading curves was compared with those obtained from a single loading-unloading curve. We found that ten loading-unloading cycles of an indentation test will result in more precise mechanical properties. [ABSTRACT FROM AUTHOR]