Determination of a material constitutive equation that includes the effects of strain rate and temperature using an optimization method

Numerical analysis of impact phenomena such as collisions and grounding of ships requires a material constitutive equation that considers the strain rate and temperature dependence. However, the constants of the material constitutive equation are often obtained from the literature, which reduces the analysis accuracy. This is because methods for selecting the material constitutive equation and determining its material constants have not been established. Therefore, we constructed a method for determining the material constitutive equation through optimization. First, the compression properties of rolled SM490B steel for welded structures at a wide strain rate (10−3–102 s−1) and temperature (-10–60 °C) were investigated. Using these reference data, the constitutive equation was determined by the Nelder-Mead method and a genetic algorithm. It was found that understanding the tendency of the strain rate dependence of material strength through experiments and the use of reference data for the results of high-temperature impact tests where temperature rise is unlikely to occur are effective in determining the constitutive constants. Finally, a flowchart was developed to describe the process for determining a material constitutive equation for hull materials that includes the effects of strain rate and temperature.