Application of instrumented indentation technique in in situ performance characterization of high-speed rail rim

A purely experimental integrated algorithm for the industrial implementation of instrumented indentation technology has been established in the present study. This study proposes a multivariable iterative decoupling optimization algorithm to solve the best Hollomon constitutive model to estimate the indentation tensile properties by performing incremental cyclic indentation to take the measured maximum force, stiffness, and indentation depth of each unloading segment as the input. The Meyer power-law model is employed to improve the accuracy of the as-estimated yield strength. In addition, the critical indentation energy model is used to estimate the equivalent fracture toughness KJC. Tensile fracture strain or elongation is used as a damage factor to calculate the critical effective indentation depth relative to the threshold of indentation cracking, which is required to obtain the necessary indentation energy for KJC. Thereafter, the indentation tensile and toughness properties of typical high-speed rail rims were evaluated without sampling, consistent with relative results from regular standardized testing. Moreover, the distribution features of strength, hardness, yield strength ratio, and toughness, along with the depth from the surface to the inner substrate of rail rims, were studied quantitively based on the estimated indentation results. This gave a practical way for short-process nonsampling and in situ mechanical property evaluation with high-throughput results for such metallic materials or components as rail rims.