An approach for Knoop and Vickers indentations to measure equi-biaxial residual stresses and material properties: A comprehensive comparison

A residual stress analysis is indispensable to anticipate engineering structure loading conditions. For this purpose, there are various methods, including indentation technique, a non-destructive test, which also enables us to measure material properties as well. Numerous studies have been conducted until now, but it is yet to be completed. Study of entire available methods indicates that any comprehensive rather simple method has not been presented yet to achieve material properties and residual stresses, simultaneously, without any insight observation using sharp indentation. In the current work, extensive experimental and numerical studies have been performed using Vickers and Knoop indentations to anticipate yield stress, work hardening exponent and equi-biaxial residual stresses of aluminum and steel samples simultaneously. First, a local estimation method was proposed to reach stress-free state parameters and then typical equations were suggested to obtain yield stress and work-hardening exponent through genetic algorithm. Based on the first step, several equations were offered for every state of tensile and compressive residual stresses and indenter types to measure residual stresses. Obtained results demonstrate how the Knoop indenter led to more accurate results than the Vickers. Moreover, the suggested method worked accurately and the results were in agreement with the experiments.