Indentation Testing Method for Determining Mechanical Properties and Tensile Flow Curve of High-Strength Rail Steels

Background Instrumented ball indentation offers a promising approach to determining mechanical properties and tensile stress–strain relationships of materials, non-destructively. Objective: Using indentation load-depth experimentation to determine mechanical properties such as Young’s modulus, yield stress, strain hardening exponent and hardness, and tensile flow curve based on conventional contact mechanics principles. Method Nine different rail steel specimens are subjected to instrumented indentation testing (IIT) using an in-house developed ball indentation equipment that considers pile-up effect for effective estimation of the contact area and specimen’s stiffness required for mechanical characterization of the rail steels. Results The mechanical property response using micro-scaled ball indentation followed a comparative outcome with tensile test outcomes. The evolution of the hardness across the depth experiences a sudden increase followed by a decrease in hardness which suggests the effect of localized hardening due to indenter size effect mechanism. In order to establish the tensile flow curve via indentation, an adjusting parameter ( κ ) is included as part of the parameter ( ϕ ) that describes the development of the plastic zone beneath the indenter tip to correct the effect of multi-axial stresses and increased stresses due to the indenter size effect. Conclusions The flow curve via the ball indentation strongly correlates with tensile stress–strain relationship, showing a promising possibility of using non-destructive indentation to determine tensile properties and flow curve for high-strength rail steels.