Quantitative Characterization of Mechanical Properties using Instrumented Indentation

Abstract

Instrumented indentation testing (IIT), an advanced version of conventional hardness tests, is widely used to evaluate the mechanical behavior of materials. Compared to conventional mechanical tests such as tensile testing, saw-cutting, CTOD, and so on, it is a relatively simple method that measures penetration load and depth continuously. In addition, IIT needs little sample preparation and can be applied from macro- to nano-scales by controlling the load and depth range, so that it is used by many researchers on metallic materials and bio-materials at all scales. Here we introduce the fundamentals of evaluating tensile properties and residual stress using IITs as published in ISO/TR 29381. Since indentation means contact between an indenter and surface of specimen, calibrating the contact area is the key issue in estimating tensile properties. By defining a representative stress and strain, indentation load-depth data can be converted to corresponding stress and strain points from the tensile curve. In evaluating residual stress, the load difference is calculated using a stress-insensitive contact hardness model.