Indentation is one of the most widely used techniques of measuring mechanical properties of materials, especially for materials of small volume. In micro- or nano- scales, performing traditional tests such as the tension test and bending test becomes less feasible because of the nontrivial task of sample preparation. In contrast, by using the indentation technique, the difficulty of sample preparation may be dramatically reduced. On the other hand, indentation test is not a direct measurement and advanced mechanics analysis is needed to correlate the material properties with the indentation response. 

In an indentation test, a hard tip is pressed into a sample. The tip can be sharp or spherical. After the tip is removed, an impression is left. The hardness is defined as the indentation load divided by the projected area of impression. Moreover, by means of instrumental indentation testers, the indentation load and indentation depth can be continuously and simultaneously measured. Many models have been developed to extract the material properties from the recorded indentation load-depth curve, including the elastic modulus, yield stress, strain hardening coefficient, residual stress, fracture toughness, etc.