Indentation load-displacement behaviour during conventional hardness testing

The behaviour of a range of materials was examined using a hardness tester instrumented to measure load and displacement during conventional Vickers indentation. For a peak load of 3 N, rise times of 0.2-0.6 s and maximum displacements of 5-25 μm were observed for three metals, two oxides, a semiconductor and a polymer. The materials with small modulus E or hardness H values exhibited large displacements during indentation loading, whereas the displacement recovery was greatest for materials with small E/H ratios. Recovery ratios varied between 0.6 and 0.1. The coefficient of restitution (measured by the area enclosed by the load-displacement response during the unloading sequence relative to that enclosed during loading) was also larger for materials with small E/H ratios. Coefficients of restitution varied between 0.9 and 0.5.