Indentation depth recovery in poly(methyl methacrylate) sheet on the microlength scale

This paper describes an experimental study designed to quantify the elastic depth recovery behaviour of indentations and grooves made in the surface of a poly(methyl methacrylate) sheet with a probe of Berkovich geometry. Significantly greater depth recovery was found for the grooves, and it is shown that this cannot be ascribed simply to differences in the imposed strain rates, Furthermore, the normal indentation and scratch hardness values at a given strain rate are similar. It is proposed that the greater recovery in the scratch case is the result of a lesser effective imposed strain due to the naturally occurring 'lift' which is created by the formation of a 'bow wave' at the front of the probe.