ABSTRACT: Recent experiments on amorphous polymers show an increase of hardness with decreasing indentation depths -- a phenomena previously well known in metallic materials. Classical plasticity theories do not contain any intrinsic material length-scale and therefore cannot capture such length-scale dependent phenomena. This shortcoming has led to the recent development of theories that attempt to capture such phenomena via dependencies on plastic strain gradients. In this study we develop a large-deformation strain-gradient theory for amorphous polymers, implement the theory in a finite element package, and perform validation experiments. All the experimental and numerical results herein are preformed on the amorphous polymer polycarbonate. We show that the numerical results from our non-local strain gradient theory agree well with the experimentally observed dependence of the hardness on depth at shallow depths of less than a micron.

Indentation Size Effect

The indentation size effect in amorphous polymers may be captured via the addition of a nonlocal strain gradient term to an already existing constitutive theory.