Effects of load and time on the hardness of a viscoelastic polymer

Vickers indentation is arguably one of the most widely used techniques for characterizing the mechanical properties of materials because it is easy, inexpensive, and nondestructive. However, its popularity has so far been limited to ceramics and metals, and very little information is available on the Vickers indentation properties of high or rigid polymers. In this paper, the effects of load and time on Vickers indentation responses of an acrylic polymer are presented. The hardness of this material is shown to be time dependent as a result of viscoelastic flow and relaxation processes. The microhardness of the acrylic polymer, unlike that of ductile metals, is not dependent on the indentation load. The elastic recovery in the Vickers impression takes place along the side-faces, but not along the diagonals. Thus, Vickers indentation is a valid tool for evaluating the hardness and viscoelastic responses of rigid polymers.