Microhardness of polymers

The deformation in crystalline solids occur by well defined mechanism such as slip or twining whereas for plastics it involves the relative movement of molecules. Since the molecules can be very large and occur in long chains, this would be a highly complex process. The microhardness studies on polymers are very limited. Being a complex elastic-plastic parameters, the hardness of polymer involves reversible and irreversible contributions to deformation. The Vicker's method is suitable for polymeric materials as the diagonal length of the indentation is not affected by the recovery of the material after the removal of load. Mason et al have studied the dependence of hardness on load and have proposed two types of load dependent hardness. They investigated the influence of different microstructures and microhardness near the glass transition temperature. (author)