Nanoindentation Response of Scratched Polymeric Surfaces

The effects of imposed strains on the polymeric surfaces during scratching on the material deformation below the visible surface have not been reported in the literature. The major concern for the polymeric surfaces is the problems related to the effective sectioning for imaging/scanning unlike metal and ceramics. This article describes an experimental qualitative methodology, based on nanoindentation data, to analyze subsurface deformations of polymers resulting from scratch deformations. Poly(styrene), a brittle polymer, poly(methylmethacrylate), a ductile polymer, and poly(etheretherketone), a semicrystalline polymer, were selected for the present study. Nanoindentation responses of the scratched poly(styrene), the scratched poly(methylmethacrylate), and the scratched poly(etheretherketone) surfaces were analyzed with emphasis on the detection of subsurface crazing damage. The polymers were scratched using a 900 conical indenter on a pendulum sclerometer. The scratched polymeric surfaces were assessed using scanning electron microscopy (SEM). The polymeric surfaces were observed to be deformed by a well-known ductile ploughing mechanism. The deformed polymeric surfaces were indented using an MTS Nanoindenter. The data show that the hard asperity scratching initiates subsurface damage, which may tentatively lead to the development of subsurface voidage or crazing in certain areas of the deformed polymers, particularly within the base of the scratch groove. Major conclusions of the work are that the nanoindentation of damaged polymeric surfaces provides a qualitative methodology to estimate the subsurface damage and craze formation. This methodology is important in the context of polymers where conventional effective sectioning of the damaged surface to analyze the subsurface deformations might not be possible.