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Carbon based materials (such as carbon fibers (CFs) and carbon nanotubes (CNTs)) are under intense investigation,due to their unique properties and their future potential for enhancement of the mechanical properties of their composites. Their interaction with matrix through the interphase is not a simple concept, but a rather complex one, consisting of areas of imperfect bonding, mechanical stresses due to shrinkage, high stress gradients or even stress singularities due to the geometry of the inclusion, voids, microcracks etc.
Despite the fact that the interactions between reinforcements and polymer at a molecular level is still not completely understood, it is clear that the interphase has a significant influence on the mechanical integrity of the composite as its distinct properties control the load transfer between matrix and fillers.Also, there is a major challenge in studying the local mechanical behavior and mechanical properties in the small volume of interphase,since the conventional methods, e.g. tensile test and micro-hardness are not applicable. Instrumented indentation technique, widely known as depth-sensing indentation or nanoindentation, is a powerful and advanced tool to characterize the interphase region by local application of various loading protocols.
The effects of reinforcing fillers on the classical nanoindentation load-displacement curves of the composites and the deformation behavior are investigated by the application of various loading protocols. Nanoscratching technique is appliedso as to determine the frictional properties in the matrix, fiber and interphase regions and estimate thethickness of the interphase. Hardness and elastic modulus are evaluated, together with quantification of wear resistance, plastic deformation and the coefficient of friction of the composites. The surface topography of the indented and scratched regions is assessed using atomic force microscopy.
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