Scratch behavior materials properties

Carbon-based polymer nano composites represent an interesting type of advanced materials with structural characteristics that allow them to be applied in a variety of fields. Functionalization of carbon nanomaterials provides homogeneous dispersion and strong interfacial interaction when they are incorporated into polymer matrices. These features confer superior properties to the polymer nanocomposites. This chapter focuses on nanodiamonds, carbon nanotubes and graphene due to their importance as reinforcement fillers in polymer nanocomposites. The most common methods of synthesis and functionalization of these carbon nanomaterials are explained and different techniques of nanocomposite preparation are briefly described. The performance achieved in polymers by the introduction of carbon nanofillers in the mechanical and tribological properties is highlighted, and the hardness and scratching behavior of the nanocomposites are also discussed. 

From the equations presented in under Theoretical Backgroimd, it can be derived that materials properties, such as modulus and yield strength, and any modifications that might affect them will influence the scratch behavior of polymers. The unique characteristics of poljnners make research in polymer scratch particularly challenging. First, as mentioned in the previous section, polymers are viscoelastic-viscoplastic in nature. This makes polymer properties very sensitive to test conditions, especially temperature and strain rate (21,34,56,63,64). 

With these complications in mind, research in this area has blossomed rapidly. Two main foci of research in this area are on (1) how external conditions (such as levels of loadings, the use of different indenters, and scratch rate) and (2) intrinsic materials properties (such as modulus and crystallinity) affect the tribological behaviors of the polymers. Apart from examining the scratch resistance of polymers, a closely related quantity which is of interest would be changes in coefficient of friction. Studies relating mechanical properties (3-5,9,36,71,75,76), deformation patterns (18,33,63,71,77-81), fabrication process (3,5,35,72,77,82-86) with respect to experimental parameters, snch as temperature (18), loading effect (24,71,72,87-96), indenter geometry (21,33,75,82,95,97), and scratch velocity (21,56,57,59,64,65,96,98) have been carried ont. In addition, scratch maps for different polymers have been produced (32,33), and various scratch resistance properties estimated (33,37,56,58,59,99). 

The nanostructure with no defects or artificial defects are not suitable to simulate the material properties of practical nanostructure, in this part, we introduce an integrated MD simulation method, in order to study the mechanical properties of nanostructure with practical processing defects. We consider the nanostructure scratched by diamond tip under the machining conditions of different scratching depth of different scratching lattice plane or direction, just like we have described above, as the practical processing defects, then, apply tension or shearing force on such nanostructure to observe their physical and mechanical behavior. 

In the literature, there has been some work done to characterize the mar behavior of polymers. Shen et al. attempt to define a mar as light damage occurring at low loads [6-8]. Although this may be the general case, their definition gives neither a reference to precedence nor any relation to material properties that set mar and scratch apart as separate entities. 

The term hardness is a relative term. Hardness is the resistance to local deformation that is often measured as the ease or difficulty for a material to be scratched, indented, marred, cut, drilled, or abraded. It involves a number of interrelated properties such as yield strength and elastic modulus. Because polymers present such a range of behavior, as they are viscoelastic... 

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