Scratch behavior hardness

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. 

In addition, Westwood and Huntington reported that both drilling rate and pendulum hardness depended on the number of carbon atoms in n-alcohols and n-alkanes, because these processes included fracture behaviors. Therefore, scratch behaviors of glass also depend on these environments. 

Vickers and Knoop indentors, Barcol hardness, and Shore durometers (2) (b) to measure the resistance of a material to scratching by another material or by a sharp point, such as the Bierbaum hardness or scratch-resistance test and the Moh one for hardness and (c) to measure rebound efficiency or resilience, such as the various Rockwell hardness tests. The various tests provide different behavior characteristics for plastics, as described by different ASTM standards such as D 785. The ASTM and other sources provide different degrees of comparison for some of these tests. 

Hardness is a somewhat ambiguous property. A dictionary definition is that it is a property of something that is not easily penetrated, spread, or scratched. These behaviors involve very different physical mechanisms. The first relates to elastic stiffness, the second to plastic deformation, and the third to fracturing. But, for many substances, the mechanisms of these are closely related because they all involve the strength of chemical bonding (cohesion). Thus discussion of the mechanism for one case may provide some understanding of all three. 

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... 

There are numerous techniques known for adhesion and delamination testing, some of the most common being a tape test, stud-pull test, scratch test, and an indentation test [1]. In the tape test, a tape is pulled off the surface containing a scratch, which provides the failure initiation. In the stud pull test, a stud held with thermosetting epoxy is pulled off the film surface. The indentation test, wherein a ball is pressed into the surface, is used for hard coatings, and the failure pattern indicates acceptable behavior. In the scratch test, where an indenter moves in both vertical (loading) and horizontal (sliding) directions, an acoustic emission sensor allows for detection of the initiation of fiacture, while the scratch pattern indicates the type of failure. 

Hardness. The hardness of a coating is examined by three types of test the scratch test, the damping test, and the indentation test with a penetrating body. The results of one of these tests do not allow conclusions to be drawn as regards the behavior in another test [9.31]. 

A rough measure for the hardness of a plastic is its behavior when scratched with a fingernail hard plastics scratch the nail hornlike plastics have about the same hardness flexible or rubbery plastics can be scratched or dented with a fingernail. 

Figure 8 from (Jochum 2013) shows the behavior in cutting of brittle hard materials, namely Circonium oxide and Yttrium oxide as it is used for dental implants. The picture shows ductile material behavior due to high compressive stresses and thus ploughing in the upper scratch. In the lower scratch an intercrystalline fracture is shown, which is due to the interaction between grain and material possibly as shear fracture, mechanism similar to the one pointed out by Kragelski in Fig. 6. 

For hardness determination, different methods are possible scratching the surface, penetration of an indenter with static or dynamic loads, or rebound as a result of elastic material behavior. The methods with a penetrating indenter are the most important ones. The applied methods are distinguished, e.g., by the shape of the indenter. Brinell hardness is determined by a ball-shaped indenter, while Vickers hardness applies a pyramid-shaped one. After the indenting test with a certain load, the surface area of the indentation is measured which delivers a value for material hardness. Determination of Rockwell hardness uses the depth of the indentation instead of the surface area (Bargel and Schulze 1988). Independent of the method, the so-called surface hardness... 

Theoretical and experimental properties of dislocations are well understood for well-defined states of stress and simple deformations, and so basic groundstates are available. However, the complex stress states present within the small volumes beneath indenters and scratch hardness and pendulum hardness testers are far from well understood. What then is the chance of applying dislocation theory to the understanding of the hardness behavior of ceramic single crystals, or rather, one might ask, why has its application been so successful and so dominant The reason is that even for complex stress states the positions of dislocations and the ways they interact can be observed using a combination of techniques on single-crystal... 

While elastic modulus is an important characteristic of a polymeric material, it mainly describes material behavior at small deformations only. This could be important for some applications (note, for example, that scratch resistance or hardness often can be directly linked to the modulus) however, in general, one requires the knowledge of mechanical response of the material over a broad range of deformations. For polyurethane elastomers and TPU s, as well as for... 

---