Scratch behavior mechanisms

The role of mast cells and histamine inducing itch remains unclear in dry skin. It has been shown that histamine concentrations increase 48 hours following acetone treatment in a dry environment.23 A subsequent study demonstrated an increased number of mast cells and histamine levels in the dermis of hairless mice in response to low environmental humidity.46 The authors did not examine a relationship between scratching behavior with the increase in mast cells and histamine. Miyamoto et al. used the mouse model treated with water followed by 1 1 acetone ether to see if they could demonstrate an increase in mast cell number or degranulation however, they found no difference.24 Furthermore, they performed the same study on mast cell deficient mice and were able to induce a similar scratching behavior, which suggests that mast cells may not play a definite role in the mechanism of itch in dry skin. 

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. 

Scratch damages inflicted on polymer surface have important consequences on the appearance and mechanical performance of the materials. Scratches, in a lot of situations, are precursors of wear and abrasion (119,120). Scratch phenomena impact on the use of polymers in automobiles, microelectronics, food packaging, and coatings. The complexity involved in research of scratch behavior of polymers has been highlighted in this article. Many factors have been considered for their influence on the subject concerned. Very often the factors that affect scratch interact with each other and are difficult to isolate the effect of individual factors. This renders the interpretation of experimental results difficult and thus explains the frequently observed contradictory results in the literature. 

With all the strategies listed above, we hope that as our imderstanding on scratch behavior of polymers accumulates, a more complete formulation of theoretical framework on surface deformation and damage phenomena can be developed. Only when such framework relating all relevant materials parameters and mechanics with deformation mechanism is available, can we establish predictive model that is useful for polymer engineering and design of scratch-resistant polymers. 

See Scratch Behavior of Polymers Surface Mechanical Damage and Wear. 

The scratch behaviors observed in the most common plastics were classified into three modes, i.e. ploughing, wedge formation, and cutting modes. However, the mechanisms of such scratch modes and the correlation between fundamental mechanical properties and scratch behaviors is not well understood yet. 

In this study, the scratch behavior on injection molded PC/ABS, that is one of the most popular materials for common use, was investigated, and the mechanism of the scratch was discussed from the observation of damage generated by scratch by means of polarized optical microscopy (POM), scanning electron microscopy (SEM), and transmitted electron microscopy (TEM). 

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. 

If compared to normal indentation and scratch tests, identical qualitative ranking of mechanical stability of the trilayered samples was obtained. The behavior of the TMS3 sample (SiC/Taj /steel) stands out clearly from the others. For this thickness of tantalum, the resistance to flaking caused by scratch and indentation tests reaches a maximum value with reduced flaking. This optimum thickness is to be linked to the state of residual stresses in the deposits as evidenced by the concomitant... 

A somewhat alternative analysis of pitting attributes pit initiation to the activation of defects in the passive film, defects such as those induced during film growth or those induced mechanically due to scratching or stress. The pit behavior is analyzed in terms of the product, xi, a parameter in which x is the pit or crevice depth (cm), and i is the corrosion current density (A/cm2) at the bottom of the pit (Ref 21). Experimental measurements confirm that, for many metal/environment systems, the active corrosion current density in a pit is of the order of 1 A/cm2. Therefore, numerical values for xi may be visualized as a pit depth in centimeters. A defect becomes a pit if the pH in the pit becomes sufficiently low to prevent maintaining the protective oxide film. Establishing the critical pH, for a specific oxide, will depend on the depth (metal ions trapped by diffiisional constraints), the current density (rate of generation of metal ions) and the external pH. In turn, the current density will be determined by the local electrochemical potential established by corrosion currents to the passive external cathodic surface or by a potentiostat. Once the critical condition for dissolution of the oxide has been reached, the pit becomes deeper and develops a still lower pH by further hydrolysis. 

Instrumentation. The experimental procedure for an AFM equipped with a suitably coated tip has been outlined above. In a study of an aluminum alloy AA2024-T3, intermetallic particles and the matrix phase could be separated clearly [98]. The different surface films on these phases could be associated with their corrosion behavior. Inclusions and their corrosive behavior have been studied with a combination of SKPFM and AFM [101]. The effect of chloride-containing solution on corrosion at the matrix and the intermetallic particles was studied with SKPFM, in addition, light scratching with the AFM in the contact mode was applied to study the effect of the mechanical destabilization [102]. The intermetallic particles dissolved immediately after the film on their surface had been destabilized by mechanical abrasion. 

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. 

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