Delamination, wear mechanism

Solid-solid Adhesion Solid suspension, adhesion, cohesion, corrosion, passivation, epitaxial growth, wear, friction, diffusion, thin films, delamination, creep, mechanical stability, durability, solid state devices, blend and alloy, charge transfer, nucleation and growth abrasion... 

The four wear mechanisms described in this section all lead to Archard s law, but the physical interpretation of the wear coefficient differs. In the adhesive wear model the wear coefficient expresses the probability that an adhesive junction leads to formation of a wear particle. In the abrasive wear model the wear coefficient depends only on the geometry of the abrasive. The wear coefficient in delamination wear characterizes the critical number of cycles leading to fatigue fracture of microscopic subsurface cracks. Finally, the wear coefficient in oxidative wear includes the growth constant and the critical thickness of a surface oxide film. 

The wear mechanism under diy contact conditions was predominated by micro-cracks, plastic deformation, debonding and detachment of fibers. Under wet contact conditions, the wear mechanism was predominant by debonding, delamination and detachment of fibers associated with loose and tom fibers. 

Jahanmir, S and Suh, N.P. (1977) Mechanics of subsurface void nucleation in delamination wear. Wear, 44,17-38. 

In view of the indirect roles of surface energetics in numerous forms of polymer wear, we can not establish a unique correlation between surface energetics and each of the above discussed mechanisms. The transfer of polymer to the counterface does not follow a certain set of rules or regularities. Pooley and Tabor concluded that the low friction and the light transfer of PTFE and polyethylenes are not affected by surface energy, e.g. or crystal texture of the polymer, or the crystallite size. The transfer is essentially due to smooth molecular profiles. On the other hand, Tanaka observed the formation of a long band on PTFE and determined the wear rate to be a function of the width of the bands rather than the crystallinity. This wear mechanism bears a similarity to that of delamin-ation ... 

Wear is the erosion of material from a solid surface induced by the action of repeated mbbing. Many wear mechanisms have been proposed such as abrasion, adhesion, surface fatigue, corrosion, erosion, and delamination. Friedrich and Sdilarb [27]... 

Reeves EA, Barton DC, FitzPatrick DP, Fisher J. Comparison of gas plasma and gamma irradiation in air sterilization on the delamination wear of the ultra-high molecular weight polyethylene used in knee replacements. Proceedings of the Institution of Mechanical Engineers 2000 214(3) 249-55. 

To increase the wear resistance of surfaces, silicon and metals are often coated with a hard nitride, carbide, boride, or oxide film. Nanoindentation and fracture simulations have been used extensively to elucidate failure mechanisms of these typically more brittle surfaces, which include crack propagation and film delamination. Considerable attention has also focused on nanocomposite materials, which possess nanocrystalline inclusions in an otherwise amorphous matrix. The nanocrystalline component is sufficiently small to preclude the formation of stable dislocations, and thus provide a higher hardness. 

The characteristics of monocrystalline diamond films are much more clearly defined. Still polycrystalline films are employed in most cases as the high price interferes with large scale application of the monocrystalline material. Even for thin layers there is no significant change to the essential characteristics of diamond. For this reason as well as to save further material, it is a common practice to employ coated substrates with a film the thickness of micrometers spread on their surface (Section 6.6.1). The endurance of such films against mechanical stress is essentially influenced by two factors Firstly, by delamination (peeUng off) of the film from the substrate, and secondly by normal, gradual wear. 

The mechanical contribution to fretting damage may include elements of adhesive wear, microscopic fatigue crack development and delamination that result in removal of small particles from the metal lattiee. The particles form a debris, which may partly adhere to the fretting surfaces and be trapped between these, and may partly escape from the fretting area. 

Figure 12.5 shows a schematic of the structure of a V-ribbed belt. The most commonly reported mechanical failure mode for this type of belt is wear, with delamination not generally perceived as a problem. This is of interest as most flexible composite elements will have a delamination failure mode of some description, and so the most obvious question to ask is why the V-ribbed belt does not. The probable answer is that the belt cord in a V-ribbed belt is isolated from the major distortions of the belt through its position above the belt/pulley interface. The large majority of the distortion of the belt takes place in the belt ribs, away from the cord. If the four shear stresses identified previously by Gerbert and Fritzson for a V-belt are considered, it can be seen that of the four i) and ii) do not apply to the cord layer in a V-ribbed belt. The cord layer in a V-ribbed belt therefore does not incur shear stress to the same extent as that in a V-belt. Thus the V-ribbed belt may be considered a better design in composite terms, with the individual elements of the composite more effectively employed and protected. 

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