Mechanical wear, definition

The stamp associated with the extreme hardness values (number 7, Fig. 4.12, left use STAMP.dat with program MULTI) is the next suspect It is identified and inspected on disassembly of the tablet press Due to mechanical wear, the movement of the stamp assembly is such that an above-average amount of granulate drops into cavity number 7, and is thus compressed to the limiting hardness supported by the granulate. The hardness for stamps 4, 8, and 11 tends to be low, and high for 12, but the data is insufficient to come to definite conclusions for these tools. The tablets from these stamps contaminated what would otherwise been a fairly acceptable product. Because... 

This is our definition of mechanical wear. It is essentially phenomenological, and in contrast to a purely conceptual model based on a pKlon. assumptions and inexorable logical reasoning, the governing conditions and conclusions of this definition are in terms of observable behavior. Nevertheless the definition is fundamental enough to fit all... 

An alternate method of classification of damage mechanisms in terms of environmental conditions such as stress, temperature, corrosion, wear, radiation is known as the failure wheel. In this representation secondary mechanisms are underlined as opposed to primary damage mechanisms. The boiler tube failure discussed can be represented in terms of failure wheel, as shown in Figure 2.31. The aim in any case is to identify definitively the underlying mechanism of failure to enable one to undertake remedial action such that future failures do not occur. 

The term tooth wear is commonly used to describe the loss of tooth hard tissue due to non-carious causes [1], This encompasses a variety of both chemical and mechanical causes of both intrinsic and extrinsic origin. The term tooth wear is preferred over some of the more precise definitions of individual hard tissue loss mechanisms, because it acknowledges the fact that wear is usually a multifactorial process one mechanism may dominate, but the overall wear is commonly due to the interaction between two or more wear mechanisms. In dentistry, the terms erosion, abrasion, attrition and abfraction are widely used to describe particular mechanisms of hard tissue loss. 

The mechanisms of tooth wear fall into two distinct types those of chemical origin (e.g. erosion) and those of physical origin (e.g. abrasion, attrition). In any individual, both chemical and physical insults to the tooth hard tissue will be present in some form or other, so tooth wear is the combined effect of these insults. Despite the clear definition of a number of distinct tooth wear mechanisms, it is uncommon to find a single wear mechanism present in the... 

Erosion is defined as the loss of hard tissue by chemical means not derived from bacteria, i.e. the dissolution of hard tissue by acid where the acid source is not the oral bacteria [5], Erosion may be caused by either intrinsic (e.g. stomach acid) or extrinsic (e.g. dietary) sources. Erosion is often associated with the consumption of acid products, such as fruits or acid beverages, or with medical conditions where reflux of acidic into the oral cavity is present. Interestingly, the term erosion is widely used in other fields where the definition is rather different. For example, in the field of tribology, erosion refers to the loss of material from a surface by solid or liquid impacts [6], In the classical tribological definitions, the mechanism dentists refer to as erosion would be described as corrosion, or tribo-chemical wear. 

The concept of adhesive interaction of contacting surfaces is already familiar to us from previous discussion of the adhesive mechanism of friction (Chapters 8 and 12). If the two bodies participating in the adhesive junction are in motion relative to each other, in particular tangential motion, the junction is ruptured shortly after it is established. Rupture of the junction at a location other than the original interface results in transfer of material from one body to the other. According to the broad definition of wear of Section 13.1, each body has been worn—one by loss of material, the other by gain—but there has been no net loss or gain in the system as a whole. 

An important aspect of the function of compounded lubricants is to increase the load that can be carried by machinery without catastrophic damage to the rubbing components. Since the typical antiwear additives affect the viscosity of the carrier oil very little, it is not a fluid film effect that is responsible for the load-carrying augmentation. Examination of the various basic wear processes leads to the choice of the adhesive mechanism as the one most likely to respond to the action of boundary or extreme-pressure additives. The type of macroscopically observed severe wear which has this mechanistic process as its primary cause is generally designated as icu i ng (c(S. Chapter 13, Sections 13.4 and 13.6), and it is in this sense, as a description rather than a definition, that the term scuffing is used in the discussion to follow. 

FYom the multitude of intricate corrosion processes in the presence of mechanical action (friction, erosion, vibration, cavitation, fretting and so on) it is justified to touch upon corrosion types joined under a single failure mode induced by mechanical stresses. These are the stresses that govern the corrosion wear rate of metals during friction. Such processes are usually called corrosion stress-induced cracking in the case that the mechanical action is effective only in one definite direction, or otherwise termed corrosion fatigue in the case that compressive and tensile stresses alternate within cycles. In spite of the differences between the appearance of these corrosion types, they have much in common, e.g. fundamental mechanisms, the causes, and they overlap to a certain degree [19]. 

Define the property limits of polymers in both structural and functional applications Tliis can entail improved or new synthetic methods which lead to highly pure starting materials improved or new synthetic methods which omit weak linkages in macromolecules and, hence, lead to a major property increase of known materials a much better understanding of characteristics such as strength, resistance to wear and various degradation mechanisms and how these relate to processing definition of the... 

Mechanochemistry (or Tribochemistry) is usually defined as a science dealing with the chemical and physicochemical changes of substances due to the influence of mechanical energy [23] (see Appendix A for other definitions of mechanochemistry). On the other hand, the term tribology is commonly used to refer to the science of interacting surfaces in relative motion with respect to friction, lubrication, and wear [41]. 

When one considers this mechanism of elastohydrodynamic lubrication, the question may arise, as to why one should ever see the failure of a lubricant. While the answer has yet to be determined definitively, two possible explanations are (1) even at the extremely high pressures involved, the extreme local temperatures that also exist surpass the critical point so that the lubricant is effectively evaporated away or (2) shear forces near points of contact are sufficient to effectively break up the solidified lubricant film, leaving bare spots that can have direct contact, leading to excessive wear and possible seizure. 

Wear maps present in graphical form the predominant wear mechanism as a function of selected system variables, usually written in dimensionless form in order to minimize their number. Figure 10.21 presents a wear map, for pin-on-disk tests of non-lubricated steel to steel contacts. The abscissa shows the dimensionless sliding velocity v i, and the ordinate gives the dimensionless normal force F. These two parameters correspond, respectively, to the two following definitions ... 

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