Tribological system

Another important issue associated with tribological simulations involves the definition of the system to be studied. For example, a simple tribological system consists of two atomically flat, defect-free surfaces sliding past one another. Because of computational convenience, it is common... 

In reality, the atmosphere of the tribological system is of particular importance. Two usual components of the atmosphere are substantial for boundary lubrication, i.e., oxygen and water vapor. The following sequence of chemical transformations is obvious ... 

Due to the continuous input of thermal energy necessary to maintain mechanical work, tribological systems are in progressive equilibrium. In the tribosystem, the flow of energy is accompanied by an increase in entropy of the total system and is reflected by the tribochemical reactions and deterioration of lubricant quality. Our understanding of tribosystems has been seriously limited by a lack of kinetic information on critical reactions in hydrocarbon formulation and critical reactions at interfaces. 

Oil formulation (a) By using specific examples, what is meant by the tribological system in progressive equilibrium , (b) What information about the molecular structure of additives is indicated by the oil formulation requirements ... 

In examining any mechanical lubrication system (the tribological system, or tribosystem), three tribometric components must be considered ... 

I) The metal surface to be lubricated constitutes the foundation of the tribological system. There are a number of tribometric parameters for a solid surface, which include friction, wear, and adhesion. Tribological processes can occur in the contact area between two friction surfaces, which include physical, chemical and tribochemical events (Buckley, 1997) such as ... 

When surfaces of tribological systems are involved in the mechanical activity of rubbing, direct reactions of surface adsorbed films with solid surfaces take place. The mechanically activated clean surface (nascent surface) of the metals and alloys is extremely reactive. Tribofilm formation is caused by the interaction between the metal (M, substrate) nascent surface under high energy and chemisorbed molecules of additive (adsorbate) (Buckley, 1981). 

Hartley claims that the effects of ion implantation on wear reduction are due to physical rather than chemical mechanisms . This is probably true for the systems considered in this model. But there are certainly cases where chemical effects are important too, especially in tribological systems, including lubrication. For fluid lubricants it is well known that certain chemical elements improve the adhesion of the lubricating films. These elements may be introduced by ion implantation. This is also possible for high-temperature lubrication where the lubricant is incorporated in the material. Here chemical methods for the production of surface films (oxides, fluorides, sulfides) are common. Ion implantation is an alternative method of incorporating the effective element into the surface region of the material. 

A highlight of the reactive compatibilisation of extremely incompatible polymers is the chemical bonding between the anti-adhesive PTFE and the polar polyamides. It had been assumed for a long time that a chemical bonding between PTFE and polyamide is impossible because there was no appropriate reaction mechanism. PTFE is a highly crystalline polymer which could only be processed by using special equipment. The utilisation in tribological systems is a well-known... 

Fig. 10 Atomic force micrograph (adhesive mode) - surface examination after wear and tear of PTFE polyamide 6 compound (wheel surface). Tribological system disc on wheel light low adhesion dark high adhesion...

In boundary lubrication, solid surfaces are so close together that appreciable contact between opposing asperities is possible. Under these conditions, friction and wear are determined predominantly by interactions between the solid and the liquid phases [15]. The chemistry of friction surfaces and their state therefore determine their interaction with the lubricant components. However, this type of interaction, especially in industrial tribological systems, is very complex and difficult to explain, even applying the most modern analytical techniques. 

Tribological test results (macroscopic effects) and molecular descriptions of a boundary layer are joined together in one dependence using the a, model [16, 17]. The model is based on the application of system analysis to tribological systems. The model s main assumption is that due to the relationship between two functions f y) and (y), describing tribological processes in a given test, the coefficient o can be treated as a property of the lubricant which is not connected with only one tribotest as follows ... 

The value of angle y depends on the system energy flux. The critical state of the tribological system is in the destruction of the protective film. It has been observed that for different additives/reactants, the critical reaction rate leading to protective layer destruction was achieved for different values of energy flux into the system (different values of applied load P). The same value of C obtained for different additives/reactants and different densities of the stream of energy introduced into the system, which is characteristic of each additive/reactant, leads to the conclusion that the same critical rate of destruction reaction was achieved and consequently for each additive/reactant different angle y is connected with the critical rate of reaction. 

For structural design, the availability of high strength polymers and liquid crystalline polymers in recent years opens up new opportunities in competing with metals as wear resistant materials. Certainly, there are still more tribological studies needed to be done in establishing low wear polymers for each tribological system. 

FIGURE 50.2 In any tribological system, friction, wear, and surface damage depend on four interrelated factors. 

It is obvious from the unusually large number of theories of synovial joint lubrication proposed, that very little is known about the subject. Synovial joints are undoubtedly the most sophisticated and complex tribological systems that exist or will ever exist. It will require a great deal more research — possibly very different approaches — before we even begin to understand the processes involved. 

The elements of such a system consist of the primary body, the counter body, the interfacial medium and surrounding medium. Wear is a result of the action of the collective stress on the structure respectively on the elements of the tribological system and manifests itself in energetic and material interactions between these elements. It is defined by the wear parameters. Basically all wear mechanisms can occur abrasion, adhesion, tribo-chemical reactions or wear caused by fatigue. In the case of the extrusion of ceramic bodies, corrosion must be considered as another harmful mechanism. When determining the elements of the tribosystem for the... 

The friction factor resulting from a certain tribological system can be determined by means of the double cup extrusion test. The plastic... 

Another important characteristic of natural tribological systems is that they usually involve soft surfaces, as exemplified by slugs, eyes, tongues, and cartilage-coated articular joints. In response to external loads, such soft surfaces deform elastically and increase the contact area, resulting in a relatively low contact pressure. This is why Uquids whose vis-... 

Our aim in this work was to develop in situ ATR spectroscopy as an analytical method for investigating tribological systems, thus using ATR FT-IR spectroscopy... 

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