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Corrosion, Wear, and Degradation of Materials
Published in Mahmoud M. Farag, Materials and Process Selection for Engineering Design, 2020
Wear can be defined as the removal of surface material and reduction of dimensions and loss of weight as a result of plastic deformation and detachment of material. This phenomenon normally occurs in components whose function involves sliding or rolling contact with other surfaces. Examples of such components include sliding and rolling bearings, gears and splines, piston rings, and breaks and clutches. Wear can also take place as a result of contact with moving liquids or gases, especially when they contain hard particles. Wear in any material can occur by a variety of mechanisms, depending on the relative motion (rolling, sliding, or a combination), service environment (dry or wet and whether abrasive particles are present), and type of motion (impact, unidirectional, or oscillating). Therefore, life under wear conditions is a function of both the wear resistance of the material and the wear system variables.
Lubricants and Lubrication
Published in Ahmed Abdelbary, Extreme Tribology, 2020
The term “lubrication” can be defined as the application of some substance(s) between two objects moving relative to each other in order to allow as much smooth operation as necessary. This is applied to solid film lubrication and fluid (liquid or gaseous) film lubrication. Fluid lubrication occurs when a thick, or thin, film of some fluid completely separates the matting surfaces. Solid lubrication arises when a soft solid film is interposed between the contacting surfaces. The situation in which the solid film arises as a result of a chemical reaction between the mating surfaces and the environment is called extreme pressure (EP) lubrication. Furthermore, a combination of solid and liquid lubrication is also feasible and may have a beneficial synergistic effect on the friction and wear performance of sliding surfaces.
Design Perspective of Wear Behavior
Published in Raymond G. Bayer, Engineering Design for Wear, 2019
This type of model is often found to be useful in journal and thrust bearing applications, since in both of these situations the contact area tends to stabilize after some initial period of small wear. In these types of applications, there are two distinct situations, which can occur and involve different concepts regarding PV factors. One is unlubricated sliding, the other is lubricated sliding. For unlubricated situations, particularly those involving a plastic, the PV limit and the behavior of K is usually associated with sliding temperature. In lubricated situations, the PV factor is generally related to lubricant behavior, that is, fluid lubrication. In the former case, PV is related to the power expended in sliding and through this, temperature. Heat conduction paths, as well as basic material wear behavior, are important factors in this situation. In the latter situation, PV is often related to the nature of the lubricant film that is maintained in the bearing and the likelihood of penetration of this film. In such situations the boundary lubrication qualities of the lubricant, the basic wear properties of the surfaces, and the possibility of fluid lubrication effects are factors that can be involved in the wear behavior. These two situations indicate some of the difficulties and concerns associated with the use of PV factors to characterize general wear behavior. However, these factors can be of use in design if their limitations and range of applicability are understood and recognized.
Bearing Models for Advanced Ball Bearing Simulation
Published in Tribology Transactions, 2023
L. Houpert, C. Penny, J. Clarke
The corresponding friction coefficients (in the and directions, as well as on a slice or entire contact) are obtained by dividing the corresponding sliding force by the normal load. Note that the total effective friction coefficient is always positive, while and (used in each slices of the contact) have a sign defined by the sliding speed sign in the and directions, respectively. As explained previously, the sign of in the slice location range () is opposite to the one defined elsewhere, so that the calculated forces in all slices are competing, leading to a net force that is quite small, even though a friction coefficient of the order of 1% is reached in many slices. One also sees how the friction coefficient is decreasing near the rolling lines (because of the low sliding speed) and near the edge of the contact (because of the low pressure).
Sliding mode controlled DC microgrid system with enhanced response
Published in Journal of Control and Decision, 2022
B. Balaji, S. Ganesan, P. Pugazhendiran, S. Subramanian
F = F(x,T) is the known function that bounds the error on f(x,t) As per (2), the sliding variable would be, Now differentiating the sliding variable Subs (4) in (8), For approximation, A form of mechanical movement among interacting surfaces is sliding and it can be contrasted with rolling movement. In bearing surfaces, both motions are possible. Friction opposes the angular velocity or propensity for these kinds of movement among contacting materials. The materials in touch may get damaged or ‘worn’ by contact. While satisfying the sliding condition the uncertainty in f would be, The controller determines the optimal u that is supplied towards the plant using a mathematical calculation known as a control law. The outcome u in a feedforward situation can produce resilience to ambiguity and be utilised to plan dynamic behaviour. Control law would be, The system with the second order form, Here, b(x,t) has been bounded as 0 ≤ bmin(x,t) ≤b(x,t)≤ bmax(x,t). The bound is the time variant.
Effect of different types of graphene coatings on friction and wear performance of aluminum alloy
Published in Mechanics of Advanced Materials and Structures, 2022
Andrea Mura, Giancarlo Canavese, Edoardo Goti, Paola Rivolo, Haozhe Wang, Xiang Ji, Jing Kong
Every engineering interface undergoing relative movement suffers wear damage. This very general statement stands for both mechanical (structural) applications and electrical ones and, unfortunately, this is the case most of the times. Friction and wear can be reduced by lubricating the interface between sliding parts. Mechanical components are usually lubricated by liquid or semi-solid lubricants such as oils and grease. This remedy is often effective, though lubricants have to meet a lot of constraints of environmental compatibility, which do not concern only pollution. Fluid lubricants are critical in food industry for instance (as they should not contaminate food) and in high vacuum applications where very low volatility is imperative. As to electrical application, liquid and semi-solid lubricants may be undesired substances because of their electrical insulating properties, e.g. electrical connectors or switches.