In the picture, the yellow dotted semi-circle indicates the extensive structural changes by adhesive wear. In addition to that severe type of adhesion wear is called as smearing, galling and scuffing and also this terms are used to describe other type of wear in sometimes. SEM picture of steel surface after adhesive wear under dry condition. Generally, the fatigue wear on surface and subsurface level can be noticed through continuous sliding and rolling atmosphere.
The continuous loading and unloading processes, which will induce the surface and subsurface to form the cracks after critical repeated cycles. Then, the surface of the material will breakup into lager fragments and producing the larger pits on the softer surface. However, the material removed through fatigue wear is not considered as major parameter.
There are much relevant is the beneficial life in terms of time or revolutions prior occur the fatigue wear. The erosive wear can be occurred due to impingement of solid hard particle with high velocity on the specimen surface. The contact stresses produce from the particle kinetic energy in liquid or air stream as it meets the surface.
In erosive wear, the impingement angle and particle velocity combined with abrasive sizes and provide the measure of kinetic energy for the impinging particle. Schematic of erosive wear with hard particle hitting on the surface; a hard abrasive particle hitting the surface, b material removed by hard particle.
The corrosive or chemical wear happens while sliding takes place in a chemical atmosphere. The oxygen is considered as a most dominant corrosive medium in air atmosphere. So that the corrosive wear in air atmosphere is normally called as oxidative wear. The corrosive wear is significant in many factories such as slurry handling, chemical processing, mining and mineral processing.
The chemical wear can arise due to the electrochemical or chemical interaction of the surfaces with the atmosphere. However, the chemical corrosive wear occurs in extremely high corrosive atmosphere and in high humidity and high temperature atmosphere. The electrochemical corrosive wear can occur with chemical reaction accompanied of an electric current. The potential variations can be observed between those two regions. The high potential region and low potential region is known as cathode and anode, respectively.
There will be a current flow between the cathode and anode over an electrolyte conductive medium, the metal dissolve at the anode side in the form of liberates electrons and ions [ 29 ]. While conducting the experiment, the electron transfers via metal to the cathode and minimize the oxygen or ions.
After corrosion test, these surfaces changes to some other appearance with corroded region. Further, the electrochemical corrosion is influenced through the electro potential. The aqueous is a most common liquid environment in corrosion atmosphere. In this working atmosphere, the less amount of gases may dissolve, normally carbon dioxide or oxygen may influence the corrosion. Macropicture of electrochemical corrosion testing setup a and corroded micrograph with layer formation b. While the presence of higher potential on the thin air film during the sliding condition, a dielectric breakdown gives that leads to arcing.
The higher power density can be produced with short time during the arcing period. The produced heating results in extensive melting, solidification, surface corrosion, phase changes and hardness changes, and sometimes ablation of metal can be occurred. This arcing creates the higher craters and after sliding either fracture or shears the material lip, causing the three-body abrasion, surface fatigue, corrosion and fretting. In this chapter, the fundamentals of tribology, friction, lubrication, and types of wear and mechanism are briefly described.
The metals such as titanium, cobalt, and magnesium with an hcp hexagonal closed packed crystal lattice provide the coefficient of friction of nearly 0.
Further, the alumina balls sliding on the alumina surface and the friction showed around 0. The friction coefficient in ceramics material with dry atmosphere is lesser around 0.
The polymer material friction coefficient ranges from 0. Besides, the solid lubricant, such as solid film and powder, was used to protect the sliding surface from the unexpected damages during the sliding process and reduce the wear rate and coefficient of friction.
Wear is defined as material removal or surface damage on the one or two surfaces while rolling, sliding or impact motion relative to one another. Therefore, the wear characteristic must be taken into account while performing the sliding wear processes in mechanical components.
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3. Help us write another book on this subject and reach those readers. Login to your personal dashboard for more detailed statistics on your publications.
Edited by Amar Patnaik. We are IntechOpen, the world's leading publisher of Open Access books. Built by scientists, for scientists. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. Downloaded: Abstract The surface properties of a bulk material are not accepted totally and independently. Keywords tribology friction lubrication wear mechanism wear resistance. Introduction Tribology is defined as the science of sliding two surfaces in relative motion.
Atmosphere Room temperature, high temperature and corrosive medium. Table 1. Necessary input parameters to be considered for wear experiment. More Print chapter. How to cite and reference Link to this chapter Copy to clipboard. Available from:. Over 21, IntechOpen readers like this topic Help us write another book on this subject and reach those readers Suggest a book topic Books open for submissions. More statistics for editors and authors Login to your personal dashboard for more detailed statistics on your publications.
If two systems are in contact and moving relative to one another, then the friction between them is called kinetic friction. For example, friction slows a hockey puck sliding on ice. But when objects are stationary, static friction can act between them; the static friction is usually greater than the kinetic friction between the objects. Imagine, for example, trying to slide a heavy crate across a concrete floor—you may push harder and harder on the crate and not move it at all.
This means that the static friction responds to what you do—it increases to be equal to and in the opposite direction of your push. But if you finally push hard enough, the crate seems to slip suddenly and starts to move. Once in motion it is easier to keep it in motion than it was to get it started, indicating that the kinetic friction force is less than the static friction force. If you add mass to the crate, say by placing a box on top of it, you need to push even harder to get it started and also to keep it moving.
Furthermore, if you oiled the concrete you would find it to be easier to get the crate started and keep it going as you might expect. Figure 1 is a crude pictorial representation of how friction occurs at the interface between two objects.
Close-up inspection of these surfaces shows them to be rough. So when you push to get an object moving in this case, a crate , you must raise the object until it can skip along with just the tips of the surface hitting, break off the points, or do both.
A considerable force can be resisted by friction with no apparent motion. The harder the surfaces are pushed together such as if another box is placed on the crate , the more force is needed to move them. Part of the friction is due to adhesive forces between the surface molecules of the two objects, which explain the dependence of friction on the nature of the substances. Adhesion varies with substances in contact and is a complicated aspect of surface physics.
Once an object is moving, there are fewer points of contact fewer molecules adhering , so less force is required to keep the object moving. At small but nonzero speeds, friction is nearly independent of speed. Frictional forces, such as f , always oppose motion or attempted motion between objects in contact. Friction arises in part because of the roughness of the surfaces in contact, as seen in the expanded view. In order for the object to move, it must rise to where the peaks can skip along the bottom surface.
Thus a force is required just to set the object in motion. Some of the peaks will be broken off, also requiring a force to maintain motion. Much of the friction is actually due to attractive forces between molecules making up the two objects, so that even perfectly smooth surfaces are not friction-free. Such adhesive forces also depend on the substances the surfaces are made of, explaining, for example, why rubber-soled shoes slip less than those with leather soles.
The magnitude of the frictional force has two forms: one for static situations static friction , the other for when there is motion kinetic friction. Static friction is a responsive force that increases to be equal and opposite to whatever force is exerted, up to its maximum limit. Once the applied force exceeds f s max , the object will move.
As seen in Table 1, the coefficients of kinetic friction are less than their static counterparts. The equations given earlier include the dependence of friction on materials and the normal force. The direction of friction is always opposite that of motion, parallel to the surface between objects, and perpendicular to the normal force. If the coefficient of static friction is 0.
Once there is motion, friction is less and the coefficient of kinetic friction might be 0. If the floor is lubricated, both coefficients are considerably less than they would be without lubrication. Coefficient of friction is a unit less quantity with a magnitude usually between 0 and 1.
The coefficient of the friction depends on the two surfaces that are in contact. Find a small plastic object such as a food container and slide it on a kitchen table by giving it a gentle tap.
Toggle navigation Toggle search. Magazine Subscribe Today! Current Issue Archive Advertise. Factors That Affect Friction A number of factors affect the frictional conditions at the interface between these two surfaces in relative motion. These factors are: Surface Finish — The number, roughness and even the directional contact points of the asperities on the surfaces can dramatically affect the frictional coefficient. Surface Interaction It is important to understand how two metal surfaces within a machine interact with each other.
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