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the action of sand paper over a metal surface. The total volume of wear particles displaced due to abrasive wear per unit distance of travel is given by; V = 2 W Cot / Po, where W = normal applied load, = ½ angle of the conical hard asperity (assumed shape of asperity) as shown in Fig.9, Po= yield pressure of the softer material. Note that as increases V decreases. The effect of asperity shape on the form of abrasive wear is shown in Fig.10. W Fig.9
Dr. Mohamed Nabhan Mechanical Engineering Department - University of Bahrain Tribology, MENG473 Date: 16 Sept. 2018 Page 14 Fig.10Effect of asperity shape on the form of abrasive wear 3.Fatigue Wear 3.1 Rolling contact: During rolling the opposing surfaces are separated by a lubricant film as in anti-friction bearings. The surfaces experience large stresses transmitted through the lubricant film. The nature and magnitude of these stresses can be found using the Hertezian equations. These
Dr. Mohamed Nabhan Mechanical Engineering Department - University of Bahrain Tribology, MENG473 Date: 16 Sept. 2018 Page 15 W(a)(b) Fig. 11 (a) Actual isochromatics obtained for the contact of a cylinder and a plane due to normal load alone (b) Isochromatics due to combined normal and tangential loads (c) Effect of contact pressure on elastic/plastic behavior of a material
Dr. Mohamed Nabhan Mechanical Engineering Department - University of Bahrain Tribology, MENG473 Date: 16 Sept. 2018 Page 16 (c) 3.2Sliding contact: Wear particles are formed after a large number of contacts in a sliding process due to adhesion or abrasion of opposing asperities. These asperities experience a sufficient number of contacts and deformations to produce a fatigue fracture of the asperities. 4.Corrosive wear: When rubbing takes place in a corrosive environment, gaseous or liquid, then surface reactions take place and reaction products (oxides) are found on one or both surfaces. These reaction products (oxides) are poorly adhere to the surfaces, and further rubbing causes their removal. Thus corrosive wear requires both corrosion and rubbing. To protect surfaces from corrosive wear a lubricant is introduced. However sometimes water is dissolved in oil, which invokes corrosive wear. Corrosion is