tailieunhanh - Engineering Tribology P02

Wear Film failure impairs the relative movement between solid bodies and inevitably causes severe damage to the contacting surfaces. The consequence of film failure is severe wear. Wear in these circumstances is the result of adhesion between contacting bodies and is termed ‘adhesive wear’. When the intervening films are partially effective then milder forms of wear occur and these are often initiated by fatigue processes due to repetitive stresses under either sliding or rolling. These milder forms of wear can therefore be termed ‘fatigue wear’. On the other hand if the film material consists of hard particles or merely flows. | Introduction 5 Wear Film failure impairs the relative movement between solid bodies and inevitably causes severe damage to the contacting surfaces. The consequence of film failure is severe wear. Wear in these circumstances is the result of adhesion between contacting bodies and is termed adhesive wear . When the intervening films are partially effective then milder forms of wear occur and these are often initiated by fatigue processes due to repetitive stresses under either sliding or rolling. These milder forms of wear can therefore be termed fatigue wear . On the other hand if the film material consists of hard particles or merely flows against one body without providing support against another body then a form of wear which sometimes can be very rapid known as abrasive wear occurs. Two other associated forms of wear are erosive wear due to impacting particles and cavitation wear which is caused by fast flowing liquids. In some practical situations the film material is formed by chemical attack of either contacting body and while this may provide some lubrication significant wear is virtually inevitable. This form of wear is known as corrosive wear and when atmospheric oxygen is the corroding agent then oxidative wear is said to occur. When the amplitude of movement between contacting bodies is restricted to for example a few micrometres the film material is trapped within the contact and may eventually become destructive. under these conditions fretting wear may result. There are also many other forms or mechanisms of wear. Almost any interaction between solid bodies will cause wear. Typical examples are impact wear caused by impact between two solids melting wear occurring when the contact loads and speeds are sufficiently high to allow for the surface layers of the solid to melt and diffusive wear occurring at high interface temperatures. This dependence of wear on various operating conditions can be summarized in a flow chart shown in Figure . COST OF