Chapter03-Introduction-to-Tribology-机械零件设计英文全套教案课件

1、 Chapter 3 Introduction to TribologyTribology is the science and technology of interacting surfaces in relative motion which involves friction, wear and lubrication.Understanding tribological principles is essential for the successful design of machine elements. Chapter 3 Introduction Importance of

2、Tribology Friction and wear can cause a staggering loss of potential power for today mechanized society.The purpose of research in tribology is to minimize and eliminate unnecessary waste at all levels of technology where the rubbing of surfaces is involved.Importance of Tribology Frict Complexity o

3、f TribologyInterdisciplinary nature: It requires a variety of knowledge such as physics, chemistry, mechanics, thermodynamics, and material science. Tribology problems are often coupled with a large, complex, and interwinded area of machine design, reliability, and performance where relative motion

4、between surfaces is involved. Complexity of TribologyInterdChapter03-Introduction-to-Tribology-机械零件设计英文全套教案课件Chapter03-Introduction-to-Tribology-机械零件设计英文全套教案课件One of the important objectives in tribology is the regulation of the magnitude of frictional forces according to whether we require a minimu

5、m friction (as in machinery) or a maximum (as in the case of anti-skid surfaces). Friction Friction Laws of FrictionThe friction force is proportional to the normal load.The friction force is not dependent on the apparent area of the contacting solids.The friction force is independent of the sliding

6、 velocity. Laws of FrictionBowden-Tabor Theory of Friction Friction is the force required to break the welds formed at the points of contact. The area of real contact between couples is proportional to the load; thus the frictional force should be proportional to the load. Since the area of real con

7、tact is independent of the apparent surface area of the body, the friction should be independent of the apparent surface area. The coefficient of friction is the shear strength of the junctions divided by the yield pressure of the softer component. Bowden-Tabor Theory of FrictioTribological Solution

8、sBy using solid surface coatings with low resistance to transverse shear By lubricating techniquesBy improving the bulk materials or metal surfaces through surface modification techniquesBy interposing rolling elements such as balls, cylinders and the like between the two surfacesBy using magnetic a

9、nd similar force fields to carry load without mechanical contact Tribological SolutionsBy usingWearWear may be viewed as the progressive loss of substance from the operating surface of a body occurring as a result of loading and relative motion at the surface. The mechanism of wear is less understoo

10、d than that of friction and lubrication.Wear can be classified by the physical nature of the underlying process, such as abrasion, adhesion, and fatigue. WearWear may be viewed as the In the same way as friction, wear of machinery is sometimes advantageous. The initial wear resulting in better matin

11、g of components (running-in), is evidently desirable. Polishing and grinding of many materials, involving positive application of wear, is a technology process where material removal can be considered as abrasive wear. WearIn the same way as friction, wAdhesive WearSolid-phase welding forms between

12、two contact asperities after normal load applies.As the moving asperities pass, the microscopic weld often breaks and material is removed from the surface with the lower yield strength to another.Adhesive Wear Abrasive WearAbrasive wear occurs when two interacting surfaces are in direct physical con

13、tact and one is significantly harder than the other. The general laws of abrasive wear : 1)Wear increases with sliding distance. 2)Wear increases with normal applied load. 3)Wear decreases as the hardness of the sliding surface increases. Abrasive WearAbrasive wear ocFatigue wear is caused by the pr

14、opagation of subsurface damage to the surface due to cyclic loadings, i.e. by fatigue mechanism.Fatigue wear occurs in non-conformal machine elements due to high stresses to the solid material, even in well-lubricated situations or “non-contact ”state. Life of fatigue wear should be treated statisti

15、cally due to its so many influencing uncertainties. Fatigue WearFatigue wear is caused by the LubricationThe object of lubrication is to reduce friction, wear, and heating of machine parts which move relative to each other.Five distinct forms of lubrication: 1. Hydrodynamic; 2. Hydrostatic; 3. Elast

16、ohydrodynamic; 4. Boundary; 5. Solid-film LubricationThe object of lubriChapter03-Introduction-to-Tribology-机械零件设计英文全套教案课件Hydrodynamic LubricationThe load-carrying surfaces of the bearing are separated by a relatively thick film of lubricant, so as to prevent metal-to-metal contact.The film pressure

17、 is created by the moving surface itself pulling the lubricant into a wedge-shaped zone at a velocity sufficiently high to create the pressure necessary to separate the surfaces against the load on the bearing.The stability can be explained by the laws of fluid mechanics. Hydrodynamic LubricationThe

18、 loHydrostatic LubricationIt is obtained by introducing the lubricant, into the load-bearing area at a pressure high enough to separate the surfaces with a relatively thick film of lubricant. Unlike hydrodynamic lubrication, motion of one surface relative to another is not required. Hydrostatic lubr

19、ication should be considered when designing bearings where the velocities are small or zero and where the frictional resistance needs to be an absolute minimum.Hydrostatic LubricationIt is oElastohydrodynamic LubricationIs a form of hydrodynamic lubrication where elastic deformation of the lubricate

20、d surfaces becomes significant.Is usually associated with non-conformal surfaces.The mathematical explanation requires the Hertzian contact theory of contact stress and fluid mechanics.Elastohydrodynamic LubricationBoundary LubricationThe highest asperities may be separated by lubricant films only several molecular dimen