CHAPTER 3 FRICTION 1
3.1 Adhesion Contents 3.2 Solid-solid contact 3.2.1 Factors affecting solid-solid contact 3.2.2 Effect of sliding on solid-solid contact 3.3 Friction 3.3.1 Introduction 3.3.2 Laws of sliding friction 3.3.3 Basic mechanisms of sliding friction 3.3.4 Friction transitions during sliding 3.3.5 Stick-slip 3.3.6 Rolling friction
3.1 Adhesion • When two surfaces are brought in to contact , adhesion or bonding across the interface can occur which requires a finite normal force, called adhesive force, to pull the two solids apart. • Cohesion represents the atomic bonding forces associated within the material . (Adhesion an opposed to cohesion) • Adhesion is the phenomenon that occurs when two surfaces are pressed together , either a pure normal force (load) under combined normal and shear forces. fig-chp3\chp3-fig1.pptx 3
m ’ = (3.1) Where m ’ : coefficient of adhesion W’ : the normal tensile force W’ required for separation (normally referred to as adhesive force) W : normal compressive force W initially applied • W’ typically increases linearly with an increase of W and m ’ generally increases with duration of static contact and separation rate . fig-chp3\chp3-fig2.pptx 4 W’ W
• Adhesion is a function of material pair and interface conditions such as : crystal structure solubility of one material into another chemical activity and separation of charges surface cleanliness normal load and temperature duration of contact and separation rate. 3-2 Solid-solid contact • A representation contact between solids is shown schematically in fig-chp3\chp3-fig3.pptx 6
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- Fall '19
- Msc. Amar Yemim