Topic 4_4 Roughness, Hardness, and Friction Flashcards
How does the Bowden and Tabor friction theory work
Calculation based on the required force to shear the junctions formed by adhesion at asperities in the contact
What does the Bowden and Tabor friction theory assume
Contact is at the tip of asperities and real contact area is small
Asperities are plastically deformed
Plastic flow occurs until area large enough tosupport the load elastically
What value does Bowden and Tabor friction predict for coefficient of frictino
0.17
What is the issue with the Bowden and Tabor friction model
Area of contact is not accounted for
massively underrepresents adhesion and only uses one of the mechanisms of friction
How can the Bowden and Tabor model be improved
Addition of ploughing (plastic deformation)
How do we know these models massively under represent the adhesion component of friction
tests done in vacuums with no contamination friction is much higher as chemical bonds form really well
What is stick slip
Process of overcoming static friction, causing sliding but force drops off after having to overcome static friction, no longer overcomes sliding friction and goes back to static, force builds
Easy to slip back to stick
What other factors contibute to friction
stick/slip
friction heating
junction growth
what is friction heating
Heat generated by friction leads to softening and greater plastic flow, friction becomes more based on liquids than solids
propogating effect, heat up. more plastic flow, more friction, heat up etc
What is junction growth
Contact area is increased as asperity is pushed along surface, increases area, increases friction
Work through Bowden and Tabor Friction model and ploughing impact
See notes
