ABSTRACT
Tribology is concerned with friction and wear and, therefore, the energy e²ciency and durability of mechanisms.
˜e friction coe²cient is independent of load and apparent area of contact. ˜is is primarily due to the small areas of real contact that carry the load at a stress level near the yield strength of the weaker material. As a result, the real area of contact is o§en about 104 times smaller than the apparent area of contact, and doubling the load just doubles the apparent area of contact. Shearing these real contact areas required a force close to the shear strength of the weaker material. So the friction coe²cient being the friction force divided by the normal force approximates the shear strength divided by the yield strength of the weaker material, or, depending on Von Mises or Hencke, 0.33 or 0.5. Surface oxides and contamination can mitigate these values. Friction is a property of a combination of two materials; the friction between a steel skate and ice is diµerent from that of the same steel skate with rubber or wood.
