In this post I have listed a few interesting relationship between material parameters which are important for wear.
Yield Strain
- For pure metals Yield Strength ~= 0.25 Elastic Modulus
- For metal alloys Yield Strength ~= 0.35 Elastic Modulus
- For polymers Yield Strength ~= (0.008 – 0.03) Elastic Modulus
With the yield stress-elasticity relationships keep in mind that the yield stress is a structurally dependent parameters (it is affected by heat treatment, cold working and other such processes which affect material micro-structure) while the modulus of elasticity is structurally insensitive. These relationships are for fully work hardened materials which is similar to the characteristics of a surface which has been stressed repeatedly in a wearing contact.
A high ratio of the yield strength to elastic modulus is associated with a high wear resistance.
Hardness tests
- 8% plastic strain is typically caused by a hardness test
- It takes ⅓ of this amount of stress to create this amount of plastic deformation in a standard compressive test because in a hardness test the material is blocked from moving out of the way
- Hardness (as calculated from a Vickers test) is about double the yield strength of a material
Hardness is typically highly associated with wear resistance. In fact it is included as a variable in the Archard equation. There are many different hardness tests each of which has results which are useful for different applications.
Reference
- Rabinowicz, E., 1995, Friction and Wear of Materials, John Wiley Sons, New York.