Rolling friction of a viscous sphere on a hard plane

A first-principle continuum-mechanics expression for the rolling friction coefficient is obtained for the rolling motion of a viscoelastic sphere on a hard plane. It relates the friction coefficient to the viscous and elastic constants of the sphere material. The relation obtained refers to the case when the deformation of the sphere $\xi$ is small, the velocity of the sphere $V$ is much less than the speed of sound in the material and when the characteristic time $\xi/V$ is much larger than the dissipative relaxation times of the viscoelastic material. To our knowledge this is the first ``first-principle'' expression of the rolling friction coefficient which does not contain empirical parameters.Comment: 6 pages, 2 figure

LASER PROCESSING OF METAL-CERAMIC COMPOSITE MULTILAYERS

Particulate metal-ceramic composite layers were formed using a CO2-Laser. Opposed to other methods hard phases (TiC, TiN, NbC) were embedded in a steel surface by liquid metal penetration into a predeposited layer of fine hard particle powders. The structure of surfaces processed by this method differs from those of conventionally treated surfaces. Hard phases incorporated in the steel matrix variied gradually in type, size and volume fraction from the surface to the substrate. Produced layers were in the range between 30 and 150 µm and free of pores and cracks