SURFACE CRACKS IN LAYERED HERTZIAN CONTACT WITH FRICTION

Stresses near the lip of a vertical surface breaking crack in a two dimensional, layered, elastic medium, subject to frictional Hertzian fine contact, are determined using finite elements. The ''stress method'' is used to extrapolate values of the stress intensity factors, K-I and K-II, for variations in crack length, layer thickness, load location and friction. The results for a layer/substrate combination of TiN/steel indicate that, for zero friction, K-I > 0 when contact is distant from the crack. K-II achieves maximum values when she contact is adjacent to the crack where Mode I stresses are compressive. KI values decrease with decreased layer thickness and significantly increase for cracks trailing a frictional load. A reduction in crack length by a factor of two does not significantly alter K-I and K-II values.