Surface Cracks in Layered Hertzian Contact with Friction

Stresses near the tip of a vertical surface breaking crack in a two dimensional, layered, elastic medium, subject to factional Hertzian line contact, are determined using finite elements. The “stress method” is used to extrapolate values of the stress intensity factors, KI and KII, 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, KI > 0 when contact is distant from the crack. KII achieves maximum values when the 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 KI and KII values.