FRACTURING AT CONTACT SURFACES SUBJECTED TO NORMAL AND TANGENTIAL LOADS

A variety of rock engineering problems including drilling, cutting, ab rasion, and milling involve rock tool contact and indentation. The pat tern of indentation fractures and the role of slip conditions, surface roughness, tool radius and initial flaw size for an arbitrarily loade d contact are not fully known, The present paper aims to identify the elastic stress field for a contact subjected to both normal and tangen tial loads, and evaluate the condition for the fracture initiation and propagation. Stress fields within two spheres at contact are availabl e when either only normal load is applied or when tangential load caus es full-slip conditions, It is shown here that through appropriate sup erposition of the above two solutions, the stress field under partial- slip conditions, as well as during the unloading of tangential force m ay be determined. Maximum tensile stress increases significantly under partial-slip conditions as compared to the full-slip case even though the same magnitude of tangential force is applied, The location of ma ximum tensile stress moves inward from the trailing edge as the tangen tial force is unloaded, The stress-intensity factors for a penny-shape d crack which initiates at the contact periphery, and follows the mini mum principal stress trajectory are obtained and utilized to study ind entation fracturing, The dependency of critical loads on initial flaw size, indenter radius and slip conditions is quantified, The predictio ns of fracture density and spacing under a sliding indenter are achiev ed through a simple estimate of shielding interaction between adjacent fractures. Relation of these evenly spaced fractures with the formati on of wear grooves on sliding surfaces is discussed. (C) 1997 Elsevier Science Ltd.