Contact damage behavior of model dental bilayer

Abstract

The mechanics of contact-induced damage in brittle layers on soft support substrates are of interest for their relevance to lifetime-limiting failures of technological laminate systems in concentrated loading. This is particularly true of biomechanical applications-dental crowns and hip prosthesis-which must withstand intense biting or body weight forces under exacting cyclic contact loading and in vivo environmental conditions. Such prostheses may consist of several different material types-ceramic, metal, polymer, and composite-in layered configurations. Other, more engineering-oriented layer applications include cutting tools, thermal barrier coatings, electronic multi-layer devices, car windscreens and eyeglasses. The recent advances in the understanding and analysis of damage initiation and evolution in brittle layer structures will be presented. The results of experiments model bilayer that enable in-situ viewing during loading with simple concentrated loads (spherical indenters) and yet simulate the essential features of damage in a wide range of engineering layer structures are described. The experiments reveal a competition between damage modes-cone cracks or quasiplasticity at the top (near-contact) brittle-layer surfaces and laterally extending radial cracks at the lower surfaces due to the brittle coating layer thickness. Brittle coating structures may be subjected to complex concentrated loading, including tangential component. Results of Hertzian contact tests investigating the effects of superposed tangential loads on the critical conditions for radial cracking at the undersurfaces of brittle coatings on compliant substrates are reported. Bilayer specimen is prepared from glass coating bonded to polycarbonate substrate and blunt indenter is load with tangential motion as well normal motion. In order to change the friction coefficient the loading geometry is changed to the inclined fixture. Changes in near-surface stress fields from tangential for...