Coating/substrate Modulus Mismatches and Margin Geometry Effects on Contact Damage in Curved Brittle Coating Systems

摘要

The effects of coating/substrate modulus mismatch and margin geometry on contact damage in bi-layer systems were investigated. Following an earlier study, convex specimens having curvature of 12 mm inner coating diameter and 1mm thick brittle layer on a polymeric and dental composite support bases were produced. Sample coating geometry at the margins was varied by grinding the edge of the glass shells in various shapes. The specimens were tested by applying single cycle load at the specimen's axis of symmetry using flat indenter of low elastic modulus. The effects of margin geometry and support layer modulus on radial crack initiation and damage evolution was examined, with particular attention paid to the relevance of such damage to lifetime limiting failures of all- ceramic dental crowns. Finite element modeling was used to evaluate stress distribution in the glass coating. Experimental trends interrupted with peak maximum principal stresses at the margins. The results of this study illustrate that the fracture behaviour of brittle layered structures is not dominated by certain variables. It is demonstrated that critical loads for initiation of radial cracks are sensitive to support layer modulus as well as margin geometry. Support layer modulus plays an important role in crack propagation and subsequent damage patterns, especially at specimen side walls.