A numerical study of fracture modes in contact damage in porcelain/Pd-alloy bilayers

Finite element analysis (FEA) is used to assess contact damage in dental prostheses, using a Hertzian contact model, consisting of a spherical tungsten carbide indenter contacting a porcelain layer over a palladium alloy substrate. Three failure modes - plastic deformation in the substrate, cone cracking in the layer and cracking in the layer at the layer/substrate interface - are examined with varying porcelain layer thicknesses. Resulting critical loads agree well with experimentally observed figures. In particular, use of an observed surface stress to predict cone cracking has given excellent agreement where high stress gradients have previously made crack onset difficult to predict using fracture toughness values. This leads to the conclusion that FEA can be a valuable tool in assessing material combinations, and design of prostheses