Application of analytical methodology in parametric analysis of the stress state in a coating-substrate system based on dental materials.

The aim of the present paper is to use analytical methodology by 2D shear-lag model in parametric analysis of the normal stress in the coating. The tension of a substrate with coatings on its top and bottom surfaces is considered. The parametric study is performed by varying coating thickness and elastic properties both the coating and the substrate. The calculations are done for different groups of dental materials - polyetheretherketone, dental resin composite and porcelain as a coating material and high gold, palladium and Co-Cr alloys as a substrate material. It is established that the coating thickness strongly influences the normal stresses parallel to the loading axis - its increasing leads to decreasing of normal stresses in the coating. However, the increase of the coating thickness results in negligible increase of the additional normal stresses (perpendicular to the loading axis) in the central part of the coating. Young's modulus of the coating considerably influences the normal stresses parallel to the loading axis, while its influence on the additional normal stresses appears mainly in the zones near the free edge of the coating. The increase of the modulus of elasticity of the coating causes increase of the both normal stresses. The increasing of Young's modulus of the substrate insignificantly influences on the both normal stress in the coating. It is found that: 1) the lowest normal stresses are generated in the porcelain layer with the largest thickness of 2.0 mm; 2) the porcelain is characterized with the highest normal stresses compared to the polymer and composite coating materials; 3) the alloy type of the substrate has negligible effect on both the normal stress in the porcelain coating. The results are validated by tensile test of Co-Cr dental alloy specimens coated with porcelain. A good agreement is found between the analytical approach and the failure behaviour of the porcelain coating. Therefore, the proposed analytical model can be used as a tool to study the stress state in the coating under tensile test of coated flat specimens.