Abstract
Present paper describes the use of Hertzian indentation with rheological models as a method for determining the fracture of multi-layered brittle coatings. The advantage of the method revealed here is that the only quantity to be measured is a deformation or a fracture load. By measuring this minimum load an accurate estimate of fracture may easily be made with application of rheological modeling. Use of rheological models for strain-deformation modeling has enabled accurate estimates to be made of the minimum loads necessary to propagate cracks by Hertzian indentation. At present the analysis only applies for the case where the sphere and the substrate are made of the same material. However, the analysis is comprehensive in that it can be applied to sphere/substrate systems with any values of mechanical properties represented by combination of plasticity, viscosity and elasticity of given materials. The only other requirement is that the surface should be coarsely polished and a sphere of relatively small radius (less than 5 millimeters) should be used. Two further points are worthy of note. Because the only quantity that must be measured is a fracture load, it is possible that this method of determining fracture can be automated with equipment and software. Also, the existence of an absolute minimum fracture load, for a given sphere size, suggests that the Hertzian indentation test could find use as a localized proof-test technique.
