Residual stress measurement by Hertzian indentation

We have used Hertzian indentation to measure surface stresses on ceramics. Surface stresses in brittle materials have the effect of shifting the minimum load to produce Hertzian fracture. Quantitative use of the method requires knowledge only of the material’s Young’s modulus, Poisson’s ratio and its fracture toughness (or measurements from a stress-free specimen). We have used this method for surface stress measurements on Al2O3 and soda lime float glass. Specimens of both types were stressed by bending. Our results are consistent with those obtained by other methods. The Hertzian technique thus provides a promising simple method for measuring surface residual stress in brittle materials.