Determination of the critical tensile stress of sapphire by spherical indentation with additional lateral forces

The comprehensive mechanical characterisation of thin films and surfaces is very important for a suitable optimisation of protection layers and layer systems. The Young’s modulus and the yield strength are widely accepted material parameters which can be determined by spherical nanoindentation in normal direction. This article reports on the determination of a further parameter, the critical tensile stress, by spherical nanoindentation with additional lateral forces. The critical tensile stress was determined for sapphire. It will be shown that the results obtained with two different nanoindentation devices equipped with spherical diamond indenters of different radii agree with less than 10% deviation.