Characterization of spherical indenter with fused silica under small deformation by Hertzian relation and Oliver and Pharr's method

Radius and area function of a spherical indenter are calibrated by performing spherical nanoindentation tests on fused silica with known properties. The spherical indenter is made of ruby with a relatively large radius of 200 μm in nominal value. Hertzian relation was found to be successful in characterizing radius of spherical indenter under purely elastic deformation condition. Oliver and Pharr's method is dependent on the measurement accuracy of residual displacement, which cannot be measured within acceptable precision under very little plastic deformation with values of residual displacement being only several nanometers. Area function calibrated with Oliver and Pharr's method on a brittle material like fused silica was found to be smaller than true value, leading to measured elastic modulus larger than true value. A softer material that can produce sufficient plastic deformation with large residual displacement is recommended as the standard material for area function calibration.