An experimental method to determine the contact radius changes during a spherical instrumented indentation

An experimental method to determine contact radius changes during a spherical instrumented indentation test is proposed in this paper. This method is based on the Hertz theory and only depends on the elastic properties of both the indenter and the sample. The programming of several loading, unloading and reloading cycles has allowed the determination of the unloading stiffness changes and consequently the contact radius changes. Numerical results have shown that the proposed method is sensitive to the piling-up or sinking-in. From the contact radius changes we have proposed a new procedure in order to obtain the real indentation load–depth curve from the measured curve. An experimental study has allowed us to validate our procedure during the beginning of the unloading cycle.