Comments on the calibration technique of the projected contact area of nanoindentation tester

The nanoindentation test techniques especially the O&P method are analyzed and the nanoindentation tests are implemented. The analysis focuses on the determination of the contact area and the depth region of the application. Analysis results show that a common area formula for all materials justified only at large indentation depth, and such a universal formula may lead to larger errors at small depth. Hence hardness values measured at small indentation depth based on O&P method must be used with care.