Uncertainty evaluation of indentation modulus in the nano-range: Contact stiffness contribution

Evaluation of indentation modulus by instrumented indentation in the nano-range can use one of two methods for contact stiffness evaluation, according to current ISO standards. The relevance of contact stiffness, suggested by a preliminary uncertainty analysis, prompted development of improved evaluation procedures. Data on a series of indentation tests, performed in an international comparison on tungsten and fused silica with forces in the millinewton range, were analyzed with standard methods, and two alternative ones. Uncertainty evaluation revealed some shortcomings in the standard methods concerning the estimation of contact stiffness and indentation modulus; some definite advantages are shown with improved procedures.