On The Efficiency Of The "Effective Truncation Length" Of Indenter Tip In Mechanical Property Determination With Nanoindentation Tests

Correction of the contact area is an important step in the extraction of the hardness and Young's modulus from the analysis of nanoindentation unloading. One of the frequently adopted method for contact area correction is to relate the contact area A to the contact depth h(c) with a so-called "effective truncation length", h(d), as A = C(h(c) + h(d))(2). In this paper, critical examinations on the applicability of the "effective truncation length" were conducted based on the analyses of nanoindentation load-displacement (P-h) curves, each of which contains several loading-unloading cycles, measured on four brittle materials. It was shown that the h(d)-value determined from a single P-h curve varies from material to material and exhibits an evident location-dependence for a given material, implying that h(d) cannot be considered simply as a correction for the rounded indenter tip. Possible sources which may result in the variation in the experimentally determined h(d) were discussed and it is concluded that h(d) should be considered to be an integrated or statistical measure of different influence factors. Further analyses proved that, despite of the existence of the significant variation in h(d), the hardness and Young's modulus determined using the corresponding h(d)-value are proven to have an enough accuracy acceptable for practical applications.