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.

接触面积的校正是从纳米压痕卸载分析中提取硬度和杨氏模量的重要步骤。接触面积校正的一种常用方法是使接触面积A与接触深度h _c相关联，即所谓的“有效截断长度” h _d，如A = C（h _c + h _d）²。本文在分析纳米压痕载荷-位移（P ― h）的基础上，对“有效截短长度”的适用性进行了严格的审查。）曲线，其中的每条曲线都包含几种加载/卸载循环，是在四种脆性材料上测得的。结果表明，根据一条P ― h曲线确定的h _d值因材料而异，并且对于给定的材料表现出明显的位置依赖性，这意味着h _d不能简单地视为圆角压头尖端的校正。 。这可能导致在实验确定的变化可能来源ħ _d进行了讨论和得出的结论是ħ _d应该被视为对不同影响因素的综合或统计量度。进一步的分析证明，尽管在显著变化的存在ħ _d，硬度和杨氏模量使用相应的确定ħ _d -值被证明具有足够的精确度为实际应用可以接受的。