纳米压痕试验中压头尺寸效应的准连续介质法分析

QUASICONTINUUM ANALYSIS OF INDENTER SIZE EFFECT IN NANOINDENTATION TESTS

采用准连续介质法模拟了单晶铝纳米压痕试验过程,分析了不同宽度的刚性矩形压头所引起的初始塑性变形特点,获得了载荷-压深、应变能-位移和硬度-压深曲线.从位错理论的角度分析了压头尺寸对纳米压痕测试结果的影响.研究发现:随着压头宽度的不断增大,压头下方位错形核所需要的载荷和压深程度增大,需要的应变能增加,应变能的变化速率递增,纳米硬度值减小,呈现出明显的尺寸效应.同时表明在一定的压入深度下,硬度与压头尺寸之间存在着一定的比例关系,不同尺寸压头获得的硬度值可以相互换算,但当矩形刚性压头宽度大于或等于120时这种尺寸效应消失.研究结果为纳米压痕实验过程中压头尺寸的选择提供了参考依据.

Using Quasicontinuum method, the nanoindentation test with a rigid knife-like indenter of different sizes was simulated to study the feature of initial plastic deformation of single crystal aluminium. The corresponding load-depth, strain energy-displacement and hardness-depth curves were obtained. Based on the dislocation theory, the influence of the indenter size on the measurement results of nanoindentation tests was analyzed. As the indenter size increases, higher load, depth and strain energy are required to promote the dislocation nucleation beneath the indenter. The rate of strain energy increases and the nanohardness decreases with the increase in indenter size. The simulated results indicate that the size effect phenomenon exists in nanohardness measurement of single crystal aluminium. Below a certain depth, there is a proportional relation between the nanohardnesses and the indenter sizes, and the obtained nanohardnesses using the indenter of different sizes can be converted each other. However, the size effect vanishes for a larger indenter size more than 120A. The work provides an important reference frame for choice of indenter size in nanoindentation tests.