考虑压头曲率半径和应变梯度的微压痕分析

在压头尖端曲率半径取100nm的前提下，采用Chen和Wang的应变梯度理论，对微压痕实验进行了系统的数值分析. 首先通过拟合载荷-位移实验曲线的后半段来确定材料的屈服应力和幂硬化指数值,然后用有限元方法数值模拟压痕实验，并将计算得到的整段载荷-位移曲线及硬度-位移曲线和实验结果进行了比较. 结果表明应变梯度理论所预测的计算结果和实验结果很好地符合,包括压痕深度在亚微米和微米范围内的整段曲线.

The influence of indenter tip radius to micro-indentation tests

In this paper, the effect of the indenter tip radius of curvature on the micro indentation hardness was investigated, using finite element method with the strain gradient theory. It is known that, when the indentation depth is large enough, the conventional J2 theoretical results agree well with the experiment results and the indentation hardness values are independent of the indentation depth. It means that there is a nearly flat section on the experimental curve of the depth versus the indentation hardness, in which the indentation hardness is nearly constant, and the influence of strain gradient effect on the indentation hardness is quite small, hence we can use the later section of the experimental curve of indenting depth versus load which corresponds to the nearly flat section of the experimental curve of indenting depth versus the indentation hardness to get three material constants (yielding stress, the exponent of the power law strain hardening and intrinsic parameter) using fitting method. Following the above thinking, we simulated the three existed indentation tests based on the strain gradient theory proposed by Chen and Wang. The simulation results confirmly show that the size effect of the micro indentation hardness for the indentation test is really existed due to the factor of the strain gradient effect.