纳米压入法测量中初始接触点判断问题研究

对于纳米压入法 ,在加载过程中 ,压头尖与试样表面的初始接触点必须判断准确 ,初始接触点判断的精度将对测量结果产生很大的影响。本文利用西安交通大学精密工程研究所研制的微力微位移测试仪 ,对初始接触点判断的相关问题进行了深入研究。在压头尖与试样表面接触前 ,由电容测微仪测得的位移值是加载装置空载下的输出值 ;而当压头尖与试样表面接触后 ,压头与试样之间将产生作用力 ,使电容测微仪的测量值偏离加载装置空载下的输出曲线趋势。分别用一直线和一多项式曲线对压头无载荷和有载荷作用时测得的电压位移曲线进行拟合 ,拟合直线和曲线的交点即可作为初始接触点。大量的实验表明 ,运用上述方法可使初始接触点的判断精度在± 10nm。

Study on judging the initial contact point in nanoindentation

For nanoindentation, the contact point should be precisely determined in the loading process, because the precision of judging the initial contact point between indenter tip and the surface of sample may have much effect on the evaluating result of the mechanical properties for samples. Based on the structure of micro load displacement tester, developed in Institute of Precision Engineering, Xi'an Jiaotong University, some issues on judging initial contact point were investigated in details. Before the indenter tip touched the surface of the sample, the displacement value measured by a capacitive displacement sensor was the output of the loading mechanism without load. And when the indenter tip touched the surface of the sample, the trend of the displacement values measured by the sensor would depart from that of the displacement values of indenter having no load. Therefore, based on the change of the trend of voltage displacement curve, the intersection point between the fitting voltage displacement line of indenter having no load and the fitting voltage displacement polynomial curve of indenter having load may be judged as an initial contact point. Sufficient experiments show that the precision of the initial contact point may be within ±10nm used the method above.