L2纯铝微纳米压痕保压阶段尺度效应研究(英文)

Size Effects at Dwell Stage of Micro-Indentation for Pure Aluminum

以工业纯铝L2为研究对象就微压痕试验过程中保压阶段的尺度效应进行研究。研究发现微压痕试验过程中有保压台阶的瞬间形成,即在达到最大载荷后的保压段,虽然载荷不变,但压入深度却在增加,保压平台的出现和保压时间的关联性不大。随后通过采用带内禀长度微塑性本构方程的有限元模拟,并引入折合材料内禀长度,将模拟结果与相同保压时间、不同载荷压痕试验过程中的尺度效应进行对比分析,并解释了微纳米压痕试验保压平台的反常规律,获得反映材料尺度效应的内禀长度为5.09μm,以及反映微纳米压痕保压阶段尺度效应的材料折合内禀长度为4.90μm,研究表明:保压平台的产生来源于保压阶段应变梯度的减小,相当于几何必需位错密度降低到保压前的96.27%,这种保压平台的形成机理和微纳米压痕试验过程中的几何尺度效应与载荷尺度效应有关。

Pure aluminum L2 was used to study the size effect during the dwell stage of micro-indentation. The experiments reveal that an indentation depth increases further and then a load-displacement platform appears when the load is held in a constant after reaching the maximum load. The results show that the emergency of instantly formed load-displacement platform has a little relevance to the dwell time. Subsequently the micro-plastic constitutive model with intrinsic material length and the reduced intrinsic material length was imported into the FEM of whole indentation process. The abnormal phenomenon at the dwell stage could be treated as a rule through comparative analysis from simulated and experimental results. The intrinsic length of pure aluminum L2 was obtained as 5.09 Ore, while the reduced intrinsic length at the end of the dwell stage decreased to 4.90 ktm. The simulated results indicate that depth variances at the dwell stage are mainly affected by the reduction of the strain gradient. This is equivalent to that the density of geometrically necessary dislocations （GNDs） reduces to about 96.27% compared with that of the beginning of the dwell stage. It is summarized that the forming mechanism of the load-displacement platform may be attributed to the geometric size effect and the mechanical size effect.