Li Hongzhou, Chen Jialian
College of Environmental Science and Engineering, Engineering Research Center of Polymer Resources Green Recycling of Ministry of Education, Fujian Normal University, Fuzhou 350007, China.
Beilstein J Nanotechnol. 2021 Feb 19;12:213-221. doi: 10.3762/bjnano.12.17. eCollection 2021.
When using the Oliver-Pharr method, the indented specimen is assumed to be a perfectly flat surface, thus ignoring the influences of surface roughness that might be encountered in experiment. For nanoindentation measurements, a flat surface is fabricated from curved specimens by mechanical polishing. However, the position of the polished curved surface cannot be controlled. There are no reliable theoretical or experimental methods to evaluate the mechanical behavior during nanoindentation of an elastic-plastic microsphere. Therefore, it is necessary to conduct reliable numerical simulations to evaluate this behavior. This article reports a systematic computational study regarding the instrumented nanoindentation of elastic-plastic microspherical materials. The ratio between elastic modulus of the microsphere and the initial yield stress of the microsphere was systematically varied from 10 to 1000 to cover the mechanical properties of most materials encountered in engineering. The simulated results indicate that contact height is unsuitable to replace contact depth for obtaining the indentation elastic modulus of microspherical materials. The extracted elastic modulus of a microsphere using the Oliver-Pharr method with the simulated unloading curve depends on the indentation depth. It demonstrates that nanoindentation on microspherical materials exhibits a "size effect".
在使用奥利弗 - 法尔方法时，假定压痕试样为完美平面，从而忽略了实验中可能遇到的表面粗糙度的影响。对于纳米压痕测量，通过机械抛光从弯曲试样制备出平面。然而，抛光后的弯曲表面位置无法控制。目前尚无可靠的理论或实验方法来评估弹塑性微球在纳米压痕过程中的力学行为。因此，有必要进行可靠的数值模拟来评估这种行为。本文报道了一项关于弹塑性微球材料仪器化纳米压痕的系统计算研究。微球弹性模量与微球初始屈服应力之比在10到1000之间系统地变化，以涵盖工程中遇到的大多数材料的力学性能。模拟结果表明，对于获得微球材料的压痕弹性模量而言，接触高度不适宜替代接触深度。使用奥利弗 - 法尔方法并结合模拟卸载曲线提取的微球弹性模量取决于压痕深度。这表明对微球材料进行纳米压痕会呈现出“尺寸效应”。
