多尺度模拟研究纳米凸体几何形貌对初始塑性的影响

研究金属表面微凸体的力学行为对深入理解摩擦、磨损和设计微纳米机电器件有很大帮助.采用准连续方法探索了纳米压痕作用在薄膜(001)表面的纳米微凸体几何形貌对铝和铜薄膜初始塑性的影响规律.结果显示,相较于平坦表面,微凸体的存在显著地降低了薄膜的屈服应力.矩形微凸体横纵比对屈服应力的影响不大.随着底角α的增大,梯形微凸体的屈服应力呈现降低的趋势,尤其是α＞54.7°.同时,在纳米尺度限制全位错形成的条件下,铝中可能容易形成挛晶结构.

Multiscale Simulation of Geometric Effect on Onset Plasticity of Nano-scale Asperities

To understand mechanical behaviors of the asperities on a metal rough surface is helpful for understanding the friction,wear property of materials and designing micro/nano electromechanical devices.In the study,multiscale quasicontinuum (QC) method was used to explore geometric effect on onset plasticity of nano-scale asperities on aluminum and copper thin films during nanoindentation on the (001) surface.The results show that existing asperities significantly reduce the yield stress of thin film,compared with the stress of the flat film.For a rectangular asperity,the aspect ratio (width/height) affects yield stress of both films without much change.For a trapezoidal asperity,the yield stress decreases with the base angle (α),especially when the α is over 54.7°.It is also found that deformation twinning can be formed in the aluminum film under the condition of constraining full dislocation formation at nanoscale.