自相似多级纳米蜂窝铝结构力学性能的分子动力学模拟

Molecular dynamics simulation on mechanical properties of nano self-similar hierarchical honeycomb Al

首次采用分子动力学方法预测了自相似多级纳米蜂窝铝面内和面外(轴向)的压缩力学性能(弹性模量和压缩强度)。重点研究了相对密度、层级数和长度比对自相似多级纳米蜂窝铝结构力学性能的影响。在Gibson模型中引入了表面效应因子,结果表明修正的Gibson-Ashby模型与分子动力学计算结果更加吻合。此外,通过比较一级、二级和三级纳米蜂窝铝结构的变形机制发现,二级和三级纳米蜂窝铝结构由于分别在单级蜂窝和二级蜂窝的角点处接入六边形,在压缩过程中,多级纳米蜂窝铝结构激发的位错远高于单级蜂窝铝结构。也就是说,在压缩载荷下,多级蜂窝铝结构可以更好地利用结构的承载能力,吸收更多的能量。但是,自相似纳米蜂窝铝结构的力学性能无法通过增加级数的方法来无限增强,在相对密度和长度比不变的情况下,当纳米蜂窝铝结构的级数达到二级时,其综合力学性能最佳。研究结果还表明,相对密度不变时,二级纳米蜂窝铝结构长度比分别在0.3和0.4附近时,二级蜂窝铝结构具有最佳的面内和面外力学性能。研究成果对自相似多级纳米蜂窝结构的优化设计具有重要的指导作用。

Molecular dynamic(MD)simulations were used to investigate the mechanical behavior(elastic moduli and compressive strength)of self-similar hierarchical honeycomb aluminum(SSHHA)subjected to in-plane and out-of-plane compressive loadings.The influence of relative density,hierarchy order,and length ratio on mechanical properties of SSHHA were especially investigated.The MD results show that,both the in-plane and out-of-plane elastic moduli of SSHHA decrease with the decrease of relative density.A modified Gibson model was proposed to consider the surface effect in nano SSHHA,which shows a good agreement with the MD results.Moreover,by comparing the deformation mechanism of the SSHHA with different orders,it is found that,the mechanical properties can be optimized in the hierarchical structures by connecting a hexagon at the angular point of the 1^st honeycomb structure.Compared to the 1^st order honeycombs,more dislocations are generated in the 2^nd and 3^th honeycomb structures under compression loadings,resulting in greater energy absorption capacity.The results also indicate that,in the case where the relative density and length ratio are constant,the 2^nd nano SSHHA has the best comprehensive mechanical properties.In other words,the mechanical behavior of nano SSHHA cannot be infinitely enhanced by increasing the number of orders.In the end,the MD results show that,in the case where the relative density is constant,when the length ratios are 0.3 and 0.4 respectively,the 2^nd SSHHA has the best in-plane and out-plane mechanical properties,respectively.This study is helpful for the optimal design of SSHHA with enhanced performance.