【作者】 李颖；

【导师】 杨勇；

【作者基本信息】 哈尔滨工程大学 ， 力学， 2020， 硕士

【摘要】 在现代社会生产活动中,纳米铜及合金材料具有优良的性能,在各个领域中得到广泛的应用。本文系统地阐述了分子动力学模拟方法,并利用该方法对铜及其合金纳米线进行研究,旨在探讨该材料在扭转作用下的形变机制,以及不同因素变化下其力学性能的影响。本文构建了圆柱体单晶铜纳米线基本模型,分析了其在扭转过程中的形变机制,并结合晶体内部微观结构的变化,详细地分析了其材料力学性能的影响。在研究中将纳米线的扭转变形过程分为三个阶段:弹性阶段、塑性阶段以及周期变形阶段。弹性阶段中,晶体在外力做功下吸收了大量能量,并且内部空间点阵结构尚未遭到破坏。在塑性阶段中,晶格间的滑移开始,位错出现在纳米线的表面,并沿着滑移面延伸到纳米线内部,扭矩与平均剪应力也迅速下降。在周期变形阶段中,晶体内部则出现了形变孪晶的生成与消亡等现象。另外又先后对中空单晶铜纳米线、铜合金纳米线基本模型进行分子动力学模拟,研究发现核壳结构的纳米线内部晶格不匹配,在晶体内部会形成位错环,而孔洞与位错环都会对纳米线的稳定性以及扭转变形过程产生影响。改变上述模型的尺寸、扭转速率和温度,分析不同因素对纳米线的变形机制与力学性能的影响。纳米线的长度尺寸会对材料的弹性系数产生影响,较高速率下纳米线的力学性能表现出小幅的强化效应,而高温下原子热运动更加剧烈,晶体更加容易生成位错,材料抵抗弹性形变的能力大大降低。本文的研究为进一步探讨纳米铜及合金材料的弹塑性变形机制提供了理论参考。更多还原

【Abstract】 In the production activities of modern society,nano-copper and its alloy are widely used in various fields due to their more excellent properties.The molecular dynamics simulation method is illustrated systematically and is used to study the copper and its alloy nanowires in this paper,in order to explore the deformation mechanisms of nanowires under torsion and the influence of different factors on its mechanical properties.In this paper,a basic model of cylindrical single crystal copper nanowires is constructed and its deformation mechanism during torsion is analyzed.In combination with the changes in the microstructure of the crystal,the mechanical properties is investigated in detail.The torsional deformation process of nanowires is divided into three phases: the elastic phase,the plastic phase,and the cyclic deformation phase.The crystal has accumulated a lot of energy under the work of torsion force in the elastic phase and the internal lattice structure has not been damaged.Slip between the lattices begins in the plastic phase,dislocations appear on the surface and extend along the slip surface into the nanowire,and the torque and average shear stress of the model also decrease rapidly.In addition,the hollow single-crystal copper nanowires and copper alloy nanowires are carried out by molecular dynamics simulations.It is found that the dislocation tangling formed due to the lattice mismatch and void will affect the stability and torsional deformation of the nanowires.The effects of different factors on the deformation mechanism and mechanical properties of the nanowires are analyzed by changing the nanowires’ size,torsion rate,and temperature.It is found in this work that the length of the nanowires has an effect on the elastic coefficient of the material.The mechanical properties of the nanowires show a small strengthening effect at higher torsional rates.And the atomic thermal movement is more intense at high temperatures,the dislocations in the nanowires will be form easier.The material’s ability to resist elastic deformation is greatly reduced.This work provides a theoretical reference for further exploring the elastoplastic deformation mechanism of nano-copper and alloy.更多还原