纳米单晶与多晶铜薄膜力学行为的数值模拟研究

通过对不同温度下单晶薄膜的拉伸性能的分子动力学模拟，从微观角度揭示了温度效应对材料性能的影响. 结果表明温度效应对材料的变形机理影响很大.0K温度下由于缺乏热激活软化的影响, 粒子运动所受到的阻碍较大, 薄膜的强度较高, 塑性变形主要来自于粒子的短程滑移.温度升高，粒子的热运动加剧，屈服强度降低, 塑性变形将主要来自于大范围的位错长程扩展.多晶薄膜的模拟结果表明, 虽然其晶粒形状较为特殊, 但是它仍然遵循反Hall-Petch关系.在模拟过程中，侧向应力最大值比拉伸方向应力的最大值滞后出现.位错只会从晶界产生并向晶粒内部传播，晶粒间界滑移是多晶薄膜塑性变形的主要来源.     

低密度和高密度水化硅酸钙的纳米压痕数值模拟

水化硅酸钙(C-S-H)是决定以硅酸盐水泥为主要组分的水泥基材料性能的关键组分,水化硅酸钙(C-S-H)是存在于水化产物中连续的固体物质,占水化水泥浆体体积的50%～60%,是水泥浆体中决定硬化水泥浆体物理结构和性能的主要成分,同时水化硅酸钙(C-S-H)也是混凝土结构宏观尺度的凝聚性和耐久性的重要影响因素．模型的建立对于预测水泥的体积性能如收缩、蠕变、渗透率和裂缝等方面越来越重要．通过将水化硅酸钙(C-S-H)分为低密度和高密度两种数值模型,并且将水化硅酸钙(C-S-H)视为在纳米尺度上具有实际微观粒子性能的离散颗粒的集合,运用分子动力学方法,通过控制水化硅酸钙(C-S-H)的紧密堆积体积分数和保持颗粒级别的其他材料属性不变来进行纳米压痕实验模拟,进而验证了压痕模量和硬度符合纳米压痕实验数据的规律．     

纳米摩擦学的分子动力学模拟研究

用分子动力学模拟研究了纳米级润滑薄膜的固液相变和界面滑移现象以及固体接触和黏着的微观机制.结果表明：纳米薄膜中液体的固化相变压力随膜厚减薄而下降,说明润滑剂可能处于类固态状态.薄膜中的界面滑移现象可能在较低的剪切速率下发生,并与液体的固化程度有较好的对应关系.光滑晶体表面在相互接近或分离过程中可能因部分原子突然跃迁而发生微观黏着,这对于理解界面摩擦的起源具有重要意义.     

纳米晶体弹性模量的模拟研究

通过分子动力学(MD)方法模拟纳米晶体(1～3nm)的结构,并对模拟的结果进行了X射线衍射的点阵常数、结合能及弹性模量等模拟计算.结果表明纳米晶体无论是晶界和晶粒都与传统的粗晶粒晶体材料没有根本的区别,只是由于晶粒尺寸变小以及晶界的体积分数等的作用而导致诸如弹性模量大幅度减少等一系列不同性能.     

单层富勒烯薄膜脱盐应用的分子动力学模拟研究

海水淡化是最有希望解决全球淡水资源短缺的有效方案之一,纳米技术的进步推动了各类用于水净化的纳米多孔膜的发展.理论和实验研究发现了纳米多孔石墨烯的超高水透过和盐离子拒绝率.然而精确创建、控制纳米级孔隙的大小和分布的操作难度极大地限制了纳米膜材料的实际化应用.通过分子动力学模拟发现具有均匀有序纳米孔排列准四边形结构(quasi-tetragonal phase, qTP)的单层富勒烯(C₆₀)薄膜在海水淡化方面的巨大潜力,在保证100%阻盐率的同时,与传统聚合物过滤膜相比,单层富勒烯薄膜展示出卓越的透水性.从原子尺度系统地研究了单层富勒烯薄膜结构的筛分机制,发现钠离子、氯离子与水分子相比,在穿膜运输过程中有大的能量障碍.结果表明,单层富勒烯薄膜是一种很有优势的海水淡化膜.     

周围应力与孔隙流体对突出煤力学性质的影响

本文在系统的实验与理论研究基础上,考查了周围应力与孔隙流体对突出煤变形与破坏的影响.提出了一个描述破坏后现象的模型,其判据是一个联系着有效围压与材料强度的无量纲参数.实验表明,吸附瓦斯对应力-应变曲线没有明显影响;有效应力中的孔隙压力项就是游离瓦斯的压力;含气体与液体的多孔介质会有不同有效应力关系.     

熔融LiCl及其急冷非晶键取向序的分子动力学模拟研究

本文进一步讨论了我们新近提出的等近邻数键球谐函数方法,并通过分子动力学模拟研究了熔融LiCl及其急冷过程。对计算机模拟各时间步产生的瞬态构型进行平均,计算了不同温度下键序Q_l谱.将模拟Q_l谱与线性组合模型Q_l谱比较,观察到模拟Q_l谱与含90％局部正四面体结构的组合模型十分相似,表明熔融Licl及其急冷非晶中局部键取向序明显倾向于正四面体序。急冷过程中不同温度下局部键取向序可用同一线性组合模型描述,但模型方差随模拟温度明显变化。方差随温度而降低,且在发生玻璃态转变时有一显著下降。不同温度下的键角分布也作了计算,观察到键角分布在109°(正四面体局部结构键角)附近且分布峰随温度升高而展宽,与键序Q_l得到的结论一致。     

桥联理论研究的最新进展

欲根据组分材料——纤维和基体性能参数预报复合材料的强度,必须解决3个方面的问题.首先,必须准确计算出纤维和基体中的内应力;其次,必须基于这些内应力,建立起复合材料的有效破坏判据,即细观力学强度理论;最后,必须根据独立测试的基体性能,准确定义其现场强度输入数据,因为后者无法测量.复合材料强度预报之所以困难,在于所涉及的每一个问题都极具挑战.由黄争鸣创建和发展的桥联理论,系统给出了这3方面问题的有效解决方案.该文简要介绍这些解决方案,包括桥联理论的最新进展及有待进一步研究的课题.     

α-因子缓冲算子的构造及其性质的研究

为了解决灰色预测模型中的随机挠动序列问题,本文在灰色系统理论以及灰色预测建模技术的基础上,通过梳理历史文献的研究结果,提出了一个具有缓冲作用强度可调整的新型缓冲算子,即α-因子缓冲算子,该算子具有强度可调整、形式统一、预测结果优良等特性.具体来说就是通过调整强度系数可以改变其缓冲作用的强度大小、形式上兼顾了弱化缓冲算子和强化缓冲算子的统一性、在一定范围内的应用中预测结果优于其他的缓冲算子.实证的结果的确显示出了这些优良性质.     

模糊图中的割点,割边及块的性质研究

在简单模糊图的基础上引入了模糊子图以及模糊图的割点、割边和块的概念,并讨论了模糊图的割点、割边及其块的一些性质.     

Comparative Studies on the Mechanical Properties of a Thermoset Polymer in Tension and Compression

Results of an experimental investigation into the mechanical properties of a polyester resin in tension and compression are reported. Features of the stress-strain curves obtained are discussed. Data on the elastic modulus, Poisson ratio, and volume strains are obtained. The results of creep behavior of the material in tension and compression are also presented. It is found that the time-dependent creep obeys a power law, but the nonlinear stress dependence can be described by using the hyperbolic sine function. The effect of load type (tension or compression) on the nonlinearity of the creep is analyzed. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 5, pp. 633–650, September–October, 2005.     

Anchoring and a Load Transfer Technique in Uniaxial Tension of Unidirectional High-Strength Composites

A simplified analytical method for calculating the stress-strain state in uniaxial tension of unidirectional composite specimens with glued wedges is developed. A numerical analysis of the influence of geometry and mechanical parameters of the specimens on the maximum stresses is carried out. The calculations are refined by finite-element modeling. Tests of the specimens have proved the suitability of the suggested technique of anchoring and load transfer in uniaxial tension of unidirectional high-strength composites.__________Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 41, No. 3, pp. 319–334, May–June, 2005.     

基于系统识别方法的围岩弹性模量及水平地应力反演分析

利用有限元软件建立隧道开挖正演模型,基于新奥法隧道施工现场实测围岩收敛数据,采用灵敏度分析建立了参数调整算法,利用系统识别方法对隧道围岩弹性模量及水平地应力进行了反演分析,并讨论了初始值的影响.结果表明,系统识别反演分析法具有自适应能力强、反演分析过程收敛计算稳定性好和计算速度快等优点,在隧道及地下工程领域具有广阔的应用前景.     

Cubic Nonlinearity in Elastic Materials: Theoretical Prediction and Computer Modelling of New Wave Effects

Our object of interest is nonlinear interaction of waves in elastic materials. The new model of a material is proposed that takes into account the mechanism of simultaneous quadratic and cubic nonlinear deformations. Introduction of cubic nonlinearity into the model makes the general wave picture more complicated and creates new possibilities for the wave analysis. We present four possibilities for the evolution of profiles of plane harmonic waves. It is noted that quadratic and cubic nonlinearities emerge first of all in the second and third harmonics generation, respectively. Further, we discuss the results of computer modelling of the wave profile evolution. The influence of the progress of second and third harmonics on the wave profile evolution is studied separately. We study separately how second and third harmonics influence the evolution of the wave profile. We also investigate how the progress of harmonics depends on the initial frequency and amplitude. We find two distinct schemes of the evolution progress: the scheme (in) with four stages for the second harmonics and the scheme with three stages for the third harmonics. As a result the influence of both harmonics could be observed simultaneously, and such a case is demonstrated in the paper. Nevertheless this phenomenon is not necessarily present in every material which explains the absence of experimental observations of the third harmonics by this time.     

A nanocomposite based on a styrene-acrylate copolymer and native montmorillonite clay 1. Preparation, testing, and properties

The preparation of a polymer nanocomposite by compounding an aqueous polymer emulsion with an aqueous dispersion of montmorillonite clay is described. A styrene-acrylate copolymer emulsion and a purified native montmorillonite clay from Latvian deposits are used. An X-ray diffraction analysis and differential scanning calorimetric thermograms are shown. Data on the influence of montmorillonite concentration on the tensile stress-strain diagram, elasticity, yield stress, breaking stress, and ultimate elongation of the processed nanocomposite material are obtained. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 1, pp. 61–74, January–February, 2006.     

Effect of Water on the Physicomechanical Properties of Composites Containing Low-Density Polyethylene and Linen Yarn Production Waste

The effect of the amount of absorbed water on the physicomechanical indices (tensile modulus and tensile strength) of composites based on low-density polyethylene (LDPE) and linen yarn production waste (LW), both with and without coupling agents (stearic acid - SA and diphenylmetane diisocyanate - DIC), is studied. It is shown that the strength properties depend considerably on the time of water sorption and on the blend composition. The tensile strength decreases with increased amount of absorbed water (with increased time of exposure to distilled water) and with increased content of LW in the composite. Somewhat different results are obtained for systems containing SA and DIC modifiers. The modifiers, intensifying the interfacial interaction, retard the process of water sorption, therefore the drop in the strength indices is not so significant. Of special interest is the behavior of systems with DIC. In some cases, a slight increase in strength (after a two to five day exposure to water) is observed, which is probably caused by cross-linking of the free diisocyanate in the system under the action of moisture.     

Deformability and strengh of expanded polystyrene (EPS) under short-term shear loading

Data obtained in investigating the ultimate strength and deformability of expanded polystyrene under short-term shear loading according to EN 12090 are discussed. Linear regression equations are used for describing the ultimate shear strength and modulus in relation to the density of EPS. A correlation is found to exist between the ultimate strength of EPS and its density and specimen thickness. An empirical dependence between the shear modulus and density of EPS is established. The strains corresponding to the conditional limit of proportionality and to the ultimate shear strength of EPS in short-term loading are determined. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 43, No. 1, pp. 121–134, January–February, 2007.     

基于非局部弹性应力场理论的纳米尺度效应研究:纳米梁的平衡条件、控制方程以及静态挠度

该文成功地解答了3个关于非局部应力理论用于纳米梁的问题:(ⅰ) 在绝大多数研究中,非局部效应增加导致纳米结构体刚度下降,其现象表现为弯曲挠度增加,固有频率减少,屈曲载荷下降,但为什么Eringen 的非局部弹性理论给出了完全相反的结论;(ⅱ) 为什么在某些研究结果中,非局部效应消失或是对研究结果无影响,比如纳米悬臂梁在集中载荷作用下的弯曲挠度; (ⅲ) 在高阶控制方程中,为什么高阶边界条件不存在．通过应用非局部弹性理论和精确变分原理分析纳米梁的弯曲问题,推导出全新的平衡条件、控制方程、边界条件和静态响应．这些方程和条件包含了与之前的相关研究结果符号相反的高阶微分项,这一差别导致了纳米效应对结构体的影响结果完全相反． 还证明之前为大家所公认的纳米梁静态或动态平衡条件实际上没有达到平衡,只有用等效弯矩代替非局部弯矩时,才可达到平衡．这些结论通常是可以被其它方法,比如应变梯度理论、耦合应力模型以及相关实验所证明．