单层石墨烯薄膜拉伸变形的分子动力学模拟

采用Tersoff势对锯齿型(Zigzag)和扶手椅型(Armchair)单层石墨烯薄膜的单向拉伸力学性能进行了分子动力学模拟,得到薄膜应力-应变演化关系,初步研究了其拉伸破坏变形机制。模拟结果表明:驰豫后的二维石墨烯薄膜并非完美的平面结构,表面不完全平整,出现类似波纹状褶皱。模拟计算得到锯齿型和扶手椅型石墨烯薄膜的杨氏模量分别为1031.36GPa和1058.42GPa,与文献报道结果一致。石墨烯薄膜在拉伸载荷作用下,薄膜边缘六角元胞首先转变为五角元胞形成缺陷,随着应变增大缺陷增多,碳-碳键逐渐断裂,最终导致薄膜破坏。     

不同尺寸的碳纳米管接枝聚酰亚胺复合材料的分子动力学模拟

本工作利用分子模拟软件Materials Studio建立了聚酰亚胺(PI)模型、不同直径的多壁碳纳米管模型(MWCNT)、不同长度的多壁碳纳米管模型(MWCNT)以及MWCNT/PI复合材料模型,探究了不同尺寸的MWCNT对MWCNT/PI复合材料模型的力学性能和玻璃化转变温度(T_g)的影响。计算结果表明,当加入长度为10～20μm、直径为10～20 nm的MWCNT,复合材料MWCNT/PI-1的杨氏模量和剪切模量分别为24.935 4 GPa和7.977 GPa;加入直径为10～20 nm、长度大于50μm的MWCNT后,复合材料MWCNT/PI-7的力学性能提高最为显著,杨氏模量和剪切模量分别为26.671 GPa和9.246 2 GPa。这表明MWCNT的直径越小或长度越长,即长径比增加,其与PI之间的相互作用力越强,从而可提高PI复合材料的力学性能,且MWCNT/PI的玻璃化转变温度升高。     

衬底偏压对四面体非晶碳膜结构和性能的影响

采用过滤阴极真空电弧技术并施加一定的衬底负偏压,在P(100)单晶硅片上制备出四面体非晶碳薄膜利用可见光Raman光谱研究薄膜的结构,通过BWF函数描述的单斜劳伦兹曲线拟合数据并获得表征曲线非对称性的耦合系数,从而反映了薄膜中sp3杂化的含量分别用原子力显微镜和纳米压入仪研究薄膜的表面形态和力学性能.结果表明:当衬底偏压为-80V时,薄膜中sp3杂化的含量最多,均方根表面粗糙度值最低(Rq=0.23nm),硬度、杨氏模量和临界刮擦载荷也最大,分别为51.49GPa、512.39GPa和11.72mN.随着衬底偏压的升高或降低,sp3键的含量减少,其它性能指标也分别降低.     

微机械悬桥法研究氮化硅薄膜力学性能

利用高精密纳米压入仪检测微机械悬桥的载荷-挠度曲线,来研究低应力LPCVD氮化硅薄膜的力学特性。通过大挠度理论分析,得到考虑了衬底变形对挠度有贡献的微桥挠度解析表达式。对于在加卸载过程中表现出完全弹性的微桥,利用最小二乘法对其挠度进行了拟合,从而得到杨氏模量、残余应力和弯曲强度等力学特性参数。低应力LPCVD氮化硅薄膜的研究结果:杨氏模量为(308.4±24.1)GPa,残余应力为(252.9±32.4)MPa,弯曲强度为(6.2±1.3)GPa。     

磁控溅射B4C薄膜的制备与力学性能

通过磁控溅射方法在不同基片温度下制备了B4C薄膜 ,利用傅立叶红外光谱、X射线衍射、透射电子显微镜表征了薄膜的微结构 ,并采用纳牛力学探针测量了薄膜的力学性能。结果表明 ,室温下制备的B4C薄膜具有很高的硬度 ( 4 2 5GPa)和杨氏模量 ( 3 0 0GPa) ,薄膜呈现非晶或纳米晶特征。随基片温度的提高 ,薄膜略有晶化 ,硬度与杨氏模量相应增加到5 0 4GPa和 4 2 0GPa。     

磁控溅射B4C薄膜的制备与力学性能

通过磁控溅射方法在不同基片温度下制备了B4C薄膜,利用傅立叶红外光谱、X射线衍射、透射电子显微镜表征了薄膜的微结构,并采用纳牛力学探针测量了薄膜的力学性能.结果表明,室温下制备的B4C薄膜具有很高的硬度(42.5 GPa)和杨氏模量(300 GPa),薄膜呈现非晶或纳米晶特征.随基片温度的提高,薄膜略有晶化,硬度与杨氏模量相应增加到50.4 GPa和420 GPa.     

石墨化易切削钢的变形抗力

石墨化易切削钢是顺应易切削钢无铅、低硫这一发展趋势而提出的。本文制备了以铁素体和石墨为组织特征的石墨化易切削钢的试验用钢,同时利用Gleeble-1500热模拟试验机,在变形温度T为850~1050℃,应变速率为1.0、10s-1条件下,对试验用钢进行了单道次高温轴向压缩试验,测得了高温应力-应变曲线。曲线分析结果表明,该钢的变形抗力随着变形温度的升高而降低,随着应变速率的增加而增加,应变速率10s-1时的应力-应变曲线呈现为再结晶型。基于上述分析,建立了试验用钢的变形抗力数学模型,并给出其具体参数。变形抗力实测值与按照模型计算的预测值吻合较好。     

膜厚对四面体非晶碳膜机械性能的影响

采用过滤阴极真空电弧技术以相同的工艺条件在p(100)单晶硅衬底上制备了不同厚度的四面体非晶碳薄膜,并利用表面轮廓仪测试薄膜的厚度和应力,利用纳米压入仪测试薄膜的硬度、杨氏模量和临界刮擦载荷.试验表明,在一定的扫描波形条件下,薄膜大约以0.7 nm/s的沉积速率稳定生长.随着膜厚的增加,薄膜的应力持续降低,当膜厚超过30nm时,应力将低于5GPa;当膜厚超过300nm时,硬度和杨氏模量分别将近70GPa和750GPa,已经十分接近体金刚石的性能指标.另外,随着膜厚增加所产生的应力变化,也导致了可见光拉曼光谱非对称宽峰的峰位逐渐向低频偏移.     

正交FeH5结构、力学和电子性质的第一性原理研究

基于密度泛函理论(DFT)对在300 GPa下正交Cmca-FeH_5晶体的结构、力学及结构电子特性进行理论研究。获得了Cmca-FeH_5的晶格常数和键长,计算结果与之前的理论数据相符合;计算分析了其能带结构和电子态密度,表明压强为300 GPa时Cmca-FeH_5呈弱金属性;采用能量-应变(E-S)和应力-应变(S-S)两种计算方法得到了Cmca-FeH_5的单晶独立弹性常数C_(ij)和s_(ij)以及其多晶弹性模量等值。分析发现在300 GPa下Cmca-FeH_5是力学稳定的且呈韧性。通过对Cmca-FeH_5的各向异性因子、杨氏模量和线性压缩系数的三维立体图像的分析,说明其具有弹性各向异性。在压强300 GPa时Cmca-FeH_5的德拜温度值相对较高,其原子之间的键合能力较强。     

聚酰胺非晶相弹性性质预测

聚合物基复合材料宏观有效力学性质的确定需要复合材料中各个组分的基本力学性质。采用基于拓扑的关联指数法对11种典型聚酰胺非结晶相的体积模量、泊松比、杨氏模量、剪切模量等弹性性能进行了预测。结果表明,当温度从1K逐步增加到(Tg-20)K时,体积模量、杨氏模量和剪切模量随温度的增加呈指数规律减小;而泊松比则呈线性增加。当温度在玻璃化温度Tg附近(Tg-20)相似文献   

水声材料小样品声学性能不同测试方法比较

介绍了水声材料声学性能的3种不同的测试方法,通过对同种样品的性能测试,分析了不同测试方法的优缺点。结果表明,与行波法相比,脉冲法和驻波法测试可靠性较高。     

Simple modifications for stabilization of the finite point method

A stabilized version of the finite point method (FPM) is presented. A source of instability due to the evaluation of the base function using a least square procedure is discussed. A suitable mapping is proposed and employed to eliminate the ill‐conditioning effect due to directional arrangement of the points. A step by step algorithm is given for finding the local rotated axes and the dimensions of the cloud using local average spacing and inertia moments of the points distribution. It is shown that the conventional version of FPM may lead to wrong results when the proposed mapping algorithm is not used. It is shown that another source for instability and non‐monotonic convergence rate in collocation methods lies in the treatment of Neumann boundary conditions. Unlike the conventional FPM, in this work the Neumann boundary conditions and the equilibrium equations appear simultaneously in a weight equation similar to that of weighted residual methods. The stabilization procedure may be considered as an interpretation of the finite calculus (FIC) method. The main difference between the two stabilization procedures lies in choosing the characteristic length in FIC and the weight of the boundary residual in the proposed method. The new approach also provides a unique definition for the sign of the stabilization terms. The reasons for using stabilization terms only at the boundaries is discussed and the two methods are compared. Several numerical examples are presented to demonstrate the performance and convergence of the proposed methods. Copyright © 2005 John Wiley & Sons, Ltd.     

A comparison of domain integral evaluation techniques for boundary element methods

In many cases, boundary integral equations contain a domain integral. This can be evaluated by discretization of the domain into domain elements. Historically, this was seen as going against the spirit of boundary element methods, and several methods were developed to avoid this discretization, notably dual and multiple reciprocity methods and particular solution methods. These involved the representation of the interior function with a set of basis functions, generally of the radial type. In this study, meshless methods (dual reciprocity and particular solution) are compared to the direct domain integration methods. The domain integrals are evaluated using traditional methods and also with multipole acceleration. It is found that the direct integration always results in better accuracy, as well as smaller computation times. In addition, the multipole method further improves on the computation times, in particular where multiple evaluations of the integral are required, as when iterative solvers are used. The additional error produced by the multipole acceleration is negligible. Copyright © 2001 John Wiley & Sons, Ltd.     

基于磁性法的钢中残余奥氏体含量测定方法与装置

阐述了磁性法测定钢中残余奥氏体含量的原理和方法,并研制了一种基于磁性法的钢中残余奥氏体含量测定装置。该测定装置可以实现换向法、甩脱法和动态法等3种残余奥氏体含量测定方法,其中换向法和甩脱法以不同方式静态测定残余奥氏体含量,动态法能够在试件拉伸过程中连续、快速地动态测定残余奥氏体含量与应变的对应关系。该测定装置以LabVIEW为平台,构成了虚拟仪器系统,对数据进行采集、分析和处理,实现了可视化操作、自动测量、曲线显示和数据保存等功能。使用该装置采用3种方法分别对M50NiL轴承钢中的残余奥氏体含量进行了测定,试验结果表明该测定装置能够精确地测定钢中的残余奥氏体含量。     

聚合物熔体界面张力测定方法的研究进展

在聚合物共混体系中,界面张力对聚合物相容性有着重要影响,决定着相与相之间的粘接性,成为控制其最终相态结构的一个重要因素,是研究多相聚合物相态结构的基础。文中综述了聚合物熔体界面张力的测定方法,这些测定方法主要有热力学方法、流变学方法以及动力学方法三大类;介绍了每种方法的基本原理,并对其优缺点及适用范围进行了简单说明。其中,动力学方法是使用最多、相对准确的,对该方法进行了重点介绍,并且讨论了动力学方法中熔体粘弹性对界面张力测定的影响。     

Combined hybrid approach to finite element schemes of high performance

Based on a combination of Hellinger–Reissner principle with its dual, a mixed/hybrid method of non‐saddle point type has been presented in the previous papers. In the paper, an application of the method to two‐dimensional elasticity problems is considered in a manner of combination of mathematical analysis with numerical investigation. How to construct a combined hybrid scheme of high performance is discussed, and several four‐node quadrilateral CH‐elements are systematically verified. In brief, this paper shows that for the hybrid element scheme, the energy compatibility condition, introduced in Zhou (Combined hybrid finite element method without requirement for Babuska‐Brezzi condition, to appear) is the ultimate key to the achievement of high performance. Copyright © 2001 John Wiley & Sons, Ltd.     

高分子田菁胶化学结构式修饰方法综述

田菁胶是从田菁种子胚乳中提取的一种天然多糖类高分子有机物。天然的化学结构反映出的理化性质限制了其应用和推广。化学结构式的修饰改进是扩大其应用的有效手段。修饰改进后的田菁胶无毒、无污染,在石油开采、煤开采、纺织、印刷、造纸和食品等领域得到了广泛应用。文中对羧甲基法、羟乙基法、羟丙基法、交联法、羟烷基-羧甲基法、羧甲基-羟烷基法、阳离子法、酶解法、氧化法和两性法等田菁胶化学结构式的主要修饰改进方法进行了详述。总结了修饰改进技术注意事项,并对前景进行了展望。     

Recent developments of free mesh method

This paper presents the recent advances on Free Mesh Method by the authors. In this method, elements are locally created at each node in an autonomous manner, so that only nodal information is necessary without global meshing. The method has been tested with various applications such as heat conduction, fluid and fracture analyses, and reliable solutions were obtained with good parallel efficiency. Modifications of Free Mesh Method have been further proposed, and the accuracy of solution has been improved.The overall review of the recent advances has demonstrated the effectiveness of Free Mesh Method. Copyright © 2000 John Wiley & Sons, Ltd.     

纳米氧化锌材料的制备方法及结构表征

文章介绍了纳米ZnO材料的常用制备方法,如应用较多的气-固-液法、气相法、水热法和有着较好应用前景的电化学法,以及各类纳米ZnO材料的结构表征,并展望了纳米ZnO材料的发展前景。