Effect of interaction of dislocations with core-shell nanowires on critical shear stress of nanocomposites

The contribution to the critical shear stress of nanocomposites caused by the interaction between screw dislocations and core-shell nanowires (coated nanowires) with interface stresses was derived by means of the MOTT and NABARRO's model. The influence of interface stresses on the critical shear stress was examined. The result indicates that, if the volume fraction of the core-shell nanowires keeps a constant, an optimal critical shear stress may be obtained when the radius of the nanowire with interface stresses reaches a critical value, which differs from the classical solution without considering the interface stresses under the same external conditions. In addition, the material may be strengthened by the soft nanowires when the interface stresses are considered. There also exist critical values of the elastic modulus and the thickness of surface coating to alter the strengthening effect produced by it.     

多铁性材料中螺型位错与含弱界面圆形夹杂的相互作用

考虑无穷远反平面力载荷和平面内电磁载荷情况下,横观各向同性的压电磁介质中广义螺型位错与含非完整界面的圆形夹杂的电磁弹性耦合效应。广义螺型位错位于基体的任意一点处并且在其位错核上作用有点力、点电荷和线电流。通过运用复变函数方法,得到了电磁弹性场的解析解。借助于广义的Peach-Koehler公式,求解出了广义螺型位错上位错力的精确表达式。研究了非完整界面对夹杂区域中电磁弹性场的影响。讨论了各种参数(非完整界面,材料匹配性和位错位置)对作用在非完整界面附近广义螺型位错上位错力的影响规律。这些基本解可以作为分析压电磁介质中相应裂纹问题的格林函数。     

Effects of thickness and elastic modulus on stress condition of fatigue-resistant coating under rolling contact

The distribution and magnitude of surface and subsurface stresses of the single-layer sprayed-coatings on monolithic substrates were investigated by finite element method (FEM). The models of coating configurations with different thicknesses and elastic modulus ratios of coating to substrate were introduced, and the effects of thickness and elastic modulus ratio on the stresses were addressed. The calculation results show that the coating/substrate interface shear stress obviously decreases with increasing coating thickness, due to the location of the maximum shear stress moving away from the coating/substrate interface. At the same time, the magnitude of von Mises stress also declines in the case of thicker coatings. However, the high elastic modulus ratio results in extremely high maximum shear stress and the severe discontinuity of the von Mises stress curves, which leads to the intensive stress concentration on the coating/substrate interface. So the coating configurations with the larger coating thickness and lower difference of elastic modulus between coating and substrate exhibit excellent resistant performance of rolling contact fatigue (RCF).     

半刚性基层沥青路面面层剪应力峰值的影响因素

目的探讨沥青路面面层剪应力峰值变化规律和影响因素.方法运用多层弹性体系理论,双圆均布荷载下,考虑路面结构层厚度、模量变化以及层间状态的不同,分析半刚性基层沥青路面剪应力峰值的变化规律和影响因素.结果沥青路面剪应力峰值会随面层厚度的增加而减小,随基层厚度的增加而增大;沥青路面使用过程中面层模量变化以及设计选取基层模量过高会导致剪应力峰值的提高;层间出现滑移也将导致沥青路面剪应力峰值的大幅度增加.结论路面结构层模量变化及层间连接状态的不同对沥青路面剪应力峰值有显著的影响;路面结构层厚度对沥青路面剪应力峰值的影响相对较小,但也不容忽视.设计和施工过程中应充分考虑沥青路面剪应力的影响因素并加以控制.     

Stress Field of Straight Edge Dislocation in Magnetic Field

To study the changes in mechanical properties of materials within magnetic fields and the motion of dislocations, stress fields of dislocation in magnetic field need to be calculated. The straight edge dislocation is of basic importance in various defects . The stress field of straight edge dislocation in an external static magnetic field is determined by the theory of elasticity and electrodynamics according to the Volterra dislocation model for continuous media. This reduces to the known stress field when the magnet field is zero. The results can be used for further study on the strain energy of dislocations and the interactions between dislocations in magnetic fields.     

白加黑路面层间剪应力影响因素的正交分析

在旧水泥混凝土路面上加铺沥青面层时,层间接触面是路面结构抵抗水平剪切应力的最薄弱环节.利用路面设计软件BISAR,在分析了影响沥青面层和水泥混凝土基层层间剪应力因素的基础上,采用正交试验方法对各影响因素的敏感性进行比较.分析表明,车辆轴载对层层间剪应力的影响最大,随着轴载的增加,层间剪应力逐渐增大,二者呈现线性关系;沥...     

Reflected Characteristics of Interface between Ceramic and Ceramic／Metal Graded Materials on Elastic Wave

The propagation characteristics of impact waves across a planar interface between a ceramic layer and a ceramic/metal ( C/ M ) composite layer were investigated. Two interfacial boundary conditions were considered : one was a shear coupling boundary condition that simulated a perfectly bonded interface between the ceramic and composite, and the other was a slip boundary condition that only allowed a transmission of the transverse motion and normal stress at the interface. The ceramic was subjected to an inchtent impact wave. The ceramic and composite was assumed to be elastic during impact. The stndy was based on a basic method provided by Furlong, Westburg and Phillips for predicting the reflection and refraction of spherical waves across a planar interface separating two elastic solids. Emphasis was put on the effect of the metal volume fraction in the composite, ceramic thickness and interfacial boundary condition on the reflected waves. New and interesting results are obtained that provide a very useful guidance for design of a ceramic/composite armor and of a C/M functionally graded applique.     

COMPUTER SIMULATION OF DISLOCATION CORES IN B2 NIAL INTERMETALLICS *

ＴｈｅｄｅｆｏｒｍａｔｉｏｎｍｅｃｈａｎｉｓｍｓａｎｄｍｅｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓｏｆＮｉＡｌｈａｖｅｂｅｎｓｔｕｄｉｅｄｅｘｔｅｎｓｉｖｅｌｙｄｕｅｔｏｉｔｓｐｏｔｅｎｔｉａｌｆｏｒｈｉｇｈｔｅｍｐｅｒａｔｕｒｅａｐｐｌｉｃａｔｉｏ...     

高等级公路沥青路面剪应力分析与应用

基于线弹性层状体系理论，采用路面结构有限元法，探讨高等级公路沥青路面剪应力的分布规律、影响因素及其评价方法。通过选取不同路面结构参数，包括各结构层厚度、模量和泊松比等，在不同的点位，利用BISAR程序进行力学计算和分析，提出了沥青路面抗剪强度的确定和评价方法。研究结果表明：在不考虑各结构层材料性能和厚度时，最大剪应力均分布在距路表3cm深度范围内；影响剪应力的最主要因素是沥青层模量、泊松比和基层模量；对于普通3层沥青层面层结构，上面层和中面层应进行剪应力验算，下面层可根据实际情况确定是否进行验算；验算时，需找到准确的计算点位才能计算出各层内最大剪应力。     

硬涂层半空间体的弹性场分析

运用Ｈａｎｋｅｌ积分变换详细推导了具有一个硬涂层的半空间体在Ｈｅｒｔｚ半椭圆接触应力作用下的轴对称弹性场。计算结果表明，涂层厚度对表层应力场有显著影响，在考虑表面粗糙度后，增加涂层厚度会使涂层底部出现较大的拉应力，导致涂层的断裂剥离，对滚动接触疲劳中陶瓷硬涂层的作用及破坏机理进行了较详尽的分析。     

An experimental study of the incipient bed shear stress partition in mobile bed channels filled with emergent rigid vegetation

This paper investigates the bed shear stress based on the condition of the incipient motion of sediment in a uniform-flow flume covered with emergent rigid vegetation,which is represented by arrays of circular cylinders arranged in a regular pattern.A total of 148 tests are performed to observe the influence of the vegetation density,bed slope,flow depth and sediment size on the bed shear stress.The tests reveal that when the sediment is in incipient motion,the resistances acting on the flow passing the rigid vegetation contain the vegetation resistance and the bed shear stress.This shear stress could be divided into two parts:the grain shear stress and the shear stress caused by sand dunes,which are the deformed bedform with the sediment incipient motion.An empirical relationship between the shear stress of the sand dune and vegetation density,the Froude number,the apparent vegetation layer velocity is developed.     

Stress distribution and effective stress intensity factor of a blunt crack after dislocation emission

The stress fields induced by a dislocation and its image dislocations around a narrow elliptic void are formulated. Based on the solution, the stress distribution and effective stress intensity factor of a blunt (elliptic) crack were calculated under mode I constant loading. The results show that a dislocation-free zone (DFZ) is formed after dislocation emission. There exists a second stress peak in the DFZ except a stress peak at the blunt crack tip. With an increase in the applied stress intensity factor Kla or the friction stress T, of the material, the DFZ size and the peak stress at the crack tip decrease, but the peak stress in the DFZ and the effective stress intensity factor Klf presiding at the crack tip increase. Because of dislocation shielding effects, shielding ratio Kla/Klf increases with increasing Kla, but it decreases with increasing Tf.     

Comparison and analysis of dislocation density, morphology and evolution in microstructure of low-carbon steel produced using different technologies

Three kinds of specimens were produced from hot strips of similar composition and same thickness （nominal gauge 4.0 mm） but produced using different technologies, and the dislocation density of these strips was quantitatively measured by positron annihilation technique test. The dislocation morphology and evolution in microstructure of each pass for producing the 1.9 mm hot strip using CSP （compact strip production） technology were observed under an H-800 transmission electron microscope; its density was also quantitatively measured using the positron annihilation technique test, and the factors influencing the dislocation density during the production process were analyzed. The experimental results show that the dislocation density in the microstructure produced using CSP technology is higher than that in the microstructure produced using conventional technology. This result was discussed and confirmed on the basis of the finite element simulation and the theory relevant to dislocations.     

装配式结构套筒灌浆连接的混凝土结合界面直剪性能试验研究

研究灌浆层厚度、纵向钢筋、配筋率、轴向压力等因素对直剪荷载作用下套筒灌浆连接的混凝土结合界面裂缝开展、破坏形态、直剪剪切强度、裂缝-滑移曲线以及荷载-滑移曲线的影响. 试验结果表明：对于无纵向钢筋试件结合界面,灌浆层厚度为1、10 mm界面的破坏荷载均值分别是灌浆层厚度为20 mm界面的1.69、1.14倍;对于纵向配筋结合界面,配筋率为0.9%、1.8%的试件界面破坏荷载均值分别是无筋试件界面的1.58、1.89倍,且结合界面直剪破坏延性显著提高,但由于未配箍筋,最终破坏形态为混凝土被纵向钢筋劈裂破坏,降低了结合界面的直剪剪切强度和延性;对于施加轴向压力试件,轴向压力为11.6、23.2 MPa的试件界面破坏荷载分别为无轴压试件界面的6.06、7.81倍,在23.2 MPa轴向压力下,破坏模式转化为界面破坏后的现浇部分混凝土本体破坏.     

梯度复合板界面对Ⅲ型内部周期裂纹影响

讨论在反平面载荷作用下功能梯度复合板条断裂问题,复合板由两类不同的功能梯度板条弱间断粘接而成,一个板条中存在内部周期裂纹。采用有限傅里叶变换和Hilbert核奇异积分方程方法求解该断裂问题。通过讨论断裂参数的数值解,分析了功能梯度非均匀参数,功能梯度层厚度,裂纹与界面间距以及周期带长等对应力强度因子的影响。     

多环交界裂纹面在谐振应力波作用下的动应力强度因子

研究埋藏圆柱体中多个环形交界裂纹面上受谐振应力波作用时的弹性波散射问题,以裂纹面的位错密度函数为未知量,利用Fourier积分变换,将问题归结为第二类奇异积分方程;然后通过数值求解奇异积分方程,获得裂纹尖端的动应力强度因子;给出了双裂纹动应力强度因子随入射波频率变化的关系曲线。     

Mode Ⅰ Plane Crack Interacting with an Interfacial Crack Along a Circular Inhomogeneity

Cracks,inhomogeneityandtheirinteractions playanimportantroleincompositematerial.Anda lotofresearchworkaboutthiscanbefoundinopen literatures[1,2].Inthispaper,theelasticinteractionofthemodeⅠplanecrackwithaninterfacialcrackalongacircu larinhomogeneityisdealtwith.Thedislocationden sity,themodesⅠstressintensityfactors(SIFs)of theplanecrackareobtainednumericallybyhandlinga newkindofdislocationequilibriumequation.1ProblemStatementandFormula tion Thegeometryandcoordinatesystemoftheprob lemareshow…     

薄板中孔边裂纹与独立裂纹的相互作用

研究有孔边裂纹与独立裂纹的薄板在远程受弯曲作用时的响应.利用叠加原理,将原问题转化为两个含有孔边裂纹的子问题,远程弯曲只存在于第一子问题.在第二子问题中,假定沿独立裂纹线的位置存在一个连续分布的角位错,使之在此处得到的面力与第一子问题所得到的相抵消,形成自由表面的裂纹,通过基于点位错解的奇异积分方程得到连续分布位错的解.给出了板弯曲问题基于位错密度函数的应力强度因子的表达式,求得孔边裂纹及独立裂纹应力强度因子的数值解,考察了薄板在远程弯曲时方形孔边裂纹和线裂纹的应力强度因子变化.     

嵌入非线性黏弹性材料弹性尖楔尖端的应力、应变场

套管损坏是石油工程研究中的重要问题之一,引起套管损坏发生的主要原因是在采油过程中油藏结构变化改变了原地应力场的分布以及不同岩层间界面的相对滑动.建立了以油藏隆起为尖楔嵌入非线性黏弹性材料的界面断裂力学模型.在平面应变条件下,通过奇异量级分析、运动方程和协调方程,推导出在尖楔尖端的非线性黏弹性材料中的控制方程.根据问题的边界条件和连续条件,通过数值计算得到了尖楔尖端连续的分离变量形式的应力、应变和位移场.数值计算表明,尖楔尖端场分布主要受材料的力学特性、地层倾角和摩擦系数的影响.模型阐明了套管剪切损坏力学机理,研究的结果为解决套管损坏问题提供了理论上的参考依据.     

局部双轴应变SiGe材料的生长与表征

利用分子束外延（MBE）对双轴应变SiGe局部区域外延生长和表征进行了研究.图形窗口边界采用多晶Si侧墙,多层SiGe薄膜分段温度生长.采用扫描电子显微镜（SEM）、原子力显微镜（AFM）、X射线双晶衍射（XRD）、透射电镜（TEM）和位错密度测试等多种实验技术,结果表明：薄膜表面窗口内双轴应变SiGe薄膜厚度和Ge组分得到精确控制,垂直应变度达到1.175%,其表面粗糙度为0.45 nm,SiGe位错密度为1.2×103 cm-2.由于采用多晶Si侧墙,外延材料表面没有发现窗口边缘处明显位错堆积.实验证实,采用该技术生长的局部双轴应变SiGe薄膜质量良好,基本满足SiGe BiCMOS器件制备要求.