真空辅助湿法斜接型挖补修理后层合板拉伸性能研究

对真空辅助玻璃纤维增强复合材料斜接型挖补修理后结构进行了拉伸强度试验研究,获得了修理后结构最终破坏模式。分别建立了挖补修理结构中母板与补片三维有限元模型,采用了各向异性连续损伤力学模型模拟了母板与补片复合材料单向带失效模式,假定母板与补片通过黏性力接触,在真空辅助湿法挖补修理形成的无厚度二次固化界面处定义了接触面, 采用指数型软化cohesive模型模拟了界面接触属性。试验结果与数值模拟结果吻合较好,表明所采用的模型能很好地预测整个修理结构的拉伸性能。分析了整个拉伸过程中层合板斜接挖补修理结构的损伤破坏过程,发现了附加补片引起的应力集中是造成母板中薄弱层过早损伤的原因。讨论了不同斜接挖补角度对修理后结构强度的影响,结论可以引导工艺人员制订合理的修补方案。     

Non-linear analysis of a metal-to-composite scarf joint

A method of analysis for an adhesively-bonded metal-to-composite scarf joint is presented, by which both the metal and the adhesive exhibit non-linear behaviour. The analysis leads to a numerical procedure capable of evaluating stresses developing by shear failure of the joint both for tensile and compressive loading, and eventually to a failure criterion, proposed for the particular type of scarf joint.     

残余应力引起的铣削变形有限元分析

应用弹性力学理论推导出了二维连续铣削过程中工件内应力再分布及其引起变形的计算递推公式.解决了有限元建模、初始应力加载、变形评估等仿真关键技术,建立了残余应力引起铣削变形的二维有限元仿真模型.最后对实例进行了仿真计算,分析了残余应力引起的加工变形规律,并用解析法对仿真结果的进行了验证.     

A novel simultaneous photoelastic and two‐beam interferometric system: I. Dynamic full‐field evaluation of the elasticity modulus profile of polymeric fibres

A novel optical setup for simultaneous capturing of photoelastic and two‐beam interference patterns was designed. The designed optical setup was used to simultaneously record two types of patterns. The first pattern is two‐beam interference pattern, and the second one is photoelastic interference pattern produced by objects under stress. This simultaneous capturing of the two patterns allowed us to calculate the full‐field distribution of the elasticity modulus profile of fibres. A mathematical expression of the profile of the elasticity modulus was derived. This was applied to evaluate the elasticity modulus of anisotropic isotactic polypropylene fibres during stretching processes. The profile of the elasticity modulus was determined for both static and dynamic in situ cases where the propagation of different structural deformations was observed and studied using the designed optical setup. Patterns were given for illustration.     

大型轴流风机叶片的气动弹性数值分析研究

在叶轮机械的流固耦合中以弹性体流固耦合问题最具难度。在这类问题中,需要考虑叶片在运转过程中的弹性变形与振动对流场的影响以及振荡流场的反作用。以北京地铁18号专用轴流风机为例,在考虑叶片变形和流场之间相互影响的耦合状态下,探讨机叶片气固耦合问题的计算方法。采用CFX软件进行流场计算、ANSYS软件进行结构计算,以MFX- ANSYS/CFX为数据耦合平台,应用弱耦合分区法对风机叶片的气动弹性进行数值模拟分析。并与不考虑叶片弹性变形的情况进行对比,发现考虑气动弹性的最大应力几乎是不考虑气动弹性的最大应力的两倍,相应的安全系数相差较大,不考虑叶片的气动弹性容易高估叶片结构的安全性。分析考虑弹性变形对叶片结构安全性的影响,说明叶片的气动弹性分析的必要性和重要性。     

基于满应变准则的受应力约束三维弹性体拓扑优化

提出一种受应力约束三维弹性体的拓扑优化方法：修改的满应变法,即通过反熨迭代修改单元的弹性模量。使三维弹性体的每个单元均处于一种满应变的状态,然后删除弹性模量较低的单元,通过逐渐删除弹性模量较低的单元,使单元最大弹性模量逐渐接近于材料实际的弹性模量,同时单元的最大应力也逐渐接近于材料的许可应力,从而获得满足应力约束条件的三维弹性体的最优拓扑。同时引入结构描述数组的概念,很方便地实现单元的重新划分。数值结果表明该方法很有效,且具有很好的通用性和稳健性。     

Development of a Granular Cohesive Model for Rolling Contact Fatigue Analysis: Crystal Anisotropy Modeling

In rolling contact fatigue (RCF), failure mechanisms are known to be very sensitive to material microstructure. Yet, among the different numerical models developed to predict RCF life, few models use a microstructure representation. A granular cohesive finite element model has been developed to simulate progressive damage of a structure subject to RCF and to investigate failure initiation mechanisms. This article focuses on the implementation of crystal elasticity in the model. The numerical analysis of a representative volume element (RVE) validates the use of cubic elasticity to represent crystal behavior. The influence of the RVE size and the influence of boundary conditions applied on the RVE are evaluated in the finite element approximation framework. With regard to the implementation of cubic elasticity in the RCF model, the generation of stress singularities at triple junctions is first highlighted. Then the average value of the intergranular shear stress is proved to be mesh size independent and therefore can be used as damage criterion. Finally, the influence of crystal elasticity on microcrack distribution is presented.     

Analytical study on elastic transition in short-fiber composites for plane strain case

An analytical approach for short-fiber-reinforced composites is developed for three-dimensional (3D) elastic stress field distribution subjected to an applied axial load. Two sets of exact displacement solutions for matrix and fiber, which are respectively called far-field and transient solutions, are derived based on the theory of elasticity. The superposition state of these solutions are then used to obtain the analytical expressions for the 3D stress field components over the entire composite system, including the fiber end region, through the adding imaginary fiber technique. The fiber/matrix 3D stress field components fully satisfy the equilibrium and compatibility conditions in the theory of elasticity. The stress field components also satisfy the overall boundary, interface continuity, and axial force equilibrium conditions. The analytical results obtained are then validated by finite element method modeling.     

Specific features of stress and strain states of disks and disk flywheels with rigid reinforcing coatings

An approach to calculation of rotating disks with reinforcing coatings taking into account emerging boundary layers is formulated within linear spatial elasticity theory. Analysis of the calculated stress fields in a disk’s base material and in coatings enables one to explain two different phenomena: a significant increase in the load capacity of disks and the energy capacity of flywheels whose face areas are covered with high-modular coatings whose thickness is 0.1–0.6 mm and a reduction in the load capacity (in some cases) if thicker coatings are used. Applicability limits of the standard theory used to calculate disks, in which the stress state is assumed to be a 2D one and boundary layers are absent, are studied.     

Investigation of constantly and transiently propagating cracks in functionally graded materials by dynamic photoelasticity

In this study, the stress intensity factors (SIFs) for steady and transient propagation of cracks in transparent homogeneous functionally graded materials were analyzed by using the photoelasticity technique. The fracture analysis was carried out for the cracks propagating from a region with high elasticity towards low elasticity, as well as the cracks propagating from a region with low elasticity towards high elasticity. The analysis includes cracks propagating (1) at an almost steady speed, and (2) with the rapid increase, followed by a decrease in speed. For cracks with almost constant velocity, the SIFs were greater when a crack started from a high elasticity region, as compared to the cracks which initiated from a low elasticity region. For cracks propagating with rapid acceleration and deceleration, when the strain energy accumulated in the material due to an increase in load or stress was released at the moment of crack propagation, the SIF was momentarily lowered by approximately 45 %–50 % of the static SIF(before crack initiation), which subsequently increases by approximately 30 % eventually, the crack acceleration approaches nearly zero; the SIF decreases and increases respectively as the crack propagates in a material with decreasing and increasing modulus of elasticity.

     

纳米尺度孔边裂纹裂尖Ⅲ型应力强度因子研究

研究了纳米尺度圆孔孔边裂纹在远场反平面剪切载荷作用下的断裂性能。基于Gurtin-Murdoch表面弹性理论和保角映射技术,利用复变弹性理论获得了该类非均匀材料应力场的解析解,给出了裂尖Ⅲ型应力强度因子的闭合解。基于所得解答,研究了孔边的应力场分布规律,讨论了裂尖应力强度因子的尺寸依赖效应以及圆孔相对尺寸对应力强度因子的影响。研究结果表明：孔边应力场呈现非单调分布,表面效应对孔边不同位置应力的影响程度不同;当圆孔裂纹的尺寸在纳米量级时,裂尖应力强度因子具有显著的尺寸依赖效应;圆孔相对裂纹尺寸对裂尖应力强度因子的影响规律受表面性能的制约,同时表面性能对应力强度因子的影响也取决于圆孔的相对尺寸。     

基于MATLAB的谐波光面摩擦传动三波柔轮的应力分析

用弹性理论推导出了谐波光面摩擦传动三波柔轮应力应变公式,并借助MATLAB软件分析了柔轮正应力与波发生器夹角β关系,为波发生器两波轮之间的夹角β的选择提供了理论依据。     

考虑弯曲效应的混元胶接单搭接头应力模型

混元胶接接头是利用多种不同剪切弹性模量的胶层来传递被粘物载荷的单搭接头。它兼具胶层连续性连接和降低端头应力集中等优点,因此能充分利用被粘物材料性能(如复合材料)以提高接头强度。以典型双元胶接接头为对象,考虑加载作用线偏心引起的弯曲效应和胶层剥离正应力,建立被粘物为各向同性的线弹性双元胶接接头应力解析模型。理论模型中的胶层切应力、剥离正应力和上被粘物纵向正应力与精细有限元模型吻合得较好,证实了理论模型的正确性。参数研究中确定了影响混元胶层应力分布的关键耦合参数。     

对边简支载流矩形薄板在电磁场中的稳定性分析

针对对边简支、另一对边固定载流矩形薄板,利用Mathieu方程解的稳定性,研究在电磁场与机械荷载共同作用下的磁弹性稳定性问题。在导出载流薄板在电磁场与机械荷载共同作用下的磁弹性动力稳定方程的基础上,应用Galerkin原理将稳定方程整理为Mathieu方程的标准形式,并将其归结为对Mathieu方程的求解问题。利用Mathieu方程系数、 的本征值关系,得出载流薄板磁弹性动力稳定临界状态的判别方程,并给出当 为小激励时的稳定区域图,以及Mathieu方程稳定解区域和非稳定解区域的分界。最后通过具体数值算例,给出该矩形薄板的磁弹性动力失稳临界状态与相关参量之间的关系曲线。研究结果表明,变化电磁场和通电电流的参数,可以改变电磁力的状态,从而达到控制载流薄板的变形,应力、应变状态及其稳定性的目的。     

NiTi合金涂层的穴蚀过程研究

本文采用磁至伸缩式穴蚀试验机研究爆炸喷涂NiTi合金涂层的穴蚀性能。试验表明，热处理对NiTi合作层的耐穴蚀性能有明显的影响，在180min的试验时间内，穴蚀失重差别可达到2倍。穴蚀形貌观察结果表明，未热处理涂层表现出严重的脱落现象。其原因是适当的热处理工艺可以有效地低涂层的热应力和机械应力，合金元素进行充分的扩散，提高合金成分均匀性，降低相应阻力，提高了NiTi合金涂层的超弹性，从而提高其耐穴蚀性。     

Interface crack of two dissimilar bonded functionally graded strips with arbitrary distributed properties under plane deformations

In this paper the plane elasticity problem of two bonded dissimilar functionally graded strips containing an interface crack with material properties varying arbitrarily is studied. The governing equation in terms of Airy stress function is formulated and exact solutions are obtained for several special variations of material properties in Fourier transformation domain. A multi-layered model is employed to model arbitrary variations of material properties based on two linear-distributed material compliance parameters. The mixed boundary problem is reduced to a system of singular integral equations that are solved numerically. Some numerical examples are given to demonstrate the accuracy, efficiency and versatility of the model. Numerical results show that fracture behavior of materials can be greatly affected by graded variation of elastic modulus and the influence of the specific form of elastic modulus on the fracture behavior of FGM is limited.     

悬转扒杆结构有限元分析

通过将悬转扒杆结构简化为梁一杆单元，进行有限元离散，对扒杆在井架最上和最下两个极端位置进行了有限元计算，主要分析了扒杆在水平吊重和垂直吊重，单臂吊重和双臂吊重等工作状态下结构的受力情况。针对悬转扒杆中的套筒结构，提出了以弹性边界单元，取代套筒的约束作用的方法。采用这种方法，可直接用通用有限元结构分析程序分析带有套筒的复杂结构，且将问题分解、简化。     

A novel approach to thick plate theory suggested by studies in foundation theory

A new approach to the statics of thick, elastic plates is presented. This approach to thick plate theory incorporates transverse normal stress and strain effects as well as those due to transverse shear deformation. The unusual boundary value problem resulting from the kinematic assumptions of this approach is obtained as a consequence of the principle of stationary potential energy. This boundary value problem is nonlinear so that the principle of superposition does not hold and it does not appear to be one which may be treated by standard methods. Therefore an iterative method of approximation is proposed. This iterative method is applied, analytically, to a problem of cylindrical plate bending for which an exact solution is known within the linear theory of elasticity. It is shown that for this particular problem the approximation method converges in two iterations to the exact elasticity solution. Since such simple results are not to be expected in general, there is some discussion of the need to develop a numerical algorithm to implement the proposed iterative method of approximation for arbitrary plate problems. Furthermore, certain theoretical difficulties with the new approach to thick plate theory are discussed.     

On the prediction improvement of transverse stress distributions in cross-ply laminated beams: advanced versus conventional beam modelling

This paper assesses the stress analysis performance of the most commonly used conventional, shear deformable beam theories as well as the advanced beam theories presented in references [Acta Mech. 1997;123:163; Math. Mech. Solids 1997;2:459; Int. J. Solids Struct. 1997;22:2857], by employing a predictor–corrector method. The assessment deals with the accuracy of the distribution of the interlaminar (transverse shear and transverse normal) stresses through the entire beam thickness. As far as simply supported, cross-ply laminated beams are concerned, it compares the corresponding stress analysis results obtained with their exact elasticity counterparts. The conclusions of this type of initial assessment are very much in favour of the advanced beam theories, which involve exponential shape functions of the transverse co-ordinate parameter. Hence, those advanced beam theories are employed for further applications that involve different sets of end boundary conditions for which explicit exact elasticity results are unavailable or very difficult to obtain.     

牵引传动中剪切弹性模量和极限剪切应力的影响

采用新的剪切应力特性公式对弹流润滑接触区的剪应力分布进行了求解，讨论了剪切弹性模量和极限剪切应力对牵引系数的影响，最后通过对剪应力的积分求出EHL下的牵引力，并且讨论了极限剪切应力特性参数的求法。