首页 | 官方网站   微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 93 毫秒
1.
Based on three-dimensional elastic equations for piezoelectric materials, the state equations for piezoelectric circular plate under axisymmetric deformation are derived. Applying Hankel transform to them and letting the free boundary terms resulting from Hankel transform be zero, a set of ordinary differential equations with constant coefficients and associated boundary conditions are obtained. Furthermore, two exact solutions corresponding to generalized rigid slipping and generalized elastic simple support are deduced. Then, the governing equations obtained reduce to equations for axisymmetric problem of transversely isotropic circular plate. Under the two types of boundary conditions of elastic simple support and rigid slipping, exact solutions are derived. Finally, numerical results are presented and applicability of the classical plate theory is discussed.  相似文献   

2.
This paper is devoted to developing a yield criterion that can model the asymmetry and anisotropy in yielding of pressure insensitive metals,in terms of accuracy and simplicity of formulation.First,a new isotropic yield criterion,which can model the asymmetry in yielding of pressure insensitive metals,is proposed.Further,using Cazacu’s generalizations to anisotropic conditions of the invariants of the deviatoric stress,the proposed isotropic yield criterion is extended to orthotropy.The proposed anisotropic criterion has a quite simple form,and the number of material constants involved is only half of that of Cazacu’s(2004) yield criterion.Compared to Hill’s(1948) yield criterion,the proposed anisotropic yield criterion has three additional constants,which are used to model the tension-compression asymmetry of materials.All the material constants involved in the criterion can be determined by simple tests.The proposed criterion reduces to Hill’s(1948) yield criterion if the tensile and compressive yield stresses are equal.In other words,the proposed anisotropic yield criterion can be considered as an extension of Hill’s(1948) criterion to tension-compression asymmetry materials.The anisotropic yield criterion is used to describe the plastic response of Cu-Al-Be shape memory alloy(data after Laydi and Lexcellent) and Ni3Al based intermetallic alloy IC10 sheets.It is shown that the proposed yield criterion can describe very well the asymmetry and anisotropy observed in those materials.  相似文献   

3.
For vision-based mobile robot navigation, images of the same scene may undergo a general affine transformation in the case of significant viewpoint changes. So, a novel method for detecting affine invariant interest points is proposed to obtain the invariant local features, which is coined polynomial local orientation tensor(PLOT). The new detector is based on image local orientation tensor that is constructed from the polynomial expansion of image signal. Firstly, the properties of local orientation tensor of PLOT are analyzed, and a suitable tuning parameter of local orientation tensor is chosen so as to extract invariant features. The initial interest points are detected by local maxima search for the smaller eigenvalues of the orientation tensor. Then, an iterative procedure is used to allow the initial interest points to converge to affine invariant interest points and regions. The performances of this detector are evaluated on the repeatability criteria and recall versus 1-precision graphs, and then are compared with other existing approaches. Experimental results for PLOT show strong performance under affine transformation in the real-world conditions.  相似文献   

4.
Research advances of un-symmetric constitutive equation of anisotropic fluid,influence of un-symmetric stress tensor on material functions,vibrational shear flow of the fluid with small amplitudes and rheology of anisotropic suspension were reported.A new concept of simple anisotropic fluid was introduced.On the basis of anisotropic principle,the simple fluid stress behaviour was described by velocity gradient tensor F and spin tensor W instead of velocity gradient tensor D in the classic Leslie-Ericksen continuum theory.Two relaxation times analyzing rheological nature of the fluid and using tensor analysis a general form of the constitutive equation of co-rotational type was introduced.More general model LCP-H for the fluid was developed.The unsymmetry of the shear stress was predicted by the present continuum theory for anisotropic viscoelastic fluid-LC polymer liquids.The influence of the relaxation times on material functions was specially studied.It is important to study the unsteady vibrational rotating flow with small amplitudes,as it is a best way to obtain knowledge of elasticity of the LC polymer,i.e.dynamic viscoelasticity.For the shear-unsymmetric stresses,two shear stresses were obtained thus two complex viscosities and two complex shear modulus(i.e.first and second one) were introduced by the constitutive equation which was defined by rotating shear rate introduced by author.For the two stability problems of fluid,such as stability of hydrodynamic flow and orientational motion,were discussed.The results show that the polymer suspension systems exhibit anisotropic character.The PNC systems can exhibit significant shear-thinning effects.For more concentrated polymer nano-suspensions,the first normal stress difference change from positive to negative,which is similar to LC polymer behavior.  相似文献   

5.
Three high dimensional spatial standardization algorithms are used for diffusion tensor image (DTI) registration, and seven kinds of methods are used to evaluate their performances. Firstly, the template used in this paper was obtained by spatial transformation of 16 subjects by means of tensor-based standardization. Then, high dimensional standardization algorithms for diffusion tensor images, including fractional anisotropy (FA) based diffeomorphic registration algorithm, FA based elastic registration algorithm and tensor-based registration algorithm, were performed. Finally, 7 kinds of evaluation methods, including normalized standard deviation, dyadic coherence, diffusion cross-correlation, overlap of eigenvalue-eigenvector pairs, Euclidean distance of diffusion tensor, and Euclidean distance of the deviatoric tensor and deviatoric of tensors, were used to qualitatively compare and summarize the above standardization algorithms. Experimental results revealed that the high-dimensional tensor-based standardization algorithms perform well and can maintain the consistency of anatomical structures.  相似文献   

6.
The present study aims at developing a new method--Random Microstructure Finite Element Method (RMFEM) for the effective properties of com posite materials.In this method, a random microstructure model is used to simulate the microstructure of the real composite materials.The physical fields in such a random microstructure model under specified boundary and initial conditions are analyzed by finite element method.The effective properties of composite materials can be obtained from the analysis results.As verification, some effective properties of composite materials, such as elastic module.thermal expansion coefficient, thermal conductivity and elastoplastic properties,are investigated by random microstructure finite element method.The numerical results are given together with the experimental data.It is revealed that the random microstructure finite element method is a very valid method for the determination of the effective properties of composite materials.  相似文献   

7.
Analytical solutions of thermal stresses in multilayered elastic system whose materials characteristics are dependent on temperature are derived by a transfer matrix and integral transformation method.The resulting formulation is used to calculate thermal stresses in the low temperature cracking problem of asphalt pavement.Numerical simulations and analyses are performed using different structural combinations and material characteristics of base course.And fracture temperatures are predicted for a given flexible pavement constructed with three types of asphalt mixtures based on the calculated results and experimental data.This approach serves as a better model for real pavement structure as it takes into account the relationships between the material characteristics and temperature in the pavement system.  相似文献   

8.
In this paper, the scattering of elastic waves by penny-shaped interface crack in a layered half space is discussed. From the solution of an integral equation, an expression of the dynamic stress intensity factor is derived which is of partictlar significance in fracture mechanics. when the incident harmonic p wave is perpendicular to the crack face, it becomes an axisymmetric elastic dynamic problem. Suppose that a layered half space is composed of a single isotropic elastic layer and an isotropic elastic half space of a different material, and in the region o≤r≤l, z=o, there is a  相似文献   

9.
Based on the basic equations of two-dimensional, transversely isotropic, piezoelectric elasticity, a group of general solutions for body force problem is obtained. And by utilizing this group of general solutions and employing the body potential theory and the integral method, the closed-form solutions of displacements and electric potential for an infinite piezoelectric plane loaded by point forces and point charge are acquired. Therefore, the fundamental solutions, which are very important and useful in the boundary element method (BEM), are presented.  相似文献   

10.
1 Introduction Two-flux method is considered as a simple model and can be used to predict heatflux in 1-D radiative heat transfer. In the original two-flux method[1,2], the radiation fieldwas assumed to be isotropic. But for gas-particles mixture in combustion environments,the scatterings of particles are usually anisotropic, and the original two-flux methodgives critical errors when ignoring this anisotropy. It is desirable to have a two-flux ra-diative transfer model to be applied rega…  相似文献   

11.
多晶体金属材料由微小晶粒集合而成,晶粒的物理性质和金属的微结构决定了该多晶体材料的宏观力学性质.常见金属多晶体材料的晶粒有面心立方、体心立方和密排六方结构.基于Voigt模型,Morris和Sayers给出了立方晶粒正交集合的弹性本构关系,Huang则给出了立方晶粒各向异性集合的弹性本构关系.假设一材料是由大量的准D5晶粒集合而成(称为准多D5晶体),利用准D5晶粒的对称性研究D5晶粒弹性本构关系,然后基于Voigt模型和Reuss模型分别推导出准D5晶粒各向异性集合的有效弹性刚度张量和有效弹性柔度张量.在本文中,品粒取向分布函数(ODF)w(R)用来描述多晶体中的晶粒取向为R的可能性密度,给出了弹性本构与织构系数之间的关系表达式.  相似文献   

12.
立方晶粒各向异性集合金属的非线性弹性本构关系   总被引:1,自引:4,他引:1  
在Voigt模型下,Barsch(1968)和Johnson(1985)分别给出了立方晶粒各向同性集合和正交集合的非线性弹性本构关系.本文推导出基于Voigt模型的、比Barsch和Johnson结果更一般的、立方晶粒各向异性集合的非线性弹性本构关系,这里金属的各向异性通过织构系数来描述.  相似文献   

13.
本文完全利用正交张量群引进并规定了划分同性概念及其基本属性;仅仅借助基本的张量代数较系统而又独立地表明如何构造有限维欧氏空间上一般的各向同性、划分同性的张量(或多项式齐次张量泛函)的结构形式。  相似文献   

14.
本文通过对损伤效应张量的变换,使损伤理论扩展到各向异性损伤的领域,变换后的损伤效应张量克服了只适用于主应力方向的局限性,从而可应用于工程实际的破坏分析。纯扭试验证实了本理论在工程实际中的应用性和损伤参数的可测性,试验还表明各向同性材料的各向异性损伤特性,且应力、应变越大,各向异性越显著。  相似文献   

15.
由于各向异性等离子体介质中的介质参数是张量形式,而在各向同性介质中为标量形式,故在研究各向异性等离子体与电磁波的相互作用与分析各向同性媒质的方法就不同.采用线性插值的方法给出各向异性等离子体介质中的FDTD离散式,编写了程序并进行了数值计算,给出与解析方法比较结果,两者符合的很好,并给出等离子体球的电磁散射的若干算例.结果可应用于等离子体的电波传播、天线等领域.  相似文献   

16.
采用损伤影响张量,研究了弹性各向异性损伤时的有效应力,按照Lemaitre应变等价性假设,建立了弹性各向异性损伤应力应变关系,并引入了材料的有效柔度张量.由于应变应该具有对称性,因此要求有效柔度张量具有对称性.本文采用Sidoroff的弹性能等值假设和弹性余能等值假设构造了材料的有效柔度张量.推导出损伤应变能释放率张量.  相似文献   

17.
各向同性损伤理论是建立在材料是均匀的、各向同性的以及损伤也是各向同性的假设基础之上.对于初始各向异性材料,损伤演化也呈明显的各向异性.一般地可用一八阶的损伤张量来描述这种材料的损伤,利用应变等效原理可将损伤张量减少到四阶.这个四阶损伤张量中独立元素的个数和材料及损伤的对称性有关,对各向同性损伤,损伤材料独立的材料参数只有两个,它们可用无损伤时材料的Lame系数和损伤参数来表示.  相似文献   

18.
通过电磁场能量密度和能流密度的关系,利用麦克斯韦方程组,推证各向异性媒质中介质张量是二阶对称张量。  相似文献   

19.
本文详细研究了重力作用下圆锥的位移和应力分布。指出在直线型各向异性体中的应力分布与各向同性体是一样的,即应力与弹性常数无关。而曲线型各向异性体的应力分布则与弹性常数有关。利用文[8]的研究结果,本文给出了自重作用下球面各向同性圆锥拉伸(或压缩)和弯曲问题的解。  相似文献   

20.
用弹性波速计算正交各向异性岩体的裂隙张量   总被引:4,自引:0,他引:4       下载免费PDF全文
初步尝试了运用弹性波速确定岩体的裂隙张量;首先将岩体视为正交各向异性介质,基于裂隙岩体的应变体积平均,从裂隙引起的间断位移出发,导出裂隙张量与由裂隙引起的柔度张量增量之间的关系;然后根据正交各向异性岩体的波动理论,建立了岩体裂隙张量、等效弹性参数和弹性波速三者之间的相关关系。根据这些关系,给出了二阶、四阶裂隙张量的弹性波速计算过程。含裂缝水泥砂浆试件的试验结果表明,采用本文计算方法获得的裂隙张量基本能反映出裂隙的分布情况。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号