共查询到20条相似文献,搜索用时 31 毫秒
1.
《International Journal of Solids and Structures》2007,44(22-23):7444-7456
Two-dimensional in-plane wave propagation and localization in the disordered layered piezoelectric phononic crystals with material 6 mm are investigated taking the electromechanical coupling into account. The electric field is approximated as quasi-static. The analytical solutions of elastic waves are obtained. The 6 × 6 transfer matrix between two consecutive unit cells is obtained by means of the mechanical and electrical continuity conditions. The expressions of the localization factor and localization length in the disordered periodic structures are presented by regarding the variables of the mechanical and electrical fields as the elements of the state vector. The numerical results of the localization factors and localization lengths are presented for two kinds of disordered piezoelectric phononic crystals, i.e. ZnO–PZT–5H and PVDF–PZT–5H piezocomposites. It is seen from the results that the incident angle of elastic waves and the thickness of the piezoelectric ceramics have significant effects on the wave localization characteristics. For different piezoelectric phononic crystals, the effects of the incident angle are very different. Moreover, with the increase of the disorder degree, the localization phenomenon is strengthened. 相似文献
2.
Considering the mechnoelectrical coupling, the localization of SH-waves in disordered periodic layered piezoelectric structures is studied. The waves propagating in directions normal and tangential to the layers are considered. The transfer matrices between two consecutive unit cells are obtained according to the continuity conditions. The expressions of localization factor and localization length in the disordered periodic structures are presented. For the disordered periodic piezoelectric structures, the numerical results of localization factor and localization length are presented and discussed. It can be seen from the results that the frequency passbands and stopbands appear for the ordered periodic structures and the wave localization phenomenon occurs in the disordered periodic ones, and the larger the coefficient of variation is, the greater the degree of wave localization is. The widths of stopbands in the ordered periodic structures are very narrow when the properties of the consecutive piezoelectric materials are similar and the intervals of stopbands become broader when a certain material parameter has large changes. For the wave propagating in the direction normal to the layers the localization length has less dependence on the frequency, but for the wave propagating in the direction tangential to the layers the localization length is strongly dependent on the frequency.The project supported by National Natural Science Foundation of China (10632020, 10672017 and 20451057). 相似文献
3.
4.
Yize Wang Fengming Li Kikuo Kishimoto Yuesheng Wang Wenhu Huang 《Acta Mechanica Solida Sinica》2008,21(6):529-535
The elastic wave localization in disordered periodic piezoelectric rods with initial stress is studied using the transfer matrix and Lyapunov exponent method. The electric field is approximated as quasi-static. The effects of the initial stress on the band gap characteristics are investigated. The numerical calculations of localization factors and localization lengths are performed. It can be observed from the results that the band structures can be tuned by exerting the suitable initial stress. For different values of the piezoelectric rod length and the elastic constant, the band structures and the localization phenomena are very different. Larger disorder degree can lead to more obvious localization phenomenon. 相似文献
5.
Summary By regarding geomaterials under loading as a mixture of intact and damaged parts, we investigate the influence of damage on the properties of strain localization in elastoplastic geomaterials at plane stress and plane strain. Conditions for the onset of strain localization including the effects of damage are derived for the cases of plane strain and plane stress. Discussed are the inclination of the localized band and the hardening modulus corresponding to the onset of strain localization. It is shown that the properties of the strain localization are dependent on the damage and the capacity of bearing hydrostatic pressure by the damaged part, and that damage may induce an earlier onset of strain localization and lead to instability of a geomaterial.accepted for publication 11 March 2004 相似文献
6.
岩石变形破坏局部化的白光数字散斑相关方法研究 总被引:7,自引:1,他引:6
本文采用白光数字散斑相关方法研究了岩石的变形局部化,通过实验测定了煤岩变形局部化的开始时刻、演经过程及局部化带的宽度,本文的测试结果为研究岩石变形非均匀演化过程及岩石细观本构参数的测定打下了基础。 相似文献
7.
8.
2010城市地质环境与可持续发展论坛(二号通知) 总被引:1,自引:0,他引:1
Zhichun Yang 《力学学报》2010,18(2):290
用峰值振幅比定义局部化度,用平尾刚度与垂尾刚度的比值定义耦合度. 基于T
尾结构的质量失调模型,从模态峰值振幅比、失调耦合比、常规摄动和近频摄动4个角度,
提出4个不同的局部化判据来预测T尾结构模态局部化的发生. 对一个T尾结构模型局部化
振动的数值分析结果表明: (1) T尾结构系统一般具有弱耦合性,小量的失调就可以使T尾
结构发生模态局部化; (2) T尾结构一旦发生模态局部化,不但使对称一弯模态和反对称一
弯模态的振型发生较大改变,而且其模态频率也将改变,模态频率的改变在失调量的正负区
间内具有唯一性; (3) 算例验证了4个模态局部化判据的可行性和有效性,为T尾结构的模
态局部化分析和设计提供了依据. 相似文献
9.
《International Journal of Solids and Structures》2005,42(24-25):6457-6474
The two-dimensional wave propagation and localization in disordered periodic layered 2-2 piezoelectric composite structures are studied by considering the mechanic-electric coupling. The transfer matrix between two consecutive sub-layers is obtained based on the continuity conditions. Regarding the variables of mechanical and electrical fields as the elements of the state vector, the expression of the localization factors in disordered periodic layered piezoelectric composite structures is derived. Numerical results are presented for two cases—disorder of the thickness of the polymers and disorder of the piezoelectric and elastic constants of the piezoelectric ceramics. The results show that due to the piezoelectric effects, the characteristics of the wave localization in disordered periodic layered piezoelectric composite structures are different from those in disordered periodic layered purely elastic ones. The wave localization is strengthened due to the piezoelectricity. And the larger the piezoelectric constant is, the larger the wave localization factors are. It is found that slight disorder in the piezoelectric or elastic constants of the piezoelectric ceramics can lead to more prominent localization phenomenon. 相似文献
10.
An explicit numerical implementation is described, for a constitutive model of glassy polymers, previously proposed and validated. Then it is exploited within a Finite Element continuum model, to simulate spontaneous strain localization (necking) occurring during extension of a prismatic bar of a typical glassy polymer. Material parameters for atactic polystyrene are employed. The material model is physically based and highly non-linearly viscoelastic. Three of its principal features are critical in simulations of strain localization: rate-dependence of plastic flow stress; strain-induced structural rejuvenation, represented by increase of Tool’s fictive temperature and leading to pronounced post-yield strain softening; and molecular alignment during extension, giving rise to strain-hardening. In all simulations there is a peak in nominal stress, satisfying the condition for localization to occur. Nevertheless, the simulations show that the process of strain localization varies considerably, depending on details of the extension sequence and on assumed values for certain material parameters. A characteristic feature observed is that strain localization in such a material occurs in two stages. There is an initial spurt associated with strain-softening, followed by a slower growth of localization that eventually subsides, ultimately giving way to uniform extension of the neck. But the details of evolution of the strain distribution vary greatly. The rapidity and severity of localization are increased by decreased temperature, increased strain-rate or greater structural rejuvenation. A simple one-dimensional stability analysis is successful in explaining the results. 相似文献
11.
《International Journal of Plasticity》1995,11(1):41-64
The basic framework for an energy-based theory of localization in dynamic viscoplasticity was recently developed by Cherukuri and Shawki [1994]. In this framework, the total kinetic energy serves as a single parameter for the characterization of the full localization history. A characteristic evolution profile of the kinetic energy was shown to correspond to a localizing deformation. Here, the energy-based characterization of localization is implemented toward the improved understanding of the mechanics of shear band formation. In particular, the influence of three primary dimensionless groups on localization is examined. These groups are referred to as the inertia number, the diffusion number, and the dissipation number. The limits of applicability of the quasistatic assumption as well as the adiabatic deformation assumption are also addressed. Computational evidence indicates that the dissipation number plays a significant role in determining the material localization sensitivity. 相似文献
12.
In this paper, the propagation and localization of Rayleigh waves in disordered piezoelectric phononic crystals with material 6 mm are studied taking the electromechanical coupling into account. The electric field is approximated as quasi-static. The analytical solutions of Rayleigh waves are obtained. The 6×6 transfer matrix between two consecutive unit cells is obtained by means of the mechanical and electrical continuity conditions. The expression of the localization factor in disordered periodic structures is presented by regarding the variables of the mechanical and electrical fields as the elements of the state vector. The numerical results for a piezoelectric phononic crystal—PVDF-PZT-2 piezocomposite—are presented and analyzed. From the results we can see that the localization is strengthened with the increase of the disorder degree. The characteristics of the passbands and stopbands are influenced by different ratios of the thickness of the polymers to that of the piezoelectric ceramics. Disorder in elastic constant c11 of PZT-2 can also result in the localization phenomenon. The propagation and localization of Rayleigh waves in piezoelectric phononic crystals may be controlled by properly designing some structural parameters. 相似文献
13.
The diffuse mode bifurcation of elastoplastic solids at finite strain is investigated. The multiplicative decomposition of deformation gradient and the hyperelasto-plastic constitutive relationship are adapted to the numerical bifurcation analysis of the elastoplastic solids. First, bifurcation analyses of rectangular plane strain specimens subjected to uniaxial compression are conducted. The onset of the diffuse mode bifurcations from a homogeneous state is detected; moreover, the post-bifurcation states for these modes are traced to arrive at localization to narrow band zones, which look like shear bands. The occurrence of diffuse mode bifurcation, followed by localization, is advanced as a possible mechanism to create complex deformation and localization patterns, such as shear bands. These computational diffuse modes and localization zones are shown to be in good agreement with the associated experimental ones observed for sand specimens to ensure the validity of this mechanism. Next, the degradation of horizontal sway stiffness of a rectangular specimen due to plane strain uniaxial compression is pointed out as a cause of the bifurcation of the first antisymmetric diffuse mode, which triggers the tilting of the specimen. Last, circular and punching failures of a footing on a foundation are simulated. 相似文献
14.
Yi-Ze Wang Feng-Ming Li Kikuo Kishimoto Yue-Sheng Wang Wen-Hu Huang 《Archive of Applied Mechanics (Ingenieur Archiv)》2010,80(6):629-640
In this paper, the propagation and localization of elastic waves in randomly disordered layered three-component phononic crystals
with thermal effects are studied. The transfer matrix is obtained by applying the continuity conditions between three consecutive
sub-cells. Based on the transfer matrix method and Bloch theory, the expressions of the localization factor and dispersion
relation are presented. The relation between the localization factors and dispersion curves is discussed. Numerical simulations
are performed to investigate the influences of the incident angle on band structures of ordered phononic crystals. For the
randomly disordered ones, disorders of structural thickness ratios and Lamé constants are considered. The incident angles,
disorder degrees, thickness ratios, Lamé constants and temperature changes have prominent effects on wave localization phenomena
in three-component systems. Furthermore, it can be observed that stopbands locate in very low-frequency regions. The localization
factor is an effective way to investigate randomly disordered phononic crystals in which the band structure cannot be described. 相似文献
15.
Mode Localization in Dynamics and Buckling of Linear Imperfect Continuous Structures 总被引:2,自引:0,他引:2
Localization phenomena in one-dimensional imperfect continuous structures are analyzed, both in dynamics and buckling. By using simple models, fundamental concepts about localization are introduced and similarities between dynamics and buckling localization are highlighted. In particular, it is shown that strong localization of the normal modes is due to turning points in which purely imaginary characteristic exponents assume a non zero real part; in contrast, if turning points do not occur, only weak localization can exist. The possibility of a disturbance propagating along the structure is also discussed. A perturbation method is then illustrated, which generalizes the classical WKB method; this allows the differential problem to be transformed into a sequence of algebraic problems in which the spatial variable appears as a parameter. Applications of the method are worked out for beams and strings on elastic soil. All these structures are found to have nearly-defective system matrices, so their characteristic exponents are highly sensitive to imperfections. 相似文献
16.
17.
Shigenobu Okazawa 《International Journal of Non》2010,45(1):35-41
Necking localization is common unstable behavior in ductile solids. This paper describes the unified necking localization mechanism. After describing one-dimensional instability problem, general material and structural instability criteria are formulated and the formulation is validated by non-linear finite element analysis. The trigger of necking localization is structural bifurcation and the behavior from a uniformly deformed state to ultimate localization just before fracture is continuous structural instability. 相似文献
18.
19.
《International Journal of Plasticity》2004,20(7):1227-1249
The issues concerning the localization of plastic deformation in commercial Zr alloys used in the nuclear power industry are addressed. The possible types of deformation localization pictures corresponding with the respective stages of plastic flow are described. These are shown to be various kinds of self-excited wave processes of plastic flow. The dislocation structure of the material occurring within and in between the nuclei of localized deformation is investigated. The use of the self-excited wave patterns of plastic flow localization as an additional source of information on the mechanical properties of metals and alloys is substantiated. 相似文献