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Under non-uniform in-situ stress, the casing collapse failure often happens easily, and especially in soft rock the problem is more serious. In addition, only the few scholars do some studies about failure mechanism of cemented casing under non-uniform in-situ stress which has a strong effect on collapse properties of cemented casing, especially testing investigation. Hence, the collapsing test was performed for cemented casing under non-uniform load (NFL) by adopting self-developed testing equipment, by which the radial deformation of cemented casing and damage rules of cement sheath have been measured and the stress-strain laws of cemented casing are obtained during the testing process by the electrical method. The initial yield load and plastic limit load of cemented casing as well as the subsequent yield load have been obtained. By analyzing testing data, the stress-hardening rate and strain-hardening rate after hardening have been determined. The effects of cement sheath on collapse properties of P110SS casing and strain and deformation laws of P110SS casing after hardening have been obtained. The hardening character and failure mechanism of cemented casing have been figured out under NFL. 相似文献
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针对固井过程中由于顶替效率过低、气窜等原因造成水泥环局部缺失的现象,基于超声脉冲反射原理,运用有限元方法建立不同大小、不同方位的水泥环缺失模型,数值模拟了超声波在套管井多层介质中的传播规律。通过提取回波首波幅度、首波的接收时间,对回波进行频谱分析,对比了胶结良好和水泥环缺失两种情况下的时域特征和频域特征。在研究不同方位缺失影响时,引入了缺陷敏感频率,发现在一定激发频率下,有缺陷的位置上敏感频率会出现极大值,不同方位的缺陷有不同的敏感频率,而且区别较为显著,以此可以判断缺失方位。 相似文献
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膨胀土地基中,土的膨胀率和刚度沿深度变化明显:较深位置的膨胀土应力水平较高,一方面遇水的膨胀率较小,另一方面土的刚度较大。该文基于桩-土相互作用机理,利用荷载传递法推导了考虑膨胀土沿深度膨胀率减小、刚度增加的单桩理论求解方程,并得到了级数形式的解析解。理论解与现场和模型试验数据符合较好,尤其是轴力沿桩身发展的模式。之后该文在膨胀土层的平均膨胀率和平均模量不变的前提下,分析了不同膨胀位移分布模式和刚度分布模式对桩受力和变形的影响,发现若按传统的土沿深度膨胀率和刚度为常值计算,将过高地估计单桩的轴力和位移。利用此解析解还讨论了膨胀土中桩的临界压重。 相似文献
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在以往的工作中,利用弹性力学理论获得了地应力场中套管—水泥环—地层系统应力分布的解析表达式。在此基础之上,应用等效介质模型的速度—应力关系式,研究了地应力场中套管井周弹性波速的空间分布规律。分析结果表明,相对裸眼井,套管井应力集中的程度更加明显,由于套管和水泥环的存在,地层应力集中的范围明显缩小到井眼附近。应力集中将导致套管井周波速空间分布的各向异性,对应不同方位径向偏振的横波速度的交叉点明显向井孔附近移动,这意味着垂直偏振的两种弯曲波频散曲线的交点会向高频移动。这一结果表明,在高频情况下,在套管井中应用正交偶极子声测井检测应力导致的各向异性是可行的。 相似文献
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An analytical solution is developed in this paper for viscoelastic axisymmetric plane problems under stress or displacement boundary condition involving time-dependent boundary regions using the Laplace transform. The explicit expressions are given for the radial and circumferential stresses under stress boundary condition and the radial displacement under displacement boundary condition. The results indicate that the two in-plane stress components and the displacement under corresponding boundary conditions have no relation with material constants. The general form of solutions for the remaining displacement or stress field is expressed by the inverse Laplace transform concerning two relaxation moduli. As an application to deep excavation of a circular tunnel or finite void growth, explicit solutions for the analysis of a deforming circular hole in both infinite and finite planes are given taking into account the rheological characteristics of the rock mass characterized by a Boltzmann or Maxwell viscoelastic model. Numerical examples are given to illustrate the displacement and stress response. The method proposed in this paper can be used for analysis of earth excavation and finite void growth. 相似文献
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The two-dimensional circular arc crack solution of Muskhelishvili (Some basic problems of the mathematical theory of elasticity,
P. Noordhoff Ltd, Groningen, Holland, 1953) has been used widely to study curved crack behavior in an infinite, homogeneous
and isotropic elastic material. However, for certain orientations and magnitudes of the remotely applied loads, portions of
the crack will close. Since the analytical solution is incorrect once the crack walls come into contact, the displacement
discontinuity method is combined with a complementarity algorithm to solve this problem. This study uses stress intensity
factors (SIFs) and displacement discontinuities along the crack to define when the analytical solution is not applicable and
to better understand the mechanism that causes partial closure under various loading conditions, including uniaxial tension
and pure shear. Closure is mainly due to material from the concave side of the crack moving toward the outer crack surface.
Solutions that allow interpenetration of the crack tips yield non-zero mode I SIFs, while crack tip closure under proper contact
boundary conditions produce mode I SIFs that are identically zero. Partial closure of a circular arc crack will alter both
mode I and II SIFs at the crack tips, regardless of the positioning or length of the closed section along the crack. Friction
on the crack surfaces in contact changes the total length and positioning of closure, as well as generally decreases the magnitude
of opening along the portions of the crack that are not closed. 相似文献
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Boundary-layer effects in lengthy cross-ply laminated circular cylindrical shell panels under uniform axial extension are investigated by two analytical solutions. First, Reddy??s layerwise theory with state-space approach is utilized to determine the local interlaminar stresses. In this method, the general displacement field is discretized through the shell thickness by a linear shape function. When the shell panel is subjected to an axial force, the axial strain is estimated by an equivalent single-layer theory. Second, the stress-function approach along with Fourier series expansion is applied to develop a novel elasticity solution. The elasticity solution, which is based on simply-support edge conditions, is presented to show the effectiveness of the first solution. The numerical results show good agreements. Interlaminar stresses within various symmetric and unsymmetric cross-ply composite shell panels are then calculated and discussed. It is shown that the normal out-of-plane stress can get high magnitudes along the physical interfaces. 相似文献
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Nonlinear thermoelastic analysis of thick-walled functionally graded piezoelectric cylinder 总被引:1,自引:0,他引:1
Mohammad Arefi 《Acta Mechanica》2013,224(11):2771-2783
This research addresses the nonlinear behavior of a functionally graded piezoelectric (FGP) cylinder under thermal, mechanical and electrical loads. Except the Poisson ratio, the other thermal, mechanical and electrical properties vary continuously along the thickness direction. The geometric nonlinearity was considered in strain–displacement relation. The present paper proposes a novel analytical method for estimating the response of the systems of nonlinear differential equations. The proposed method is modification and combination of Adomian’s decomposition and successive approximation methods. The governing nonlinear differential equations were solved using the proposed analytical method. The nonlinear solutions were presented for different values of nonhomogenous index. For validation of the results and justifying the necessity of the present study, the present results were compared with results obtained using the linear analysis. Due to using the functionally graded cylinder in serious environments such as chemical and weapon equipments or adjustable and precise condition, a nonlinear analysis for these materials is necessary. A nonlinear analysis improves the results significantly. A maximum of 5% improvement for electric potential and 9% for radial displacement were attained employing this nonlinear analysis rather than a linear analysis. These considerable improvements can present a confidence and adjustable tool for manufacturing and design of sensors and actuators with better accuracy. 相似文献
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《Composites Part B》2013,45(1):274-282
The plane stress problem of an orthotropic functionally graded beam with arbitrary graded material properties along the thickness direction is investigated by the displacement function approach for the first time. A general two-dimensional solution is obtained for a functionally graded beam subjected to normal and shear tractions of arbitrary form on the top and bottom surfaces and under various end boundary conditions. For isotropic case explicit solutions are given to some specific through-the-thickness variations of Young’s modulus such as exponential model, linear model and reciprocal model. The influence of different grade models on the stress and displacement fields are illustrated in numerical examples. These analytical solutions can serve as a basis for establishing simplified theories and evaluating numerical solutions of functionally graded beams. 相似文献
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Some soil and most rock masses contained defects (joints, cracks, bedding planes, fissures in clay, etc.). Beyond the peak shear strength of a mass of soil or rock, the stress falls as the strain increases. In this paper, the plane strain problem with double edge-cracks under shear loads is analysed based on linear elastic fracture mechanics but with finite stress concentration concept. We assumed that the fissured clay is a kind of strain-softening material and the growth of slip surface is along the maximum shear stress plane. The growth of slip surfaces in the progressive failure is expressed by the shear loads and slip displacement curves, which are obtained under the crack tip opening displacement criteria (CTODc) or the energy release rate criteria (Jc). The residual slip displacements are also taken into account by cumulating the elastic ones. 相似文献
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Erik Steen Kristensen Niels Flemming Madsen 《International journal for numerical methods in engineering》1976,10(5):1007-1019
The shape of a plate in plane stress is determined, such that the maximum elastic stress corresponding to given loads is minimized. The shape of the boundary is approximated by a series and optimization is carried out by solving a sequence of linearized minimum–maximum problems using linear programming. The optimization problem is extended to include multiple loading cases and geometrical constraints. The stress derivatives are found using analytical expressions for stiffnesses and stiffness derivatives of the finite elements. For the optimum design of a hole in an infinite plate under biaxial stretching the numerical result is compared with an analytical solution. As another example the method is used to optimize the edge shape of a shape of a junction in a web frame. 相似文献
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Applying the Stroh theory and based on the works of Hwu and Ting (1989), the complex function solution of stress and displacement fields around an open borehole in intrinsic anisotropic formation under horizontal terrestrial stress field is obtained. For cross-dipole flexural wave propagation along borehole axis, using the perturbation method, the acoustoelastic equation describing the relation between the alteration in phase velocity and terrestrial stress as well as formation intrinsic anisotropy is derived. At last, the numerical examples are provided for both the cases of fast and slow formation where the symmetry axis of a transversely isotropic (TI) formation makes an angle with the borehole axis. The phase velocity dispersion curves of borehole flexural wave and the corresponding velocity-stress coefficient are investigated. Computational results indicate that different from the stressed intrinsic isotropic formation situation, the variation in the phase velocity of flexural wave in stressed intrinsic anisotropic formation is dominated by two factors, one is the intrinsic formation anisotropy itself and the other is the stress-induced anisotropy. The former factor merely causes the borehole flexural wave split while the latter factor induces the dispersion curves intersection for two flexural waves polarized orthogonally. The combined effect of the two factors could strengthen or weaken the phenomenon of crossover for flexural wave dispersion curves. Thus, the dispersion curves of flexural waves may not intersect even under the unequal horizontal terrestrial stress field, whereas it is still possible to observe the crossover of the flexural wave dispersion curves under the equal horizontal terrestrial stress field. The polarized direction of the low-frequency fast flexural wave is no longer consistent with the direction of the maximum horizontal terrestrial stress all the time. Therefore, the crossover of the borehole flexural wave dispersion curves means that the terrestrial stress must exist. On the other hand, we can't exclude the possibility of the existence of terrestrial stress even if the flexural wave dispersion curves do not intersect. Based on the above researches, the method for terrestrial stress inversion from borehole flexural wave dispersion curves obtained by cross-dipole sonic logging in stressed intrinsic anisotropic formation is simply discussed. 相似文献