Numerical solution of the curved rigid line problem in an infinite plate

Summary This paper deals with the problem of evaluating the stress singularity coefficients at the tips of a rigid line in an infinite plate. If the traction difference between the upper and lower borders of the rigid line is taken as an unknown function and the displacement of the curved rigid line as the right-hand term of the integral equation, then a new integral equation for the curved rigid line problem is obtained which is presented in this paper. The newly obtained integral equation has a logarithmic singular kernel. To solve the integral equation an interpolation equation for the traction difference functions (the undetermined functions in the integral equation) is proposed. A numerical examination is carried out to demonstrate the efficiency of the proposed technique. Also two numerical examples are given in this paper.

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Numerische lösung des problems einer gekrümmten linie als starrer einschlu\ in einer unendlichen platte

Übersicht Vorgeführt wird die Bestimmung von Spannungssingularitätsfaktoren an den Enden einer starren Kurve in einer unendlichen Platte. Wenn die Spannungsdifferenz an beiden Seiten der starren Linie als unbekannte Funktion und die Verschiebung dieser Linie als rechte Seite der Integralgleichung gewählt werden, erhält man eine neue Integralgleichung, die hier vorgestellt wird. Diese enthält einen logarithmisch singulären Kern. Um sie zu lösen, wird eine Interpolationsfunktion für die unbekannten Funktionen der Spannungsdifferenzen vorgeschlagen und ein numerischer Test zur Demonstration der Leistungsfähigkeit der Methode durchgeführt. Zwei numerische Beispiele werden vorgestellt.

     

穿过两相材料界面的曲线型刚性线

利用两相材料中集中力的基本解，建立了求解曲线型刚性线夹杂和两相材料界面相交问题的弱奇异积分方程。通过Cauchy型奇异积分方程主部分析方法，得出穿过两相材料界面的曲线型刚线性在交点处的奇性应力指数及交点处角形域内的奇性应力，并利用奇性应力定义了交点处的应力奇异因子。通过对弱奇异积分方程的数值求解，得出了刚性线端点和交点处的应力奇异因子。     

穿过反平面圆形夹杂界面的曲线型刚性线

利用复变函数方法和叠加原理建立了求解刚性线夹杂问题的弱奇积分方程,利用Ｃａｕｃｈｙ型奇异积分方程主部分方法,研究了穿过反平面圆夹杂界面的曲线型刚性线夹杂在界面交点处点处的奇性应力指数以及交点处角形域内的奇性应力,并定义了交点处的应力奇性因子。利用所得的奇性应力指数,通过对弱奇异积分方程的数值求解,得出了刚性线端点和交点处的应力奇性因子。     

饱和地基上弹性圆板的动力响应

研究弹性圆板在饱和地基上的垂直振动特性,即首先应用Hankel变换方法求解饱和土波动方程,然后按混合边值条件建立饱和地基上圆板垂直振动的对偶积分方程,用一种简便的方法,对偶积分方程可化为易于数值计算的第二类Fredholm积分方程。文末的数值分析得出了板振动的一些规律性,由此表明当板的挠曲刚度D趋于无穷大且不计板的质量时,其结果和无质量刚性圆盘在饱和地基上的振动特性完全一致。     

A cracked beam or plate transversely loaded by a stamp

In this paper the problem of an infinite elastic beam or a plate containing a crack is considered. The medium is loaded transversely through a stamp which may be rigid or elastic. The problem is a coupled crack-contact problem which cannot be solved by treating the crack and contact problems separately and by using a superposition technique. First the Green's functions for the general case are obtained. Then the integral equations for a cracked infinite strip loaded by a frictionless stamp are obtained. With the question of fracture in mind, the primary interest in the paper has been in calculating the stress intensity factors. The results are given for a rigid flat stamp with sharp edges and for an elastic curved stamp. The effect of friction at the supports on the stress intensity factors is also studied and a numerical example is given.     

用面力边界积分方程求解断裂力学J积分

证明面力边界积分方程被积函数的散度等于零，应用Stokes公式，对平面线弹性问题，将面力边界积分的求解转化为边界点的位移势函数的点值计算。应用边界积分方程的求解结果，推导出J积分亦可表示为边界点的积分势函数的点值计算，无需进行数值积分，实例计算说明该方法的有效性。     

Solutions of the integral equations for shearing stresses in two-material curved beams

In the same way as shearing stresses for curved beams made of one material, the problem of evaluating the shearing stresses of composite curved beams is also reduced to one of solving the integral equations. Solving directly two integral equations can derive the formulae of shearing stresses, which satisfy not only the equilibrium equations but also the static boundary conditions on the boundary surfaces of the beams. The present analysis will be used to investigate the shearing stresses of a cantilevered curved beam made of two materials, which is loaded by a concentrated force at its free end. The comparison between the numerical results of shearing stresses obtained using the equations developed in this paper and a three-dimensional finite element analysis shows excellent agreement.     

Dynamic Response of a Piezoelectric Material with a Conducting Rigid Inclusion

The problem of a conducting rigid inclusion embedded in an infinite piezoelectric matrix is considered under the action of combined electromechanical impact loads. By using integral transform techniques, the mixed initial-boundary value problem for the case of anti-plane shear load and in-plane electric field is transformed into two systems of dual integral equations, the solutions of which give the singularity coefficients of electroelastic field near the inclusion tips in closed-form in the Laplace transform domain. Numerical results for the stress singularity coefficient in the physical space are presented graphically by numerically solving the resulting Fredholm integral equation and carrying out the numerical inversion of Laplace transform for a PZT-5H material with a conducting rigid line inclusion.     

和界面接触的刚性线夹杂对SH波的散射

利用积分变换方法，得出了两相材料中单位简谐力的格林函数。根据简谐集中力的格林函数得出了和界面接触的刚性线的散射场。利用无穷积分的性质，把和界面接触刚性线的散射场分解为奇异部分和有界部分。通过分解后的散射场建立了和界面接触剐性线在SH波作用下的Cauchy型奇异积分方程。根据所得奇异积分方程和刚性线的散射场得到了刚性线端点的奇异性阶数及奇性应力。应用刚性线端点的奇性应力定义了刚性线端点的应力奇异因子。对所得Cauchy型奇异积分方程的数值求解，可得刚性线端点的应力奇异因子。     

Stress-strain state of an anisotropic plate with an elliptic hole and thin rigid inclusions

The stress-strain state of an anisotropic plate containing an elliptic hole and thin, absolutely rigid, curvilinear inclusions is studied. General integral representations of the solution of the problem are constructed that satisfy automatically the boundary conditions on the elliptic-hole contour and at infinity. The unknown density functions appearing in the potential representations of the solution are determined from the boundary conditions at the rigid inclusion contours. The problem is reduced to a system of singular integral equations which is solved by a numerical method. The effects of the material anisotropy, the degree of ellipticity of the elliptic hole, and the geometry of the rigid inclusions on the stress concentration in the plate are studied. The numerical results obtained are compared with existing analytical solutions. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 173–180, July–August, 2007.     

Multiple cracks in pressurized hollow cylinder

Presented is a particular solution of the hollow cylinder with one crack; it consists of two parts. The first corresponds to a pair of equal and opposite normal and tangential concentrated forces acting on a crack in an infinite plane region and the second to distributed tractions on both crack surfaces such that the sum of the first and second parts satisfies the prescribed traction boundary conditions on the cracks and cylinder surfaces. The particular solution can be expressed in terms of a density function for each crack giving rise to a system of Fredholm integral equations for the multiple crack system. Several numerical examples will be provided to illustrate the method of solution.     

Winkler地基模型上功能梯度材料涂层的摩擦接触问题

研究Winker地基模型上功能梯度材料涂层在一刚性圆柱形冲头作用下的摩擦接触问题。功能梯度材料涂层表面作用有法线向和切线向集中作用力。假设材料非均匀参数呈指数形式变化,泊松比为常量,利用Fourier积分变换技术将求解模型的接触问题转化为奇异积分方程组,再利用切比雪夫多项式对所得奇异积分方程组进行数值求解。最后,给出了功能梯度材料非均匀参数、摩擦系数、Winker地基模型刚度系数及冲头曲率半径对接触应力分布和接触区宽度的影响情况。     

Stress-strain state of an anisotropic plate with curved cracks and thin rigid inclusions

We solve the bending problem for an anisotropic plate with flaws like smooth curved nonoverlapping through cracks and rigid inclusions. The problem is solved by the method of Lekhnitskii complex potentials specified as Cauchy type integrals over the flaw contours with an unknown integrand density function. We use the Sokhotskii—Plemelj formulas to reduce the boundary-value problem to a system of singular integral equations with the additional conditions that the displacements in the plate are single-valued when going around the cut contours and the equilibrium conditions for stress-free rigid inclusions. After the singular integrals are approximated by the Gauss-Chebyshev quadrature formulas, the problem is reduced to solving a system of linear algebraic equations. We study the local stress distribution near flaw tips. We analyze the mutual influence of flaws on the stress distribution character near their vertices and compare the well-known solutions for isotropic plates with the solutions obtained by passing to the limit in the anisotropy parameters (“weakly anisotropic material”) and by using the method proposed here.     

反平面弹性中边缘内分叉裂纹的奇异积分方程解法

利用复变函数和奇异积分方程方法,求解反平面弹性中半平面边缘内分叉裂纹问题。提出了满足半平面边界自由的由分布位错密度表示的半平面中单裂纹的基本解,此基本解由主要部分和辅助部分组成。将半平面边缘内分叉裂纹问题看作是许多单裂纹问题的叠加,建立了以分布位错密度为未知函数的Cauchy型奇异积分方程组。然后,利用半开型积分法则求解奇异积分方程,得到了裂纹端处的应力强度因子。文中给出两个数值算例的计算结果。     

Scattering far field solution of SH-wave by movable rigid cylindrical interface inclusion

The Green's function is used to solve the scattering far field solution of SH-wave by a movable rigid cylindrical interface inclusion in a linear elastic body. First, a suitable Green's function is developed, which is the fundamental displacement solution of an elastic half space with a movable rigid half-cylindrical inclusion impacted by out-of-plane harmonic line source loaded at any point of its horizontal surface. By using the Green's function, a series of Fredholm integral equations of the first kind which determine the scattering far field can be set up. Then the paper gives the expressions on the far field including the displacement mode of scattering wave and the solution of scattering cross-section. Finally, some examples and numerical results are discussed to analyze the influence of the combination of different media parameters on the answer of far field.     

Stress Intensity Factor for the Interaction between a Straight Crack and a Curved Crack in Plane Elasticity

Formulation in terms of hypersingular integral equations for the interaction between straight and curved cracks in plane elasticity is obtained using the complex variable functions method. The curved length coordinate method and a suitable numerical scheme are used to solve such integrals numerically for the unknown function, which are later used to find the stress intensity factor, SIF.     

线性船舶兴波阻力边界元新方法

采用常数边界元对船舶与流体界面进行离散，求解船舶兴波势及船舶兴波阻力。这种方法可避免在船舶与流体自由面交线上安置节点，因而避免了这些节点建立补充方程。因为满足自由面条件的Ｈａｖｅｌｏｃｋ源函数的源点和场点不能同时在自由面上，使得自由面上的节点无法用Ｈａｖｅｌｏｃｋ源函数的建立方程。如对自由面交线上的节点建立补充方程，则要对线性自由面条件中包含的未知势函数的二阶导数用差分形式表达，引入较大误差。     

反平面圆形夹杂和多圆孔多裂纹相互作用问题

动用复变函数及积分方法方法求解了反平面圆形夹杂和多圆孔多裂纹相互作用问题。为解决该问题,建立了两种类型的基本解。利用叠加原理和所得的基本解没圆孔和裂纹表面取待定的基本解密度函数,可得一组Ｆｒｅｄｈｏｌｍ积分方程,通过积分方程组的数值求解,可以得到密度函数的离散值,进而得到应力强度因子。     

Explicit solutions for shearing and radial stresses in curved beams

In this paper the formulae for the shearing and radial stresses in curved beams are derived analytically based on the solution for a Volterra integral equation of the second kind. These formulae satisfy both the equilibrium equations and the static boundary conditions on the surfaces of the beams. As some applications, the resulting solutions are used to calculate the shearing and radial stresses in a cantilevered curved beam subjected to a concentrated force at its free end. The numerical results are compared with other existing approximate solutions as well as the corresponding solutions based on the theory of elasticity. The calculations show a better agreement between the present solution and the one based on the theory of elasticity. The resulting formulae can be applied to more general cases of curved beams with arbitrary shapes of cross-sections.     

A promising boundary element formulation for three‐dimensional viscous flow

In this paper, a new set of boundary‐domain integral equations is derived from the continuity and momentum equations for three‐dimensional viscous flows. The primary variables involved in these integral equations are velocity, traction, and pressure. The final system of equations entering the iteration procedure only involves velocities and tractions as unknowns. In the use of the continuity equation, a complex‐variable technique is used to compute the divergence of velocity for internal points, while the traction‐recovery method is adopted for boundary points. Although the derived equations are valid for steady, unsteady, compressible, and incompressible problems, the numerical implementation is only focused on steady incompressible flows. Two commonly cited numerical examples and one practical pipe flow problem are presented to validate the derived equations. Copyright © 2004 John Wiley & Sons, Ltd.