裂纹尖端场弹塑性分析的加权残数法及塑性应力强度因子的计算

本文以幂强化材料,平面应变情形为例,系统地提出了裂纹尖端场弹塑性分析的加权残数法,并根据此法,得出了裂纹尖端场的解析式弹塑性近似解.在此基础上.对整个裂纹区域,构造了弹塑性解叠加非线性有限元计算塑性应力强度因子的方法,从而为裂纹尖端场和整个裂纹体的分析和计算,提供了一个方法.     

理想塑性固体中逐步扩展裂纹的弹塑性场

本文从三维的塑性流动理论出发,导出了关于理想塑性固体平面应变问题的基本方程。利用这些方程,分析了不可压缩理想塑性固体的逐步扩展裂纹顶端的弹塑性场。得到了关于应力和速度的一阶渐近场。分析了弹性卸载区的演变过程和中心扇形区的发展过程。预示了出现二次塑性区的可能性。最后给出了关于应力场二阶渐近分析。     

轴对称金属模具电磁热裂纹止裂中热应力场的分析

为求解金属模具脉冲放电止裂瞬间裂纹尖端附近的热应力场,选择具有半埋藏环形裂纹的金属凹模为研究对象,采用复变函数方法求解了凹模内外环面均匀通入强脉冲电流放电止裂时的热应力场．理论分析结果证实:由于放电瞬间脉冲电流的绕流集中效应,使金属凹模内部环形裂纹尖端附近金属迅速升温,金属熔化形成堆焊,并由于瞬间温升产生热压应力场．研究结果表明:应用电磁热效应止裂技术可以减小裂纹尖端的应力集中,形成的热压应力场有效地阻止金属模具中干线裂纹源的开裂趋势,达到了裂纹止裂目的．     

含圆形孔口和水平直裂纹的平面问题的应力分析

利用复变函数方法和积分方程理论研究了既含有圆形孔口又含有水平裂纹的无限大平面的平面弹性问题,将复杂的解析函数的边值问题化成了求解只在裂纹上的奇异积分方程的问题.此外,还给出了裂纹尖端附近的应力场和应力强度因子的公式.     

Two-dimensional analysis of a crack in quasicrystal materials

The two-dimensional problem of a crack in three-dimensional quasicrystals subject to far field loadings is studied. The analysis is based on the generalized Lekhnitskii's formalism. The analytical expressions for both the entire fields and the asymptotic fields near the crack tip are determined. The fracture quantities of quasicrystals, i.e., field intensity factors, energy release rates and so on, is a prerequisite. Numerical results for a Griffith crack under phason loading Mode I and II conditions are poltted. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

纯弯曲矩形截面梁Ⅰ型单边裂纹端部的应力应变场及裂纹失稳扩展临界应力的计算

本文应用文[1]的分析方法,研究了纯弯曲矩形载面梁Ⅰ型单边裂纹端部的应力应变场,给出了裂纹尖端的应力应变分量和计算裂纹端部弹性变形区和变形强化区宽度的公式以及计算裂纹失稳扩展临界应力的方程组。最后用计算实例对裂纹失稳扩展临界应力方程组进行了验证,最大误差不超过0.18%.     

Dynamic response of planar interface crack between viscoelastic bodies

IntroductionThe dynamic stress intensity factor (SIF) plays an important role in dynamic fracture underboth harmonic and transient loads. It predicts whether or not the fracture toughness of thematerial will be exceeded and catastrophic crack propagation will follow. The dynamic SIFof interfaCe cracks between two dissimilar elastic materials has been studied widely. Kundull]studied the dynamic SIF of interface crack under transient loading with the method based onBetti's reciprocal theore…     

Ⅱ型平面应力裂纹线场的弹塑性精确解

本文采用线场分析方法对理想弹塑性Ⅱ型平面应力裂纹裂纹线附近的应力场及弹塑性边界进行了精确分析。本文完全放弃了小范围屈服条件,探讨了弹塑性边界上弹塑性应力场匹配条件的正确提法,通过将裂纹线附近塑性区应力场的通解(而不是过去采用的特解)与弹性应力场的精确解(而不是通常的裂尖应力强度因子K场)在裂纹线附近的弹塑性边界上匹配,本文得出了塑性区应力场,塑性区长度及弹塑性边界的单位法向量在裂纹线附近的足够精确的表达式。     

一维六方压电准晶中正六边形孔边裂纹的反平面问题

研究了一维六方压电准晶中正六边形孔边裂纹的反平面问题,利用复变函数中的Cauchy积分公式,通过构造保角映射函数,在电非渗透型的边界条件下得到了孔边裂纹尖端的应力分布以及场强度因子的解析解.通过数值算例,讨论了正六边形的边长和裂纹长度以及剪应力对场强度因子的影响.     

正交异性双材料的Ⅱ型界面裂纹尖端场

通过引入含16个待定实系数和两个实应力奇异指数的应力函数,再借助边界条件,得到了两个八元非齐次线性方程组.求解该方程组,在双材料工程参数满足适当条件下,确定了两个实应力奇异指数.根据极限唯一性定理,求出了全部系数,得到了应力函数的表示式.代入相应的力学公式,推出了当特征方程组两个判别式都小于0时,每种材料的裂纹尖端应力强度因子、应力场和位移场的理论解.裂纹尖端附近的应力和位移有混合型断裂特征,但没有振荡奇异性和裂纹面相互嵌入现象作为特例,当两种正交异性材料相同时,可以推出正交异性单材料Ⅱ型断裂的应力奇异指数、应力强度因子公式、应力场、位移场表示式.     

Experimental study about nano-deformation field near quasi-cleavage crack tip

Using the nano-moiré method, we measure the near tip nanoscopic deformation on the [111] plane of single crystal silicon with a loaded quasi-cleavage crack running in the [110] direction. The measured strain distribution ahead of the crack tip agrees with the linear elastic fracture mechanics prediction up to 10 nm from the crack tip. Dislocations of Peierls type are detected and they extend from the crack tip over a length of hundreds of Burgers vectors.     

纯扭正交异性复合材料板的断裂分析

对受纯扭载荷作用的线弹性正交异性复合材料板裂纹尖端附近的断裂性态进行探讨。利用复变函数方法，通过求解偏微分方程的边值问题，推出了裂纹尖端附近的弯矩、扭矩、应力和位移的表达式，最后给出了数值算例。     

纯扭各向异性复合材料板断裂分析的复变函数方法

对受纯扭载荷作用的线弹性各向异性纤维复合材料板裂纹尖端附近的应力场进行探讨.选取带复参数的挠度函数,利用复变函数方法和待定系数法,借助边界条件,确定复参数,从而推出了裂纹尖端附近的弯矩、扭矩、应力和位移计算公式.所得到的公式在有关的断裂分析中有一定的实用价值和参考作用,最后给出了数值算例.     

压电陶瓷板中非电渗透型反平面裂纹的电弹性场

对受4种机电载荷的内含裂纹的压电陶瓷板的电弹性行为进行了分析。利用积分变换方法将非电渗透型反平面裂纹问题化为对偶积分方程组,求解这些方程组可以获得裂纹线上电弹性场的明显解析表达式,及裂尖处一些量的强度因子和机械应变能释放率。当板的厚度趋近于无穷大时,所得结果还原为熟知结果。     

Biaxial tension of a homogeneous isotropic plate with two equal coaxial cracks with regard for plastic zones near their tips

We investigate the problem of determination of the stress-strain state of an isotropic plate with two equal cracks at a set homogeneous field of forces at infinity. It is assumed that the lips of the cracks are free of load and that, near their tips, plastic zones are formed. Using Kolosov–Muskhelishvili complex potentials, we seek a solution of the problem in the class of functions bounded at the tips of the cracks and reduce it to problems of linear conjugation. Relations for the determination of the values of plastic zones and crack tip opening displacements are obtained. We perform a numerical analysis of the problem and construct graphs of dependences of the lengths of plastic zones and crack tip opening displacements on the distance between the centers of the cracks.     

圆形杂质对裂纹扩展的影响

在单轴拉伸载荷作用下，运用分布位错方法对无限大平面内含有一个裂纹和一个任意方向的杂质问题进行求解，得到了裂纹尖端的应力强度因子、应力场以及应变能密度.利用最小应变能密度因子准则来判断裂纹扩展方向.结果显示:软杂质对裂纹尖端应力强度因子、应变能密度和应力场有增强作用，而硬杂质则具有屏蔽作用.在 -30°<θ<30°范围内，杂质对裂纹扩展方向的影响较小，而在 -90°<θ<-30°或30°<θ<90°范围内，杂质对裂纹扩展方向的影响较大.软杂质对裂纹扩展有吸引作用，而硬杂质具有排斥作用.     

A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals

A Yoffe-type moving crack in one-dimensional hexagonal piezoelectric quasicrystals is considered. The Fourier transform technique is used to solve a moving crack problem under the action of antiplane shear and inplane electric field. Full elastic stresses of phonon and phason fields and electric fields are derived for a crack running with constant speed in the periodic plane. Obtained results show that the coupled elastic fields inside piezoelectric quasicrystals depend on the speed of crack propagation, and exhibit the usual square-root singularity at the moving crack tip. Electric field and phason stresses do not have singularity and electric displacement and phonon stresses have the inverse square-root singularity at the crack tip for a permeable crack. The field intensity factors and energy release rates are obtained in closed form. The crack velocity does not affect the field intensity factors, but alters the dynamic energy release rate. Bifurcation angle of a moving crack in a 1D hexagonal piezoelectric quasicrystal is evaluated from the viewpoint of energy balance. Obtained results are helpful to better understanding crack advance in piezoelectric quasicrystals.     

Non-local theory solution of two collinear mode-I cracks in piezoelectric materials

In this paper, the basic solution of two collinear cracks in a piezoelectric material plane subjected to a uniform tension loading is investigated by means of the non-local theory. Through the Fourier transform, the problem is solved with the help of two pairs of integral equations, in which the unknown variables are the jumps of displacements across the crack surfaces. To solve the integral equations, the jumps of displacements across the crack surfaces are directly expanded in a series of Jacobi polynomials. Numerical examples are provided to show the effects of the interaction of two cracks, the materials constants and the lattice parameter on the stress field and the electric displacement field near crack tips. Unlike the classical elasticity solution, it is found that no stress and electric displacement singularities are present at crack tips. The non-local elastic solutions yield a finite hoop stress at the crack tip, thus allowing us to using the maximum stress as a fracture criterion in piezoelectric materials.     

Inplane Stress Singularities at the Corner of an Anisotropic Material Discontinuity

In the mechanics of composite laminates the local mechanical inplane fields at corners of anisotropic material discontinuities are of particular interest since they can have singular behavior. In the present study, the stress and strain fields in the local near field of such corners are investigated by an asymptotic analysis. The order of the singularity of these mechanical inplane fields are determined in closed‐form manner by use of the complex potential method based on Lekhnitskii's approach. Various different geometrical setups and material combinations of corners with material discontinuities are investigated with regard to their effect on the singular behavior of the mechanical fields present. These examples show that the order of singularity considered is clearly weaker than the typical crack tip singularity in fracture mechanics. Nevertheless, it may render the corner a critical location for the onset of failure. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An interface crack moving between magnetoelectroelastic and functionally graded elastic layers

A constant crack moving along the interface of magnetoelectroelastic and functionally graded elastic layers under anti-plane shear and in-plane electric and magnetic loading is investigated by the integral transform method. Fourier transforms are applied to reduce the mixed boundary value problem of the crack to dual integral equations, which are expressed in terms of Fredholm integral equations of the second kind. The singular stress, electric displacement and magnetic induction near the crack tip are obtained asymptotically and the corresponding field intensity factors are defined. Numerical results show that the stress intensity factors are influenced by the crack moving velocity, the material properties, the functionally graded parameter and the geometric size ratios. The propagation of the moving crack may bring about crack kinking, depending on the crack moving velocity and the material properties across the interface.