Determining Prefracture Zones at a Crack Tip Between Two Elastic Orthotropic Bodies

The model of prefracture zones is generalized to a crack between two anisotropic materials. An exact analytical solution is found on the assumptions that the prefracture zone is localized on the crack continuation and that only the normal displacements undergo discontinuity in the zone. From this solution, equations for determining the prefracture length and crack tip opening are derived     

Initial Development of the Prefracture Zone Near the Tip of a Crack Reaching the Interface Between Dissimilar Media

The Wiener–Hopf method is used to analyze, within the framework of a plane static problem, the prefracture zone near the tip of a mode I crack reaching the interface separating two isotropic media and containing a corner point     

裂纹在冲击载荷作用下起裂的临界载荷面

采用有限元方法研究裂纹在I型短脉冲载荷作用下应力强度因子随时间的变化 ,用应力强度因子的初始上升时间Tr 对时间坐标无量纲化 ,对应力强度因子初始上升段进行曲线拟合 ,得到了上升段的曲线表达式。运用简单弹性梁理论和Lagrangian运动方程 ,获得载荷与时间对裂纹作用的关系式 ,结合有限元的结果 ,得到了上升时间Tr 的计算表达式 ,并进一步推出了裂纹在冲击载荷作用下起裂的临界载荷面。     

Nucleation of cracks in a perforated fuel cell

A mathematical model is constructed for crack nucleation in an isotropic fuel cell (heat-releasing solid material) attenuated by a biperiodic system of cooling cylindrical channels with a circular cross section. Cracks are assumed to appear with increasing heat-release intensity in the bulk of the material. The solution of the problem on equilibrium of an isotropic perforated fuel cell with crack nuclei reduces to the solution of a nonlinear singular integral equation with a Cauchy-type kernel. The solution of the latter equation yields the forces in the band of crack nucleation. The condition of crack nucleation is formulated with allowance for the criterion of ultimate extension of bonds in the material. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 5, pp. 121–133, September–October, 2007.     

Crack propagation in a functionally graded plate under thermal shock

Summary Thermal cracking in a ceramic/metal functionally graded plate is discussed. When a functionally graded plate is cooled from high temperature, curved or straight crack paths are experimentally observed on the ceramic surface. One of the reasons that make the crack paths to differ are the thermal or mechanical conditions. In order to clarify the influence of these conditions on the crack path, the crack propagation is simulated using finite element method. Received 29 September 1998; accepted for publication 2 August 1999     

Wedging an Orthotropic Body by a Rectangular Wedge of Finite Length

Galin's method is used to derive equations that relate the basic parameters of the problem on wedging an orthotropic space by a rigid rectangular wedge. To eliminate the stress singularity at the wedging crack tips, a Leonov–Panasyuk–Dugdale prefracture zone is assumed to exist at the crack front. The equations are derived using the COD criterion     

40Cr钢疲劳裂纹萌生寿命的测量

用系统分析的方法，通过三点弯曲疲劳试验，分别跟踪监测了40Cr钢及它的两种表面处理试样疲劳损伤过程，得出了40Cr钢经过两种表面处理对其疲劳裂纹萌生寿命有显著影响的结果，提出了对疲劳裂纹萌生寿命测量的一种新方法。     

Stress State of a Transversely Isotropic Ferromagnetic with an Elliptic Crack in a Homogeneous Magnetic Field

The magnetoelastic stress-strain problem for a transversely isotropic ferromagnetic body with an elliptical crack in the isotropy plane is solved explicitly. The body is in an external magnetic field perpendicular to the isotropy plane. The magnetic field induces elastic strains and an internal magnetic field in the body. The main characteristics of stress-strain state and induced magnetic field are determined and their features in the neighborhood of the crack are analyzed. Formulas for the stress intensity factors of the mechanical and magnetic fields near the crack tip are presented__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 1, pp. 48–59, January 2005.     

The Stress State of a Transversely Isotropic Ferromagnetic with a Parabolic Crack in a Homogeneous Magnetic Field

The magnetoelastic problem for a transversely isotropic ferromagnetic body with a parabolic crack in the plane of isotropy is solved explicitly. The body is in an external magnetic field, which is perpendicular to the plane of isotropy. The field induces elastic strains and a magnetic field in the body. The characteristics of the stress–strain distribution and induced magnetic field are determined; and their singularities in the neighborhood of the crack are analyzed. Formulas for the stress intensity factors of the mechanical and magnetic fields near the crack tip are presented     

缺口裂纹起裂和扩展检测的直流电位法

本文从解析法、有限元分析和试验三方面探讨了直流电位法用于缺口问题的有效性。当缺口宽度与试样宽度之比较小时(如小于0.05),根据电位的改变量,解析法才能给出缺口裂纹扩展满意的推算.分析和试验说明,利用电位的改变反推缺口裂纹的扩展时,必须引入由于变形引起的缺口宽度变化对电位影响的修正.     

On the direction of development of a thin fracture process zone at the tip of an interfacial crack between dissimilar media

The Wiener-Hopf method is used to study, under the conditions of plane strain, the direction of development of a thin fracture process zone at the tip of an interfacial crack in a piecewise homogeneous isotropic elastoplastic body. The zone is modeled by a straight line of tangential displacement discontinuity that emerges from the crack tip at an angle to the interface. The dependences of the zone length and the angle on the load and other parameters of the problem are investigated __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 2, pp. 14–23, February 2006.     

薄膜涂层材料中币形界面裂纹的弹性波散射

研究了薄膜涂层材料中币形界面裂纹的弹性波散射问题,建立了含有币形界面裂纹的覆层半空间模型,采用Hankel积分变换,将裂纹对弹性波散射的问题转化为求解矩阵形式的奇异积分方程。结合渐近分析和围道积分技术得到积分方程的解,进一步推导了散射波的应力场和位移场,以及动应力强度因子的理论计算公式。在数值算例中,分析了不同材料组合和裂纹尺寸情况下动应力强度因子与入射波频率的关系,并给出了裂纹张开位移的结果。为薄膜涂层材料的动态破坏分析提供了一定的理论基础。     

Study into the kinetics of a crack with a nonsmall fracture process zone in an aging viscoelastic plate

The subcritical growth of a mode I crack with nonsmall end zones in an aging viscoelastic plate under tensile loads applied at infinity is studied assuming that the fracture process zone is of constant length. The equations of incubation, transition, and major crack growth stages are obtained on the basis of the Volterra principle and critical crack opening criterion. The crack subcritical growth of a specific material is studied as an example __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 8, pp. 92–101, August 2007.     

粘弹性双材料界面裂缝的缝端位移场及动态断裂分析

本文研究的是经常在实际工程中遇到的粘弹性双材料界面裂缝的动断裂问题.由于粘弹性自身的复杂性,使得粘弹性双材料界面裂缝缝端应力的奇异性较弹性呈现出更为复杂的形式,从而使动断裂问题的分析变得更为困难.根据此情况,本文采用复阻尼理论反映粘弹性体的运动规律,用复势理论和平面问题复变函数解答的科洛索夫公式推导了粘弹性双材料界面裂缝缝端位移场及动态应力强度因子的求解公式,利用特解边界元进行了粘弹性双域耦合动力响应计算,按求得的公式用位移外推法计算了单边裂纹板在动荷载作用下的动态应力强度因子.分析了粘性,弹模比和缝长对动态应力强度因子的影响,得出了一些有益的结论.     

Study of orthotropic materials: the interphase model and the crack initiation

Summary In this paper, a survey on the orthotropic composite materials is given. The model of the interphase, assuming a third phase between fibre and matrix with some different properties, is used for the calculation of the elastic constants of a unidirectional fibre-reinforced epoxy resin composite. Their values are used to determine the stress field at the crack tip and the stress intensity factor of a cracked orthotropic plate. The recently developed Det-criterion of fracture is taken into account to study the crack initiation.     

冲击载荷下纤维复合材料裂纹起裂的实验研

采用SHTB技术对纤维增强复合材料裂纹动态起裂行为进行了实验研究。使用应变片方法确定了裂纹的起裂时间 ,结合有限元数值模拟得到了裂纹的起裂韧性 ;同时观察了裂纹在冲击载荷作用下的裂纹起裂和扩展方式 ,分析了纤维的铺层角度对裂纹起裂和扩展的影响。     

Crack tip plasticity of a half-infinite Dugdale crack embedded in an infinite space of one-dimensional hexagonal quasicrystal

The present paper is devoted to determining the crack tip plasticity of a half-infinite Dugdale crack embedded in an infinite space of one-dimensional hexagonal quasicrystal. A pair of equal but opposite line loadings is assumed to be exerted on the upper and lower crack lips. By applying the Dugdale hypothesis together with the elastic results for a half-infinite crack, the extent of the plastic zone in the crack front is estimated. The normal stress outside the enlarged crack and crack surface displacements are explicitly presented, via the principle of superposition. The validity of the present solutions is discussed analytically by examining the overall equilibrium of the half-space.     

CRACK PROPAGATION IN POLYCRYSTALLINE ELASTIC-VISCOPLASTIC MATERIALS USING COHESIVE ZONE MODELS

Cohesive zone model was used to simulate two-dimensional plane strain crack propagation at the grain level model including grain boundary zones. Simulated results show that the original crack-tip may not be separated firstly in an elastic-viscoplastic polycrystals. The grain interior's material properties (e.g. strain rate sensitivity) characterize the competitions between plastic and cohesive energy dissipation mechanisms. The higher the strain rate sensitivity is, the larger amount of the external work is transformed into plastic dissipation energy than into cohesive energy, which delays the cohesive zone rupturing. With the strain rate sensitivity decreased, the material property tends to approach the elastic-plastic responses. In this case, the plastic dissipation energy decreases and the cohesive dissipation energy increases which accelerates the cohesive zones debonding. Increasing the cohesive strength or the critical separation displacement will reduce the stress triaxiality at grain interiors and grain boundaries. Enhancing the cohesive zones ductility can improve the matrix materials resistance to void damage.     

On the study of the initiation of the micro crack on the smooth surface of polycrystalline

Crystallographic plasticity was applied to study the initiation of micro cracks on the smooth surface of polycrystalline under uniform applied stress. Even under the uniform external stress, due to the different crystallographic orientations of the grains in the polycrystalline, there is un-uniform stress distribution and the deformation is also not uniform. Under the fatigue loading, the roughness increases with the number of fatigue, and deformation will localize in some places, where micro cracks form.     

关于界面下裂纹对界面裂纹的屏蔽参数

讨论了界面下裂纹对界面裂干涉的合理屏蔽参数问题。对于一条在远场载荷作用下、受到附近界面下裂纹干涉的界面裂纹,采用伪力法计算不同长度单位时界面裂纹的G／G0、k1/k10和k11/k110以及K1／K10和K11／K110（G是能量释放率、k1 ik110是通常定义的应力强度因子、K10＋iK110是含标定长度的应力强度因子;G0、k10 ik110、K10＋iK110对应单一界面裂纹情况）。结果表明,G／G0、K1／K10和K11／K110是较为合理的描述界面下裂纹对界面裂纹屏蔽的参数。