Modeling of the Crack Tip Plastic Zone by Two Slip Lines and the Order of Stress Singularity

Modeling of initial plastic zone by two slip-lines is considered. It is shown that such a model does not remove stress singularity at the crack tip.     

The Shielding Effect of the Plastic Zone at Mode-II Crack Tip

An analytical solution for prediction of the stress intensity factor (SIF) induced by plastically deformed zone at mode-II crack tip is presented under small scale yielding conditions. A significant shielding effect has been indicated, which is strongly affected by the strain-hardening behavior of the material, the applied stress and the T -stress.     

On Higher Order Terms in the Crack Tip Stress Field

The influence of higher order terms on the stress field of a cracked plate under in plane loading may not be negligible in some engineering applications. The aim of this note is to present a more accurate analysis of these terms.     

On the Plastic Zone Size and the Crack Tip Opening Displacement of an Interface Crack Between two Dissimilar Materials

In the paper, the elastic-plastic fracture behavior of an interface crack between two dissimilar materials is investigated. The mixed-mode Dugdale model is applied to examine the plastic zone size and the crack tip opening displacement. In numerical examples, the plastic zone size and the crack tip opening displacement of an interface crack under uniform loads are studied in detail. Two formulae are proposed to calculate the plastic zone size and the crack tip opening displacement of an interface crack under small scale yielding conditions.     

The Effect of a Plastically Deformed Zone Near Crack Tip on the Stress Intensity Factors

A plastically deformed particle ahead of a crack-tip is treated as an equivalent transformation inclusion by means of Eshelby equivalent inclusion theory. A general solution to determine the effect of the plastically deformed particle on the stress intensity factor of mode I crack is obtained.     

On Evolution of Plasticity Zone in the Vicinity of Crack Tip

An in situ investigation has been performed on plasticity zone evolution in a loaded specimen in the vicinity of crack tip using the technique of speckle interferometry. The motion of the boundary separating the elastic and the plastically deforming region of the loaded specimen was followed. In the plasticity zone deformation waves were found to emerge and disappear subsequently.     

Eigenspectra and Orders of Singularity at a Crack Tip for a Power-Law Creeping Medium

The objective of this paper is to study the eigenspectrum of a creeping body with a static mode I crack. The coordinate perturbation technique is employed to pose the required asymptotic equations. To attain eigensolutions a numerical scheme is worked out and the results obtained provide the information including the number of singularities, and their orders, as well as the angular distributions of stresses. In particular, additional eigenvalues of the HRR/RR problem that have not been reported previously are presented in the context, indicating the fact that other singular fields may exist for the problem. The discussion is also performed to the higher order asymptotic solutions that differ from those resulting from the eigen expansion treatment. This revised version was published online in August 2006 with corrections to the Cover Date.     

型材中裂纹应力强度因子计算方法

本文应用分区广义变分原理,提出了求解含有裂纹的型材应力强度因子的计算方法。并对角材中含有边缘裂纹和槽形型材中含有中心裂纹的应力强度因子进行了数值计算,计算结果绘成了曲线。     

Closed-Form Solutions for the Mode ii Crack tip Plastic Zone Shape

Analytical closed-form solutions for the Mode II crack tip plastic zone shape have been derived for a semi-infinite crack in an isotropic elastic-plastic solid under both plane stress and plane strain conditions. Two yield criteria have been applied: the Von Mises and Tresca yield criteria. The results indicate that the Tresca zone is larger in size than the Von Mises zone. The results also reveal an intricate dependence on Poisson's ratio in plane strain conditions.     

载流金属材料裂纹尖端电磁应力的数值模拟

用数值模拟方法研究了金属裂纹尖端电磁应力的分布情况,给出了电流分布、磁场分布和电磁应力的分布.模拟结果表明,金属材料裂纹尖端受的电磁应力是最大的,并且这个力的大小随着电流密度的增加而增大,裂纹尖端的电磁力指向金属的内部.通过具体算例表明,在金属能承受的电流密度下,金属材料裂纹尖端的电磁应力约能达到1MPa的数量级.因此,在研究电磁场处理金属裂纹时,不能忽略电磁应力.     

基于eM-Plant对注塑企业的生产线建模仿真

分析了注塑企业生产流程,并建立其生产工序的数学模型和仿真程序。根据企业的订单数量、车间生产线的规模等因素,通过对生产过程中批量的控制,研究批量和在制品库存水平的关系,提出了通过控制批量实现控制在制品的数学关系。     

Plastic Deformation at the Tip of a Tensile Crack in a Non-linear Kinematic Hardening Material

The plastic deformation at the tip of a tensile crack in a non-linear kinematic hardening material under small-scale yielding conditions is investigated, with a view to quantifying the functional dependence of crack-tip plastic blunting size on material's strain hardening parameters. It is shown by dimensional analysis that, for materials being characterised by the Armstrong-Frederick non-linear kinematic hardening rule, the crack-tip blunting parameter depends parametrically on only two non-dimensional parameters; the functional dependence is determined using a parametric finite element analysis.     

Role of Crack Tip Blunting in Stress Corrosion Cracking of High-strength Steels

This paper analyzes the role of crack tip blunting in stress corrosion cracking by localized anodic dissolution of high-strength eutectoid steel. The results of the tests show an apparent improvement of fracture resistance in aggressive environment — measured in terms of critical stress intensity factor - in relation to its reference value in an inert (air) environment. The explanation can be sought in the effects of crack tip blunting, i.e., of the increase of crack tip radius as a consequence of the dissolution process. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stress Intensity Factor Variations near the Edge Crack Tip upon Its Stepwise Growth

Calculation results to evaluate time variations of the stress intensity factor near the tip of the edge crack upon its stepwise growth are presented. The crack pop-in in a thick plate under tensile loading is shown to result in cyclic K ₁ variations with a period and amplitude that are dependent on the initial crack length, pop-in length and plate dimensions. Time-average K ₁ values correspond to those calculated for the stationary crack.__________Translated from Problemy Prochnosti, No. 2, pp. 66 – 71, March – April, 2005.     

高温合金CT试样裂纹前沿应力分布及第二相影响的模拟计算

利用有限元方法分析了IN718合金CT试样裂纹区域的应力应变分布、裂纹尖端应力强度因子及第二相状态对它的影响，计算结果与实测数据基本一致，表明采用有限元方法研究含裂纹体构件的蠕变行为是一种较好的研究手段。通过计算认为，IN718合金在时效初期虽然有α-Cr相的析出而不至于促进蠕变裂纹扩展，是由于α—Cr于δ相周围γ″贫化区(微塑性区)内析出而处于微塑性区内使得裂纹尖端钝化，不利于裂纹扩展。     

混凝土裂缝端部粘聚力的计算

混凝土裂缝端部断裂过程区的粘聚力分布是导致混凝土断裂呈现非线性特性的重要原因。基于混凝土的断裂特性和虚拟裂缝端部存在粘聚力的分析模型，并通过分布函数的特性分析，提出了粘聚力分布函数的两种简化表达式：一为单参数待定式，另一为双参数待定式。由变形体叠加原理，推导出计算单参数待定函数公式和计算双参数待定函数代数方程组。进而通过裂缝张开位移实测数据即可求得粘聚力分布，并且给出了适当的算例分析和讨论。     

Evaluation of the Three-Dimensional Region Around a Crack Tip by Caustics

A study of the extent of the three-dimensional region around the border of a straight through-crack in mode-I loading was undertaken by the method of caustics. A series of experiments were performed in single edge-notched specimens made of PMMA (Plexiglas). It was found that the state of stress very close to the crack tip can be approximated as plane strain. Following this region, three-dimensional stress conditions hold in the neighborhood of the crack tip, up to a critical distance which depends on the thickness of the plate and the crack length. Beyond this critical distance plane stress conditions dominate. Results were obtained for the extent of the three-dimensional region as a function of the specimen thickness. The present investigation illuminates the complicated problem of the changing state of stress around cracks and establishes the limits of applicability of the method of caustics for the determination of stress intensity factors. This revised version was published online in July 2006 with corrections to the Cover Date.     

Stress Corrosion Cracking in Plastic Pipes: Observation and Modeling

Stress corrosion cracking (SCC) in engineering thermoplastics is commonly observed in the form of a microcrack colony within a surface layer of degraded polymer exposed to a combined action of mechanical stresses and chemically aggressive environment. A probabilistic modeling of SCC initiation is briefly discussed. A deterministic modeling of slow stress corrosion (SC) crack growth process is developed using Crack Layer (CL) theory. Numerical solution of SC crack growth equations is discussed. Comparison of the kinetics of cracks driven by SC and by stress only is presented. Conventional plot of SC crack growth rate vs. the stress intensity factor is constructed and analyzed. An algorithm for conservative estimation of lifetime of engineering thermoplastic subject to a combination of mechanical stresses and chemically aggressive environment is discussed.     

The Stress Intensity Factor of an Edge Dislocation Near an Elliptically Blunted Crack Tip

The stress field around the tip of an elliptically blunted crack induced by an edge dislocation has been obtained in closed form, from which the mode I and mode II stress intensity factors induced by the edge dislocation are obtained. The solutions apply to the edge dislocation either emitted from crack-tip surface or originated elsewhere, and for the dislocation located anywhere around the crack tip. The effects of the crack length, the crack-tip bluntness, the origination and position of the dislocation on the stress intensity factors are examined.