Interaction between a screw dislocation and an elastic elliptical inhomogeneity with interfacial cracks

The elastic interaction between a screw dislocation and an elliptical inhomogeneity with interfacial cracks is studied. The screw dislocation may be located outside or inside the inhomogeneity. An efficient complex variable method for the complex multiply connected region is developed, and the general solutions to the problem are derived. As illustrative examples, solutions in explicit series form for complex potentials are presented in the case of one or two interfacial cracks. Image forces on the dislocation are calculated by using the Peach-Koehler formula. The influence of crack geometries and material properties on the image forces is evaluated and discussed. It is shown that the interfacial crack has a significant effect on the equilibrium position of the dislocation near an elliptical-arc interface. The main results indicate, when the length of the crack goes up to a critical value, the presence of the interfacial crack can change the interaction mechanism between a screw dislocation and an elliptical inclusion. The present solutions can include a number of previously known results as special cases.The project supported by the National Natural Science Foundation of China(10272009 and 10472030) and the Natural Science Foundation of Hunan Province(02JJY2014)     

Plane Problem of Three-Dimensional Stability for a Hinged Plate with Two Symmetric End Cracks

The plane stability problem for a rectangular plate with two symmetric end cracks is solved in three-dimensional formulation. The three-dimensional linearized theory of stability and the finite-difference method are used. The effect of the crack parameter on the critical load is examined__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 4, pp. 47–52, April 2005.     

自紧身管疲劳寿命的可靠性分析

基于概率断裂力学理论和Monte Carlo模拟方法，给出了自紧身管疲劳寿命的可靠性分析方法．自紧残余应力采用了符合身管材料具有强化和包辛格效应性能推导的公式计算，身管工作的应力强度因子通过权函数方法得到．实例分析结果表明，对数正态分布为身管疲劳寿命的最佳分布，同时给出了各种置信度和可靠度下的身管疲劳寿命．另外，还分析了初始裂纹尺寸和材料的断裂韧性对身管疲劳寿命的影响．该研究对保证身管的安全，避免灾难性事故的发生具有重要意义．     

Ultrasonic sizing of embedded vertical cracks in ferritic steel welds

Embedded vertical cracks are very often encountered in structural components necessitating reliable procedure for determining their size. Specialized ultrasonic techniques are required for estimation of through thickness height of these cracks [Mater. Eval. (1970) 28; J. NDI 26 (1977) 320; NND (1975) 146]. The conventional pulse-echo technique has serious limitations for quantitative estimation of vertical cracks because it is subject to variations due to reflectivity, coupling factors etc. The present study aims to improve the accuracy of embedded crack height measurement based on transit time rather than the reflected amplitude [NDT Int. (1982) 315; J. JSNDT 27 (1978) 118]. A unique method has been developed for generating known sizes of fatigue cracks ranging from 2.5 to 18 mm in height and 15 mm in length. These cracks were generated in rectangular steel specimens and subsequently embedded at predetermined locations using welding. These welded specimens containing the embedded vertical cracks were examined using ultrasonic techniques based on transit time like (a) flaw tip echo method and (b) mode conversion method. Using both the techniques excellent agreement was obtained between the estimated crack height and actual crack height with an accuracy of ±1 mm.     

缺口疲劳门槛值的实验研究

本文报告了对常用高强材料３０ＣｒＭｎＳｉＡ的双边Ｖ型缺口疲劳门槛值进行的实验测量。通过测试结果分析，证实了对不同缺口半径的试样（△Ｋ１／√Ｐ）ｔｈ基本一致的结论。     

用升降法求95连杆疲劳极限的探讨

为了较精确地求出95连杆的疲劳极限,本文将在材料疲劳试验中应用较广的升降法推广应用于连杆,给出了用升降法求构件疲劳极限的基本过程。文中首先选取了试验的控制因素并确定了连杆的控制点(应力被选定为控制应力的点定义为控制点)。然后在四级应力水平下进行了连杆的疲劳试验,并以最大应力幅点的应力为计算应力求出了连杆的疲劳极限。     

沥青混凝土面板低温疲劳破坏的实验研究

我国北方地区的土石坝和水池的防渗沥青混凝土面板,常出现低温裂缝。因此,对沥青混凝土在低温条件下的温度应力疲劳进行实验研究很有必要.本项研究研制了适用于沥青混凝土低温低周大变形的弯曲疲劳试验机,进行了沥青混凝土在不同低温下的疲劳破坏性能试验。对试验结果用粘弹性理论和推广的应变区分法(SRP)和应变能区分法(SEP)进行了分析,首次得出了沥青混凝土的疲劳寿命与弯曲应力、应变和应变能的关系,并试用于实际工程的予测.     

Dynamic analysis of interacting coplanar cracks in a half space with a clamped boundary condition using boundary integral equations

The three-dimensional dynamic problem of coplanar circular cracks in an elastic half-space with a clamped boundary condition is considered. The crack faces are subjected to harmonic loads. The problem is reduced to a system of two-dimensional boundary integral equations of the type of the Helmholtz potential for unknown discontinuities in the displacements of the opposite faces of the cracks. The stress intensity factors at the crack contours are obtained and discussed.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 153–159, January–February, 2005     

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基于27种合金钢与铝合金的机械、力学性能，分析对比了3种理论估算疲劳极限方法的估 算结果，发现3种方法中只有两种方法能够比较精确地估算材料的疲劳极限; 当引 入强度系数和应变硬化指数与常规机械与力学性能的关系之后，这两种方法都可借助材料的 常规机械与力学性能估算疲劳极限，估算过程中的限制性条件``高强度钢'应予取消.     

疲劳可靠性二维概率MINER准则

给出在裂纹起始阶段疲劳损伤演化规律的四个基本假设，即单调增、无耦合、可分高、不相交，由损伤力学原理得到等幅加载下个体Ｄ－Ｓ＿ａ－Ｓ＿ｍ－Ｎ等损伤曲面，推导出二维个体Ｍｉｎｅｒ准则，进而建立了母体在变幅以及随机时间历程加载下的二维概率Ｍｉｎｅｒ准则（Ｔｗｏ－ｄｉｍｅｎｓｉｏｎａｌＰｒｏｂａｂｉｌｉｓｔｉｃＭｉｎｅｒ’ｓＲｕｌｅ，即ＴＰＭＩＮＥＲ），并用测度论给予了证明．试验数据验证结果显示ＴＰＭＩＮＥＲ的预测值与试验值吻合良好，对工程结构疲劳可靠性分析有较好的应用价值．