应力场强计算裂纹应力强度因子的方法研究

探讨通过应力场强得到应力强度因子的方法,并以典型的四类平面裂纹状态为例,着重探讨各类平面裂纹如何应用该方法计算应力强度因子.结果显示,所提方法能快速地求解各类裂纹布置的应力强度因子,可为断裂力学中裂纹扩展、断裂判断问题以及疲劳多裂纹问题的研究提供良好的支持.     

板条裂纹问题的位错模拟解法

假设沿分叉裂纹各分支和板条边界有某位错分布,利用半平面内分叉裂纹问题的复势函数,将板条分叉裂纹问题转化为半平面内的多分叉裂纹问题处理。根据板条边界和裂纹面上的应力边界条件,建立以集中位错强度和分布位错密度为未知函数的Cauchy型奇异积分方程,利用半开型积分法则将该奇异积分方程化为代数方程求解。最后,由位错密度函数得到各裂纹分支端的应力强度因子值。文中分别给出集中力和分布力作用情况下内分叉和边缘分叉裂纹的3个算例,其极限情况的计算结果与精确解是一致的。     

压电材料中螺型位错和偶极子与半椭圆槽表面裂纹的干涉效应

运用弹性复势方法,研究纵向剪切和面内电场共同作用下无限半平面压电材料中螺型位错和偶极子与半椭圆槽表面裂纹的电弹干涉效应,得到该问题复势函数的封闭形式解答,并由此导出广义应力场、裂纹尖端的广义应力强度因子以及作用在螺型位错上的位错力.算例结果表明:增大材料压电常数会相应增大位错力、位错对裂纹尖端的屏蔽和反屏蔽效应;增大位错离裂纹尖端的距离,位错力会相应减小;变化φ(偶极子臂与x轴正半轴夹角)值会出现一个改变位错偶极子对应力强度因子作用方向的临界值.     

含半埋藏空间裂纹的Cr12冷冲凹模电磁热止裂分析

对内表面含有半埋藏半椭圆裂纹的Cr12冷冲凹模进行了电磁热止裂研究。采用数值分析的方法,对放电瞬间的耦合场进行了分析,给出了半埋藏半椭圆裂纹尖端附近温度场的分布状态;通过ZL-2型放电装置实现了半椭圆裂纹切片试样的止裂实验研究。研究结果表明：脉冲电流放电瞬间,围绕裂纹尖端的金属熔化,钝化了裂尖,得到了超细化的金属组织,提高了裂纹尖端的机械性能,阻止了干线裂纹源的开裂趋势,达到了止裂的目的。在数值模拟研究过程中采用热-电耦合的分析方法,综合考虑了材料非线性、状态变化非线性和几何非线性,数值模拟结果与实验结果比较相符。     

压电材料中非对称十字裂纹反平面问题

研究含非对称十字裂纹无限大压电弹性体在无穷远纵向剪切下任意位置作用广义集中载荷的电弹干涉效应。运用弹性复势方法,获得问题的封闭形式解答,导出非对称十字裂纹尖端的Ⅲ型广义强度因子、能量释放率和应变能密度因子表达式,并由此获得T型裂纹的相应新解答。讨论支裂纹对主裂纹尖端广义强度因子、能量释放率和应变能密度因子的影响。算例结果表明,广义集中载荷作用下非对称十字裂纹上、下半平面竖向支裂纹对横向主裂纹的干涉效应明显不同,与广义集中载荷同一半平面的支裂纹促进主裂纹扩展,而另一支裂纹抑制主裂纹扩展,且支裂纹越长,影响越大。其得到的退化结果与已有文献若干结果完全吻合。     

含损伤裂纹的前梁疲劳寿命分析

根据强度及疲劳计算结果划定前梁的危险区,在危险区域内建立局部坐标系以确定裂纹的位置、添加裂纹单元,建立前梁含不同尺寸的半椭圆表面裂纹的有限元模型。采用ANSYS Workbench软件对前梁的疲劳寿命进行估算,研究含有裂纹的前梁剩余寿命问题,分析裂纹长度、深度等参数对疲劳寿命的影响,探究疲劳寿命随影响因素的变化规律。     

不锈钢表面裂纹方向电磁检测方法

针对传统交流电磁场检测表面不定方向裂纹容易出现漏检的问题,研究了旋转磁场下感应电流方向、裂纹方向变化对平板表面裂纹检测幅值的影响,推导了裂纹走向角度与平面磁场分量波谷幅值的关系表达式,从检测机理角度提出了裂纹方向判定方法及影响因素.建立了奥氏体不锈钢表面裂纹交流电磁场检测有限元仿真模型,开发了基于双U形激励和高分辨率隧...     

十字轴表面裂纹仿真与材料的断裂韧性试验

针对万向联轴器十字轴结构安全性问题，从表面缺陷裂纹应力强度因子角度分析十字轴断裂情况。建立十字轴三维模型，运用ANSYS WorkBench对十字轴进行静力学分析，找出十字轴轴径圆弧处应力最大。然后在分析后的模型中插入半椭圆形裂纹，进行表面裂纹分析。最后，在低周疲劳试验机上进行三点弯曲试验与柔度法得到十字轴材料的平面断裂韧性。研究结果表明：在十字轴轴径处裂纹大小长半轴半径c=5mm，短半轴半径a=1mm的半椭圆形裂纹得到十字轴应力强度因子大于材料试验的KIC，十字轴出现裂纹断裂。     

半椭圆裂纹参数对压力容器应力疲劳的影响

对外壁含有半椭圆裂纹压力容器在单调递增裂纹缺陷尺寸下进行有限元计算,得到了压力容器在不同裂纹缺陷尺寸大小下的裂纹前缘应力、应力强度因子、应力循环次数的演变规律。研究结果表明,裂纹长度和深度对裂纹前缘应力及其毗邻的筒体外壁区域的弹塑性影响较大;对相同立式安装的固定式压力容器,A类焊缝裂纹缺陷压力容器的安全风险较大。所得结论为压力容器对裂纹缺陷的研究提供了参考依据。     

直角平面内圆形刚性动夹杂对边界出平面点源载荷的动态响应

采用复变函数法和多极坐标移动技术研究二维直角平面区域内可动圆形刚性夹杂在边界出平面点源载荷作用下的动态响应问题.首先构造出直角平面区域内不含有夹杂时满足直角边界应力条件的格林(Green)函数解;其次求解波动方程边值问题,建立直角平面区域内含有夹杂时满足直边界应力自由条件的散射波解,利用叠加原理写出问题的总波场.借助于夹杂边界处的位移条件和夹杂运动的动力学条件,确定夹杂运动的位移幅度和散射波解中的未知系数.给出的算例结果表明本文方法的有效实用性.     

双材料平面斜裂纹问题超奇异积分方程方法

由双材料平面问题的弹性力学基本解，应用互等功定律和坐标变换，得到双材料平面任意斜裂纹问题位移场及应力分量表达式，经代入裂纹岸应力边界条件，获得以裂纹岸位移间断作为基本未知量的超奇异积分方程组；通过适当的积分变换，用有限部积分原理处理超奇异积分，建立该问题的相应数值算法。文中对任意位置的裂纹问题进行计算，并较为系统地分析界面对裂纹应力强度因子的影响，当裂纹垂直或平行于双材料界面时，计算结果与已有结果一致。     

Effect of Internal Cooling on Tool-Chip Interface Temperature in Orthogonal Cutting

A numerical method to study the effect of internal heat sink variables on the tool-chip interface temperature in orthogonal cutting was presented. The analytical method is based on two main assumptions that the chip can be treated as a semi-infinite body with a moving heat source at the tool-chip interface and the tool can be treated as a semi-infinite body with a stationary heat source at the tool-chip interface and a uniform plane heat sink inside the semi-infinite body. An approach using the point heat partition coefficient is employed to obtain the tool-chip interface temperature distribution. The temperature distributions along the tool-chip interface with different heat sink intensities, heat sink distances from the tool-chip interface, and heat sink areas were presented. The effects of the heat sink intensity, heat sink distance from the tool-chip interface, and heat sink area on the tool-chip interface temperature were investigated. It was found that the internal cooling with a heat sink in the cutting tool could greatly affect the tool-chip interface temperature.     

双材平面中环形界面环向裂纹问题的超奇异积分方程方法

从研究环形界面双相材料平面任点处沿径向、环向作用单位力时的弹性力学基本解出发,利用Betti定律、几何关系和虎克定律得到双材料平面环向裂纹问题的位移场和应力场表达式,经代入裂纹岸应力边界条件,导出极坐标下以裂纹岸位移间断为基本未知量的超奇异积分方程组;通过适当的积分变换,用有限部积分原理处理方程组中所包含的两类奇异积分—Cauchy奇异积分和超奇异积分,解决极坐标下环形界面双材料平面环向裂纹问题用超奇异积分方程法的理论描述与数值算法。在嵌入物半径足够大时,计算结果与已发表文献对直线界面情况下平行于界面裂纹问题的计算结果一致。     

裂纹张开位移的边界配位法计算方法

提出新的应力函数，该应力函数对于表面自由的或随均布载荷的裂纹都适用。利用该应力函数导出了各种裂纹模型，在各种边界条件下的应力强度因子的计算公式及裂纹面上各点位移的计算公式。并利用边界配位法，计算了方形中心裂纹板在各种条件下裂纹面上各点的位移。     

Moving interfacial crack between two dissimilar soft ferromagnetic materials in uniform magnetic field

This paper presents the dynamic magnetoelastic stress intensity factors of a Yoffe-type moving crack at the interface between two dissimilar soft ferromagnetic elastic half-planes. The solids are subjected to a uniform in-plane magnetic field and the crack is opened by internal normal and shear tractions. The problem is considered within the framework of linear magnetoelasticity. By application of the Fourier integral transform, the mixed boundary problem is reduced to a pair of integral equations of the second kind with Cauchy-type singularities. The singular integral equations are solved by means of a Jacobi polynomial expansion method. For a particular case, closed-form solutions are obtained. It is shown that the magnetoelastic stress intensity factors depend on the moving velocity of the crack, the magnetic field and the magnetoelastic properties of the materials.     

Modified boundary layer analysis for a mode III crack problem

A modified boundary layer problem of a semi-infinite crack in an elastic-perfectly plastic material under a Mode III load is analyzed. The analytic solution of elastic fields is derived by using complex function theory. It is found that the size and the shape of the plastic zone near the crack tip depend on the elastic T-stress given on the remote boundary. A method for determining higher order singular solutions of elastic fields is also proposed. In order to determine the higher order singular solutions of the elastic fields, Williams expansion of the solution is used. Higher order terms in the Williams expansion are obtained through simple mathematical manipulation. The coefficients of each term in the Williams expansion are also calculated numerically with the J-based mutual integral     

Analysis of a conducting crack in an electrostrictive ceramic under combined electric and mechanical loading

A conducting crack in an electrostrictive ceramic under combined electric and mechanical loading is investigated. Analysis based on linear dielectric model predicts that the surfaces of the crack are not open completely but they are contact near the crack tip. The complete solution for the crack with a contact zone in a linear electrostrictive ceramic under combined electric and mechanical loading is obtained by using the complex variable formula. The asymptotic problems for a semi-infinite crack with a partial opening zone as well as for a fully open semi-infinite crack in a nonlinear electrostrictive ceramic are analyzed in order to investigate the effect of the electrical nonlinearity on the stress intensity factor under small scale nonlinear conditions. Particular attention is devoted to a finite crack in the nonlinear electrostrictive ceramic subjected to combined electric and mechanical loading. The stress intensity factor for the finite crack under small scale nonlinear conditions is obtained from the asymptotic analysis.     

Development of plastic zones and residual stress in elasto-plastic contact problems with stress singularities in elastic range

Stress singularities appear in such elastic contact problems as a plane indenter compressing a semi-infinite body, or the axisymmetric case of a turbine disc shrunk onto a shaft. The stress is infinite at the edge of the corner of the indenter and the disc as well as in neighbouring areas of the semi-infinite body and the shaft.In this paper the complex investigation of the distributions of plastic zones, deformations, pressure and residual stress has been presented for plane indenters of different shapes being in elasto-plastic contact with semi-infinite bodies. Different strain-hardening characteristics of the material, different yield criteria and states of stress/strain have been considered.The aim of the investigation is to find an answer to the question, what happens to the stress singularity, which appears in the elastic solution? The considered problem is of interest from the cognitive point of view and is of real importance in engineering practice.     

The identification and study of the critical state of a transverse crack in a zone with a lap based on artificial neural networks

A method for the identification of the geometry of a transverse crack in a layer with a lap with subsequent estimation of the critical state of its structure is proposed. The solution of the problem proceeds in two steps, which form the general method. The determination of a crack in a layer is performed with the use of artificial neural networks, which use the data of an ultrasonic study. To determine an internal crack, the problem of the pulse excitation of a wave field in a considered object was studied. Using a piezotransducer on a free coating surface, the results of an action are obtained. The input vectors for the artificial neural network are considered to be a regularly digitized echo signal. Based on the generated database of input vectors, the optimal training algorithm and the structure of the network were determined. After reconstruction of the geometry of a crack, the critical state is estimated with the use of integral equations, which were obtained from the solution of the corresponding linear problem of elasticity theory. In this problem, the coating medium is replaced by special boundary conditions on the upper surface of the layer. When using a generalized Fourier transform in the equilibrium equations in displacements, the problem is reduced to a singular first-order integral equation, whose solutions were derived by the small parameter and collocation methods. The stress-intensity coefficients were obtained and analyzed directly near the tops of the crack for various coating materials and geometric parameters of the crack.     

应用无网格法进行发动机悬置软垫裂纹扩展模拟

根据发动机悬置软垫的工作环境及橡胶材料的力学特性,将空间问题简化成平面问题。针对传统有限元方法和边界元方法模拟裂纹沿任意方向扩展存在的不足,应用新型数值模拟方法-无网格局部彼得洛夫-迦辽金方法,一种纯无网格法,对具有初始裂纹的发动机悬置软垫进行了断裂模拟,得到了裂纹的轨迹。