弯曲载荷作用下工字形截面梁腹板中心穿透裂纹的应力强度因子

工字形梁是工程中最常见的结构之一。其中的任何裂纹都将成为结构断裂失效的隐患。带有裂纹的工字形梁是典型的三维有限边界问题,用经典方法求解其裂纹的应力强度因子通常是相当困难的。文中利用裂纹非自发扩展的能量释放率建立一个求解弯曲载荷作用下工字形截面梁中心裂纹的应力强度因子的新方法。给出工字形截面梁裂纹非自发扩展能量释放率G^＊ -积分与应力强度因子的关系,同时也给出G^＊ -积分与载荷、几何参量以及力学性能参数的关系,进而得到工字形截面梁腹板中心裂纹的应力强度因子。     

G*积分理论求解应力强度因子及有限元法验证

利用G*积分理论求解管道裂纹应力强度因子.再应用ANSYS有限元分析软件,计算出纯弯曲、三点弯对称环向穿透裂纹和拉伸周期裂纹的应力强度因子.将应力强度因子的G*积分解与有限元解相比较,它们的相近验证了G*积分理论的适用性.     

平椭圆形截面管应力强度因子

作为评估管裂纹断裂韧性的重要参量,应力强度因子的确定尤为重要。为了更好地解决工程实际问题,大多数为三维裂纹问题,采用基于虚功原理和弯曲理论的裂纹张开能量释放率,即G*积分理论来求解带边界平椭圆截面管裂纹问题,得到拉伸载荷作用下平椭圆形截面管裂纹应力强度因子的G*积分表达式。给出的方法计算简单,能够得到封闭解。     

弯曲载荷作用下圆柱壳环向周期裂纹应力强度因子

应力强度因子作为表征裂纹尖端应力场强弱和断裂分析的一个重要参量,其简单而有效的求解方法具有重要的工程实际意义。利用J_2守恒积分建立了一个求解弯曲载荷作用下圆柱壳环向周期裂纹应力强度因子的计算方法。该方法原理清晰,计算简单。     

含纵向裂纹提升机主轴数值模拟分析

用数值模拟技术工具，以含纵向裂纹的提升机主轴为研究对象，分别求出裂纹位于轴心和近表面的主轴应力分布状况，利用ANSYS中子模型技术探讨了提升机主轴裂纹尖端应力应变场强度和三维裂纹J积分、应力强度因子K的计算技术，为轴类零件完整性评价判据的建立提供了一定的理论基础。     

内压圆筒中表面裂纹蠕变扩展的数值分析

金属蠕变的研究逐渐趋向对含缺陷材料与结构进行探讨,但针对金属构件表面裂纹蠕变扩展特性的研究仍然有限。基于三维有限元方法,对高温内压下含轴向表面裂纹的低合金Cr-Mo钢圆筒进行研究。有限元计算得到的应力强度因子K和蠕变裂纹驱动力参量C*积分与前人的研究进行比较,提出一种基于软件ABAQUS的步步分析方法来描述蠕变裂纹的扩展行为。最后,通过对若干不同初始形状裂纹的研究,得到四种不同初始形状的表面裂纹的形貌变化特性,以及裂纹深度、裂纹长度、C*积分和剩余寿命的变化规律。     

三维压电介质中不同电边界条件的裂纹分析

在不可导通、可导通和半可导通等三种电边界条件下，系统研究并给出三维无限横观各向同性压电介质中平行于各向同性面的、任意形状的平片裂纹在任意载荷作用下的不连续位移和不连续电势边界积分方程方法。无论平片裂纹的形状如何，结果都表明：对不可导通裂纹，应力强度因子只与机械载荷有关，电位移强度因子只与电载荷有关；而可导通裂纹的应力强度因子和电位移强度因子只与机械载荷有关，电位移强度因子由机械载荷通过压电效应产生。半可导通裂纹所对应的边界积分方程组为非线性方程组，文中给出一种迭代解法。在均布的机械载荷和电载荷作用下。裂纹腔内的电位移为一常数，只与外加载荷有关，而与裂纹形状无关。     

纵向剪切问题中圆边界上分叉裂纹的应力强度因子

采用位错配置法,研究弹性纵向剪切情况下圆边界上的分叉裂纹问题.在给出无限大域中点位错复势的基础上引入补充项,以满足圆边界自由的条件,得到圆边界上分叉裂纹问题的基本解.再由裂纹边界条件,建立奇异积分方程.然后利用半开型数值积分公式,把奇异积分方程化为代数方程,通过数值计算,直接得到裂纹端的应力强度因子值.这是一种解析数值相结合求解应力强度因子的方法,充分利用解析方法精度高和数值方法适用性广的特点,各裂纹位置可以是任意的.特例的计算结果和保角变换结果是一致的.文中算例给出远处作用纵向载荷时圆孔边缘上分叉裂纹的若干应力强度因子,以及圆柱边上作用纵向集中力时柱边缘处分叉裂纹的若干应力强度因子,讨论裂纹各分支之间的相互影响,所得的图表可以应用于工程实际.     

基于ABAQUS的货叉三维裂纹应力强度因子有限元分析

基于奇异单元法和断裂力学理论,针对叉车货叉由于锻造缺陷和疲劳引起的三维裂纹,应用ABAQUS软件研究了一种三维裂纹的建模方法,给出了计算货叉三维裂纹应力强度因子的途径,分析了裂纹深度对应力强度因子的影响。结果表明货叉三维裂纹应力强度因子随裂纹深度的增加而增加,为预测含裂纹货叉的承载能力和剩余寿命、制定判废标准等提供了相关的疲劳断裂分析参数。     

应用改进的虚拟裂纹闭合方法求解三维裂纹应力强度因子

基于有限元计算结果计算结构的能量释放率,利用能量释放率来计算结构的应力强度因子。本文对现有的虚拟裂纹闭合方法作了改进,即应用本文改进的虚拟裂纹闭合方法求解三维裂纹体应力强度因子时,裂纹前缘的裂纹面可以是任意形状,且裂纹前缘的有限元单元宽度可以不等。文中以三维表面裂纹为例,应用改进的虚拟裂纹闭合方法计算了该结构的应力强度因子,同时讨论了裂纹前缘有限单元宽度对应力强度因子的影响。     

厚壁筒双轴向表面裂纹尖端应力强度因子影响因素的研究

在现有文献对平面结构任意分布多裂纹间相互作用影响因素及厚壁筒轴向表面单裂纹尖端应力强度因子分析的基础上,提出了包含裂纹尖端应力强度因子影响因素的厚壁筒双轴向表面裂纹尖端应力强度因子公式.根据有限元方法,利用ANSYS软件对不同厚壁筒壁厚比、不同裂纹深度比及不同裂纹夹角情况下双轴向表面裂纹尖端应力强度因子进行了计算,分析...     

计算Reissner理论各向异性板应力强度因子的半权函数法

由功能互等定理导出用半权函数表示的各向异性板应力强度因子的解析表达式，并给出基于Reissner板理论含裂纹的各向异性板受弯曲、扭转和剪切作用的半权函数。计算含中心裂纹四边自由受纯弯曲作用板的应力强度因子，并与有关的结果进行比较，表明此方法简便、可靠。     

Static behaviour of a shaft with an elliptical crack

Cracks in mechanical components produce changes in their behaviour like increases of displacements or decreases of frequencies due to the flexibility increase. Some works related to the analysis of the behaviour of cracked shafts consider the front of the transversal fatigue cracks to be straight, but experience says that the front of these kind of cracks is approximately elliptical. Many expressions have been given for the flexibility of a cracked shaft with a straight front whereas, for elliptical cracks, only an approximate expression for the flexibility has been found in the literature. In the present work, flexibility expressions for cracked shafts having elliptical cracks are obtained, based on the polynomial fitting of the stress intensity factors, taking into account the size and shape of the elliptical cracks showing results according with reality. The static displacements in bending of the shaft for different support conditions have been calculated. The comparisons between these results and those obtained by FEM analysis and by experimental tests show that the closed-form expressions for the flexibility give us a very good approximation to the behaviour of the cracked shaft.     

三维有限大体中小尺寸孔边角裂纹应力强度因子显式闭合解

采用能量差率方法，导出耐久性设计中相对小尺寸孔边角裂纹应力强度因子解析形式的闭合解。根据此方法，可充分利用二维结果解决三维问题。由此所得的解答与现有数值结果符合得很好。     

含多条裂纹梁的模态与振动疲劳寿命分析

基于Paris公式,提出了一种含多条裂纹梁疲劳寿命预估的方法。在模态分析中,基于传递矩阵方法,利用无质量的弯曲弹簧等效裂纹,提出一种求解含有多条裂纹梁固有振型的方法,分析裂纹数目、裂纹位置、裂纹深度对裂纹梁固有频率的影响。在振动疲劳分析中,研究了在简谐激励作用下裂纹数目对裂纹尖端应力强度因子的影响。通过Paris疲劳裂纹扩展方程和同步分析法,考虑裂纹梁振动与裂纹扩展的相互作用,分析了裂纹数目和裂纹位置对裂纹梁疲劳寿命的影响。结果表明,裂纹数量、裂纹位置和深度对梁的模态参数和疲劳寿命有重要影响。     

Stress intensity factors for elliptical arc through cracks in mechanical joints by virtual crack closure technique

The reliable stress intensity factor analysis is required for fracture mechanics design or safety evaluation of mechanical joints at which cracks often initiate and grow. It has been reported that cracks in mechanical joints usually nucleate as corner cracks at the faying surface of joints and grow as elliptical arc through cracks, In this paper, three dimensional finite element analyses are performed for elliptical arc through cracks in mechanical joints. Thereafter stress intensity factors along elliptical crack front including two surface points are determined by the virtual crack closure technique. Virtual crack closure technique is a method to calculate stress intensity factor using the finite element analysis and can be applied to non-orthogonal mesh. As a result, the effects of clearance on the stress intensity factor are investigated and crack shape are then predicted.     

An experimental study on bending fretting fatigue characteristics of 316L austenitic stainless steel

Bending fretting fatigue tests of 316L austenitic stainless steel plates against 52100 steel cylinders have been carried out under same normal load and varied bending loads. Tests of plain bending fatigue were carried out as a control group. The S-N curves of the bending fatigue were made. The results indicated that there was an obvious drop of life under the condition of bending fretting fatigue due to higher local contact stress. A dislocation model of micro-crack nucleation mechanism, as a manner of zig-zag mode, was created to explain the nucleation of fretting fatigue cracks.     

A numerical study of crack interactions under thermo-mechanical load using EFGM

In this work, element free Galerkin method (EFGM) has been used to obtain the solution of various edge crack problems under thermo-mechanical loads as it provides a versatile technique to model stationary as well as moving crack problems without re-meshing. Standard diffraction criterion has been modified with multiple crack weight technique to characterize the presence of various cracks in the domain of influence of a particular node. The effect of crack inclination has been studied for single as well as two edge cracks, whereas the cracks interaction has been studied for two edge cracks lying on same as well as opposite edges under plane stress conditions. The values of mode-I and mode-II stress intensity factors have been evaluated by the interaction integral approach.     

Numerical studies on crack growth in a steel tubular T-joint

The results of a numerical investigation on fatigue crack growth of an offshore tubular T-joint under the action of axial, in-plane and out-of-plane bending loads are presented in this paper. Extensive stress analysis has been carried out to determine the location of the hot spot stress along the brace—chord intersection for each load case. Semi-elliptical cracks with varying crack lengths and crack depths were introduced at the hot spot location by means of line spring elements for stress intensity factor evaluation. The line springs were properly constrained to prevent the problem of crack surface penetration. The stress intensity factors obtained are then used in a crack growth law for life estimation.