轴承表面裂纹应力强度因子有限元分析

在ANSYS中建立152726QT铁路用滚动轴承的模型,在受力最大处建立裂纹,手动生成裂纹尖端处的奇异单元,建立接触对并且编写受力函数,设置路径在不同载荷作用下分别对不同长度的裂纹在不同深度的应力强度因子进行有限元计算,分析裂纹长度及载荷对应力强度因子的影响。     

铝合金点焊拉剪接头疲劳性能及寿命分析

研究了铝合金AA5754点焊拉剪接头的疲劳性能,获得了不同厚度试件的载荷寿命曲线。研究了铝合金焊点的疲劳失效模式,讨论了焊点疲劳裂纹的扩展形式,并测量了裂纹扩展路径与点焊熔核界面之间的角度。分析了点焊拉剪试件在同时承受I型和II型载荷时,疲劳裂纹的扩展方向,并与测量值进行了比较。利用疲劳破坏后沿铝板厚度方向的实际裂纹长度修正了裂纹尖端的局部应力强度因子,提出了评价焊点寿命的疲劳参量K(i),并对试验数据进行了分析比较。结果证明K(i)可以有效关联试件尺寸效应和焊点疲劳寿命,能够用于预测焊点疲劳寿命。     

平衡轴力作用下K节点焊缝周围应力分布规律

首先建立了焊接K节点的有限元分析模型,计算了承受平衡轴力作用下的K型管节点在焊缝周围的应力分布情况.然后通过对420个K节点模型进行的参数分析,研究了表征K节点的几个主要几何参数对热点应力分布规律的影响.通过模型分析,发现在平衡轴力作用下K型管节点焊缝周围应力分布情况是要受几何参数影响的.在几何参数不同的情况下,热点应力的位置会在冠点和鞍点之间发生移动.由于热点应力处是疲劳裂纹出现的位置,因此K节点疲劳断裂过程是要受到几何参数影响的.     

Ring crack propagation in silicon nitride under rolling contact

Silicon nitride has been found to have the optimum combination of properties which are suitable for rolling element bearing applications to withstand high loads, severe environments, and high speeds. Surface ring cracks are difficult to detect but are found on the surface of silicon nitride balls. These ring crack defects decrease the rolling contact fatigue life considerably. This paper presents an experimental study and numerical analysis of ring crack propagation in rolling contact. The contribution of this study is to provide understanding of ring crack propagation behaviour and life prediction in rolling contact. Rolling contact tests are performed on the silicon nitride/steel elements. Silicon nitride ball surfaces are examined before testing using a dye-penetrant technique and optical microscopy. The surfaces are examined using optical microscopy and scanning electron microscopy during testing and after failure. The numerical calculations are based on a 3D model of ring crack growth. The rolling contact loading is simulated by a repeated Hertzian surface load with normal pressure and tangential traction. Fracture mechanics analysis is utilised to determine the stress intensity along the crack front and the stress intensity factors are analysed using a 3D boundary element model. Life predictions from the present calculations are in line with the experimental observations.     

Gear crack propagation investigations

Analytical and experimental studies were performed to investigate the effect of gear rim thickness on crack propagation life. The FRANC (FRacture Analysis Code) computer program was used to simulate crack propagation. The FRANC program used principles of linear elastic fracture mechanics, finite element modelling, and a unique re-meshing scheme to determine crack tip stress distributions, estimate stress intensity factors, and model crack propagation. Various fatigue crack growth models were used to estimate crack propagation life, based on the calculated stress intensity factors. Experimental tests were performed in a gear fatigue rig to validate predicted crack propagation results. Test gears were installed with special crack propagation gauges in the tooth fillet region to measure bending fatigue crack growth. Good correlation between predicted and measured crack growth was achieved when the fatigue crack closure concept was introduced into the analysis. As the gear rim thickness decreased, the compressive cyclic stress in the gear tooth fillet region increased. This retarded crack growth and increased the number of crack propagation cycles to failure.     

全断面隧道掘进机刀盘裂纹尖端应力强度因子收敛性分析

针对全断面隧道掘进机刀盘裂纹损伤及寿命预测等工程问题,提出了基于子模型技术的应力强度因子求解方法,并用含裂纹的矩形钢板对该方法进行了验证,分析了裂纹网格参数对刀盘裂纹尖端应力强度因子的收敛性影响。结果表明,钢板的应力强度因子数值和理论计算结果最大相对误差为3.6%。同时得到了保证刀盘应力强度因子求解精度和效率的裂纹单元网格参数,为结构的裂纹扩展寿命预测提供了参考。     

基于扩展有限元模型的动态应力强度因子计算

为准确计算基于扩展有限元法（XFEM）的裂纹扩展模型中的应力强度因子,在ABAQUS软件中建立中心裂纹平板和三点弯曲的XFEM模型,采用相互作用积分法,通过用户子程序接口分别实现了Ⅰ型、Ⅱ型断裂模式下裂纹扩展过程中应力强度因子的计算;研究了网格密度与积分半径对XFEM模型应力强度因子计算精度的影响规律,研究结果表明：当网格密度因子为0.012~0.016、相对积分半径为3时,应力强度因子收敛至稳定值,计算误差不超过3%。利用所提方法与程序计算了单边带孔疲劳裂纹扩展试样的动态应力强度因子,试验结果表明：基于Paris理论预测的剩余寿命与疲劳试验结果误差为5.3%,进一步验证了所提方法与程序的正确性。     

基于ABAQUS的圆柱直齿轮齿根裂纹扩展与寿命估计

以渐开线直齿轮为研究对象,通过齿轮应力分析确定轮齿裂纹易萌生位置,利用ABAQUS软件建立齿轮裂纹扩展有限元模型,获取齿根裂纹扩展路径,计算不同阶段裂纹尖端应力强度因子。通过多种曲线拟合方式的对比,选取指数函数建立的裂纹长度与裂纹尖端应力强度因子幅之间的函数关系。运用Paris公式构建裂纹扩展速率模型,实现含齿根裂纹齿轮的寿命估计。     

裂纹位置对焊接接头断裂参量的影响

结合焊接结构的工程安全评定,针对焊接接头熔合线上容易出现缺陷的问题,本文利用有限元计算方法,编写了断裂参量J积分计算的有限元程序,并对裂纹位置不同时的焊接接头进行了有限元计算。结果表明,无论是平面应变还是平面应力条件下,焊接接头J积分值都与全母材和全焊缝材料不同;与此同时,裂纹位于熔合线上和裂纹处于焊缝中,焊接接头的J积分值也是有所差异的,并且,这种差异在平面应变状态下表现得更加明显。在实际工作中,对焊接接头的断裂参量的计算必须考虑裂纹所处位置的影响。     

固体发动机药柱表面裂纹分析

为确保含表面裂纹的固体发动机能正常点火发射，基于线粘弹性三维有限元。确定发动机药柱点火发射时的危险部位，在危险部位设置不同深度的裂纹，于裂纹尖端构建奇异三维裂纹元。模拟裂纹扩展，分别计算随着裂纹扩展所对应裂纹深度的各类应力强度因子，由此判断裂纹的稳定性。通过对某翼锥柱组合型并含前后伞盘的固体发动机药柱在点火发射时的数值分析，评估了药柱表面裂纹的稳定性。     

Pipe crack identification based on finite element method of second generation wavelets

In this paper, a new method is presented to identify crack location and size, which is based on stress intensity factor suitable for pipe structure and finite element method of second generation wavelets (SGW-FEM). Pipe structure is dispersed into a series of nested thin-walled pipes. By making use of stress intensity factor of the thin-walled pipe, a new calculation method of crack equivalent stiffness is proposed to solve the stress intensity factor of the pipe structure. On this basis, finite element method of second generation wavelets is used to establish the dynamic model of cracked pipe. Then we combine forward problem with inverse problem in order to establish quantitative identification method of the crack based on frequency change, which provides a non-destructive testing technology with vibration for the pipe structure. The efficiency of the proposed method is verified by experiments.     

中间轴一系簧垂向刚度对2C0机车构架安全性的影响

以资阳机车厂出口到纳米比亚的Co-Co轴式机车转向架构架为例。首先对整体构架进行有限元分析,然后利用子模型法对危险部位进行精确分析,并利用热点应力法提取焊缝附近的热点应力。研究了中间轴一系簧垂向刚度对构架各危险部位热点应力值的影响。从构架安全性及机车动力学性能综合考虑,认为中间轴一系簧垂向刚度为端轴的0.75倍是比较合理的。     

Growth simulation for 3D surface and through-thickness cracks using SGBEM-FEM alternating method

An SGBEM-FEM alternating method had been proposed by Nikishkov, Park and Atluri for the analysis of three-dimensional planar and non-planar cracks and their growth. The proposed method is an effective method for fatigue or stress corrosion crack growth simulation. During crack growth simulation, however, an oscillation phenomenon is observed in crack advance or stress intensity factor distribution. If oscillating amplitude in SIF or crack advance does not decrease during next increment steps, the crack growth simulation fails. In this paper several methods are examined to remove the oscillation phenomenon. As a result, it is found that smoothing in stress intensity factor distribution or in crack front geometry can remove or weaken the oscillation phenomenon. Using the smoothing techniques, stress corrosion crack growth simulation is performed for a semi-elliptical surface crack and a through-thickness crack embedded in a plate. Crack front shape and stress intensity factor distribution are obtained after each increment during the crack growth. And the depth and length of a crack are obtained as a function of time. It is noted that the SGBEM-FEM alternating method is a very effective method for SCC growth simulation for a surface crack and a through-thickness crack.     

点焊搭接接头中的应力分布及接头疲劳行为研究

基于实际点焊接头硬度分布的分析,建立了包括熔核,热影响区和母材的单点点焊搭接接头计算模型。用三维弹塑性有限元分析方法,全面分析了点焊搭接头的应力分布情况。分析结果表明：接头搭接区内表面上焊点边缘处的应力集中是接头高周疲劳裂纹起裂和扩展的决定因素。焊点边缘附近区域中的存在的高应力,导致高周疲劳裂纹由强度较低的母材起裂并扩展。     

Three-Dimensional Simulation of Rolling Contact Fatigue Crack Growth in UIC60 Rails

In this article, a UIC60 rail with accurate geometry is studied by employing the finite element method. For this purpose, a three-dimensional elastic-plastic finite element model is conducted using model. In addition, the stress distribution of wheel-rail operation is acquired, and its effects on fatigue life are specified by damage mechanic methods. In the finite element model, the displacements and stress intensity factors (SIFs) are computed on the crack near the leading edge to calculate crack propagation trajectories and crack growth rate. The modified Paris model is used to estimate fatigue crack growth rates.     

运用无网格伽辽金法(EFGM)评价点焊节点的应力强度因子

在设计汽车骨架等薄壁点焊结构时,必须对薄壁构件焊点的疲劳强度进行精确评估。点焊点处的接触界面可以看作是一种环形裂纹,对其疲劳强度的评估可以通过计算线性弹性断裂力学中的应力强度因子K来完成。对于多轴疲劳载荷试验而制作的双杯（double cup）薄板点焊试件,在对焊点处裂纹扩展分析的基础研究中,利用无网格伽辽金法（enriched element-free Galerkin method,Enriched EFGM）对双杯试件点焊接触点进行分析,同时验证应力强度因子的精确性。     

Criteria for crack initiation during rubber abrasion

The crack initiation process during blade abrasion of a rubber surface has been investigated both experimentally and using a FEA simulation. At first the crack initiates at the location of the maximum tensile stress, yielding a crack growth angle of between 30° and 50° with the rubber surface, with the angle increasing with the normal load applied on the blade. The crack growth angle reduces as the initial crack propagates. It passes through several steps, each with a reduced crack growth angle and eventually reaches a much smaller angle generally observed at the steady state of abrasion. This initial crack growth process is predicted well by the FEA simulation. Both the experimental and the calculated results suggest that the initial cracks in rubber abrasion originate from micro-vibrations generated during the slip stage of stick-slip motion, which arises during the frictional contact between a soft rubber and hard abrader.     

Statistical aspects of fatigue crack growth life of base metal,weld metal and heat affected zone in FSWed 7075-T651 aluminum alloy

The statistical aspects of fatigue crack growth life of base metal (BM), weld metal (WM) and heat affected zone (HAZ) in friction stir welded (FSWed) 7075-T651 aluminum alloy has been studied by Weibull statistical analysis. The fatigue crack growth tests were performed at room temperature on ASTM standard CT specimens under three different constant stress intensity factor range controls. The main objective of this paper is to investigate the effects of statistical aspects of fatigue crack growth life on stress intensity factor ranges and material properties, namely BM, WM and HAZ specimens. In this work, the Weibull distribution was employed to estimate the statistical aspects of fatigue crack growth life. The shape parameter of Weibull distribution for fatigue crack growth life was significantly affected by material properties and the stress intensity factor range. The scale parameter of WM specimen exhibited the lowest value at all stress intensity factor ranges.     

Effect of circular cavity on maximum equivalent stress and stress intensity factor at a crack in buried pipeline

The effects of cavities on maximum equivalent stresses of buried pipelines are investigated in terms of two factors such as size and location of the underground cavities by using a finite element code. It has been found that the cavities affect maximum equivalent stresses of buried pipeline significantly in case that the diameters of cavities are larger than that of the pipeline. The variation of the stress intensity factors for a crack existing on the buried pipeline nearby cavities is also studied. The mode II stress intensity factor, K_II, for a tilt crack located at the top portion of a buried pipeline is found to be influenced significantly regardless of the location of the underground cavities.     

大型隔膜泵曲轴三维裂纹起裂裕度有限元分析

讨论基于断裂力学理论求解应力强度因子的方法。在此基础上介绍利用Ansys有限元分析软件对含有三维裂纹的隔膜泵曲轴应力强度因子进行计算的过程,同时介绍使用Ansys软件自带的宏命令建立含三维裂纹模型的方法,并使用该方法对含三维裂纹曲轴各个截面在12种工况下分别进行分析,得出各个截面存在裂纹时的危险等级。通过有限元分析计算,可以判断曲轴裂纹是否扩展,从而为生产过程中的探伤等工艺提供参考。