基于ANSYS的含裂纹核级承压设备剩余寿命预测

含裂纹核级承压设备剩余寿命是一个关于应力强度因子KI和极限裂纹尺寸aN有关的函数,求得应力强度因子KI,便可估算剩余寿命。针对核级设备中,裂纹尖端应力强度因子难以测量的问题,本文提出了一种基于ANSYS软件的求解方法,从而预测含裂纹核级设备的剩余寿命。计算结果表明,该方法具有很高的精度,适用于复杂的核级承压设备。     

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。     

计算应力强度因子的无网格-直接位移法

目前计算裂纹尖端应力强度因子的无网格法一般均采用。积分方法,但由于该方法为间接求解,降低了求解精度与求解效率。文中采用无网格—伽辽金方法,选取带有扩展基的奇异基函数,以精确计算裂纹尖端位移场,并借鉴有限元法中计算应力强度因子的直接位移法,提出一种计算含裂结构裂纹尖端应力强度因子的新方法,即无网格—直接位移法。数值计算结果表明,该方法具有简捷、高效的特点,可以准确计算裂纹尖端应力强度因子。     

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。     

SL450水龙头中心管螺纹齿根表面裂纹应力强度因子三维有限元分析

采用三维有限元位移法求解水龙头中心管齿根危险截面上含不同形态和不同深度椭圆表面裂纹，在拉伸和内压载荷作用下的应力强度因子。较精确地给出了应力强度因子沿裂纹前缘的变化规律。在大量有限元数据结果的基础上，拟合出应力强度因子的计算表达式，为预测带裂纹的水龙头中心管的承载能力、剩余寿命、确定探伤周期、制定判废标准提供了必要的断裂分析参数。     

裂纹前沿网格参数对皮带轮应力强度因子的影响

针对皮带轮三维裂纹体端面网格数和轴向网格数的优化问题,基于应力强度因子理论,对皮带轮张开型表面裂纹前沿的网格参数进行了正交实验研究.首先,研究了正交设计理论和应力强度因子的位移法计算原理;然后,在皮带轮应力集中位置,建立了一定大小的裂纹,并对该裂纹的应力强度因子进行了有限元计算;最后,用正交设计方法设计了裂纹体周边网格...     

CD350套管吊卡应力场三维有限元分析及危险截面上裂纹应力强度因子求解

首先对ＣＤ３５０套管吊卡三维应力场进行分析，进而采用有限元位移法，求解危险截面处不同深度和形态表面角裂纹的应力强度因子。在大量有限元计算基础上，拟合出关于角裂纹特征参数的无量纲应力强度因子表达式，为预测带裂纹的套管吊卡的承载能力、剩余寿命、确定探伤周期、制定判废标准等提供了必要的断裂分析参数。     

曲轴的疲劳断裂分析

系统阐述利用有限元法对机械结构零部件进行疲劳断裂分析的相关理论和方法。在此基础上对16V240机车柴油机曲轴的最危险曲拐进行最大和最小工况下的三维有限元分析，确定裂纹易产生的危险截面，求解危险截面处不同深度和形态的表面椭圆裂纹的应力强度因子，并拟合关于椭圆裂纹特征参数及总体坐标下的等效应力强度因子的近似表达式。为预测含裂纹曲轴的承载能力、剩余寿命、制定判废标准等提供相关的疲劳断裂参数。     

多点分布载荷作用下TBM刀盘裂纹萌生寿命预测

隧道掘进机(TBM)是用于隧道掘进的大型复杂工程机械,刀盘是TBM的关键部件承载数十把滚刀与岩石作用。掘进时的反力和扭矩作用在刀盘上容易产生裂纹降低寿命,刀盘的寿命制约着TBM的寿命。为了研究刀盘的寿命,提出了综合运用多体动力学和有限元计算刀盘动应力的一种方法并使用此方法计算了刀盘的动应力,计算结果与实测数据的均值误差仅为13%。对动应力进行统计计数并按照幅值的分布规律将其分为八级,结合材料的应力-寿命曲线对刀盘裂纹萌生寿命进行了预测,预测结果表明刀盘的裂纹萌生寿命为84天。裂纹萌生寿命预测结果可以为TBM刀盘的抗疲劳设计提供参考,也可以为安排施工检修周期提供依据。     

T形焊接接头根部裂纹应力强度因子研究

建立T形焊接接头根部裂纹的半椭圆裂纹模型,定义裂纹模型的构形参数以及边界条件,分析裂纹尖端的应力强度因子。采用奇异单元法,通过有限元计算,模拟裂纹尖端的应力奇异性。并通过收敛性检验确定裂纹尖端的单元尺寸。在此基础上,计算裂纹尖端量纲一应力强度因子,并分析其受几何参数影响的变化规律。计算结果表明,对于给定的载荷条件下,不同初始裂纹尺寸时,裂纹尖端的应力强度因子存在一定的规律性,且不同几何参数对应力强度因子的影响程度存在一定差异,因此,对焊接结构疲劳强度研究时需要有一定的侧重点。采用多重线性回归方法拟合仿真计算结果,这些结果为进一步研究T形焊接接头根部裂纹扩展和疲劳寿命预测提供参考。     

Numerical analysis for prediction of fatigue crack opening level

Finite element analysis (FEA) is the most popular numerical method to simulate plasticity-induced fatigue crack closure and can predict fatigue crack closure behavior. Finite element analysis under plane stress state using 4-node isoparametric elements is performed to investigate the detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The mesh of constant size elements on the crack surface can not correctly predict the opening level for fatigue crack as shown in the previous works. The crack opening behavior for the size mesh with a linear change shows almost flat stress level after a crack tip has passed by the monotonic plastic zone. The prediction of crack opening level presents a good agreement with published experimental data regardless of stress ratios, which are using the mesh of the elements that are in proportion to the reversed plastic zone size considering the opening stress intensity factors. Numerical interpolation results of finite element analysis can precisely predict the crack opening level. This method shows a good agreement with the experimental data regardless of the stress ratios and kinds of materials.     

A study on the determination of closing level for finite element analysis of fatigue crack closure

An elastic-plastic finite element analysis is performed to investigate detailed closure behavior of fatigue cracks and the numerical results are compared with experimental results. The finite element analysis performed under plane stress using 4-node isoparametric elements can predict fatigue crack closure behavior. The mesh of constant element size along crack surface can not predict the opening level of fatigue crack. The crack opening level for the constant mesh size increases linearly from initial crack growth. The crack opening level for variable mesh size, is almost flat after crack tip has passed the monotonic plastic zone. The prediction of crack opening level using the variable mesh size proportioning the reversed plastic zone size with the opening stress intensity factors presents a good agreement with the experimental data regardless of stress ratios.     

复合材料补片参数对裂纹尖端应力强度因子的影响

利用有限元法对复合材料补片修补前后的铝合金薄板的裂纹尖端应力强度因子KI进行研究,分析各类补片参数对裂纹尖端应力强度因子的影响.结果表明,在正确选择复合材料补片的参数后,修补后铝合金板裂纹尖端的应力强度因子有显著地下降.     

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.     

Optimisation Method for Determination of Crack Tip Position Based on Gauss-Newton Iterative Technique

In the digital image correlation research of fatigue crack growth rate,the accuracy of the crack tip position determines the accuracy of the calculation of the stress intensity factor,thereby affecting the life prediction.This paper proposes a Gauss-Newton iteration method for solving the crack tip position.The conventional linear fitting method provides an iterative initial solution for this method,and the preconditioned conjugate gradient method is used to solve the ill-conditioned matrix.A noise-added artificial displacement field is used to verify the feasibility of the method,which shows that all parameters can be solved with satisfactory results.The actual stress intensity factor solution case shows that the stress intensity factor value obtained by the method in this paper is very close to the finite element result,and the relative error between the two is only-0.621％;The Williams coefficient obtained by this method can also better define the contour of the plastic zone at the crack tip,and the maximum relative error with the test plastic zone area is-11.29％.The relative error between the contour of the plastic zone defined by the conventional method and the area of the experimental plastic zone reached a maximum of 26.05％.The crack tip coordinates,stress intensity factors,and plastic zone contour changes in the loading and unloading phases are explored.The results show that the crack tip change during the loading process is faster than the change during the unloading process;the stress intensity factor during the unloading process under the same load condition is larger than that during the loading process;under the same load,the theoretical plastic zone during the unloading process is higher than that during the loading process.     

研究冷挤压孔附近残余应力强度因子分布的激光散斑—权函数混合法

根据确定裂纹应力强度因子权函数法基本理论的特征，提出实验力学－权函数混合法的构想，为解决更复杂和三维问题等难提供一种有效的新途径。用激光散斑－权函数混合法研究了冷挤压孔附近残余应力强度因子的变化规律，得到的结果对冷挤压孔加工工艺中控制裂纹长度，提高构件的疲劳寿命和可靠性设计可起到指导性的作用。     

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.     

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.