应力强度因子计算的边界元法

本文利用非连续元离散边界的积分方程，推导了奇异积分的具体表达式，将非连续边界元和多域缩聚法用于二维弹性断裂应力强度因子计算，得到了合理的计算结果。     

双轴弯曲载荷下表面裂纹应力强度因子的数值计算

本文通过FRANC3D软件计算双轴弯曲载荷下表面裂纹前缘的应力强度因子,数值计算和理论计算结果基本吻合;通过等裂纹面积不同纵横比的表面裂纹前缘应力强度因子的分析可知:当表面裂纹为浅裂纹时,等裂纹面积下a/c=1/3时椭圆表面裂纹最为危险;当表面裂纹为深裂纹时,等裂纹面积下a/c=2时椭圆表面裂纹最为危险。     

表面裂纹应力强度因子计算及扩展跟踪的权函数法

 介绍了一种显式的权函数法,并将这种方法用于圆柱形容器接管外拐角表面裂纹的应力强度因子计算和扩展跟踪上.结果表明,权函数法可以用于分析各种载荷下不同形状的裂纹.就一般的工程问题而言,权函数法不失为一种与有限元法互补的方便有效的分析方法.     

一个简化的表面裂纹应力强度因子的计算公式

通过三点弯曲加载的表面裂纹试样研究了碳氮共渗、渗氮及调质几种不同热处理的(?)面裂纹疲劳扩展行为。试验证实:半椭圆表面疲劳裂纹的长轴(c)、短轴(α)与试样厚度(B)符合α/c α/B=0.99±,,12的关系式。并且在我们的试验范围内(0.33≤α/c≤0.71;0.29≤α/B≤0.67),其长轴端应力强度因子可用简单的放学式进行计算:△K_c=A·△,(πc)/(1/2)·M_w.其中A≈0.5。由此大大简化了表面裂纹应力强度因子的计算。     

应力强度因子计算的样条虚边界元法

含有裂纹的工程结构在荷载作用时在裂纹尖端会产生应力奇异的现象,其严重的程度可用应力强度因子来表征。采用基于Kelvin基本解的样条虚边界元法,结合位移外推法,给出了断裂问题应力强度因子的求解方法。通过对两个典型断裂问题的分析,对边界子段与虚边界元的划分、小单元的采用以及拟合点位置的确定等关键问题展开了讨论,获得了相关计算参数的选取规律,为该法在断裂问题的进一步应用打下良好的基础。     

区域分裂法用于抽油杆表面椭圆裂纹应力强度因子的三维有限元计算

本文用三维有限元方法求解抽油杆表面椭圆裂纹在拉伸载荷下的应力强度因子。采用区域分裂算法，由裂端２７节点奇异单元位移场可精确、连续地给出应力强度因子沿裂纹的变化．算例与数值计算吻合得很好，表明本文结果有较高的精度。     

裂纹面荷载作用下多裂纹应力强度因子计算

该文基于比例边界有限元法计算了裂纹面荷载作用下平面多裂纹应力强度因子.比例边界有限元法可以给出裂纹尖端位移场和应力场的解析表达式,该特点可以使应力强度因子根据定义直接计算,同时不需要对裂纹尖端进行特殊处理.联合子结构技术可以计算多裂纹问题的应力强度因子.数值算例表明该文方法是有效且高精确的,进而推广了比例边界有限元法的...     

含曲线裂纹柱体扭转问题的新边界元法

研究了带曲线裂纹柱体的扭转断裂问题,推导出了可以直接应用于任意形状截面含有任意形状曲线裂纹的柱体扭转问题的新的边界积分方程,并建立了带裂纹柱体扭转问题的边界元数值计算方法,提出了裂纹尖端的奇异元和线性元插值模型,给出了抗扭刚度和应力强度因子的边界元计算公式。该文对含有圆弧裂纹、曲线裂纹及直线裂纹的不同截面形状柱体的典型问题进行了数值计算,所得结果证明了边界元方法的正确性和有效性。     

新的估算表面裂纹应力强度因子经验公式

该文给出了新的估算拉伸和纯弯曲载荷下表面裂纹应力强度因子的经验公式。根据疲劳裂纹扩展的数值模拟结果确定强度因子分布函数;利用按已知应力强度因子分布函数求裂纹形状及相应应力强度因子的方法计算给定尺寸的表面裂纹的应力强度因子;通过对数值结果的曲线回归得到估算表面裂纹应力强度因子经验公式。利用该公式对有限厚度和宽度平板内表面裂纹的应力强度因子进行了估算,并与已知的半椭圆形表面裂纹的应力强度因子解进行了比较。该文结果为估算表面裂纹应力强度因子提供了一种新的途径。     

自增强厚壁圆筒轴向内表面裂纹的应力强度因子

本文研究用有限元通用程序计算具有残余应力的自增强厚壁圆筒内半椭圆形表面裂纹的应力强度因子的方法。所考虑的应力强度因子被分为相应于工作内压及残余应力两部分,分别用三维有限元通用程序算得的裂纹前沿单元节点的垂直位移直接计算,对后者又运用了“叠加原理”.结果表明,残余应力的存在能有效地降低内裂纹的应力强度因子值,自增强度高者这一作用亦显著,残余应力引起的应力强度因子对裂织数目不敏感。     

动载荷下应力强度因子的边界元计算

用Ｎａｒｄｉｎｉ－Ｂｒｅｂｂｉａ边界元法计算了动载荷下的应力强度因子，与解析解及有限元解相比较，效果较好。最后对计算结果进行了分析讨论。     

STRESS INTENSITY FACTORS FOR SURFACE CRACKS AT A HOLE BY A THREE-DIMENSIONAL WEIGHT FUNCTION METHOD WITH STRESSES FROM THE FINITE ELEMENT METHOD

Stress intensity factors for semielliptical surface cracks emanating from a circular hole are reported in this paper. The three-dimensional weight function method with three-dimensional finite element solutions for the uncracked stress distribution is used for the analysis. Two different loading conditions, i.e. remote tension and wedge loading, are considered for a wide range of geometrical parameters. Both single and double surface cracks are studied and compared with other solutions available in the literature. Typical crack opening displacements are also provided.     

STRESS INTENSITY FACTORS FOR A FUNCTIONALLY GRADED MATERIAL CYLINDER WITH AN EXTERNAL CIRCUMFERENTIAL CRACK

This paper presents mode I stress intensity factors for external circumferentially cracked hollow cylinders, which are assumed to be made of functionally graded materials and subjected to remote uniform tension. The conventional finite element method is improved by introducing isoparametric transformation for simulating the gradient variations of material properties in the finite elements. This improved finite element method is verified to be effective and efficient. Various types of functionally graded materials and different gradient compositions for each type are investigated. The results show that the material property distribution has a quite considerable influence on the stress intensity factors.     

STRESS INTENSITY FACTORS FOR CORNER CRACKS AT A HOLE BY A 3-D WEIGHT FUNCTION METHOD WITH STRESSES FROM THE FINITE ELEMENT METHOD

Abstract— Stress intensity factors for quarter-elliptical corner cracks emanating from a circular hole are determined using a 3-D weight function method combined with a 3-D finite element method. The 3-D finite element method is used to analyze uncracked configurations and provide stress distributions in the region where a crack is likely to occur. Using this stress distribution as input, the 3-D weight function method is used to determine stress intensity factors. Three different loading conditions, i.e. remote tension, remote bending and wedge loading, are considered for a wide range of geometrical parameters. The significance of using 3-D uncracked stress distributions is studied. Comparisons are made with solutions available in the literature.     

STRESS INTENSITY FACTORS AND WEIGHT FUNCTIONS FOR SEMI-ELLIPTICAL SURFACE CRACKS IN FINITE-THICKNESS PLATES UNDER TWO-DIMENSIONAL STRESS DISTRIBUTION

Abstract— A Fourier series approach is proposed to calculate stress intensity factors using weight functions for semi-elliptical surface cracks in flat plates subjected to two-dimensional stress distributions. The weight functions were derived from reference stress intensity factors obtained by three-dimensional finite element analyses. The close form weight functions derived are suitable for the calculation of stress intensity factors for semi-elliptical surface cracks in flat plates under two-dimensional stress distributions with the crack aspect ratio in the range of 0.1 ≤ a/c ≤ 1 and relative depth in the range of 0 ≤ a/t ≤ 0.8. Solutions were verified using several two-dimensional non-linear stress distributions; the maximum difference being 6%.     

A LOCAL GRID REFINEMENT METHOD FOR DETERMINING STRESS INTENSITY FACTORS FOR CRACKS AT NOTCHES

Abstract— Stress intensity calibrations have been determined for cracks at the root of a semi-circular edge notch loaded in tension using a localised grid refinement technique for finite element analysis. The technique is of particular value in situations where a fully connected mesh model is difficult to achieve or where enhanced accuracy is needed in a small sub-region of a model. Solutions were as accurate as those from a conventional refined mesh but with an approximately two fold reduction in run time. The resulting stress intensity factors are in good agreement with those estimated using a notch correction function and the equivalent un-notched crack solution.     

WEIGHT FUNCTIONS AND STRESS INTENSITY FACTORS FOR SEMI-ELLIPTICAL CRACKS IN T-PLATE WELDED JOINTS

Weight functions were derived for the deepest point and surface point of a semi-elliptical surface crack in T-plate joints with weld angles between 0 and 45°. These weight functions were derived from reference stress intensity factor solutions obtained from three-dimensional finite element calculations, and verified using stress intensity factors for different non-linear stress fields and for far-field tension and bending cases. The differences between the weight function predictions and the finite element data were less than 10%. They are suitable for semi-elliptical surface cracks with aspect ratios in the range 0.05 ≤ a/c ≤ 1, together with relative depths 0 ≤ a/t ≤ 0.6 and weld angles 0 ≤ φ ≤ 45°.     

关于瞬态应力强度因子和裂纹扩展加速度之间的关系探讨

将动态焦散线法与高速摄影技术相结合,本文记录了高分子材料悬臂梁内裂纹扩展加速、减速过程。一方面,利用动态焦散线可确定扩展裂尖的瞬态应力强度因子;另一方面,利用最小二乘法将裂纹扩展的水平、垂直位移分量拟合成时间(t)的四次多项式,描述了裂纹扩展方向、裂纹扩展加速度以及裂纹扩展加速度与动态应力强度因子的关系。结果表明:裂纹扩展加速度与动态应力强度因子之间存在一定的依赖关系;利用最小二乘法将裂纹扩展的水平、垂直分量拟合成时间(t)的四次多项式,可以对裂纹的扩展方向、加速度进行定量分析。     

ON DETERMINING STRESS INTENSITY FACTORS FOR MIXED MODE CRACKS FROM THERMOELASTIC DATA

Abstract— An alternative methodology is presented for determining stress intensity factors for cracks subject to mixed-mode displacements. The methodology involves thermoelastic data generated from a SPATE (Stress Pattern Analysis by Thermal Emission) system and has been adapted from one used successfully in photoelasticity. The thermoelastic data is collected throughout the elastic stress field dominated by the crack tip singularity. The stress field is described using a Fourier series within Muskhelishvili's approach. This method allows different applied stress fields to be described which may include transient or non-uniform stress fields. The results obtained using the new methodology are at least as good as those obtained previously for pure mode I cases, and generally better for mixed mode displacement conditions.