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...     

基于Kirchhoff板中裂纹尖端辛本征解的有限元应力恢复方法

对于含穿透裂纹的板结构,裂纹尖端应力场及应力强度因子的计算精度对评估板的安全性具有非常重要的影响。基于含裂纹Kirchhoff板弯曲问题中裂纹尖端场的辛本征解析解,该文提出了一个提高裂纹尖端应力场计算精度的有限元应力恢复方法。首先利用常规有限元程序对含裂纹板弯曲问题进行分析,得到裂纹尖端附近的单元节点位移;然后根据节点位移确定辛本征解中的待定系数,得到裂纹尖端附近应力场的显式表达式。数值结果表明,该方法给出的应力分析精度得到较大提高,并具有良好的数值稳定性。     

裂纹板贴补应力分析

本文采用含裂纹无限大板特殊基本解和合力边界条件,用体积力法对含裂纹金属薄板的胶贴补强问题进行应力分析。使用一满足胶贴层位移连续条件的剪切单元,把问题转化为对裂纹板和贴片的分析。由于使用的特殊基本解精确满足裂纹面自由力边界条件,避免了对裂纹尖端附近的奇异场进行离散处理,因而可以比较精确地求出裂纹尖端附近的应力分布,同时由于单位集中力引起的裂纹尖端应力强度因子可以解析得到,因而可以较准确地反映出用应力强度因子的降低来表征的贴补效果。作为贴补计算的例子,文中计算了受拉力和剪力作用时,含中心裂纹的金属裂纹板在贴补前后裂纹尖端应力强度因子的降低,给出了贴片的厚度、弹性模量和尺寸及肢贴层厚度等对贴补效果的影响。     

在反平面变形下功能梯度压电板条的应力强度因子分析

利用Fourier变换技术将混合边值问题化为对偶积分方程,求解对偶积分方程得到应力强度因子以及电位移强度因子的表达式。最后通过数值计算讨论了材料参数、载荷条件以及裂纹的几何参数等对功能梯度压电材料中裂纹尖端应力强度因子的影响。     

基于裂纹尖端应力比值的含裂纹功能梯度材料圆筒应力强度因子计算方法

由于功能梯度材料（FGM）性质的特殊性,现有含裂纹FGM结构应力强度因子计算方法难以避免复杂的矩阵运算以及数值积分。该文针对含外表面环向裂纹FGM圆筒,利用FGM圆筒与均匀材料圆筒裂纹尖端应力之间的比例关系,将复杂的FGM圆筒应力强度因子求解问题转化为简单的应力值提取问题以及经验公式计算问题,仅由均匀材料圆筒应力强度因子经验公式、均匀材料圆筒和FGM圆筒裂纹尖端应力比值即可得到任意含裂纹FGM圆筒应力强度因子。该方法仅需建立2D轴对称模型即可满足计算要求,在保证精度的基础上成功回避了传统方法中的复杂矩阵运算以及数值积分,且适用于不同FGM、筒体尺寸、裂纹深度等情况下的应力强度因子计算。通过多组算例对比分析,证明该方法计算精度高、计算过程简便,便于工程应用。     

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。     

金属裂纹板复合材料修补结构的超奇异积分方程方法

根据应力强度因子在线弹性范围内具有可叠加性,将金属裂纹板复合材料修补结构进行简化,在表面裂纹线弹簧模型的基础上,建立了基于超奇异积分方程的Line-Spring模型。利用第二类Chebyshev多项式展开的方法,将超奇异积分方程转化为线性方程组,推导出以裂纹面位移表示的应力强度因子表达式,得到了裂纹尖端应力强度因子的数值解,并利用虚拟裂纹闭合法加以验证。参数分析确定了影响对称修补裂纹板应力强度因子的两个主要参数:胶层界面刚度和补片与金属板刚度比,为胶接修补结构的承载能力分析以及改进设计提供理论依据。     

薄壁结构剩余强度预测方法研究进展

综述了目前比较重要的薄壁结构剩余强度预测方法,介绍了采用应力强度因子、裂纹尖端张开位移δCTOD、裂纹尖端张开角度ψCTOA、内聚力模型参数、能量耗散、临界拉伸应力以及GTN损伤模型等方法预测剩余强度的详细过程,并比较了各种方法在预测薄壁结构剩余强度时的优缺点。此外对整体结构和非整体结构在预测时的一些细节问题也进行了分析,包括多位置损伤、裂纹偏移和分叉、焊接残余应力和强度适配以及粘接结构的问题等。     

线弹性断裂力学问题的扩展自然单元法

为了更加有效地求解线弹性断裂问题,提出了扩展自然单元法。该方法基于单位分解的思想,在自然单元法的位移模式中加入扩展项表征不连续位移场和裂纹尖端奇异场。通过水平集方法确定裂纹面和裂纹尖端区域,并基于虚位移原理推导了平衡方程的离散线性方程。由于自然单元法的形函数满足Kronecker delta函数性质,本质边界条件易于施加。混合模式裂纹的应力强度因子由相互作用能量积分方法计算。数值算例结果表明扩展自然单元法可以方便地求解线弹性断裂力学问题。     

共面三维裂纹应力强度因子干涉的研究

利用奇异有限元理论与方法对三维多裂纹的应力强度因子干涉问题进行了研究,通过构造裂纹前缘位移场的局部解,提出了一种新的裂纹前缘位移场的位移模式,通过最小势能原理和变分原理直接得到裂纹前缘干涉的应力强度因子,较好地解决了含多裂纹有限体的强度分析问题.算例说明了该方法的有效性,其计算结果为多裂纹简化为单裂纹提供了理论依据.     

计算圆筒动态应力强度因子的有限元方法与叠加积分方法

本文计算了厚壁筒的动态应力强度因子，研究了有限单元法计算动态应力强度因子的几个主要问题，提供了合理计算方案，本文还提供了计算厚壁筒动态应力强度因子的叠加积分法，方便于各种动态内压下的动态应力强度因子的计算。     

Influence of anisotropy,porosity and initial stresses on crack propagation due to Love‐type wave in a poroelastic medium

An analytical solution has been attained to establish the closed form expression of stress intensity factor at the tip of a semi‐infinite crack, dynamically propagating in an initially stressed transversely isotropic poroelastic strip due to Love‐type wave for the case of concentrated force of constant intensity as well as for the case of constant load. The study presents the sound effect of various affecting parameters viz. speed of the crack, length of the crack, horizontal compressive/tensile initial stress, vertical compressive/tensile initial stress, porosity parameter and anisotropy parameter on the stress intensity factor. In order to delineate the effects of these aforementioned parameters on the stress intensity factor graphically, numerical simulations have been accomplished. One of the major highlight of the paper is the comparative study carried out for horizontal compressive/tensile initial stress, vertical compressive/tensile initial stress, porosity parameter and anisotropy parameter with the case when the strip is isotropic, non‐porous and free from initial stresses. Wiener–Hopf technique and the Fourier integral transform has been effectuated for the procurement of the closed form expression (exact solution) of stress intensity factor.     

On Influence of Non-Singular Stress States on Brittle Fracture

In the case of sufficiently brittle material the use of stress intensity factor as a fracture parameter alone is well justified within the Linear-Elastic Fracture Mechanics. This is because the singular stress field associated with the stress intensity factor is dominant near the crack tip. However, there are numerous experimental evidences that the critical stress intensity factor to cause fracture initiation (or fracture toughness) can be affected by the specimen geometry as well as loading conditions. To address this issue a number of twoparameter criteria have been proposed in the past, which often utilise non-singular terms of the classical asymptotic expansion of the stress field near the crack tip. Therefore, there is a problem of the selection of an appropriate parameter in addition to the stress intensity factor, which could account for various effects induced by the specimen geometry and loading on initiation of brittle fracture. This short paper demonstrates that brittle fracture conditions can be successfully predicted with various two-parameter criteria, and there are no clear advantages in the use of T-stress as the additional parameter in fracture criterion, in comparison with the next non-singular term, A ₁, of the asymptotic expansion.     

Prediction of Stress Intensity Factor on Precracked Composite Wing Rib Made up of Carbon-Epoxy IM7-8552

Journal of Failure Analysis and Prevention - The stress intensity factor (SIF), K, is an important parameter to predict the stress state (“stress intensity”) near the tip of a crack...     

Effects of weld geometry and sheet thickness on stress intensity factor solutions for spot and spot friction welds in lap-shear specimens of similar and dissimilar materials

In this paper, three-dimensional finite element analyses for spot welds with ideal geometry in lap-shear specimens of different materials and thicknesses were first conducted. The computational results indicate that the stress intensity factor and J integral solutions based on the finite element analyses agree well with the analytical solutions and that the analytical solutions can be used with a reasonable accuracy. Three-dimensional finite element analyses based on the micrographs of an aluminum 6111 resistance spot weld, an aluminum 5754 spot friction weld, and a dissimilar Al/Fe spot friction weld were also conducted. The computational results indicate that the stress intensity factor and J integral solutions based on the finite element analyses for the aluminum 6111 resistance spot weld and aluminum 5754 spot friction weld with complex geometry are in good agreement with the analytical solutions for the equivalent spot welds with ideal geometry. However, the stress intensity factor and J integral solutions based on the finite element analysis for the Al/Fe spot friction weld with complex geometry are completely different from the analytical solutions for the equivalent spot weld with ideal geometry. Different three-dimensional finite element analyses based on the meshes that represent different features of the complex geometry of the Al/Fe spot friction weld were then conducted. The computational results indicate that the stress intensity factor and J integral solutions for the Al/Fe spot friction weld based on the finite element analysis agree reasonably well with the analytical solutions for the equivalent spot weld with consideration of gap and bend. The computational and analytical results suggest that the stress intensity factor and J integral solutions based on the finite element analysis and the analytical solutions with consideration of gap and bend may be used to correlate with the fatigue crack growth patterns of Al/Fe spot friction welds observed in experiments.     

Collocated interfacial stress intensity factors for finite bi-material plates

This paper deals with elastic stress intensity factors associated with stress fields near partially debonded interfaces in finite, bi-material plates. Bi-materiai stress intensity factors K₁ and K₂ are not associated, respectively, with symmetric and skew-symmetric loading and are functions of an arbitrary length parameter. Any fracture condition involving bi-material stress intensity factors must be independent of the arbitrary length parameter and must be consistent with experiment. We define a new parameter K_i called the interfacial stress intensity factor which satisfies the former condition. A truncated Williams power series stress function for stresses in a cracked bi-material plate, as modified by Sih and Rice, is used with a modified boundary collocation procedure to generate interfacial stress intensity factors for finite bi-material plates. This modified collocation technique eliminates the need for tuning the boundary points. The method is exemplified by application to a centrally cracked bi-material plate and to a partially debonded composite laminate.     

Stress intensity factor solutions for estimation of fatigue lives of laser welds in lap-shear specimens

Fatigue behavior of laser welds in lap-shear specimens of high strength low alloy (HSLA) steel is investigated based on experimental observations and two fatigue life estimation models. Fatigue experiments of laser welded lap-shear specimens are first reviewed. Analytical stress intensity factor solutions for laser welded lap-shear specimens based on the beam bending theory are derived and compared with the analytical solutions for two semi-infinite solids with connection. Finite element analyses of laser welded lap-shear specimens with different weld widths were also conducted to obtain the stress intensity factor solutions. Approximate closed-form stress intensity factor solutions based on the results of the finite element analyses in combination with the analytical solutions based on the beam bending theory and Westergaard stress function for a full range of the normalized weld widths are developed for future engineering applications. Next, finite element analyses for laser welded lap-shear specimens with three weld widths were conducted to obtain the local stress intensity factor solutions for kinked cracks as functions of the kink length. The computational results indicate that the kinked cracks are under dominant mode I loading conditions and the normalized local stress intensity factor solutions can be used in combination with the global stress intensity factor solutions to estimate fatigue lives of laser welds with the weld width as small as the sheet thickness. The global stress intensity factor solutions and the local stress intensity factor solutions for vanishing and finite kinked cracks are then adopted in a fatigue crack growth model to estimate the fatigue lives of the laser welds. Also, a structural stress model based on the beam bending theory is adopted to estimate the fatigue lives of the welds. The fatigue life estimations based on the kinked fatigue crack growth model agree well with the experimental results whereas the fatigue life estimations based on the structural stress model agree with the experimental results under larger load ranges but are higher than the experimental results under smaller load ranges.     

无限长条板中弹性与粘弹性界面裂纹尖端场

研究无限长条板中粘弹性-弹性界面Griffith裂纹在 Ⅰ 型突加载荷作用下,裂纹尖端动态应力强度因子的时间响应。利用积分变换方法、Fourier和Laplace变换,分别推导出了弹性和粘弹性问题的控制方程组;引入位错密度函数,并结合边界条件,导出了反映裂纹尖端奇异性的Cauchy型奇异积分方程组,运用Chebyshev正交多项式化奇异积分方程组为代数方程组,用配点法进行求解;最后用Laplace积分变换数值反演方法,将拉氏域内的解反演到时间域内,求得动态应力强度因子的时间响应,并对材料参数的影响进行了分析。结果表明,剪切松弛参量对 Ⅰ 型动应力强度因子的影响小于对 Ⅱ 型的影响,而膨胀松弛参量对 Ⅰ 型动应力强度因子的影响大于对 Ⅱ 型的影响。      

应力场强法中场径参数的研究

针对应力场强法中场径计算方法存在争议且不易求取的问题,基于应力场强法假设,研究了场径参数计算方法的理论依据;在考虑场径求取可行性的基础上,提出一种在任意载荷条件下确定试件场径的方法.给出了场径的求取步骤,选取6块不同应力集中系数的缺口试件在4种应力比下,按照步骤求取场径.对场径计算结果拟合并作图,由图所示分析影响场径大小的因素.得出结论:在相同应力比下,场径与应力集中系数呈很强的线性关系;在相同应力集中系数下,场径与应力比呈很强的二次曲线关系.通过实例对所提出的方法进行了验证,结果表明:由提出方法确定的场径计算得出的疲劳寿命更贴近于试验寿命,在保证安全的基础上提高了疲劳寿命预测的准确性.