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在依据Reissner理论得出的球壳裂纹尖端应力应变场展开式基础上,采用局部—整体分析法和权函数方法分别计算承受内压的含孔边裂纹球壳的应力强度因子.在有限元的模式中考虑剪切变形的影响,并对奇异元模式的应力应变场展开式的项数选择、奇异元最佳尺寸的选取进行了分析.本文计算和分析了在不同几何尺寸,不同开孔大小以及不同剪切参量条件下承受内压的含孔边裂纹球壳的应力强度因子及其变化规律. 相似文献
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在较小范围屈服条件下,将D-M模型和弹塑性线弹簧模型相结合,建立了屈服后一般扁壳表面裂纹的计算模型,导出了其控制方程和相应的COD计算公式。在此基础上,提出了屈服后一般扁壳表面裂纹与平板穿透裂纹的等COD换算方法。通过各种影响因素的分析并去除次要因素,最终给出了该等效换算关系的简单拟合公式。计算结果表明,该分析方法简便且有足够的工程精度,适应于在役压力容器等结构的现场快速断裂评定。 相似文献
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《应用力学学报》2021,(3)
为了得到含环向裂纹压弯薄壁圆柱壳失稳的极限荷载,基于Je?ek解析法,先利用裂纹面的平衡方程、变形几何关系和物理方程,得到在压弯荷载作用下圆柱壳轴力与裂纹面挠度的关系式;再利用极值条件,推导出在轴压和弯矩共同作用下含裂纹薄壁圆柱壳失稳时极限荷载的解析表达式。利用数值计算分析裂纹长度、长细比以及端部施加弯矩对圆柱壳极限荷载、弹性区高度和圆柱壳裂纹截面处挠度的影响,通过有限元数值结果验证极限荷载解析解的准确性。计算结果表明:与无裂纹完善构件相比,弯矩对含裂纹圆柱壳的极限荷载Pu的影响最为显著,其降低幅值可达3.78%~23.18%;弯矩的增加也会导致构件弹性区高度逐渐减小,裂纹面处的挠度呈非线性增长。本文研究弥补了目前该类问题缺乏理论解析解的不足。 相似文献
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研究了振动波在含有环向表面裂纹的无限长圆柱壳中的传播特性.圆柱壳体的振动用Flügge方程来描述.运用线弹性断裂力学的理论,考虑到裂纹的张开、滑移和撕裂3种模式以及它们相互之间的耦合,利用分布的线弹簧来模拟裂纹并建立了裂纹所在区域的局部柔度矩阵,得到由此引起的附加位移和壳体中内力之间的关系.在入射波已知的情况下,根据裂纹两侧区域的位移和内力的连续性条件得到了反射和透射波的幅值系数.分析了入射波通过裂纹后的透射、反射系数与激励频率和裂纹尺寸之间的关系.为基于振动功率流方法识别圆柱壳表面损伤提供了理论基础. 相似文献
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提出球壳轴对称弯曲问题共轭二阶挠度微分方程并给出了初等函数解.
球壳微分方程是薄壳理论三大壳之一旋转壳的典型方程. 共轭二阶挠度微分方程是球
壳中微分方程形式最简单的, 是人们最喜爱的挠度微分方程. 挠度微分方程满足边
界条件非常简单, 使球壳的计算得到很大的简化. 相似文献
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利用小扰动分析法 ,导出不可压缩球壳结构的馈通增长方程 ,数值模拟了高压气体驱动外表面有初始扰动的明胶球壳的瑞利 泰勒不稳定性模型。计算结果表明 :对于低波数扰动 ,外界面比较稳定 ,内表面的馈通增长较快 ,具有比较明显的三个演化阶段和波形反转现象。高波数扰动的增长恰好与低波数相反。球壳会聚结构比柱壳会聚结构的界面稳定性要好些。 相似文献
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本文从复变量形式的扁壳基本方程出发,通过建立复Green函数导出了在环状线载和线偶作用下扁球壳的位移和内力分布,通过积分可以求得轴对称的表面受变化分布载荷情况的解答,本文方法还可求得圆饭、圆柱壳等问题的解答,而且适用于各种轴对称边界条件。 相似文献
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界面端附近裂纹的应力强度因子 总被引:3,自引:1,他引:3
结合材料的断裂形式可分为从界面端产生裂纹(沿界面或向母材内部层折)然后断裂与稍稍离开界面端处产生裂纹然后断裂这两种情况,在金属/陶瓷类结合材料中,后者出现的概率更大,本文利用结合材料界面端的奇异应力场和叠加原理,给出了界面端附近裂纹的应力强度因子近似计算公式,并用边界元数值计算验证了其有效性。 相似文献
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裂纹动态起始问题的研究进展 总被引:9,自引:0,他引:9
力图就前人提出的冲击载荷下裂纹的起始判据进行较全面的综述.这些较著名的判据有:(1)动态应力强度因子判据;(2)动态J积分判据;(3)最小作用量判据;(4)极小作用时间判据等.简要介绍了近年来有关裂纹在冲击载荷(特别是短脉冲)下动态起始的一些重要实验和实验中所发现的一些重要结论.实验公认,一般对于小范围屈服而言,材料的动态断裂韧性随加载(应变)率的提高而减小,此时材料的断裂形式为解理型;而对于大范围屈服则韧性随加载率的提高而增大,此时材料的断裂形式为纤维型.特别指出,Brown大学的平板撞击实验表明,裂纹在起始时,观察到一个不再满足二分之一阶奇异性的“尖峰”,按Clifton和Freund等人所给出的模型,在裂纹起始断裂瞬间,在裂纹顶端会突然形成一个小洞,该洞的半径作为一个参数等于二相粒子的间距. 相似文献
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Guo Ruiping Liu Guanting Fan Tianyou 《Acta Mechanica Solida Sinica》2006,19(2):122-127
In this paper a semi-elliptic surface crack problem in an elastic solid of finite size under impact loading is investigated. An analysis is performed by means of fracture dynamics and the finite element method, and a three-dimensional finite element program is developed to compute the dynamic stress intensity factor. The results reveal that the effects of the solid's boundary surface, crack surface, material inertia and stress wave interactions play significant roles in dynamic fracture. 相似文献
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On anti-plane shear behavior of a Griffith permeable crack in piezoelectric materials by use of the non-local theory 总被引:3,自引:0,他引:3
In this paper, the non-local theory of elasticity is applied to obtain the behavior of a Griffith crack in the piezoelectric
materials under anti-plane shear loading for permeable crack surface conditions. By means of the Fourier transform the problem
can be solved with the help of a pair of dual integral equations with the unknown variable being the jump of the displacement
across the crack surfaces. These equations are solved by the Schmidt method. Numerical examples are provided. Unlike the classical
elasticity solutions, it is found that no stress and electric displacement singularity is present at the crack tip. The non-local
elastic solutions yield a finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum
stress hypothesis. The finite hoop stress at the crack tip depends on the crack length and the lattice parameter of the materials,
respectively.
The project supported by the National Natural Science Foundation of China (50232030 and 10172030) 相似文献
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研究纳米尺度时开裂椭圆孔的III型断裂性能。基于表面弹性理论和保角映射技术,利用复势函数理论获得了缺陷(裂纹和椭圆孔)周围应力场和裂纹尖端应力强度因子的闭合解答。所得结果具有一般性,许多已有和新的解答可由本文退化的特殊情形得到。利用解析结果讨论了缺陷的绝对尺寸、椭圆孔的形状比以及裂纹的相对尺寸对应力强度因子的影响。结果表明:考虑表面效应且缺陷尺寸在纳米尺度时,应力强度因子具有显著的尺寸依赖效应;应力强度因子随椭圆孔形状比的变化规律受缺陷表面常数的影响;缺陷表面效应的影响取决于椭圆孔的形状比,非常大的形状比屏蔽了表面效应的影响;裂纹相对尺寸非常小时表面效应影响较弱,裂纹相对尺寸较大时表面效应较为明显。 相似文献
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《Acta Mechanica Solida Sinica》2015,(3)
A radial crack emanating from a semi-circular notch is of significant engineering importance. Accurate determination of key fracture mechanics parameters is essential for damage tolerance design and fatigue crack growth life predictions. The purpose of this paper is to provide an efficient and accurate closed-form weight function approach to the calculation of crack surface displacements for a radial crack emanating from a semi-circular notch in a semi-infinite plate.Results are presented for two load conditions: remote applied stress and uniform stress segment applied to crack surfaces. Based on a correction of stress intensity factor ratio, highly accurate analytical equations of crack surface displacements under the two load conditions are developed by fitting the data obtained with the weight function method. It is demonstrated that the WuCarlsson closed-form weight functions are very efficient, accurate and easy-to-use for calculating crack surface displacements for arbitrary load conditions. The method will facilitate fatigue crack closure and other fracture mechanics analyses where accurate crack surface displacements are required. 相似文献
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In this paper, the dynamic behavior of a Griffith crack in a piezoelectric material strip subjected to the harmonic anti-plane shear waves is investigated by use of the non-local theory for impermeable crack surface conditions. To overcome the mathematical difficulties, a one-dimensional non-local kernel is used instead of a two-dimensional one for the anti-plane dynamic problem to obtain the stress and the electric displacement near at the crack tip. By means of the Fourier transform, the problem can be solved with the help of two pairs of dual integral equations. These equations are solved using the Schmidt method. Contrary to the classical solution, it is found that no stress and electric displacement singularity is present near the crack tip. The non-local dynamic elastic solutions yield a finite hoop stress near the crack tip, thus allowing for a fracture criterion based on the maximum dynamic stress hypothesis. The finite hoop stress at the crack tip depends on the crack length, the thickness of the strip, the circular frequency of incident wave and the lattice parameter. 相似文献
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This work is concerned with the dynamic response of two coplanar cracks in a piezoelectric ceramic under antiplane mechanical and inplane electric time-dependent load. The cracks are assumed to act either as an insulator or as a conductor. Laplace and Fourier transforms are used to reduce the mixed boundary value problems to Cauchy-type singular integral equations in Laplace transform domain. A numerical Laplace inversion algorithm is used to determine the dynamic stress and electric displacement factors that depend on time and geometry. A normalized equivalent parameter describing the ratio of the equivalent magnitude of electric load to that of mechanical load is introduced in the numerical computation of the dynamic stress intensity factor (DSIF) which has a similar trend as that for the pure elastic material. The results show that the dynamic electric field will impede or enhance crack propagation in a piezoelectric ceramic material at different stages of the dynamic electromechanical load. Moreover, the electromechanical response is greatly affected by the ratio of the crack length to the ligament between the cracks. The stress and electric displacement intensity factor can be combined by the energy density factor or function to address the fracture of piezoelectric materials under the combined influence of electromechanical loading. 相似文献
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In this paper, the dynamic interaction between two collinear cracks in a piezoelectric material plate under anti-plane shear
waves is investigated by using the non-local theory for impermeable crack surface conditions. By using the Fourier transform,
the problem can be solved with the help of two pairs of triple integral equations. These equations are solved using the Schmidt
method. This method is more reasonable and more appropriate. Unlike the classical elasticity solution, it is found that no
stress and electric displacement singularity is present at the crack tip. The non-local dynamic elastic solutions yield a
finite hoop stress at the crack tip, thus allowing for a fracture criterion based on the maximum dynamic stress hypothesis.
The project supported by the Natural Science Foundation of Heilongjiang Province and the National Natural Science Foundation
of China(10172030, 50232030) 相似文献
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Asymmetrical dynamic fracture model of bridging fiber pull-out of unidirectional composite materials
An elastic analysis of an internal crack with bridging fibers parallel to the free surface in an infinite orthotropic anisotropic elastic plane is studied, and asymmetrical dynamic fracture model of bridging fiber pull-out of unidirectional composite materials is presented for analyzing the distributions of stress and displacement with the internal asymmetrical crack under the loading conditions of an applied non-homogenous stress and the traction forces on crack faces yielded by the bridging fiber pull-out model. Thus the fiber failure is ascertained by maximum tensile stress, the fiber ruptures and hence the crack propagation should also appear in the modality of self-similarity. The formulation involves the development of a Riemann-Hilbert problem. Analytical solution of an asymmetrical propagation crack of unidirectional composite materials under the conditions of two increasing loads given is obtained, respectively. In terms of correlative material properties, the variable rule of dynamic stress intensity factor was depicted very well. After those analytical solutions were utilized by superposition theorem, the solutions of arbitrary complex problems could be gained. 相似文献