共查询到20条相似文献,搜索用时 984 毫秒
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LI Bing CHEN Xuefeng HE Zhengjia State Key Laboratory for Manufacturing System Xi'an Jiaotong University Xi'an China Received April revised April accepted April published electronically May 《机械工程学报(英文版)》2011,(6):1116-1122
Local flexibility of crack plays an important role in crack identification of structures.Analytical methods on local flexibility in a cracked beam with simple geometric crossing sections,such as rectangle,circle,have been made,but there are some difficulties in calculating local flexibility in a cracked beam with complex crossing section,such as pipe and I-beam.In this paper,an analytical method to calculate the local flexibility and rotational spring stiffness due to crack in I-beam is proposed.The local flexibility with respect to various crack depths can be calculated by dividing a cracked I-beam into a series of thin rectangles.The forward and inverse problems in crack detection of I-beam are studied.The forward problem comprises the construction of crack model exclusively for crack section and the construction of a numerically I-beam model to gain crack detection database.The inverse problem consists of the measurement of modal parameters and the detection of crack parameters.Two experiments including measurement of rotational spring stiffness and prediction of cracks in I-beam are conducted.Experimental results based on the current methods indicate that relative error of crack location is less than 3%,while the error of crack depth identification is less than 6%.Crack identification of I-beam is expected to contribute to the development of automated crack detection techniques for railway lines and building skeletons. 相似文献
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局部柔度可描述结构上出现的裂纹,结构的模态参数将随着裂纹的扩展而改变,利用这一变化可辨识出裂纹发生的位置和深度。由此,建立了一种基于局部柔度变化的管道裂纹定量识别方法。该方法通过将管道结构沿径向离散为一系列依次嵌套的薄壁环,从而求得裂纹引起的局部柔度的变化规律,进而获得局部柔度与管道固有频率的特征关系,绘制裂纹管道的各阶固有频率曲面。采用实测前3阶固有频率去截取相应的固有频率曲面,获得各阶频率等高线,利用其交点定量诊断裂纹的位置与深度。实验结果验证了该方法的有效性。 相似文献
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Junjie Ye Yumin He Xuefeng Chen Zhi Zhai Youming Wang Zhengjia He 《Mechanical Systems and Signal Processing》2010,24(2):379-393
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. 相似文献
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当齿轮发生故障时,时变啮合刚度的变化能够反映齿轮故障特征大小。因此,时变啮合刚度在齿轮传动过程中是一个重要的动力学参数。提出一种新的齿根裂纹啮合刚度计算方法,即解析有限元法(Analytical-finite element method,A-FM)。考虑到齿轮发生故障时,啮合刚度解析模型计算精度较低,将应力强度因子引入裂纹齿轮的啮合刚度计算过程。首先定义应力强度因子与啮合刚度之间的关系,通过建立齿轮接触模型计算裂纹尖端附近的应力强度因子,然后将计算结果替代解析模型中故障刚度部分。由于应力强度因子能够敏感地识别齿根裂纹的局部微小变化,故该方法相比于解析法具有更高的计算精度,相比于有限元法具备更快的计算效率。同时,建立6自由度动力学模型,通过对其振动响应进行分析,仿真结果验证了所提方法的可行性。 相似文献
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工字形梁是工程中最常见的结构之一。其中的任何裂纹都将成为结构断裂失效的隐患。带有裂纹的工字形梁是典型的三维有限边界问题,用经典方法求解其裂纹的应力强度因子通常是相当困难的。文中利用裂纹非自发扩展的能量释放率建立一个求解弯曲载荷作用下工字形截面梁中心裂纹的应力强度因子的新方法。给出工字形截面梁裂纹非自发扩展能量释放率G^* -积分与应力强度因子的关系,同时也给出G^* -积分与载荷、几何参量以及力学性能参数的关系,进而得到工字形截面梁腹板中心裂纹的应力强度因子。 相似文献
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A cracked plate with a patch bonded on one side was treated with a crack-bridging model using weight function : assuming continuous
distribution of springs acting between th crack surfaces, the stress intensity factor of the patched crack was numerically
obtained. Especially in the case of a patched crack subjected to residual non-uniform stress, the stress intensity factor
was easily with the corresponding approximate weight function. This paper presented the stress intensity factors for a crack
partially patched within a finite plate or a patched crack initiated from a notch. 相似文献
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《Mechanical Systems and Signal Processing》2007,21(1):502-513
A new model for vibration analysis of a crankshaft with a slant crack in crankpin is proposed, and the influence of crack depth on the transient response of a cracked crankshaft is investigated. A slant cracked shaft element is developed by deducing the local flexibility due to a slant crack. The frequently occurred slant crack in crankpin is studied, and a new finite element model of crankshaft including the slant crack in crankpin, which combines the slant cracked shaft element and Timoshenko beam elements, is derived. The support of engine block and the switching behaviour of the crack are considered, and the non-linear equation of motion for cracked crankshaft-bearing system is set up in a rotating coordinate system. The motion of a crankshaft of a four in-line cylinder engine with and without an initial crack is simulated. The influence of the crack depth on the transient response is investigated. The numerical simulation demonstrates that the current model is valid for simulating the motion of cracked crankshaft system. The results show that a useful foundation is laid for crack detection of crankshaft. 相似文献
10.
本文研究含裂纹转子的振动特性。文章首先根据裂纹结构的应力强度因子,得到含裂纹单元体的刚度矩阵,进而得到裂纹转子的整体刚度矩阵和质量矩阵,列写出裂纹转子的运动微分方程,导出裂纹引起转子系统刚度变化与系统振动特性参数变化间的关系,从而可由实时在线测得的振动参数判断裂纹的位置。通过对模拟转子的计算和实测,表明本文提出的方法是一种可用于大型旋转机械转子轴裂纹在线检测的极为有效的方法. 相似文献
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提出新的应力函数,该应力函数对于表面自由的或随均布载荷的裂纹都适用。利用该应力函数导出了各种裂纹模型,在各种边界条件下的应力强度因子的计算公式及裂纹面上各点位移的计算公式。并利用边界配位法,计算了方形中心裂纹板在各种条件下裂纹面上各点的位移。 相似文献
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Cracks in mechanical components produce changes in their behaviour like increases of displacements or decreases of frequencies due to the flexibility increase. Some works related to the analysis of the behaviour of cracked shafts consider the front of the transversal fatigue cracks to be straight, but experience says that the front of these kind of cracks is approximately elliptical. Many expressions have been given for the flexibility of a cracked shaft with a straight front whereas, for elliptical cracks, only an approximate expression for the flexibility has been found in the literature. In the present work, flexibility expressions for cracked shafts having elliptical cracks are obtained, based on the polynomial fitting of the stress intensity factors, taking into account the size and shape of the elliptical cracks showing results according with reality. The static displacements in bending of the shaft for different support conditions have been calculated. The comparisons between these results and those obtained by FEM analysis and by experimental tests show that the closed-form expressions for the flexibility give us a very good approximation to the behaviour of the cracked shaft. 相似文献
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In this paper we studied about the effect of the open crack and the moving mass on the dynamic behavior of simply supported
pipe conveying fluid. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method. The
crack section is represented by a local flexibility matrix connecting two undamaged pipe segments i.e. the crack is modeled
as a rotational spring. The influences of the crack severity, the position of the crack, the moving mass and its velocity,
the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the mid-span displacement
of the simply supported pipe are depicted. 相似文献
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In this paper, we studied about the effect of the open crack and a tip mass on the dynamic behavior of a cantilever pipe conveying
fluid with a moving mass. The equation of motion is derived by using Lagrange’s equation and analyzed by numerical method.
The cantilever pipe is modelled by the Euler-Bernoulli beam theory. The crack section is represented by a local flexibility
matrix connecting two undamaged pipe segments. The influences of the crack, the moving mass, the tip mass and its moment of
inertia, the velocity of fluid, and the coupling of these factors on the vibration mode, the frequency, and the tip-displacement
of the cantilever pipe are analytically clarified. 相似文献
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热疲劳裂纹网的屏蔽规律及主裂纹应力强度因子的计算方法 总被引:2,自引:0,他引:2
热疲劳裂纹网中主裂纹的应力强度因子可反映构件的损伤程度,然而由于裂纹间的屏蔽效应,直接计算裂纹网中主裂纹的应力强度因子是困难的。根据热疲劳试验提出假设:① 主裂纹不会位于裂纹网的边缘;② 裂纹网中的裂纹互相平行,且垂直于约束方向。定义主裂纹的屏蔽剩余百分数s,裂纹的比间距n,裂纹长度比f。分别研究两条长度相等裂纹、两任意长度裂纹、三条裂纹和多条裂纹屏蔽效应的规律。发现s-f-n有确定的关系,这一关系由裂纹网的结构确定,而与边界条件、裂纹尺寸等因素无关。利用屏蔽效应的规律可由单条裂纹时的应力强度因子推算裂纹网中屏蔽效应发生时主裂纹的应力强度因子。算例表明此方法精确、简便、快捷。 相似文献
19.
《Measurement》2016
In this paper, an experimental technique based on strain gauge has been proposed to measure the gear mesh stiffness of healthy spur gear as well as of cracked spur gear pair system. Calculation of mesh stiffness of healthy and cracked spur gear tooth are based on strain energy and strain energy release rate respectively. The location of strain gauge plays an important role in calculation of strain energy stored in gear tooth. The locations of strain gauge on gear tooth are illustrated for healthy and cracked gear. Stress intensity factor (SIF) has been calculated by strain gauge technique for calculating the stiffness of cracked pinion tooth. The effect of crack length on mesh stiffness has been investigated by strain gauge technique and results are compared with the established analytical method. 相似文献