共查询到19条相似文献,搜索用时 203 毫秒
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接管是核压力容器的一种重要结构形式,在内压作用下接管内壁角裂纹应力强度因子K_1是规范要求的对该部位作断裂评定的重要依据。用改进的1/4边中节点三维20节点等参奇异元和位移法计算了球接管内壁角裂纹的应力强度因子K_1及其变化分布规律,分析了K_1与裂纹及结构的几何参数关系。所得结果和三维光弹性冻结切片法试验分析结果十分吻合。进一步计算分析了柱接管内壁角裂纹应力强度因子K_1及其与裂纹和结构几何参 相似文献
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《中国核科技报告》1996,(1)
接管是核压力容器的一种重要结构形式,在内压作用下接管内壁角裂纹应力强度因子K_1是规范要求的对该部位作断裂评定的重要依据。用改进的1/4边中节点三维20节点等参奇异元和位移法计算了球接管内壁角裂纹的应力强度因子K_1及其变化分布规律,分析了K_1与裂纹及结构的几何参数关系。所得结果和三维光弹性冻结切片法试验分析结果十分吻合。进一步计算分析了柱接管内壁角裂纹应力强度因子K_1及其与裂纹和结构几何参数关系。在计算分析的基础上所得出的计算核压力容器接管内壁角裂纹在内压作用下的应力强度因子K_1的近似公式简单而又偏保守,且为三维光弹试验所证实,可供工程参考使用。 相似文献
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本文针对反应堆压力容器接管嘴内隅角,采用含真实裂纹的三维有限元法对温度与压力作用下应力强度因子的计算进行了研究。以某工程压力容器接管嘴内隅角为例,用含真实裂纹的三维有限元法和目前使用的简化工程算法对压力与热载荷作用下的接管嘴内隅角应力强度因子进行了计算,并对两种方法的计算结果进行对比分析。结果表明:当简化工程算法得到的应力强度因子接近规范限值时,应对热载荷引起的应力强度因子进行详细有限元计算,以规避简化工程算法的不保守性给压力容器带来的快速断裂风险。 相似文献
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核电蒸汽发生器(SG)接管嘴处由于其结构的特殊性,易在制造及服役过程中产生缺陷。为评价该处缺陷的安全性,需要工程可用的应力强度因子解。本文以核电SG接管嘴外表面裂纹为研究对象,采用有限元方法(FEM)及RSE-M规范计算获得了不同方向及尺寸裂纹在内压、弯矩和温度载荷下的等效应力强度因子值,并分析了不同载荷作用下等效应力强度因子在裂纹前沿的分布规律。将计算结果与RSE-M规范的直管应力强度因子解进行比较,发现RSE-M规范的直管应力强度因子计算方法可保守地应用于SG接管嘴处裂纹,并且随着裂纹深度的增加保守度增大。为实现SG接管嘴处缺陷安全的准确评价,基于有限元计算和RSE-M影响系数法给出了适用于SG接管嘴外表面裂纹的应力强度因子计算方法,该方法可以为SG的设计与维护提供指导。 相似文献
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N. Miyazaki 《Nuclear Engineering and Design》1982,68(1):71-85
A finite element computer program EPAS-J1 was developed to calculate the stress intensity factors of three-dimensional cracks. In this program, the stress intensity factor is determined by the virtual crack extension method together with the distorted elements allocated along the crack front. The program also includes the connection elements based on the Lagrange multiplier concept to connect such different kinds of elements as the solid and shell elements, or the shell and beam elements. For the structure including the three-dimensional surface cracks, the solid elements are employed only at the neighborhood of the surface crack, while the remainder of the structure is modeled by the shell or beam elements since the crack singularity is very local. Computer storage and computational time can be highly reduced with the application of the above modeling for calculation of the stress intensity factors of the three-dimensional surface cracks, because the three-dimensional solid elements are required only around the crack front.Several numerical analyses were performed by the EPAS-J1 program. At first, the accuracies of the connection element and the virtual crack extension method were confirmed using the simple structures. Compared with other techniques of connecting different kinds of elements such as the tying method or the method using an anisotropic plate element, it is found that the present connection element provides better results than the others. It is also found that the virtual crack extension method provided the accurate stress intensity factor. Furthermore, the results are also presented for the stress intensity factor analyses of cylinders with longitudinal or circumferential surface cracks using the combination of various kinds of elements together with the connection elements. 相似文献
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Assuming a small axial surface crack inside a steam generate (S/G) tube, stress corrosion crack growth is simulated by using finite element method. Pressure difference and residual stresses induced from the roll expansion are considered as applied forces and Scott's crack growth equation based on the stress intensity factor is used. Stress intensity factor distribution along crack front, variation of crack shape and crack growth rate are obtained during the crack growth. From the results, it is noted that for the given residual stress distribution, variation curve of the crack aspect ratio during the crack growth is uniquely determined. In addition, the curve shows nearly constant crack aspect ratio during the initial crack growth stage. When adjacently growing two small cracks are coalesced to form a longer crack, the growth rate of crack depth is increasing but that of crack length is decreasing, and the crack aspect ratio is converging to the original variation curve during the subsequent crack growth. 相似文献
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This paper presents the results of a benchmark on thermal fatigue crack growth evaluation for a thick-wall cylinder subjected to cyclic thermal transients. The simplified crack growth evaluation methods of both JNC in JAPAN and A16 procedures proposed by CEA in France are presented. The predictions obtained using both methods are compared with the experimental data. The JNC method, which accounts for the non-linear stress component provides predictions of crack advance in a good agreement with the experimental data. In contrast, significant differences are observed between the A16 predictions and the experimental data. The discrepancies are mainly due to the non-linear stress component which is not accounted for in the A16 method. When using the JNC stress intensity factor solution determined by finite element analysis to account for the non-linear stress component, the A16 method well predicts the thermal fatigue crack growth behavior. 相似文献
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Thomas Menouillard 《Nuclear Engineering and Design》2010,240(10):2579-2588
This paper deals with the evaluation of the static mixed-mode stress intensity factors in case of thermal and mechanical loadings. A method and a formulation based on the J-integral and the energy release rate formulation is developed. The numerical results emphasize the effects of the temperature field on the stress intensity factors; thus, we show that an increasing temperature in the direction of the crack increases the mode 1 stress intensity factor. In addition, the formulation is also applied to the computation of an experiment consisting in a precracked glass specimen into a temperature gradient induced by a water bath and an oven. 相似文献
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Electricité de France has conducted during these last years an experimental and numerical research programme in order to evaluate fracture mechanics analyses used in nuclear reactor pressure vessels integrity assessment, regarding the risk of brittle fracture. Two cladded specimens made of ferritic steel A508 Cl3 with stainless steel cladding, and containing shallow subclad flaws, have been tested in four point bending at very low temperature to obtain cleavage failure. The crack instability was obtained in base metal by cleavage fracture, without crack arrest. The tests have been interpreted by local approach to cleavage fracture (Beremin model) using three-dimensional finite element computations. After the elastic–plastic computation of stress intensity factor KJ along the crack front, the probability of cleavage failure of each specimen is evaluated using m, σu Beremin model parameters identified on the same material. The failure of two specimens is conservatively predicted by both analyses. The elastic–plastic stress intensity factor KJ in base metal is always greater than base metal fracture toughness K1c. The calculated probabilities of cleavage failure are in agreement with experimental results. The sensitivity of Beremin model to numerical aspects is finally exposed. 相似文献
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Proportional extrapolation techniques are proposed to compute simply and accurately the stress intensity factor by use of the boundary element method (BEM). They are based on the procedures that the effects of boundary division near crack tip on stresses and displacements are corrected by comparing with a standard problem and the corrected results are only accurate in the limit as r → 0 (r = distance from crack tip). Comparisons of a few crack problems are made between results using the proposed techniques and those obtained by previously recommended methods. They are seen to be less sensitive than any other techniques regarding human work and accurate results are obtained even in the case of coarse boundary division. 相似文献
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The stress intensity factors of an elliptical crack front embedded with a round bar have been evaluated by collapsed singular element with detailed mesh on crack front and appropriating adjacent area. Using
newly developed model with sweeping capability, the mesh of the cracked shaft model can be easily built. The three-dimensional finite element analyses are then performed to calculate the stress intensity factors of elliptical crack front of a round bar subjected to tension and bending. The ratio of crack depth to shaft diameter is considered in the range between 0.1 and 0.6, and the elliptical ratio of crack area is in the range between 0.0 and 1.0. By comparing the stress intensity factors for different crack profiles with appropriated published results, the variation of stress intensity factors on the center and near edge location have been discussed. It also addresses the related change of the equivalent elliptical ratio of crack profile with respect to crack depth ratio. Based on stress intensity factor results, the three-parameter stress intensity factor relationships of the crack front are then determined by curve fitting technique. 相似文献
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S. W. Zhang Y. T. Song Z. W. Wang H. Jin S. S. Du X. Ji Z. R. Luo 《Journal of Fusion Energy》2014,33(3):304-308
The brackets are the important components of ITER edge localized modes (ELM) coils to connect the coils and rails. In order to assure the structural integrity and security of the bracket, the maximum tresca stress and stress intensity factor are examined from the viewpoints of structural and fracture mechanics. Based on the finite element method, the global upper ELM coils with simplified and detailed bracket are investigated. Since it is difficult to perform in-service inspection due to inaccessibility of in-vessel coils, it is important to estimate the allowable initial defect. Assuming an initial crack in the maximum first principal stress region on the bracket, the fracture mechanics analyses under different loads are performed. Results show that the bracket design is valid and feasible and the calculation method of finite element for stress intensity factor is feasible and reliable. Assuming the initial crack of 7 mm depth, the bracket can meet the crack growth criteria. The stress intensity factor of the bracket is mainly caused by electromagnetic (EM) load and the thermal load can reduce the stress intensity factor under EM load. The thermal load can make the crack grow on the surface of the bracket and the EM load can cause the crack to extend in the inner of the bracket. 相似文献