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 The singularity of stress and strain at the tip of three dimensional notch is analysed by the power expansion method, the eigen equation of the notch is gained by the boundary conditions of the notch, the eigenvalues under different inner angles of the notch are solved. The expression of stress and strain at the tip of the notch is finally derived.  本文利用双重幂级数展开法分析三维切口尖端应力应变奇异性，通过切口边界条件导出切口特征方程，进而求得不同切口内角下特征值序列解答，最后推得切口尖端应力应变场。  In this paper,the boundary element method(BEM)simulation for surface blunt crack problens is studied.A calculation model for 3D blunt cracks is established based on the plane strain analogy.Thedisplacement and stress fields near the crack front are calculated by a 3D BEM computer program andthen the stress intensity factor(SIF)along the crack front can be obtained using the crack front opening displacement.We assume that both the upper and the lower surface of the crack,except the region near crackfront,are... In this paper,the boundary element method(BEM)simulation for surface blunt crack problens is studied.A calculation model for 3D blunt cracks is established based on the plane strain analogy.Thedisplacement and stress fields near the crack front are calculated by a 3D BEM computer program andthen the stress intensity factor(SIF)along the crack front can be obtained using the crack front opening displacement.We assume that both the upper and the lower surface of the crack,except the region near crackfront,are planes and the contour of the crack front is a semicircle with radius p for all cross section ofthe crack.Therefore,the space between the upper and lower crack planes is 2 p. Comparing the 2Dand 3D stress and displacement field structures for sharp cracks and blunt crack s(with small curvature radius)respectively,we find that, for sharp cracks,the stress and displacement field Structuresnear an internal buried elliptical crack obtained by Green and Sneddon are exactly the same as those inthe case of plane strain,So we hold that for a 3D blunt crack with a small curvature radius,thestress and displacement field structures should be the same as those of a 2Dnotch in the case of plane stuan.Both the validation of the model and convergence of the grid pattern are examined numerically, The SIF values are calculated for thickness plates with surface blunt crack.The results show that:(1)The calculation model of 3D blunt cracks proposed in this paper combined with boundary element method can effectively deal with sur face blunt c ra cks with a radius ofcurvature.(2)when the curvature radius of the crack root is very small(p/0≤0.03),a bluntcrack may be regarded as a sharp one, since their SIF values are very close.(3)When the curvatureradius is quite small(p/a≤0.10),the model produces satisfactory results, The SIF values of ablunt crack will be modified com pa red with those of a sharp one and variation s along the crack frontwtll be more even,The local stress and displacement fields are still controlled by SIP,(4)when thecurvature radius is relatively large(p/>0.10),the model is invalid and the classical stress concentration factor of a 3D notch will be used as the controlling parameter  研究了表面钝裂纹问题的边界元模拟方法·文中通过平面应变比拟，建立了三维钝裂纹的计算模型和局部场结构；并由三维边界元程序计算了表面钝裂纹前沿附近的位移场和应力场；进而利用裂纹面前沿的“张开位移”推算应力强度因子的分布。文中对钝裂纹模型的有效性和离散格式的收敛性进行了考核，应力强度因子计算针对含表面裂纹的平板进行。计算结果表明：当ρ／α≤０．１时，此钝裂纹模型是有效的；当ρ／α≤０．３时，钝裂纹模型和理想尖裂纹模型趋于等效；而当ρ／α＞０．１时，钝裂纹模型将不再适用，此时应借助于经典的三维切口应力集中模型。  Based on three dimensional (3D) elastoplastic finite element analyses, various aspects of 3D characters ahead of the notch root in the deep double edges U notched plates are been investigated. By comparison with the planar notch root fields, the characters of the 3D elastoplastic stress strain fields near the notch front are revealed: (1) the thickness of the plate has the strong effects on the stress concentration factor Kt (SCF). In the elastic phase, the SCF is higher in finite thickness specimen than... Based on three dimensional (3D) elastoplastic finite element analyses, various aspects of 3D characters ahead of the notch root in the deep double edges U notched plates are been investigated. By comparison with the planar notch root fields, the characters of the 3D elastoplastic stress strain fields near the notch front are revealed: (1) the thickness of the plate has the strong effects on the stress concentration factor Kt (SCF). In the elastic phase, the SCF is higher in finite thickness specimen than that in the plane stress and plane strain cases, and reaches its peak when the ratio of plate thickness to the notch root curvature radius B/ρ equals to 4 or so. However, in plastic phase, the SCF in finite thickness specimen falls into between two extreme plane stress and strain cases with the plastic deformation increasing. (2) Due to combined actions of the stress triaxiality and the opening stress, the distribution of the effective strain is different from usual intuition. The effective strainon the midplane, where the triaxial constraint is highest, is as twice high as the effective strain on the free surface, where the constraint is lowest. (3) In thinner plates, the plastic zone size x p/ρ reaches its peak on the midplane, but the peak of plastic zone size x p/ρ removes toward the free surface with the plate thickness B/ρ increasing. (4) The distributions of inplane constraint T x on different layers of the finite thickness specimens are insensitive to the specimen thickness and load levels within the plastic zone, and can be well approximated by Hills Slipline solution. Added to these, the regularities of distribution of some important 3Dconstraint parameters within the 3Deffect zone are also given out.  针对单向拉伸载荷作用下的有限厚双边 U型切口板 ,本文对其切口根部的三维效应进行了详细的三维弹塑性大变形有限元分析 ,得到了不同于平面切口问题的新结果 :( 1 )在线弹性阶段 ,三维切口根部的应力集中因子 Kt高于二维情形 ,且 Kt在板厚 ( B)约为 8倍切口根部半径 (ρ)时达到峰值 ;进入塑性后 ,切口根部的 Kt随载荷水平的增加逐渐下降 ,并介于平面应力和平面应变情形之间 ;( 2 )切口前缘等效应变εe的最大值出现在约束最高的中面 ,且可比约束最低的自由表面处的应变值高一倍 ;( 3)薄板中 ,塑性区尺寸 xp 的最大值不是出现在约束较低的自由表面 ,而是出现在约束较高的中面 ,但随 B/ρ的增大逐渐向自由表面外推 ;( 4 )面内应力比 Tx在切口根部塑性区内的分布对板厚和载荷水平不敏感 ,可以用 Hill的滑移线解很好地近似。另外 ,对三维影响区内一些重要的三维约束参量进行了详细分析 ,总结了它们的三维分布规律。  
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