功能梯度条硬币型裂纹扭转冲击响应

研究非均匀条中硬币型裂纹的扭转冲击问题．材料的剪切模量假定按特定的梯度变化．采用Laplace 和Hankel 变换将问题化为求解Fredholm积分方程,通过将Bessel函数渐进展开获得裂纹尖端动态应力场．考查非均匀参数和功能梯度条高度对裂尖动态断裂行为的影响．动应力强度因子和能量密度因子的清晰表达式表明,作为裂纹扩展力,对于这里所研究的问题,二者是等价的．动应力强度因子的数值结果显示,增加剪切模量的非均匀参数可以抑制动应力强度因子的幅度,而条形域的高度对动态断裂特性的影响较小．     

The Problem of an External Circular Crack Under Asymmetric Loadings

ＩｎｔｒｏｄｕｃｔｉｏｎＷｈｅｎｔｈｅｂｏｕｎｄａｒｙｉｎｔｅｇｒａｌｅｑｕａｔｉｏｎｍｅｔｈｏｄｉｓａｐｐｌｉｅｄｔｏｃｒａｃｋａｎａｌｙｓｉｓ,ｏｎｌｙｎｕｍｅｒｉｃａｌｓｏｌｕｔｉｏｎｓｃａｎｂｅｏｂｔａｉｎｅｄ ,ｓｕｃｈａｓ:ｔｈｅｔｙｐｉｃａｌｗｏｒｋｓｏｆＳｎｙｄｅｒａｎｄＣｒｕｓｅ[1],Ｃｒｏｕｃｈ[2 ],Ｂｌａｎｄｆｏｒｄｅｔａｌ.[3],Ｐｏｒｔｅｌａｅｔａｌ.[4 ],Ｂｕｉ[5 ],Ｗｅａｖｅｒ[6 ]ａｎｄＷＡＮＧｅｔａｌ.[7- 9].Ｉｔｉｓｖｅｒｙｄｉｆｆｉｃｕｌｔｔｏａｐｐｌｙｔｈｅｂｏｕｎｄａｒ…     

Conservation Law and Application of J-Integral in Multi-Materials

The conservation law of J-integral in two-media with a crack paralleling to the interface of the two media was firstly proved by analytical and numerical finite element method. Then a schedule model was established that an interface crack is inserted in four media. According to the J-integral conservation law on multi-media, the energy release ratio of Ⅰ-type crack was considered to be conservation when the middle medium layers are very thin. And the conservation law was also convinced by numerical method. By means of the dimension analysis on the model, the asymptotic results and formula calculating the energy release ratio and complex stress intensity factor are presented.     

Ⅰ型裂纹对薄壁偏心柱弹性挠度的影响

本文重点研究了裂纹对薄壁截面偏心受压柱弹性挠度的影响,分析模型假设偏心柱两墙铰支;截面绕强轴发生单向弯曲变形：I型裂纹位于受力最为严重的中间截面的受拉翼缘上,首先简单介绍了Rayleigh-Ritz变分法求得的弹性挠度三角函数级数解,该解的优点是可以在裂纹截面满足变形协调条件,适应于裂纹在薄壁截面上的沿弯矩面外方向扩展的情况,然后针对工字形,箱形两种双轴对称薄壁截面柱,具体地分析了在不同荷载,偏心距和长细比条件下裂纹长度对偏心柱挠度的影响规律和范围,理论分析和数值结果表明,在其它条件不变的情况下,柱的长细比越小或偏心距越大,裂纹引起的挠度增量越明显。,     

An Investigation of Random Fatigue Strength of K-Type Tubular Joints and Crack Propagation Behaviors

ＩｎｔｒｏｄｕｃｔｉｏｎＡｓａｓｐｅｃｉａｌｆｏｒｍｏｆｓｔｒｕｃｔｕｒｅｓ,ｔｕｂｕｌａｒｊｏｉｎｔｓ (ｍｕｌｔｉ＿ｄｕｃｔｐｉｐｅｓ)ｗｅｌｄｅｄｂｙｃｉｒｃｕｌａｒｃｙｌｉｎｄｒｉｃａｌｓｈｅｌｌｓ (ｃｉｒｃｕｌａｒｔｕｂｅｓ)ｈａｖｅｂｅｅｎｗｉｄｅｌｙｕｓｅｄｉｎｅｎｇｉｎｅｅｒｉｎｇ .Ｏｎｅｏｆｔｈｅｐｒｉｍａｒｙｆａｃｔｏｒｓｔｈａｔａｒｅｒｅｓｐｏｎｓｉｂｌｅｆｏｒｍａｎｙｓｅｒｉｏｕｓａｃｃｉｄｅｎｔｓｉｓｔｈｅｉｎｓｕｆｆｉｃｉｅｎｔｆａｔｉｇｕｅｓｔｒｅｎｇｔｈｏｆｔｈｅｊｏ…     

Fatigue crack shapes development of plate-to-plate welded joints

This paper presents crack shapes development of 3D surface semielliptical cracks which are always found at the weld toe of non-load-carrying cruciform welded joints. The alternating current potential drop technique has been used to measure the eight crack depths along the weld toe where probes are placed at 10-mm intervals. 3D crack shapes can be obtained at any particular cycle during the fatigue test. Subregion boundary element methods incorporating the transition and quarter-point elements along the crack front are used to validate the experimental stress intensity factors along the crack front. A method for evaluating the effective stress intensity factors is proposed. It is found that the numerical results generally agree with the experimental results.     

Three-Dimensional Variational Analysis of Composite Structures Using Bernstein Polynomial Approximations. Report 2

The application of the previously developed 3D varionational analysis approach to the investigation of crack propagation in composite bonded joints is presented. In this application, the propagation of three different types of a 2D planar crack (adhesive, cohesive, and interfacial) is modeled by relaxing the respective continuity conditions for displacements between adjacent bricks in the mosaic structure. The crack propagation process is then characterized by the release rate of the total potential energy between two consecutive states of the mosaic body with different crack lengths. Numerical examples illustrate the 3D analysis of double-lap adhesively bonded joints with unidirectional and cross-ply laminated composite adherends. The numerical results provide an illustration of various characteristics of the crack propagation process. The values of the ultimate failure load predicted by analyzing the initial stage of crack propagation are found to be in a good agreement with experimental data.     

An Edge Crack Problem in a Semi-Infinite Plane Subjected to Concentrated Forces

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｅｄｇｅｃｒａｃｋｐｒｏｂｌｅｍｉｎａｓｅｍｉ＿ｉｎｆｉｎｉｔｅｐｌａｎｅｗａｓｃｏｎｓｉｄｅｒｅｄｂｙｍａｎｙｉｎｖｅｓｔｉｇａｔｏｒｓ.ＵｓｉｎｇｔｈｅＦｒｅｄｈｏｌｍｉｎｔｅｇｒａｌｅｑｕａｔｉｏｎａｎｄｔｈｅａｌｔｅｒｎａｔｉｎｇｍｅｔｈｏｄ ,ａｎｅｄｇｅｃｒａｃｋｐｒｏｂｌｅｍｉｎａｓｅｍｉ＿ｉｎｆｉｎｉｔｅｐｌａｎｅｗａｓｓｏｌｖｅｄ[1].Ｔｈｅｏｂｔａｉｎｅｄｒｅｓｕｌｔｓａｒｅｌｉｍｉｔｅｄｔｏｔｈｅｃａｓｅｔｈａｔｔｈｅｅｄｇｅｃｒａｃｋｉｓｎｏｒｍ…     

夹杂和裂纹相互影响时的界面应力分析

本文结合无限域上单根夹杂和单根裂纹的基本解,将裂纹与夹杂相互作用的问题归结为解一组柯西型奇异积分的积分方程组,使问题得到解决。本文还使用夹杂两侧的未知界面应力差,进一步推导了夹杂两侧的界面应力,并做了数值计算。有关这方面的计算可以作为研究与设计纤维与基体的联结强度的工程参考。     

A penny-shaped crack in a transversely isotropic piezoelectric layer

In this paper, we develop a model to treat penny-shaped crack configuration in a piezoelectric layer of finite thickness. The piezoelectric layer is subjected to axially symmetric mechanical and electrical loads. Hankel transform technique is used to reduce the problem to the solution of a system of integral equations. A numerical solution for the crack tip fields is obtained for different crack radius and crack position.