用裂纹张开位移计算三点弯曲试样的动态应力强度因子

给出了一种由裂纹的动态张开位移计算三点弯曲试样的动态应力强度因子的简单方法。对于两种不同几何尺寸的试样,在三类不同载荷作用下给出了数植算例,并与完全的动态有限元方法的计算结果进行了比较。结果表明:两种方法的计算结果相当一致。最后,还给出了由测定三点弯曲试样的裂纹张开位移确定试样的动态应力强度因子,最终确定材料动态起裂韧性的方法。     

Transient response of a cracked piezoelectric strip under arbitrary electro-mechanical impact

By using the well-developed integral transform methodology, the dynamic response of stress and electric displacement around a finite crack in an infinite piezoelectric strip are investigated under arbitrary dynamic anti-plane loads. The dynamic stress intensity factors and electric displacement are obtained analytically. It is shown that the dynamic crack-tip stress and electric field still have a square-root singularity. Numerical computations for the dynamic stress intensity factor show that the electric load has a significant influence on the dynamic response of stress field. The higher the ratio of the crack length to the width of the strip, the higher the peak value of the dynamic stress intensity factor is. On the other hand, the dynamic response of the electric field is determined solely by the applied electric load. The electric field will promote or retard the propagation of the crack depending on the time elapse since the application of the external electro-mechanical loads. The project supported by the National Natural Science Foundation of China and the Post-Doctor Science Foundation of China     

An extension of CVDV model to Zeldovich exchange reactions for hypersonic non-equilibrium air flows

A new preferential vibration-dissociation-exchange reactions coupling model – labelled CVDEV – resulting from an extension of the well-known Treanor and Marrone CVDV model, has been derived to take into account the coupling between the vibrational excitation of the and molecules and the two Zeldovich exchange reactions. Analytical expressions for the exchange reactions coupling factor and for the average vibrational energy lost – or gained – by a molecule through an exchange reaction have been developed. The influence of such a coupling has been shown by means of numerical simulations of hypersonic air flows through normal and bow shock waves. Code-to-code comparisons between our model and other recent approaches have been conducted. The infrared radiation of nitric oxide behind a normal shock wave resulting from computations with the CVDEV model has been compared with other coupling model results and to recent shock tube experimental data. These comparisons have shown a good agreement of our model results with the experimental data. In this context, the results show the prominent influence of vibration coupling on the first Zeldovich reaction, and the absence of vibration coupling effects on the second Zeldovich reaction. Received 30 June 1997 / Accepted 3 December 1997     

脆性材料在双向应力下的断裂实验与理论分析

研究了脆性材料在双向应力下的断裂特性和失效机理，特别是在平行于裂纹的应力对临界断裂参数的影响方面进行了实验上和理论上的研究．采用玻璃、陶瓷等脆性材料进行了平面双向拉伸和单向拉伸试验，并对实验结果进行比较．观测直通裂纹的启裂和扩展过程，证明了双向应力对裂纹驱动力有明显影响，讨论了裂纹扩展的应变准则．     

焊趾表面裂纹应力强度因子计算的基本模式法

给出一个用来计算对接和角接焊接接头焊趾半椭圆表面裂纹在复杂应力场中，例如在残余应力场中，裂纹前缘应力强度因子（ＳＩＦ）分布的工程实用计算法——基本模式法。本文先通过高自由度的三维有限元分析，给出接头和裂纹几何参数Ｔ１／Ｔ、ａ／Ｔ、ａ／ｃ一系列组合的基本几何模型（文中给出２７种）在选定的基本应力模式（本文给出８种）作用下，沿裂纹前缘的ＳＩＦ分布，并形成一个数据库。利用这些基本模式解的插值和组合，可以非常迅速地求得一般几何参数情况下焊趾半随圆表面裂纹在复杂应力场中沿裂纹前缘的ＳＩＦ分布。在本方法中，可以考虑角接接头板厚比Ｔ１／Ｔ对ＳＩＦ分布的影响。计算过程极简单而迅速，因此特别适用于疲劳裂纹扩展行为及寿命计算问题。     

任意梯度分布功能梯度涂层平面裂纹分析

提出可以分析任意梯度功能梯度材料的分层模型,并采用该模型研究功能梯度涂层平面裂纹问题.采用Fourier变换和传递矩阵法将该混合边值问题化为奇异积分方程组,通过数值求解获得应力强度因子.考察了分层模型的有效性,以及材料梯度变化形式、结构几何尺寸和材料梯度参数对裂纹应力强度因子的影响,发现结构几何尺寸、材料梯度变化形式、...     

Interior layer phenomena of semilinear systems

In this paper,we study the interior layer phenomena of singular perturbation boundaryvalue problems for semilinear systems:εy” = f(t,y.ε)(a0 is a small parameter,y.f. A and B are n-dimensional vector functions.Thisvector boundary value peoblem does not appear to have been studied,although the scalarboundary problem has been treated extensively.Under appopriate assumptions we obtainexistence of solution as in the scalar problem and the estimate of this solution in terms ofappropriate inequalities as well.     

山形切口三点弯曲试样的SIF柔度标定及应用

本文对三组不同比例尺寸的山形切口三点弯曲试样,进行了直接实验柔度标定,由此确定了应力强度因子(SIF)系数表达式.以此标定结果,测定了工具铜 T10A 的断裂韧度 K_(ICV),并同 GB4161-84方法测定的断裂韧度 K_(IC)进行了比较,二者符合较好.     

孔洞对平面裂纹应力强度因子影响分析的广义参数Williams单元

本文采用圆形奇异区广义参数Williams单元（W单元）建立了中心裂纹与圆孔共存的平面应力模型,奇异区外围利用ABAQUS有限元软件自动网格离散技术与FORTRAN95编程前处理相结合,克服了自主编程中网格离散的局限性．算例分析了圆孔位置和几何参数对I-II混合型裂纹尖端应力强度因子(SIFs)的影响,并与扩展有限元法(XFEM)计算结果进行比较．结果表明：靠近圆孔一侧的裂尖SIFs大于远离圆孔一侧的裂尖SIFs;控制圆孔左边缘到裂纹中心的距离,则两侧裂尖SIFs随圆孔半径的增大而增大;圆孔中心与裂纹中心水平距离越远,圆孔对裂纹扩展的影响越小．同时,基于圆形奇异区的W单元直接计算得到的裂尖SIFs与扩展有限元法得到的解吻合较好,证明了W单元对奇异区离散形状不敏感,且具有高效率和高精度．     

An analytical solution for the stress field and stress intensity factor in an infinite plane containing an elliptical hole with two unequal aligned cracks

The existing analytical solutions are extended to obtain the stress fields and the stress intensity factors (SIFs) of two unequal aligned cracks emanating from an elliptical hole in an infinite isotropic plane. A conformal mapping is proposed and combined with the complex variable method. Due to some difficulties in the calculation of the stress function, the mapping function is approximated and simplified via the applications of the series expansion. To validate the obtained solution, several examples are analyzed with the proposed method, the finite element method, etc. In addition, the effects of the lengths of the cracks and the ratio of the semi-axes of the elliptical hole (a/b) on the SIFs are studied. The results show that the present analytical solution is applicable to the SIFs for small cracks.