无限大板椭圆孔的分支裂纹的边界元分析

采用常位移不连续单元和裂尖位移不连续单元构成的边界元方法研究内部压力作用下无限大板中源于椭圆孔的分支裂纹.在该边界元方法的实施过程中,左、右裂尖位移不连续单元分别置于裂纹的左、右裂尖处,而常位移不连续单元则分布于除了裂尖位移不连续单元占据的位置之外的整个裂纹面及其他边界.结果表明,该数值方法对计算无限大板中复杂裂纹的应力强度因子是有效的,可以揭示裂纹体几何对应力强度因子的影响.     

双向载荷作用下无限大板中源于正方形孔的分支裂纹的应力强度因子

为研究源于正方形孔的一对分支裂纹问题提出一种边界元法,该边界元方法由Crouch与Starfield提出的常位移不连续单元和裂尖位移不连续单元构成.在该边界元方法的实施过程中,左、右裂尖位移不连续单元分别置于裂纹的左、右裂尖处,而常位移不连续单元则分布于除了裂尖位移不连续单元占据的位置之外的整个裂纹面及其他边界.算例说明,这种边界元法对计算平面弹性复杂裂纹的应力强度因子非常有效.给出的双向载荷作用下无限大板中源于正方形孔的一对分支裂纹的应力强度因子的详细数值结果,可以揭示双向载荷参数对应力强度因子的影响.     

三点弯曲-剪切试样的应力强度因子

利用一种边界元法研究具有偏移边裂纹的三点弯曲-剪切试样.该边界元方法由Crouch与Starfield提出的常位移不连续单元和笔者最近提出的裂尖位移不连续单元构成.在该边界元方法实施过程中,左、右裂尖位移不连续单元分别置于裂纹的左、右裂尖处,而常位移不连续单元则分布于除了裂尖位移不连续单元占据的位置之外的整个裂纹面及其他边界.算例说明这种边界元法不论对无限大还是对有限大平面弹性复杂裂纹问题的应力强度因子的计算都是非常有效的.对具有偏移边裂纹的三点弯曲-剪切试样的应力强度因子进行了详细的研究,给出了数值结果.     

共线界面裂纹问题的一个边界无单元法

借助于边界积分方程方法提出了一个适用于界面裂纹问题的无单元法.通过对不同情况界面共线裂纹问题的数值模拟,分析了界面裂纹之间的影响,算例证明该方法有效,且精度较高.     

考虑初始等距共线微裂纹列影响的Ⅲ型裂纹体的蠕变断裂分析

在工程中,特别是对长期持续荷载作用下带裂纹的构件,裂纹扩展寿命的预测是一个十分的问题,由于混凝土、岩石等材料中存在着大量的初始微裂纹,要研究这一类材料断裂问题就必须研究主裂纹与微裂纹之间的相互作用,依据宏观裂纹－微裂纹相互作用模型和蠕变裂应力强度因子理论,对具有初始等距共线微裂纹列影响的反平面Ⅲ型裂纹体的蠕变断裂问题进行了分析,并给出了混凝土Ⅲ型裂纹体的蠕变断裂应力强度因子与裂纹体初始应力强度因子的关系。     

方孔分支裂纹的一种边界元分析

方孔分支裂纹是一个很复杂裂纹问题.本文利用笔者最近提出的边界元方法来研究内部压力作用下方孔分支裂纹问题.数值算例与文献报道的结果进行比较,发现这种数值方法无论对无限大板还是对有限大板中复杂裂纹的应力强度因子计算都非常有效.另外本文报道的方孔分支裂纹的应力强度因子数值结果可以揭示裂纹体几何对应力强度因子的影响.     

弹性半空间中矩形平片裂纹问题分析

通过使用超奇异积分方程方法,对弹性半空间中与自由边界面垂直的I型三维矩形平片裂纹问题进行了研究.首先根据弹性半空间问题的弹性力学基本解,使用边界积分方程方法,在有限部积分的意义下导出了以裂纹面位移间断为未知函数的超奇异积分方程.通过将位移间断函数近似地表示为特征函数与一组多项式之积的形式,建立了数值计算方法.通过对几个典型数值算例的计算,分析了自由边界面对裂纹前沿应力强度因子的影响.     

有限平板共线裂纹断裂过程的数值模拟和实验研究

采用有限元数值模拟和光弹实验方法分析了各向同性材料共线多裂纹应力场及其强度参量.建立了有限弹性平板内三条共线裂纹计算模型,应用ABAQUS软件的VCCT方法分析计算各向同性材料共线裂纹的裂纹尖端的应力场、应变场分布规律及应力强度因子.并通过光弹实验实测了6061铝板共线裂纹试件的裂纹尖端的应力强度因子.研究结果表明,实验和数值模拟所得的应力云图相似,应力强度因子值基本一致,验证了提出的应力强度因子计算模型的有效性.     

复合型裂纹疲劳扩展的新准则

把最近提出的及计材料拉压屈服强度不同对材料断裂影响的复合型裂纹断裂准则扩充到疲劳裂纹扩展的情况，建立了一个新的复合型裂纹疲劳扩展准则，进而将位移不连续法(一种边界元方法)和本文提出的复合型裂纹疲劳扩展准则结合在一起，用于数值模拟复合型裂纹疲劳扩展过程．对中心斜裂纹板的疲劳扩展的数值模拟结果揭示了材料拉压屈服强度不同对复合型裂纹疲劳扩展的影响。     

颗粒复合材料微裂纹增韧的数值模拟

将弹性复合材料体中主裂纹尖端划分为3个不同的区域,导出了各个区域的本构模型及饱和区域的范围。在最大饱和区域内,应用Monte-Carlo技术产生均匀分布的微裂纹来表示损伤的各向同性,并采用轮流迭代数值技术来评估主裂纹和微裂纹相互作用。在稀疏微裂纹的假设前提下,忽略微裂纹间的相互作用,主裂纹与每一个微裂纹相互作用的应力强度因子可以叠加。分析了两种荷载源,一个是在无限远荷载作用下主裂纹和微裂纹的相互作用,另一个是伴随着微裂纹面上残余应力的释放主裂纹和微裂纹的相互作用。结果表明,两种荷载源都对主裂纹有屏蔽作用,且主裂尖后的微裂纹有最大的屏蔽作用,主裂尖前的微裂纹没有屏蔽作用。     

A numerical method for multiple cracks in an infinite elastic plate

This article examines the interaction of multiple cracks in an infinite plate by using a numerical method. The numerical method consists of the non-singular displacement discontinuity element presented by Crouch and Startled and the crack tip displacement discontinuity elements proposed by the author. In the numerical method implementation, the left or the right crack tip element is placed locally at the corresponding left or right crack tip on top of the constant displacement discontinuity elements that cover the entire crack surface and the other boundaries. The numerical method is called a hybrid displacement discontinuity method. The following test examples of crack problems in an infinite plate under tension are included： “ center-inclined cracked plate”, “interaction of two collinear cracks with equal length”, “interaction of three collinear cracks with equal length”, “interaction of two parallel cracks with equal length”, and “interaction of one horizontal crack and one inclined crack”. The present numerical results show that the numerical method is simple yet very accurate for analyzing the interaction of multiple cracks in an infinite plate.     

Simulation of crack coalescence mechanism underneath single and double disc cutters by higher order displacement discontinuity method

The present research is focused on the numerical crack coalescence analysis of the micro-cracks and cracks produced during the cutting action of TBM disc cutters. The linear elastic fracture mechanics(LEFM) concepts and the maximum tangential stress criterion are used to investigate the micro crack propagation and its direction underneath the excavating discs. A higher order displacement discontinuity method with quadratic displacement discontinuity elements is used to estimate the stress intensity factors near the crack tips. Rock cutting mechanisms under single and double type discs are simulated by the proposed numerical method.The main purposes of the present modeling are to simulate the chip formation process of indented rocks by single and double discs.The effects of specific disc parameters(except speed) on the thrust force Ft, the rolling force Fr, and the specific energy ES are investigated. It has been shown that the specific energy(energy required to cut through a unit volume of rock) of the double disc is less than that of the single disc. Crack propagation in rocks under disc cutters is numerically modeled and the optimum ratio of disc spacing S to penetration depth Pd(i.e. S/Pd ratio) of about 10 is obtained, which is in good agreement with the theoretical and experimental results cited in the literature.     

A numerical analysis of stress intensity factors for cracks emanating from an elliptical hole in a rectangular plate under biaxial loads

Due to the stress concentration effect around ahole, cracks are likely to initiate at the hole under theaction of fatigue loading. Consequently, a number ofpapers dealing with hole edge crack problems are avail-able. Bowie[1]gave solutions of a circular hole with asingle edge crack and a pair of symmetrical edge cracksin a plate under tension. Newman[2]provided a solu-tion by means of the boundary collocation method, andNisitani and Isida[3]by using the body force methodperformed analysis of …     

Experimental and numerical study on crack propagation in pre-cracked beam specimens under three-point bending

A simultaneous experimental and numerical study on crack propagation in the pre-cracked beams specimens(concrete-like materials) is carried out using three-point bending flexural test. The crack propagation and coalescence paths of internal cracks in side beam specimens are experimentally studied by inserting double internal cracks. The effects of crack positions on the fracturing path in the bridge areas of the double cracked beam specimens are also studied. It has been observed that the breaking of concrete-like cracked beams specimens occurs mainly by the propagation of wing cracks emanating from the tips of the pre-existing cracks in the numerical and experimental analyses, respectively. The same specimens are numerically simulated by an indirect boundary element method(IBEM) known as displacement discontinuity method(DDM) using higher displacement discontinuity. These numerical results are compared with the existing experimental results. This comparison illustrates the higher accuracy of the results obtained by the indirect boundary element method by using only a small number of elements compared with the discrete element method(PFC2D code).     

中心裂纹板张开位移研究

首先对ＥＰＲＩ方法建立的裂纹中心板张开位移的工程解进行了实例计算。然后用有限元法对平板中心穿透裂纹张开位移计算得到的有限元解与其进行了比较,得出工程解偏于保守的结论。     

一种十分有效的裂纹尖端特殊单元

提出了一种可以模拟裂纹尖端附近位移非连续单元，研制了一个边界元分析软件。结果表明，该单元在对于计算应力强度因子十分有效。     

基于裂缝扩展准则的混凝土重力坝裂缝扩展全过程数值分析

将裂缝扩展准则应用于混凝土重力坝裂缝扩展全过程分析,结合虚拟裂缝模型计算了经典混凝土重力坝模型的断裂特性,并与其他数值方法进行了对比。结果表明：利用该数值方法得到的混凝土重力坝模型的外荷载一裂缝口张开位移曲线及裂缝扩展路径与试验结果均吻合良好;当给定了混凝土材料的起裂断裂韧度、断裂能、抗拉强度等参数后,即可采用该数值方法对混凝土重力坝裂缝扩展全过程进行分析。