脆性岩石断裂破坏机理的边界配位法分析

针对裂纹表面承受载荷时的应力条件，提出了新的应力函数，该应力函数对于各种裂纹模型、各种边界条件、各种边界形状、裂纹表面自由或承受均布载荷等均适用．并利用边界配位法，计算了在压缩载荷下，岩石内部裂纹的应力强度因子（ＳＩＦ），给出了关于岩石断裂破坏的一些新结论     

拉压性能不同材料的几种结构的极限分析

给出了拉压性能不同材料（简称具有Ｓ－Ｄ效应的材料）的几种结构的极限载荷公式。揭示出材料的拉压性能不同对几种结构承载能力的影响规律。所给出的极限载荷公式可供工程设计人员参考。     

裂纹表面承受均布载荷时的应力强度因子及裂纹张开位移的边界配…

本文针对裂纹表面承受载荷时的应力条件，提出了新的应力函数，对于各种裂纹模型，各种边界条件，各种边界形状，裂纹表面自由或承受均布载荷等均适用。并利用边界配位法，计算了裂纹表面承受均布载荷的方型板内中心裂纹的应力强度因子及裂纹的张开位移。     

裂纹表面承受均布载荷时的应力强度因子及裂纹张开位移的边界配位法

本文针对裂纹表面承受载荷时的应力条件，提出了新的应力函数，对于各种裂纹模型、各种边界条件、各种边界形状、裂纹表面自由或承受均布载荷等均适用。并利用边界配位法，计算了裂纹表面承受均布载荷时的方型板内中心裂纹的应力强度因子（ＳＩＦ）及裂纹的张开位移（ＣＯＤ）。     

刚性弹丸撞击下混凝土板侵彻极限深度与痂斑极限厚度经验公式的验算

为了估算混凝土板在外来飞射体撞击下的侵彻极限深度与痂斑极限厚度,总结了以往试验与理论研究成果,评价了几种有代表性的经验公式,对4种具有不同特征参数的导弹撞击混凝土板时的侵彻极限深度与痂斑极限厚度进行了对比。结果表明,现有的经验公式估算侵彻极限深度的差异不大,而估算痂斑极限厚度有时差异较大。     

Dugdale模型与压力容器长表面裂纹的CTOD

本文把压力容器长表面裂纹简化为狭长条的单边裂纹。利用Dugdale模型和二维混合边值问题的奇异积分方程解法,计算了在均匀拉伸和纯弯曲两种载荷下,裂纹尖端前沿的韧带区没有完全屈服时的裂纹尖端张开位移CTOD。最后介绍如何把计算结果应用到工程实际问题。     

考虑拉压强度差效应的厚壁圆筒承载能力分析

应用双剪统一强度理论，考虑材料的拉压异性和同性，推导了在内压力和轴力联合作用下的厚壁圆筒的塑性极限载荷表达式．在该表达式中，当反映中间主应力效应的系数取不同的值时，就能得到按Tresca屈服准则、线性逼近的Mises屈服准则和双剪应力屈服准则的计算结果，并且绘制了在相应准则下的极限应力线图．从而可知：在三维应力状态下，应用该理论，可以获得极限载荷分析的精确解；极限载荷线图与三种屈服准则的屈服曲线是相吻合的；计算的结果可以用于拉压异性和同性的材料，为工程应用提供了理论依据．     

扁壳在任意法向载荷下的极限分析

本文利用对偶变分原理,从极限分析上限定理导得扁壳在任意法向载荷下的极限计算变分公式,通过把扁壳划分为有限元和叠代的方法获得极限载荷的近似值,通过算例显示了这种新的变分方法是解决扁壳极限分析的有效方法,可以用来对飞行器、船舶、防护罩等结构进行极限分析,具有一定现实意义。     

集中弯矩作用下圆弧裂纹的弯曲问题

Ｓｃｈｗａｒｚ对称原理结合复应力函数的奇异性分析的方法，对于分析集中载荷问题有独特的优越性。本文利用这个方法研究了任意位置的集中弯矩作用下含共圆圆弧裂纹板的弯曲问题，获得了一般问题解答，给出一个实际重要情形的封闭形式解；最后求得弯曲应力强度因子公式。本文公式的特殊情形，与现有经典结果吻合。     

任意分布参数疲劳裂纹扩展寿命的可靠性分析

针对工程中疲劳裂纹扩展过程带有很大的随机性,采用Paris-Erdogan公式计算了两端承受均布拉伸载荷的边缘斜裂纹板的疲劳裂纹扩展寿命.裂纹扩展方向采用最大周向应力准则.在此基础上,以材料属性和载荷为随机变量,用随机有限元法结合计算可靠度的四阶矩法,分析了分布参数为任意分布时的疲劳裂纹扩展寿命可靠度对极限寿命的变化规律.通过算例说明本文方法的结果与Monte-Carlo Simulation的结果误差很小,对疲劳设计有一定的指导意义.     

Influence of late-breaking ligaments on crack propagation in compact specimens—A photoelastic study

Dynamic photoelasticity and high-speed photography were utilized to study the influence of tough ligaments on crack propagation in compact specimens. The data obtained during the fracture experiments were analyzed to obtain crack velocity, instantaneous stress-intensity factor and the energy losses away from the crack tip. The results showed that the ligaments can behave as crack arrestors or decelerators. The crack if not arrested at the ligament slowly tunnels in between the ligaments without immediately rupturing them. The ligaments also tend to increase damping losses in the specimens.     

A coupled kinetic-constitutive approach to the study of high temperature crack initiation in single crystal nickel-base superalloys

A rate-dependent crystallographic constitutive theory coupled with a mass diffusion model has been used to study crack initiation in single crystal nickel-base superalloys, exposed to an oxidising environment and subjected to mechanical loading. The time to crack initiation under constant load has been predicted using a strain-based failure criterion. A notched compact tension (CT) specimen containing a single casting defect, idealised as a cylindrical void close to the notch surface, has been studied. Finite element analysis of the CT specimen revealed that, due to the strong localisation of inelastic strain at the void, a microcrack will initiate in the vicinity of the void rather than at the notch surface. The numerical results have also shown that the time to crack initiation depends strongly on the void location. The coupled diffusion-deformation studies have revealed that environmental effects reduce the time to crack initiation due to the oxidation-induced material softening in the vicinity of the notch and void. The applicability of a failure assessment approach, based on the linear elastic stress intensity factor, K, to predict the crack initiation time under creep loading is examined and a probabilistic framework for prediction of component lifetime is proposed.     

A simpliied fatigue assessment method for transverse illet welded joints

Under the as-welded condition the fatigue crack initiation period was considered nonexistent and Linear Elastic Fracture Mechanics(LEFM) was used to calculate fatigue strength for a range of weld geometries. Fracture mechanics assessment of welded joints requires accurate solutions for stress intensity factor(SIF). However, the solutions for the SIF of complex welded joints are dificult to determine due to the complicated correction factors. Three methods for SIF prediction are discussed on illet welded specimens containing continuous or semi-elliptical surface cracks, including the traditional correction method Mk, the approximate correction method Kt, and the suggested additional crack size method(ac+ae).The new additional crack parameter ae is used to replace the stress concentration effect of weld proile Mk, which simpliies the calculation process. Experimental results are collected to support fatigue strength assessment of the additional crack size method.     

Numerical investigation of ductile tearing in surface cracked pipes using line-springs

Accurate prediction of crack-driving force equations is important in any pipeline fracture assessment program. In highly ductile materials, such as pipeline steel, a considerable amount of stable crack growth can be tolerated before the failure of the structure. The existing methods use simplified analytical procedures to account for ductile tearing, and they often result in conservative critical crack sizes. Further, none of the published numerical tools for modelling crack growth is suitable for engineering applications. This work describes a simple method for simulating through-thickness ductile tearing in surface cracked pipes, using line-spring finite elements. The crack growth resistance curve is used to advance the crack front. The line-spring results are verified using crack growth simulations employing the Gurson damage model. Finally, a detailed parametric study is carried out to examine the effect of ductile tearing on crack driving force relationships in circumferentially surface cracked pipes. The results demonstrate that considering ductile tearing is important in fracture assessment procedures for pipelines.     

Limiting toughness of a ligament toughened brittle material: crack size and loading effect

Many brittle materials have the characteristic that the crack tip stress intensity increases during crack growth; a ligament zone forms behind the crack tip and the restraining stresses due to the crack-bridging elements within this zone impede the crack extension process. The present paper's theoretical analysis shows that the initial crack size and loading condition both have a marked effect on the limiting toughness associated with the full development of a ligament zone.     

Limit load analysis of a spring-supported shallow arch of variable thickness given by a power-law,exponential, or logarithmic formula

Thin shallow arches may become unstable under transverse loading as the built-up internal compressive forces reach a limiting value beyond which the structure undergoes a sudden large displacement towards a new stable configuration. This phenomenon could be both desirable (in toggle switches) and disastrous (collapse of a dome or truss). Hence, it is important to carry out the so-called snap- or limit-load analysis to reveal the factors influence the phenomenon and to give guidelines in designing structures to behave favorably. Although energy methods are a common means of this analysis, the phenomenon could also be analyzed by considering the equations governing the displacement of the arch and by monitoring the load-displacement characteristic of the structure until it reaches the limit point. This is the procedure adopted here. Researches on the subject mostly consider constant thickness arches with common pin-ended or fixed supports. Here the thickness is varied along the arch in three forms: power-law, exponential, and logarithmic. The supports are considered to be nonrigid fixed; i.e., pinned ends are equipped with torsional springs with constant stiffness. By changing these stiffnesses, various combinations of pinned and/or fixed states, or an intermediate state at each end could be developed. By considering the analytical solution for the transverse displacement for the general power-law case, the limit-load is obtained by numerical solution of the limit-load condition, which is a highly complicated function of the derived displacement field. Several parameter studies, such as that of the effects of shallowness and slenderness of arch and spring stiffnesses on the critical load, are carried out. The results are verified by those of simpler cases available in the literature, as well as those from a finite-element approach.     

Numerical and experimental determination of three-dimensional multiple crack growth in fatigue

This work is concerned with the assessment of propagation of multiple fatigue cracks in three-dimensions. Computational modelling of fatigue crack propagation is made together with detection and monitoring of the crack shape development. The boundary element method (BEM) is used for automating the modelling of crack propagation in linear elastic as well as elastic–plastic regimes. Strain at several positions on the specimen surface near the crack mouth is measured to monitor crack initiation, shape development and closure levels. Examples are provided to validate the model by comparing the experimental results with those obtained by numerical predictions.     

残余应力对压力容器破坏模式的影响分析

破前漏(简称LBB)是压力容器、核电站设备结构设计与评价中的一个重要准则.表面裂纹准静态扩展的几何形貌变化规律的预测是破前漏(LBB)评判十分重要的课题之一.本文对特定焊接残余应力场加载作用下,含三维表面裂纹的压力容器模型,用有限元软件(ABAQUS)进行了表面裂纹准静态扩展模拟计算,得到在此残余应力场作用下应力强度因子沿裂纹前缘的分布规律.结合外载引起的应力强度因子,就可以判别裂纹的扩展形貌,从而判断结构是否满足LBB要求.     

Fracture mechanics based design procedures for pressurized components having part-through cracks

This paper presents a fracture mechanics based design procedure for pressurized components having part-through cracks. Fracture critical stresses are evaluated for the assumed crack configurations and the fracture envelopes are obtained for these configurations. For small size crack configurations, Feddersen's type correction is made for proper estimation of critical stress values. Residual strength of unbroken ligament is a more appropriate criterion for the design of thin sections with parth-through cracks. A criterion based on the ligament failure is defined for cases where the critical fracture stresses are above the material yield stress value. The procedure is illustrated by presenting an example of a pressurized tankage used in aerospace industry.     

纤维增强复合材料圆柱型界面裂纹分析

以裂纹面上的位错函数为未知量将圆柱型界面裂纹问题化成一组奇异积分方程的求解问题．应用Ｍｕｓｋｈｅｌｉｓｈｖｉｌｉ的奇异积分方程理论，分析了圆柱型界面裂纹尖端应力场．针对裂纹尖端分别存在和不存在接触区两种情况，确定了裂纹尖端应力场的奇异性．利用数值方法计算了圆柱型界面裂纹尖端接触区尺寸对剪应力强度因子的影响．