用裂纹扩展片测量SFRC的静,动态裂纹扩展

本文用箔式裂纹扩展片测试，研究了钢纤维增强砼三点弯曲切口梁试件在蠕变断裂和动态断裂时的裂纹扩展，分别得到了裂纹扩展量与时间，裂纹扩展量与加载点位移及动态裂纹扩展速度与应变率的关系，根据实验结果分析了ＳＦＲＣ的静，动态裂纹展规律。     

能量平衡结合有限元数值计算分析天然气管道裂纹稳定扩展问题

本文提出了在天然气管道裂纹稳定扩展问题中，应用能量平衡方法结合有限元数值计算结果来分析计算裂纹驱动力。能量数值计算采用了可模拟动裂纹在管道上扩展的有限元程序ＰＦＲＡＣ，它包括了对未开裂管道和裂纹扩展管道的能量计算。通过分析外力作功和内部能量在裂纹扩展时的变化率，应用能量平衡方法计算了裂纹驱动力，并与在ＰＦＲＡＣ程序中应用节点力释放方法计算的裂纹驱动力的结果进行了比较     

用裂纹驱动力分析管道的承压能力

本文以弹塑性断裂力学的Ｊ积分理论为基础，综合考虑裂纹的Ｊ积分弹性解和全塑性解，导出了促使管道的轴向内表面裂纹扩展的裂纹驱动力Ｊ。通过裂纹驱动力图与管材的ＪＲ阻力曲线的叠加，实现了对含有一定初始裂纹管道的承压能力的分析评定，本文的分析结果与相关文献的完整性评定结论基本吻合。     

含非贯穿直裂纹输流管道振动与模态功率流分析

针对含非贯穿直裂纹输流管道的振动与模态功率流进行研究，将输流管道以Euler-Bernoulli梁模型建模并据此推导其弯曲振动方程，采用断裂力学方法将裂纹模拟成无质量的转动弹簧，用波动法分析含裂纹输流管道的自由振动特性。通过计算结果与相关文献对比验证了该方法的可靠性。探讨裂纹位置、深度以及管内流速对固有频率的影响。基于模态功率流的概念进行算例分析，讨论裂纹位置、深度以及振动模态对模态功率流的影响，研究表明，裂纹处的模态功率流曲线产生突变，裂纹位置与深度和模态功率流密切相关。     

SiC_w/ZrO_2(6mol%Y_2O_3)陶瓷中晶须增韧的数值模型

SiCw／ZrO2（6mol％Y2O3）陶瓷的实验研究表明，晶须桥联和裂纹偏转是其主要增韧机制在两种机制协同增韧的基础上，建立了晶须增韧的数值模型，对材料的三点弯曲断裂过程的计算结果表明：载荷／位移曲线呈锯齿状，是由于晶须桥联作用使得裂纹扩展与停止这一过程反复出现而引起的；随晶须含量增加，复合材料韧性提高，晶须桥联和裂纹偏转两种增韧贡献都增加，但是占主导地位的增韧机制由裂纹偏转机制逐步过渡到裂纹桥联机制．计算结果与材料的测试结果很吻合．     

锅炉压力容器压力管道检验中的裂纹问题分析

在锅炉压力容器压力管道检验过程中，主要应用超声波技术进行裂纹检测，但极易出现检测盲区，使得裂纹检测结果 F1分数较低。本文建立一种新型锅炉压力容器压力管道裂纹检验方法，并提出裂纹预防方案。依托于X射线检测原理，全方位采集压力管道图像，作为裂纹检测的基础。运用多重小波分解原理，将X射线图像分解为高频子图和低频子图，并融合非局部均值滤波算法处理图像噪声信息。经过二值图像分析和缺陷特征分析标注出裂纹缺陷，得出压力管道裂纹检验结果。同时，从材料质量、运行安全管理、操作水平三方面入手，建立锅炉压力容器压力管道裂纹预防方案。实验结果表明：所提方法应用后得出的裂纹检验结果 F1分数为0.97，更好地满足压力管道裂纹检验要求。     

多裂纹弹塑性干涉效应及其工程解

本文针对Ｒａｍｂｅｒｇ－Ｏｓｇｏｏｄ关系材料进行弹塑性有限元计算，研究分析了平面应力问题下的近似无限宽板中双共线裂纹弹塑性干涉效应的变化规律，利用双裂纹裂纹Ｊ积分值和等载荷比下单裂纹尖Ｊ积分值之比来确定双裂纹间的弹塑性干涉效应，研究发现，弹塑性干涉效应不同于线弹性干步效应。除了与裂纹几何尺寸有关外，且是载荷比和材料性能的函数，由此证明线弹性分析作为裂纹问题处理的依据有可能出现危险的结果，在此基础上     

蠕变裂纹启裂和扩展的局部损伤理论

根据局部损伤理论和相似原理，给出了蠕谱裂纹启列前的孕育上下限时间并推导了蠕变裂纹扩展率方程。在常载荷下用２．２５Ｃｒ－１Ｍｏ钢作了蠕变裂纹扩展试验，高拘束度使早期局部损伤发展迅速，实验结果与孕育时间下限接近。稳态预测值由于忽略未开裂部分材质劣化而略氏于实验结果值。有限元模拟损伤演变过程。表明稳态裂纹扩展民实验结果吻合。     

磨辊开裂原因分析

磨辊在热处理之后发生开裂，裂纹宏观形貌平直。为寻找开裂原因，对开裂磨辊进行了化学成分和高、低倍组织及断口的宏、微观分析。检验结果，宏观断口上有较多白亮斑，低倍试样上分布大量锯齿状白点裂纹；用SEM观察断口的白亮斑区有不连续二次裂纹，二次裂纹边缘分布多个穿晶准解理平台，平台微观形貌与白点的微观形貌特征相符；金相组织是由粗大马氏体、贝氏体和珠光体与铁素体组成的混合组织，且有不连续分布的穿晶锯齿状裂纹，裂纹周围未脱碳。结果表明，磨辊开裂是由白点引起的，而白点裂纹的形成与磨辊材料的氢含量和热处理组织缺陷等因素有关。     

求解受钉传载荷正交各向异性板双边缺口边缘裂纹应力强度因子的复变－广义变分解法

本文以单边边缘裂纹二维应力场与位移场展开式为基础，采用广义变分方法研究受钉传载菏各向异性板双边缺口边缘裂纹应力强度因子。首先建立精确满足正文各向异性板基本微分方程、裂纹表面边界条件、钉载孔处位移单值条件与合力平衡条件的应力场和位移场的级数表达式。然后应用广义变分方法满足边界条件从而确定应力强度因子，在变分方程中只存在沿板边界的线积分、计算程序简单，输入数据很少，结果收敛迅速，并与已知结果相当吻合而且所需机时较少。     

Evaluating J‐integral from Displacement Fields Measured by Digital Image Correlation

Path integral, domain integral and least squares methods for evaluating J‐integral from measured displacement fields for a power‐law hardening material are described in this paper. The values of the J‐integral are evaluated by applying the path and domain integral methods to the displacement fields obtained by elastoplastic finite element analysis and the displacement fields obtained through the measurement using digital image correlation. Results show that the values obtained by the domain integral method are slightly better than those by the path integral method, because the domain integral method efficiently uses the full‐field measurement data. The values of the J‐integral are also evaluated by the least squares method with the Hutchinson, Rice, and, Rosengren displacement fields. Results show that the J‐integral can be obtained by the least squares method simply and easily without any calculation of the integration. The J‐integral values obtained by the least squares method agree well with the values obtained using other methods. Because J‐integral can be evaluated easily by any method described in this paper, it is expected that these methods are applicable to various fracture problems during experimental evaluation of structural components.     

Theoretisch-numerische Untersuchungen zu Experimenten mit Kriechrißwachstum

Theoretical-Numerical Investigations of Experiments with Creep Crack Growth Numerical results are presented to calculate the C* -integral that is path independent only in the long-time range. The crack tip modelling – elastic or elastic-plastic – is of minor influence on C* – whereas values of C* depend strongly on the material constants describing the creep law. The agreement between numerically and experimentally determined C* data is rather satisfactory in the secondary creep regime. A line integral R* is proposed that is path independent in the whole time domain.     

A comparison of theJ* integral with other methods of post yield fracture mechanics

TheJ ^* integral approach to post yield fracture analysis is compared with a wide variety of other methods by means of experimental testing of specimens invalid in the sense of ASTM. The significance of J* and its relationship to other integrals is discussed.     

3D J‐integral evaluation using the computation of line and surface integrals

In the analysis of fracture mechanics of structures using three‐dimensional (3D) J‐integral, an integral evaluation of line and surface is required. However, because surface integral evaluation requires the calculation of the second derivative of displacement field and commercial finite element codes cannot calculate it, then this portion of the integral is neglected in some research. In this paper, a method for computing 3D J‐integral is presented using finite element analysis. In the analysis, the second derivative evaluation of displacement field is employed. The method is implemented in calculating the J‐integral of some 3D cracks and results are compared to well‐known reference values. The results show that the method is reliable and is suitable for applications in engineering. The portion of 3D J‐integral, namely the surface integral value is investigated and it is shown that neglecting this portion can introduce considerable error in the final results.     

A finite element treatment of ductile crack extension

Abstract

To provide a realistic analysis for fracture, this paper is devoted to finite element approaches which attempt to describe ductile crack extension. A rigorous hybrid displacement finite‐element modeling, involving the translation of entire “singular” near‐tip elements and consideration of global energy balance, is successfully developed. To investigate the variation of global energy release rate G* and J‐integral for single‐step extensions at various levels of applied loads (extension ^δa = constant), the Kfouri et al.’s center‐cracked problem together with A533B compact tension specimen are solved. In addition, an available experimental J resistance curve for the compact tension specimen (made of Ni‐Cr‐Mo‐V rotor steel) is simulated by the present finite element analysis procedure to study the actual process of ductile fracture. The effect of unloading process occurred in the plastic region behind the advancing crack‐tip is also discussed.     

Boundary element analysis of ductile crack growth using the traction-free fundamental solution

A new boundary element formulation in two-dimensional rate-independent plasticity is given. This new formulation uses a so-called traction-free fundamental solution so that the resulting boundary integral equation converges in the normal sense, and more important, a formal differentiation of the boundary integral equation leads to a valid integral representation for the in-plane stress component on the boundary. No finite difference approximation is needed to construct the stress recovery routine. The new boundary element method is then used to solve the problem of quasi-static ductile crack growth. Numerical simulations based on a set of experimental data have been carried out to evaluate a new path-independent integral,T* _M . TheT* _M ,-integral is a modified version of Atluri'sT*-integral. This modified version has an advantage of having a less singular domain integral near the crack flank so that it is numericaly preferable toT*.     

二次应力存在时的J积分和断裂准则

本文对二次应力存在时的修正Ｊ积分参量进行了较全面的介绍和总结，用有限元法对各修正Ｊ积分的守恒性及其相互关系进行了比较和讨论，结果表明Ｊ′积分是适用于二次应力存在的具有明确物理意义的最普遍有效断裂参量，并建立了相应的Ｊ积分断裂准则     

Life assessment of HK40 reformer tube by fracture mechanics

Creep crack growth measurements have been made at 871°C (design temperature) on HK40 steel which was taken from a reformer tube in service for 81000 h. The path-independent integral C* is a proper parameter correlating creep crack growth rates of different specimen geometries. The residual life of the reformer tube was calculated by the equation da/dt with C* and Webster's model. It has been shown that the results by the two methods are consistent.     

Equivalence of J Integral and Stress Intensity Factor Approaches for Large Scale Bridging Problems

The application of the J integral to problems involving large scale crack bridging is discussed. Using some simple examples for which close form analytical solutions exist, it is shown that there is a complete agreement between analysis based on stress intensity factors and the J integral. A simple method for deriving the bridging law from J integral measurements is outlined.