常幅载荷下结构元件断裂可靠性分析的裂纹长度模型

从瞬时裂纹长度及应力强度因子服从对数正态分布的假设出发,基于Paris裂纹扩展速率公式讨论当实验数据较少时,常幅载荷下结构元件临界裂纹长度和瞬时裂纹长度的分布特性,给出一个计算瞬时裂纹长度分布参数的方法,建立常幅载荷下结构元件断裂可靠性分析的裂纹长度模型,阐述元件断裂可靠性的分析方法.对2024-T351材料的CT(compact tension)试件试验数据分析表明,文中给出的模型是合理的,预测结果和试验结果吻合良好.     

高应力集中区中的疲劳裂纹扩展

本文对高应力集中区中疲劳裂纹扩展进行了研究,对两种材料的中心椭圆孔边裂纹板共6个试件进行了低周疲劳试验。为了减少参量计算引起的误差,首先给出了有限宽板中心椭圆孔边裂纹应力强度因子的计算公式,同时对弹塑性材料引入了大范围塑性区修正方法。为了考证公式和方法的正确性,进行了有限元计算。应力强度因子 K 和大范围塑性区修正形式的 K两者都被用作为相应的参量,结果表明:本文发展的大范围塑性修正形式的代表 J 积分的 K,对高应力区疲劳裂纹扩展是一个合适的参量。     

非均质焊接接头断裂行为预测研究

基于局部法定量研究了焊接接头中强度匹配、试样几何形式对接头断裂行为的影响。首先由标准三点弯曲试样的断裂韧度值,得出反映材料脆性断裂的控制参量,再根据该参量对不同接头强度匹配下三点弯曲和双边裂纹拉伸试样的断裂行为进行了定量预测,当考虑由于延性裂纹扩展所造成的应力升高后,其结果与试验结果相当吻合。表明局部法能很好地描述材料的断裂行为。     

缺口疲劳裂纹的萌生和扩展

本文使用AI-4Zn-2.5Mg-1.5Cu高强度铝合金研究了缺口疲劳短裂纹的萌生和扩展。结果表明,缺口有效应力强度因子可以用试验方法标定,它是缺口几何形状、裂纹尺寸和材料组织特征参量的函数。试验标定的缺口有效应力强度因子可以用来定量描述缺口短裂纹的萌生和扩展。     

管线钢表面裂纹体的三维断裂特性和断裂判据研究

采用中心表面裂纹试样的三点弯曲试验,研究X70管线钢表面裂纹体的断裂特性.结果表明,二维断裂力学参量KⅠ已不能客观描述和表征表面裂纹体断裂现象和裂端应力场强度.采用三维断裂力学参量KZ,能很好描述和表征表面裂纹体的试验现象和裂纹尖端应力场强度,三维断裂韧度K ZC与表面裂纹的几何尺寸和裂纹形态无关,是管线钢表面裂纹体的客观韧性指标.建立穿透裂纹和表面裂纹的统一断裂准则,即三维断裂力学准则,KZ=K FTZ≤KZC ,将该准则和失效评估图(failure assessment diagram, FAD)技术相结合,可以进行含表面裂纹管道的安全性评定.     

Q345钢疲劳裂纹扩展Paris公式中参数的统计分布

针对Q345钢疲劳裂纹扩展Paris公式中两个材料参数的不确定性问题,基于恒幅载荷下Q345钢疲劳裂纹扩展速率批量试验中所获得的裂纹扩展长度与疲劳循环次数等数据,采用七点递增多项法对试验数据进行分析整理。采用最小二乘法对Paris公式进行拟合,给出该公式中两个材料参数值的随机数,并引入概率统计方法对其分布类型进行研究。结果表明,Q345钢疲劳裂纹扩展Paris公式中两个材料参数值的最佳分布类型均为正态分布,正态分布能较好地表征出Q345钢材料参数值的分布特性,为Q345钢制工程结构疲劳裂纹扩展寿命的可靠性研究提供理论参考。     

基于可靠性的集装箱起重机疲劳裂纹扩展控制

为更好地对集装箱起重机的裂纹扩展进行控制,需要对材料特性和受力情况的分散特性进行分析,把可靠性分析应用于裂纹扩展的控制.首先确定裂纹扩展的断裂韧性是影响板材的裂纹扩展寿命的主要影响因素,通过对材料断裂韧性的统计特性分析,确定材料的断裂韧性服从正态分布.根据对集装箱起重机实际测试得到的应力分布情况,运用Monte-Carlo模型来分析该测点的临界裂纹长度和裂纹扩展寿命.得出裂纹的临界裂纹长度服从正态分布,而裂纹的扩展寿命是一个服从三参数的威布尔分布,这个结论为集装箱起重机的设备巡检周期提供了理论依据.     

基于微观损伤模型的强度非均质焊接接头抗延性裂纹扩展阻力 …

基于材料微观损伤模型,采用三维有限元数值方法,定量研究了焊接接头中强度匹配、试件几何型式对接头抗延性裂纹扩展阻力特性的影响。首先由标准三点弯曲试件的阻力曲线,得出反映材料微观损伤的特殊单元模型控制参量,再根据该参量对不同接头强度匹配下双边缺口拉伸试件的阻力曲线进行了定量预测,其结果与试验结果相当吻合。表明特殊单元模型能委好地描述材料的抗延性裂纹扩展阻力特性。     

基于微观损伤模型的强度非均质焊接接头抗延性裂纹扩展阻力特性研究

基于材料微观损伤模型,采用三维有限元数值方法,定量研究了焊接接头中强度匹配、试件几何型式对接头抗延性裂纹扩展阻力特性的影响。首先由标准三点弯曲试件的阻力曲线,得出反映材料微观损伤的特殊单元模型控制参量,再根据该参量对不同接头强度匹配下双边缺口拉伸试件的阻力曲线进行了定量预测,其结果与试验结果相当吻合。表明特殊单元模型能很好地描述材料的抗延性裂纹扩展阻力特性。     

保证试验后钙钠玻璃的循环疲劳强度及寿命

研究了保证试验对钙钠玻璃的循环疲劳强度及寿命的影响。在实际操作条件下,保证试验过程中试件中会发生亚临界裂纹扩展,因而对试件造成损伤。对试件的寿命估算和强度分析中需考虑这种损伤的影响。材料的亚临界裂纹扩展参量（Ｖｃ、ｎ）和保证试验中的卸载速率对保证试验的效果有极为重要的影响。选择高卸载速率和惰性试验环境可提高保证试验后陶瓷构件的最小强度。保证试验的最佳σｐ值可根据实用卸载速率和材料的亚临界裂纹扩展参     

Statistical modeling of the residual life of an oil and gas pipeline under alternating pressure

According to a deterministic formula, using the method of statistical modeling, it was found that the residual life of an oil and gas pipeline has a lognormal distribution, where the input arguments: Paris’ coefficients, the annual number of cycles, the diameter and the pipeline wall thickness, the initial and critical crack depth, and the maximum and minimum stresses are subject to the normal law. According to these data, limiting safe operation lifetimes of the pipeline sections analyzed are determined.     

Monte-Carlo法计算含缺陷油气输送管线的失效概率

利用Monte-Carlo方法全面分析了裂纹深度、裂纹深长比、断裂韧度、屈服强度和输送压力等主要随机参数对含裂纹长输油气管线结构的失效概率的影响。利用故障树分析中的参数敏感性方法确定了随机参数的敏感性。计算结果表明,断裂韧度和裂纹深度对结构的失效概率影响较大,裂纹深长比对结构的失效概率也有重要影响。此外,还分析了焊接接头在不同的裂纹深度下,强度匹配对失效概率的影响,并还给出了管线在不同的失效模式下的年失效概率。     

Using vibration-assisted grinding to reduce subsurface damage

This paper discusses a technique for reducing subsurface damage and/or increasing material removal rate (MRR) in ceramics grinding. An indentation damage model shows that intermittent unloading can produce a lateral crack before the median crack fully develops. It shows that upon reloading, the lateral crack shields against further median crack penetration. Furthermore, intermittent unloading produces shielding even for oblique indentation events and intermediate locations of lateral cracks. Single-grit scratch tests provide experimental validation of the beneficial effects of intermittent unloading. A magnetostrictive actuator modulated the workpiece to create the intermittent unloading. Simulation studies predict that force per grit can be doubled under modulated conditions without an increase in normal damage in the finished workpiece. Our experimental observations show a 62% increase in MRR with minimal associated increase in depth of penetration of the median crack. Alternatively, the experimental results also show that modulations could be used to reduce the depth of median crack penetration by 24% at the same MRR. In addition, we observed that damage depth increases with an increase in the ratio of cutting speed to modulation frequency. Finally, both depth of cut modulation and cutting direction modulation were effective in reducing subsurface damage.     

含横向裂纹简单转子刚度的计算

以两端简支的 Ｊｅｆｆｃｏｔ 转子为对象,运用断裂力学和材料力学理论推导出含横向弓形裂纹的转子刚度计算公式,并在此基础上研究裂纹位置、裂纹深度和轴细长比 Ｒ／ Ｌ等参数对转子刚度的影响。计算结果表明,裂纹位置距转子中心越近、裂纹深度越深,转子的刚度就越小;转轴细长比越大,裂纹对转子刚度的影响就越大;当裂纹较浅时,可忽略平行于裂纹方向的刚度变化,而当裂纹较深时,应同时考虑与裂纹平行和垂直方向上的刚度变化。     

中碳钢疲劳短裂纹行为的统计特性研究

通过对两种晶粒尺寸的中碳钢光滑试样的疲劳试验,研究了疲劳短裂纹形成和扩展的统计特性。结果表明,短裂纹形成和扩展寿命均可由二参数或三参数Ｗｅｉｂｕｌｌ分布函数表示。裂纹长度分布呈混合型Ｗｅｉｂｕｌｌ分布形式,分布曲线的拐点值和微观结构的特征尺寸有关。拐点值之前的裂纹长度分布可由二参数Ｗｅｉｂｕｌｌ分布函数表示,而在拐点值之后可由二参数或三参数Ｗｅｉｂｕｌｌ分布函数表示。晶粒尺寸对形成寿命,扩展寿命和     

基于磁记忆的油气管道应力损伤检测方法研究

应力集中是油气管道损坏的关键因素,对管道安全构成重大威胁。对其进行有效检测,既可发现由应力集中引起的机械损伤亦可实现对管道早期损伤的预判。磁记忆检测技术作为一种应力检测方法得到了业界认可。从能量平衡角度出发,分别从宏观和微观的角度对应力作用下的铁磁体磁记忆信号特征进行分析,建立应力与材料磁化率及原子磁矩之间的理论关系模型。采用基于第一性原理的CASTEP软件对铁碳金属体系的磁记忆力磁耦合过程进行仿真。结果表明,铁磁体在外力作用下,体系能量将重新平衡并达到稳定状态,电子能带及态密度分布特征发生改变,导致材料磁性下降,原子磁矩及材料磁化率随应力增大呈线性减小的变化趋势。通过对含裂纹管道的磁记忆检测,验证了应力损伤磁记忆检测方法的理论分析正确性及工程应用有效性。     

Calculating the reliability of a straight line segment of a gas pipeline under crack-like defects

In the framework of the random number theory, a mathematical model describing gas pipeline nonfailure reliability according to crack growth resistance criterion when the crack resistance of the pipe steel, the operation pressure of the cargo gas, the diameter and wall thickness of the pipe, the Poisson ratio, the linear expansion coefficient of the pipe metal, the Young modulus, and the temperature drop through the wall are all distributed according to the normal distribution law, has been obtained. The permissible value of the mathematical expectation of the longitudinal crack length has been found under which the standard reliability and safe operation of a defect segment of a gas pipeline is guaranteed.     

A probabilistic analysis on variability of fatigue crack growth using the markov chain

Understanding the stochastic properties of variability in fatigue crack growth is important to maintaining the reliability and safety of structures. In this study, a stochastic model is proposed to describe crack growth behavior considering the variability of fatigue crack growth rates due to the heterogeneity of material. Fatigue life distribution is then predicted based on this model To construct this model, fatigue tests are conducted on a high strength aluminum alloy 7075 T6 under constant stress intensity factor range control. The variability of fatigue crack growth rates is expressed by random variablesZ and Γ based on the variability of material constantsC andm of the Paris-Erdogan equation. The distribution of fatigue life under constant stress intensity factor ranges is evaluated by the stochastic Markov chain model based on the Paris-Erdogan equation. The merit of the proposed model is that only a small number of tests are required to determine this function, and fatigue life required to reach certain crack length at a given stress intensity factor range can be easily predicted. Department of Mechanical Design and Production Eng.     

油气输送管线钢的分层机理及其对断裂的影响

对不同厚度油气输送管线钢进行各种裂纹的断裂试验，对各裂纹的断口进行了分析，探讨了分层机理及其对不同形式裂纹体承载能力的影响。结果表明，分层在各裂纹形式中均存在，此钢在室温为韧性断裂。对于非穿透裂纹，裂纹先起裂，穿透后情形就与穿透裂纹相似，由于扩展初期无分层，裂纹端部保持高的三维应力约束，所以其起裂应力强度比穿透裂纹要低。因此不能直接用穿透裂纹试验得到的断裂韧度值来评定管道中的非穿透裂纹起裂。     

Creep crack growth analysis using <Emphasis Type="Italic">C</Emphasis><Subscript><Emphasis Type="Italic">t</Emphasis></Subscript>-parameter for internal circumferential and external axial surface cracks in a pressurized cylinder

Creep crack growth at elevated temperatures is a critical consideration in estimating the remaining life of high temperature structural components and in deciding their inspection interval. In this study, creep crack growth analyses for external radial-axial and internal radial-circumferential surface cracks in a pressurized cylinder were conducted by an analytical method. The effect of crack depth and crack length on the variations in C _t and remaining life predictions were investigated for surface cracks with various initial aspect ratios. It was observed that the remaining life of an internal radial-circumferential surface crack was approximately 53 times longer than that of an external radial-axial surface crack for the same crack size and loading conditions with 316 stainless steel material. It was also observed that the variations in remaining life, crack propagations, and the C _t values were considerably sensitive to the crack location and crack depth. Convergence of crack aspect ratio was not observed when the crack depth ratio was increased. Since the method is independent of material properties and location of the crack geometries, it can be extended to various material properties and various locations of the surface crack geometries.