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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。 相似文献
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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。 相似文献
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管线钢表面裂纹体的三维断裂特性和断裂判据研究 总被引:1,自引:0,他引:1
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. 相似文献
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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. 相似文献
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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。 相似文献
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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 相似文献
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V. I. Kucheryavyi S. N. Mil’kov 《Journal of Machinery Manufacture and Reliability》2014,43(2):176-181
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. 相似文献
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Using vibration-assisted grinding to reduce subsurface damage 总被引:8,自引:0,他引:8
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. 相似文献
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含横向裂纹简单转子刚度的计算 总被引:14,自引:0,他引:14
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。 相似文献
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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 相似文献
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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。 相似文献
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V. I. Kucheryavyi S. N. Mil’kov 《Journal of Machinery Manufacture and Reliability》2009,38(3):306-309
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. 相似文献
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A probabilistic analysis on variability of fatigue crack growth using the markov chain 总被引:1,自引:0,他引:1
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. 相似文献
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Nwe Ni Tun Hee Seung Yang Jong Min Yu Kee Bong Yoon 《Journal of Mechanical Science and Technology》2016,30(12):5447-5458
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. 相似文献