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利用概率断裂力学方法中的一次二阶矩法和蒙特卡洛方法分别计算含裂纹类缺陷输送油气管线结构的失效概率。在计算过程中,不仅把材料的屈服强度、裂纹深度、外加载荷和断裂韧度等当作随机变量处理,还考虑了裂纹深长比的影响。结果表明,一次二阶矩法计算管线的失效概率为1.69×10-3,MonteCarlo方法计算该管线的失效概率为1.724×10-3,这两种方法的计算结果基本一致,计算误差为1.97%。两种方法的参数敏感性分析结果一样,裂纹深度对结构失效概率的影响最大,材料屈服强度的影响最小,裂纹深长比对结构的失效概率也有一定的影响。 相似文献
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粉末冶金涡轮盘裂纹扩展失效概率分析 总被引:6,自引:0,他引:6
建立了考虑应力及断裂参数随机性的裂纹扩展失效功能函数 ,提出了亚表面裂纹扩展寿命计算方法。用 Hasofer- L ind方法分析某粉末冶金涡轮盘裂纹扩展失效概率 ,通过敏感性分析指出提高发动机可靠性的主要途径 ,具有工程指导意义。并用蒙特卡罗法和β球法进行验证 相似文献
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机械结构中普遍存在疲劳裂纹,由于受各种随机因素的影响,裂纹扩展过程下的结构安全性评价往往具有很大的不确定性。针对有限板宽问题,通过灵敏度分析,优选出了对疲劳裂纹扩展速率影响较大的因素(载荷水平、裂纹初始长度和材料参数),并将其视作随机变量,推导出疲劳裂纹扩展下的断裂失效可靠性模型,在此基础上建立了可靠性指标的优化数学模型,并基于序列二次规划算法给出了裂纹结构断裂失效及静强度联合失效的可靠性指标。最后根据一个具体实例,得到了联合失效模式下的可靠性指标随应力循环次数扩展的曲线,并同单一失效模式下的可靠性变化进行对比分析,说明了基于联合失效模式下的可靠性分析的合理性,实现了对裂纹结构在扩展过程中可靠性变化的评价。 相似文献
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刀座焊接处是全断面岩石隧道掘进机(Full face rock tunnel boring machine,TBM)刀盘上最易发生疲劳破坏的部分。基于线弹性断裂力学,以裂纹疲劳寿命为基本变量,建立裂纹扩展可靠性模型,通过JC法计算刀座正面焊缝在不同滚刀实验载荷下的疲劳可靠性,并分析了不同因素对失效概率的影响。结果显示:中心滚刀刀座焊缝的失效概率比正滚刀小,正滚刀的失效概率随着安装半径的增大而减小;刀座焊缝失效概率随着初始裂纹深度的增大而显著增大,而临界裂纹深度的变化对失效概率的影响不大;裂纹形状比越大,刀座焊缝的失效概率越小。 相似文献
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核压力容器缺陷验收确定性准则的失效概率分析 总被引:1,自引:0,他引:1
在含缺陷结构完整性评定中,即使满足确定性分析要求,结构也会存在发生失效的可能。提出确定性缺陷验收准则所对应失效概率的分析方法,以计算在满足确定性分析要求的临界条件下结构的失效概率。采用该方法可以验证确定性缺陷验收准则是否能够满足结构的概率要求,也可依据概率要求指导确定性缺陷验收准则中安全系数的制定。针对ASME BPVC第XI卷中基于应力强度因子的缺陷验收准则,以正常降温工况和承压热冲击事故工况为例,对一典型含缺陷反应堆压力容器(Reactor pressure vessel,RPV)进行确定性分析和概率分析,得到相应工况下的临界裂纹尺寸及失效概率,并讨论安全系数对含缺陷RPV失效概率的影响。所分析案例表明,ASME标准中规定的安全系数在正常降温工况下尚不能保证RPV临界失效概率低于核安全的概率要求。 相似文献
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Ouk-Sub Lee Dong-Hyeok Kim 《International Journal of Precision Engineering and Manufacturing》2009,10(3):119-126
The methodologies to estimate the reliability of cracked structures using the fracture toughness and the SIF are developed.
The probability theories such as the FORM and the SORM are utilized to calculate the failure probability. It is found that
the failure probability increases with the increase of the crack size and the applied stress, and the decrease of the fracture
toughness. It is also found that the failure probabilities obtained by the FORM and the SORM are similar each other for the
through crack,the edge crack, and the single and the double crack emanated from a hole, and turn out different for the elliptical
and semi-elliptical surface cracks. It is noted that the tensile stress affects significantly on the failure probability among
the other random variables on the various crack geometries. 相似文献
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This paper presents the effect of external corrosion, material properties, operation condition and design thickness in pipeline
on failure prediction using a failure probability model. The predicted failure assessment for the simulated corrosion defects
discovered in corroded pipeline is compared with that determined by ANSI/ASME B31G code and a modified B31G method. The effects
of environmental, operational, and random design variables such as defect depth, pipe diameter, defect length, fluid pressure,
corrosion rate, material yield stress and pipe thickness on the failure probability are systematically studied using a failure
probability model for the corrosion pipeline. 相似文献
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In the context of the theory of random variables, a mathematical model is obtained for the probability of the nondestruction
of a gas pipeline beam section in the presence of a longitudinal crack, which is located by means of pigging. A solution is
obtained for the case when the fracture toughness of pipe steel, its physical and mechanical characteristics, loads, and the
pipeline dimensions are nor mally distributed. An allowable mathematical expectation of the crack length is found for which
the standard pipeline reliability and operational safety for the remainder of the service life are provided. 相似文献
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随机因素对疲劳裂纹扩展分散性影响的探讨 总被引:4,自引:2,他引:2
采用概率有限元和可靠性分析相结合的方法,将影响裂纹扩展的主要随机因素作为随机变量处理,研究裂纹扩展失效概率的计算问题。文中采用梯度投影方法,对各种主要随机因素作为随机变量时用于失效概率计算的可靠性指标进行了计算,在此基础上用一阶可靠性方法计算了疲劳裂纹扩展的失效概率。 相似文献
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In this paper, the reliability estimation of pipelines is performed by employing the probabilistic method, which accounts
for the uncertainties in the load and resistance parameters of the limit state function. The FORM (first order reliability
method) and the SORM (second order reliability method) are carried out to estimate the failure probability of pipeline utilizing
the FAD (failure assessment diagram). And the reliability of pipeline is assessed by using this failure probability and analyzed
in accordance with a target safety level. Furthermore, the MCS (Monte Carlo Simulation) is used to verify the results of the
FORM and the SORM. It is noted that the failure probability increases with the increase of dent depth, gouge depth, operating
pressure, outside radius, and the decrease of wall thickness. It is found that the FORM utilizing the FAD is a useful and
is an efficient method to estimate the failure probability in the reliability assessment of a pipeline. Furthermore, the pipeline
safety assessment technique with the deterministic procedure utilizing the FAD only is turned out more conservative than those
obtained by using the probability theory together with the FAD. The probabilistic method such as the FORM, the SORM and the
MCS can be used by most plant designers regarding the operating condition and design parameters. 相似文献
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Deng CaiyanZhang YufengHuo LixingSchool of Material Scienceand Engineering Tianjin University Tianjin China 《机械工程学报(英文版)》2005,18(3):389-392
0 INTRODUCTIONFlaw assessment concepts based on fracture mechanics arebeing increasingly used in industrial regulations and standards. Aconsiderable number of guidelines and procedures are availablewhich are partly based on each other but also exhibit sig… 相似文献
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含裂纹结构剩余强度的一种估算方法 总被引:5,自引:0,他引:5
剩余强度分析对结构断裂安全性评价十分重要。现有的剩余强度分析方法中,Feddersen工程分析法具有代表性,它对简单含裂纹结构比较有效。但这类方法一般需要预先得到弹性断裂应力的连续曲线,才有可能进行短裂纹阶段的弹塑性修正和长裂纹时的净截面屈服修正,使用不方便,有时甚至不适用。本文认为含裂纹结构的破坏是静力学模式破坏和断裂力学模式破坏共同作用的结果,从而建议一种结构剩余强度的实用估算方法。通过表观断裂韧度准则确定的弹性断裂强度和净截面全面屈服后的静力学破坏强度的结合,估算剩余强度许用值。该方法可以方便地估算任意时刻的剩余强度。分别进行含中心裂纹的有限宽板和含裂纹耳片结构的剩余强度试验,并与估算结果进行比较,表明本文方法预测精度良好,有望推广到其他结构形式。文中强调,表观断裂韧度Kapp值的合理与否对估算结果有明显影响。 相似文献