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疲劳裂纹扩展寿命的随机模型 总被引:6,自引:0,他引:6
结合断裂力学的概念和随机过程理论,将疲劳裂纹扩展近似为连续型马尔可夫过程,对于相应的向后Fokker-Plank方程和边界条件,采用本征函数法进行求解,以收敛的无穷级数形式表示出给定临界裂纹尺寸疲劳扩展寿命的分布函数。对两组实验数据,应用该文的方法进行了具体计算,理论结果和实验吻和良好。 相似文献
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给定寿命下的焊趾疲劳裂纹深度尺寸分析 总被引:1,自引:0,他引:1
本文提供并用统计方法研究了焊趾疲劳裂纹扩展的N~α曲线族,给出了联系给定裂纹尺寸下的疲劳分布,给定疲劳寿命下的裂纹尺寸分布以及随机初始条件的概率相容条件。研究表明,给定寿命下的焊趾疲劳裂纹深度尺寸α服从分布Ф[(μ(a)-logN)/σ(a)]。 相似文献
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可靠性设计中的疲劳裂纹扩展随机模型 总被引:2,自引:0,他引:2
首先导出了疲劳裂纹扩展的确定性方程,然后将疲劳裂纹扩展确定性方程随机化,导出了疲劳裂纹随机扩展的概率公式,并推导了疲劳裂纹随机扩展的置信限公式,最后,给出了二种材料疲劳裂纹随机扩展数据的处理结果。 相似文献
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针对疲劳损伤过程的随机性,该文开展了等幅谱大子样疲劳裂纹形成,扩展至破坏全寿命过程的试验研究。在计算确立了裂纹形成,扩发界工程小裂纹长度的基础上,事理得到了裂纹形成,扩展寿命的统计分布数据,根据断口金相SEM观察,进一步定性分析了疲劳条纹分布的相关性特征。 相似文献
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基于断裂力学的疲劳裂纹扩展寿命问题的研究常常将裂纹尖端应力展开项的高次项忽略,引起了裂纹扩展模拟的误差,本文考虑高次项T-stress对裂纹扩展角的影响,对裂纹扩展过程做了数值模拟,结果显示相同裂纹扩展长度下,考虑T-stress会延长裂纹扩展寿命。文章首先采用修正的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,裂纹扩展方向采用两参数修正的最大拉应力准则。由于结构尺寸,材料特性和载荷等因素具有不确定性,导致疲劳裂纹扩展过程带有一定的随机性,本文以材料属性和载荷为随机变量,在随机有限元法的基础上,结合计算可靠度的四阶矩法,Edgeworth级数展开方法,提出随机参数服从任意分布时的结构疲劳裂纹扩展寿命可靠度的计算方法。分析了参数为非正态分布时的平板裂纹扩展寿命可靠度随裂纹扩展的变化过程。本文方法可预测工程中板裂纹的扩展行为,以及预测裂纹板的可靠度。 相似文献
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焊接接头低周疲劳裂纹扩展的统计分析与可靠性最弱环模型 总被引:4,自引:0,他引:4
在相同的试验条件下,对16MnR压力容器用钢焊接接头焊缝区、热影响区和母材区,分别做了15 根试样的低周疲劳试验,获得了三个区的低周疲劳寿命分布与裂纹扩展规律。试验表明,Paris公式中的两个参数m 和c 分别服从正态分布和对数正态分布,m 和log c 呈现统计线性关系。根据文中的统计结果,采用蒙特卡洛法对给定的两个裂纹长度间的扩展寿命进行了预测,预测结果与试验结果符合良好。文中还对焊接接头三个区的低周疲劳寿命进行了统计分析,获得了相应的概率密度函数,初步提出了整个焊接接头的可靠性最弱环模型。 相似文献
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疲劳裂纹扩展分析的随机方法 总被引:1,自引:0,他引:1
本文介绍了近年发展起来的疲劳裂纹扩展分析的随机方法,即疲劳裂纹扩展随机模型建立方法和疲劳裂纹扩展统计分析方法。这一分析方法为金属构件疲劳裂纹扩展寿命及可靠性研究提供了有力的工具。 相似文献
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Fatigue life prediction of in-plane gusset welded joints using strain energy density factor approach
Fatigue crack growth behavior of in-plane gusset welded joints is studied using the strain energy density factor approach. Fatigue tests were performed in order to estimate fatigue strength under tension. Fatigue crack growth analysis was carried out to show the effects of the initial crack shape, the initial crack length, and the stress ratio on the crack types of in-plane gusset welded joints. The assumed crack types were edge crack, semi-elliptical crack, and corner crack. Fatigue crack growth parameters were obtained from crack growth curves assuming constant crack shapes for the given crack types. The results of analysis for the assumed crack types agreed well with the experimental data. The fatigue life did not change as initial crack shape varied for a given initial crack length. 相似文献
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基于局域分析的疲劳短裂纹群体演化随机模型 总被引:4,自引:0,他引:4
采用局域裂纹数密度描述金属材料中不同局部区域的疲劳短裂纹群体损伤的发展情况通过考虑在不同局域存在的材料性质的随机涨落及局部损伤对损伤总量发展的影响,建立了局域裂纹数密度演化随机方程对方程数值求解从而模拟了材料的疲劳短裂纹损伤过程结果显示出主裂纹出现的随机性,并讨论了裂纹总数与最大裂纹尺度在统计意义上的演化特征 相似文献
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Jiang Mingxiao Zhu Weiqiu Zhejiang University Hangzhou P. R. China 《Acta Mechanica Solida Sinica》1996,9(2):169-178
Two stochastic models of fatigue crack growth under constant amplitude cyclic loadingare proposed and studied by using the stochastic averaging method and total probability theorem to ac-count for high frequency component and low frequency component, respectively, of the irregular na-ture of fatigue crack growth observed in Virkler's experiment. Particular attention is paid to the predic-tion performance of the models under a change in the initial crack length. It is shown that the modelsproposed in the present paper yields better agreement with experimental data than other models avail-able in literature. 相似文献
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Rotary bending fatigue tests were carried out by using smooth specimens of medium carbon steel with two ferrite grain sizes.
In order to clarity the physical background of the scatter in fatigue behaviour, the statistical characteristics of the initiation
and growth of short fatigue crack were investigated. Results show that the short crack initiation and growth life distribution
can be express by two-or three-parameter Weibull distribution. The Weibull distribution of the mixed type is well fitted to
the crack length distribution for both steels. The knee values of Weibull plots are related to the grain size. The crack length
distribution before the knee point can be expressed by a two-parameter Weibull distribution, and that after the knee point
can be represented by two-or three-parameter Weibull distribution. It was found that the initiation Life, growth life and
crack length distribution were affected by the grain size. 相似文献
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Summary A statistical theory of the fatigue crack growth at damage cumulation is proposed. The theory gives the average of fatigue
crack length at any time t, and deduces the evolution of failure probability with time varying. Furthermore, the variance and relative error of fatigue
crack length at any time t are acquired. The Paris equation for the average of the crack length at any time t is derived from the statistical theory. Therefore, the prediction of the probability distribution of the crack length can
be given for any time t. Actual applications of the theory are given, which conform to the experiments.
Accepted for publication 17 June 1996 相似文献
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本文从J.L.Bogdanoff提出的一种新的疲劳裂纹扩展模型出发,假定在裂纹扩展过程中存在不同的等概率均匀扩展区间,采用Z变换和其复数反演理论,推导出疲劳裂纹经任意次载荷循环后的失效概率计算的解析公式,计算结果与实验值符合较好、偏保守。 相似文献