基于小子样机械零件全寿命试验数据的处理方法

用三参数威布尔模型对机械零件的可靠度、应力及寿命之间的关系建模。与传统数据处理方法相比 ,这一模型将所有失效数据或几个应力水平的数据一起分析 ,所需样本容量小、需估计的参数总数少、计算过程简单。本文方法的计算结果与传统分析方法的计算结果一致 ,但所需的样本只是传统方法的 6 0 %。而且 ,机械零件的 R- S- N方程和强度分布用新方法可直接导出 ,没有附加误差产生。实例分析表明 ,本文方法是一种分析机械零件全寿命试验小子样样本的有效方法。     

三参数威布尔分布的齿轮接触疲劳寿命分析

三参数威布尔分布在齿轮设计初期对于齿轮接触疲劳寿命和可靠性分析有重要应用。基于Locati法与常规成组法对18CrNiMo合金材料的齿轮在机械封闭流齿轮试验台架上进行了接触疲劳试验。利用三参数威布尔分布对试验所得数据进行拟合处理,获得该种材料齿轮的R-S-N曲线,为该材料齿轮的寿命设计和可靠性设计提供了参考。结果表明:三参数威布尔分布对数据拟合效果较好,利用三组试验数据即可获得材料的R-S-N曲线,大幅节省试验时间,为类似工程问题提供参考。     

基于威布尔分布的疲劳剩余寿命可靠性预测方法

在变应力作用下,机械零件的疲劳寿命为具有分散性的随机变量.威布尔分布是一种连续的概率分布,可以用来描述各种不确定因素对机械零件疲劳寿命的影响.文中用三参数威布尔分布描述零件疲劳寿命的分布规律,建立疲劳剩余寿命的分布模型,并采用解析方法获得疲劳寿命分布参数的点估计值.对在同一应力水平下疲劳剩余寿命的分布规律进行了探讨,结果表明:当前年龄越大,可靠度曲线越陡峭,疲劳剩余寿命的可靠度越低;而年龄越小,疲劳剩余寿命的概率密度曲线越平坦,剩余寿命的分散性越大.     

疲劳寿命分布模型比较

比较了对数正态分布、成布尔分布及反高斯分布等三种寿命模型的异同，并讨论了它们的适用性。作为疲劳寿命的统计分布模型，目前大都采用对数正态分布或威布尔分布。研究表明，如果用随机过程的方法来研究疲劳过程，在某些假定条件下，疲劳裂纹的扩展寿命遵从反高斯分布(Inverse Gaussian Distribution)。本文分析了反高斯分布的特征，说明它作为寿命模型的优点及合理性。     

有机玻璃结构疲劳寿命预测的损伤力学方法

采用连续损伤力学模型对YB-3有机玻璃在常温下的疲劳寿命进行预测.计算结果与试验结果对照表明,该方法能够较好地预测有机玻璃结构的疲劳寿命.     

基于试验数据的气缸疲劳寿命预测

该文以气缸信赖性试验平台为基础,依据国际标准规定的试验规则,进行气缸信赖性试验,获取相关试验数据;运用威布尔分布理论,对所测试验数据进行分析,建立气缸疲劳寿命分布模型,依此预测气缸的疲劳寿命,并对预测结果进行分析。     

发动机Ⅲ级涡轮叶片高低周复合疲劳寿命研究

对现役的涡轮叶片采用了喷丸等方法进行了改进;为了验证该方法的可行性和确定新叶片相对于旧叶片的安全寿命,分别对新旧叶片进行了高温高低周复合疲劳试验研究。在进行试验数据处理时分别使用了秩回归法和极大似然法,对威布尔参数β,η进行了计算。根据β,η两个参数,计算了合格和不合格叶片在故障概率为0.1时的安全寿命值。     

齿轮疲劳特性小样本试验统计分析方法

利用STRONl603型电磁谐振疲劳试验机,采用双齿脉动加载法,对38Si Mn Mo调质齿轮试件进行了弯曲疲劳试验,在短寿命区采用4级恒定应力水平成组试验法,在长寿命区采用应力升降法,获得了齿轮弯曲疲劳寿命。对试验数据采用Monte-Carlo模拟法估计分位秩,再利用回归法得到了不同应力水平下的三参数威布尔分布参数及应力-寿命曲线,这套方法将为齿轮的弯曲疲劳试验数据的整理提供真实可靠的基础。     

用三参数威布尔分布求升降法试验的疲劳极限

在一定置信度下,运用优化的方法对机械零件升降法疲劳试验数据进行三参数威布尔分布参数估计,并求出一定可靠度下的疲劳极限应力。     

汽车底盘件疲劳寿命威布尔分布参数估计方法的研究

汽车底盘件疲劳寿命的可靠性评估是汽车安全的重要组成部分。根据转向节的疲劳寿命分布情况建立其三参数威布尔分布模型,利用右逼近估计法和修正的遗传算法分别确定出3个参数值,验证参数估计方法的准确性和实用性。所提出的修正遗传算法建立在右逼近估计法的基准参数之上,可以有效解决右逼近估计法存在的局部最优解的问题并提高参数估算的精度,为汽车底盘件的可靠性评估提供新的方法和理论依据。     

基于遗传算法三参数概率S-N曲线参量估计

引入遗传算法对40MnB调质齿轮三参数概率S-N曲线参量进行估计.方法将三参数概率S-N曲线表示为对数疲劳寿命均值和均方差线的广义形式,并利用遗传算法进行求解.综合考虑总体拟合效果,遗传算法以表示拟合效果的最小拟合误差均方值Min（ETP）参量作为目标函数,并定义了Min（ETP）均值和均方差形式.对40MnB调质齿轮弯曲疲劳强度的成组法试验数据进行研究表明,基于遗传算法的三参数概率S-N曲线参量估计是有效的,且优化过程无需进行求导操作,无需引入附加方程.     

Reliability prediction of the fatigue life of a crankshaft

Crankshaft, the core element of the engine of a vehicle, transforms the translational motion generated by combustion to rotational motion. Its failure will cause serious damage to the engine so its reliability verification must be performed. In this study, the S-N data of the bending fatigue limit of a crankshaft are derived. To evaluate the reliability of the crankshaft, reliability verification and analysis are performed. For the purpose of further evaluation, the bending test of the original crankshaft is carried out, and failure mode analysis is made. The appropriate number of samples, the applied load, and the test time are computed. On the basis of the test results, Weibull analysis for the shape and scale parameters of the crankshaft is estimated. Likewise, the B10 life under 50% of the confidence level and the MTTF are exactly calculated, and the groundwork for improving the reliability of the crankshaft is laid. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Do-Hyun Jung received his B.S. and M.S. degrees in Mechanical Engineering from Ajou University in 1988 and 1990, respectively. He then obtained his Ph.D. degree from Changwon National University in 2006. Dr. Jung is currently an Adjunct Professor at the School of Mechanical Engineering of Sunmoon University, Korea. He also manages the Reliability Application Research Center of the Reliability Division of KATECH. Dr. Jung’s fields of study include fatigue, reliability, and remanufacturing issues.     

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.     

估计构件疲劳极限的Bayes极小样本方法

从材料的S-N曲线与构件的S-N曲线形状相似原理出发,结合Bayes估计理论和加速寿命试验理论,提出一个估计构件疲劳极限的极小样本方法.在疲劳寿命服从对数正态函数分布的假设下,研究常幅和变幅载荷作用下由构件的疲劳寿命计算其疲劳极限的问题.两个算例表明,文中提出的方法利用以往积累的大量疲劳试验数据和现场试验数据,估计构件的疲劳极限,计算方便.计算结果与传统方法确定的疲劳极限的结果符合较好.     

试验数据服从Weibull分布时可靠性试验最少试件数的确定

试验试件数的确定是产品疲劳寿命试验过程中的一个重要问题,为节省时间和费用,要求在满足一定精度前提下使得试件数最少.研究在试验数据服从双参数Weibull分布的情况下,如何确定可靠性试验中最少试件数(最小子样容量)的问题.提出以估计量的相对偏差作为精度指标,并推导出确定最少试件数的公式.通过实例计算,给出在一定精度指标和置信水平下,估计特征寿命和安全寿命时所需的最少试件数.     

应用修正的P-S-N曲线计算齿轮疲劳寿命

疲劳破坏是机械结构的主要破坏形式之一,准确预测机械结构工作疲劳寿命至关重要.一般的线性损伤累积理论忽略了高频率低疲劳应力所引起的构件疲劳损伤,致使预测结果与实际寿命相差很大.为准确确定双圆弧齿轮的疲劳寿命,提出以修正的材料P-S-N曲线为基础,采用传统的名义应力法和Miner法则估算双圆弧齿轮的疲劳寿命,计算结果表明该方法可行,为预估螺杆泵的井下工作寿命提供了参考依据.     

The effect of fretting on the fatigue behaviour of plasma nitrided stainless steels

The plain fatigue and fretting fatigue behaviour of a plasma nitrided dual phase stainless steel known as 3CR12 and an AISI 316 austentic stainless steel have been studied in the present work, using a modified Wohler rotating-bending configuration. Test specimens were produced at two nitriding temperatures, namely 400 and 520 °C, representing low temperature and conventional nitriding temperature, respectively. The test results demonstrate that both nitriding processes can enhance the plain fatigue limit of these steels by approximately 10-25%, with the high temperature process being slightly more effective. Under fretting fatigue conditions, the beneficial effect of plasma nitriding is even more significant and the fretting fatigue limit is increased between 50 and 100% for 3CR12 and at least 50-150% for the AISI steel as the nitriding temperature is raised from 400 to 520 °C.     

Characteristics of fatigue crack initiation and fatigue strength of nitrided lCr-lMo-0.25V turbine rotor steels

To investigate the effect of nitriding layer on both fatigue crack initiation and fatigue life, turbine rotor steel (lCr-IMo-0.25V steel) specimens were nitrided by the nitemper method and then put to a rotary bending fatigue test at room and elevated temperatures. In nitriding, temperature and time were controlled to obtain a different nitrided thickness. Microstructure analysis, micro-Vickers hardness test, and scanning electron microscope observation were carried out for evaluating experiments. In results, the fatigue cracks of nitrided specimens were initiated at inclusion near the interface between nitrided layer and substrate, which showed fish-eye type appearance in fractograph. The fatigue life of nitrided specimens at every temperature was prolonged compared to that of the non-nitrided. However, there was not observable improvement in fatigue characteristics with the increase of a nitrided thickness.     

Experimental investigations on the contact fatigue life under starved conditions

Over the last decades, severisation of the operating conditions in lubricated contact has led to the decrease of film thicknesses and to a new failure mode. For example, starvation occurs in high-speed or grease-lubricated bearings and in mechanisms operating with a limited lubricant supply. The film thickness under starved conditions depends on the amount of lubricant in the contact inlet and can be calculated or measured. But in many industrial applications, the lubricant supply is unknown. This paper presents the effect of starvation on the fatigue life of machine elements. The first part links the operating conditions, the lubricant supply and the traction coefficient. The second part presents fatigue life measurements for different lubricant flow rates.