小样本加速寿命试验设计与评估方法

针对工程上加速寿命试验仍然存在时间长、试样多的问题,提出一种小样本加速寿命试验设计与评估方法。该方法只需在两个加速应力水平下进行加速寿命试验,即可对产品在正常使用应力水平下高置信度、高可靠度的可靠寿命进行评估。文中首先利用工程上常用的线性加速模型（如阿伦尼斯模型、逆幂律模型和指数模型等）建立了正常使用应力水平下可靠寿命的单侧置信下限与两个加速应力水平下的可靠寿命置信限之间的数学关系式,给出了正常使用应力水平下高置信度、高可靠度的可靠寿命单侧置信下限评估方法。然后分别对指数分布、两参数Weibull分布和对数正态分布的定数截尾加速寿命试验情况进行了详细讨论,给出了相应的正常使用应力水平下高置信度、高可靠度的可靠寿命单侧置信下限计算公式。该方法计算简单,而且对完全数据、不完全数据以及各种分布均适用。大量工程算例和Monte Carlo模拟验证表明,与需要在多个加速应力水平下进行寿命试验的传统方法相比,本文方法不但可以节省大量试样和试验时间,而且理论上更加严谨,精度更高。     

机电产品积木式可靠性评估与外场实时更新方法

针对工程上无法进行整机寿命试验,只能进行关键子系统寿命试验的大型机电产品,提出一种机电产品积木式可靠性评估与外场实时更新方法。首先,该方法能够根据机电产品关键子系统的寿命试验数据,对其整机高置信度、高可靠度的可靠寿命进行评估,从而解决了大型机电产品无法进行整机寿命试验时的可靠性评估难题,为其外场使用提供了科学依据。然后,还可以进一步根据该机电产品大量的外场服役寿命数据对上述可靠寿命评估结果进行实时更新,增大了信息量,从而显著提高其可靠性评估精度。文中针对电子产品寿命遵循指数分布的情况,给出了其整机高置信度的失效率、平均寿命、可靠寿命和可靠度的评估和更新公式。同时针对机电产品寿命遵循Weibull分布情况,给出了其整机高置信度的可靠寿命和可靠度评估和更新公式。     

基于联合梯度算法的结构可靠寿命预计

基于功能度量法,建立机械结构可靠寿命模型,给出可靠寿命求解方法。该方法将可靠寿命的计算问题转换为一个球面约束的优化问题,只需要进行一次优化迭代求解即可获得可靠寿命;针对寿命函数非线性较高,改进均值法易出现难以收敛问题,在此基础上提出了联合梯度算法,并从理论上证明了该算法的收敛性。对某车用轴进行可靠寿命分析,分析结果表明基于联合梯度算法的结构可靠寿命预计方法具有较好的效率和精度。     

滚动轴承寿命及疲劳试验数据的处理方法

因滚动轴承寿命及疲劳试验的数据极其离散,为了得到可靠的结果,本文对轴承寿命试验数据处理方法进行了分析对比的研究。对韦布尔分布函数中的 二参数的估计方法,可用最小二乘法、改进最小二乘法、平均法等、其计算结果,差别都很小。在均可适用的情况下,建议采用较简便的平均法。同时提出了应用平均法,对截尾法快速试验的数据处理方法。     

电子产品小样本可靠性评估与更新方法

首先建立子系统可靠度积商及线性组合的置信限公式,解决了一般复杂系统可靠度和可靠寿命置信限计算难题。然后针对大型电子产品难以进行大量可靠性试验的问题,提出一种电子产品小样本可靠性评估与更新方法,包括整机小样本可靠性评估方法和整机小样本可靠性更新方法。小样本可靠性评估方法能够根据电子产品子系统的试验结果给出整机可靠度和可靠寿命的置信限,而小样本可靠性更新方法则能够根据整机试验结果或外场实际使用数据,对其整机可靠度和可靠寿命的置信限进行更新。文中详细讨论了工程中常见的定时截尾试验和定数截尾试验的情况,给出了整机小样本可靠性评估和更新的公式。大量工程算例和Monte Carlo模拟验证表明,本文方法能够显著提高整机寿命预测和可靠性评估精度。     

某驱动后桥半轴疲劳寿命仿真分析方法研究

以某驱动后桥半轴为研究对象。联合使用Hypermesh及ABAQUS软件计算其结构应力,将结果文件导入MSC.PATRAN软件中,计算其疲劳寿命。仿真计算得出的疲劳寿命结果合理、可靠,表明以此方法进行半轴疲劳寿命仿真分析可行,为半轴的疲劳寿命仿真分析提供了一种可行和有效的方法和途径。     

基于Bootstrap方法的密封寿命可靠性评估

针对高可靠、长寿命密封件在小样本试验下的可靠性寿命评估需求,提出一种基于虚拟增广样本和Bootstrap方法的密封寿命小样本数据可靠性评估方法。并以轴用阶梯圈为例,进行寿命可靠性评估。首先通过虚拟增广法将轴用阶梯圈台架寿命试验数据样本数增广至10个,使得样本数满足Bootstrap方法的适用条件;然后再利用Bootstrap方法得到轴用阶梯圈的寿命可靠性评估结果。     

大型排灌泵机组耐久性分析

排灌泵导轴承的磨损、汽蚀和电机的绝缘老化是机组耐久性的主要控制因素。本文分析了影响上述三者的诸因素。介绍了导轴承耐磨损可靠寿命、汽蚀破坏深度和电机绝缘剩余寿命的计算方法。提出了延长机组耐久性的措施。     

正态分布定数和定时截尾数据可靠性评估方法

定数和定时截尾试验是工程上非常重要的一类寿命试验,目前对于产品寿命遵循指数分布情况已有成熟的可靠性评估方法,但是对于工程上常见的产品对数寿命遵循正态分布的情况,还难以根据定数和定时截尾寿命试验数据进行可靠性评估。为此,本文首先提出一种正态分布定数截尾数据可靠性评估方法,能够根据定数截尾寿命试验数据评估产品高置信度、高可靠度的可靠寿命单侧置信限,以及给定时刻下高置信度的可靠度单侧置信下限。然后进一步将该方法推广到定时截尾试验的情况,给出一种正态分布定时截尾数据可靠性评估方法,能够根据定时截尾寿命试验数据进行高置信水平的可靠性评估。从而使工程上许多无法处理的定数或定时截尾寿命试验数据得以统计分析,实现小样本可靠性评估。     

水润滑石墨推力轴承可靠寿命研究

水润滑石墨推力轴承是影响屏蔽泵可靠寿命的关键部件,本文依据可靠性理论,导出了水润滑石墨推力轴承可靠寿命的数学模型,并通过屏蔽泵水润滑石墨推力轴承的寿命试验数据对模型中的参数进行了估算,此研究成果对水润滑轴承可靠寿命预测及设计计算具有普遍的指导意义.     

动车组轴箱轴承基于实测载荷的寿命预测方法*

针对动车组轴箱轴承所受载荷的复杂随机性,在轴箱弹簧和转臂载荷测试技术基础上,对某型动车组动力转向架轴箱进行线路实测,获取典型线路段弹簧和转臂的载荷时间历程以及列车运行速度信息,以ISO 281：2007标准方法为基础,研究结合损伤的轴承寿命预测方法。同时也分析动车组轴箱轴承复杂的受载特性,给出将所测弹簧和转臂载荷近似转化为轴承的径向和轴向载荷的方法;计算轴箱轴承在实际运行的复杂载荷下不同可靠度的预测寿命,并与传统ISO标准方法计算结果进行对比,结果表明该预测方法相对保守,偏于安全;另外,计算低速进出库路段轴承疲劳寿命,其寿命比正常高速运行小很多,从损伤角度来看,动车组轴箱轴承低速进出库比正线高速运行的每公里损伤值更大;结合不同工况百分占比,给出轴承预测寿命,结果表明该寿命预测方法合理,可用于指导高铁轴箱轴承设计以及相关理论研究。     

Unbalance Response of a Super-Critical Rotor Supported by Foil Bearings—Comparison with Test Results©

This article compares theoretical and experimental results on the unbalance response of a super-critical rotor supported by two kinds of gas foil bearings. Analysis of the super-critical rotor is performed with viscoelastic foil bearings (VEFB) and conventional bump foil bearings and compared with early published experimental data. The vibration orbits obtained by theoretical investigation on the viscoelastic foil bearings (VEFB) and the conventional bump foil bearings are compared with the experimental vibration orbits of the super-critical rotor supported by both foil bearings. A numerical analysis program can calculate the static and dynamic characteristics of the elastically supported gas foil bearing using the measured stiffness and damping of the elastic foundation. After the stiffness and damping of both foil bearings are calculated using the perturbation method, vibration orbits of the flexible rotor modeled by the finite element method are calculated. Vibration orbits calculated by numerical analysis agree well with experimental data when the vibration amplitude is small and the rotating speed is below the bending critical speed. The numerical results also show that the enhanced structural damping of the elastic foundation reduces vibration near the bending critical speed.     

外圈旋转轴承润滑寿命计算及分析

以汽车发动机张紧轮深沟球轴承和空调电磁离合器双列角接触球轴承为对象,分别利用基于润滑脂基础油和稠化剂类型与基于DIN 51821-FE9寿命试验结果的轴承润滑寿命计算方法,对外圈旋转和内圈旋转轴承润滑寿命之比进行了推导计算,结果表明,两者之比为0.6～0.8,同时指出了基于润滑脂基础油和稠化剂类型计算方法存在的问题和局限,对外圈旋转轴承的摩擦学设计、延长功能寿命具有重要的现实意义。     

纺杯轴承系统动力优化设计

对试件的测试表明,优化的纺杯轴承系统的功耗、轴承座振动和轴承所受动载荷等均得到有效降低。这对延长高速件工作寿命、提高工作转速和节能等均有明显的实际意义。     

Reevaluation of Rolling Element Bearing Load-Life Equation Based on Fatigue Endurance Data

The load-life exponents used in the modified life rating equation for rolling element bearings were determined by statistical analysis of the experimental data generated in the 1940s, following Lundberg and Palmgren's seminal work. Based on fracture mechanics arguments, the fatigue life is known to be inversely proportional to the square root of the size of the nonmetallic inclusions. However, modern high-performance vacuum induction melt–vacuum arc remelt (VIMVAR) bearing steels are clean and nonmetallic inclusions are no longer the weak link. Fatigue life predictions (L₁₀ life) for modern bearings using the modified load-life relations greatly underpredict observed life. Hence, there is a need to update parameters of these equations using more recent life data. Based on the endurance data reported in Harris and McCool (1), validation analysis of the modified life rating equation was performed to reevaluate the values of load-life exponent for both ball and cylindrical roller bearings. The results from this study indicate that the load-life exponent for ball bearings should be 4.1, instead of 3, and for roller bearings it should be 5.5, instead of 3.33. Bearing L₁₀ life calculated using the corrected load-life exponents values shows better agreement with observed life. Details of the sampling technique used for reducing epistemic uncertainty in experimental data and the process of statistical reevaluation using Bayesian updating are discussed in detail. The accuracy of reevaluated results is presented using logarithmic plots of the ratio of predicted to actual fatigue lives for all data samples.     

Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than that of an all-steel rolling element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives of the deep-groove, angular-contact, and cylindrical roller hybrid bearings with races made of post-1960 bearing steel increased by factors of 3.7, 3.2, and 5.5, respectively, from those calculated using the Lundberg-Palmgren equations. An all-steel bearing under the same load will have a longer life than the equivalent hybrid bearing under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than all-steel bearings by 58% for deep-groove bearings, 41% for angular contact bearings, and 28% for cylindrical roller bearings.     

基于修正L-P模型的轮毂轴承载荷分布与弯曲疲劳寿命分析

以第三代轮毂轴承为研究对象,推导了弯矩作用下滚动体与内滚道、外滚道的接触变形与接触载荷,提出了更为准确的接触载荷分布计算模型,分析了不同工况下轮毂轴承内部接触载荷和接触角的周向分布规律。在轮毂轴承内部载荷分布的一次修正基础上,考虑不同位置角的滚道材料和滚动体的接触疲劳,利用乘积定律进行统计处理,得到了第三代轮毂轴承疲劳寿命的修正L-P模型。结合ISO281—2007寿命修正计算方法,针对润滑现象进行二次修正,得到了经过润滑修正的第三代轮毂轴承疲劳寿命模型。利用旋转弯曲疲劳试验机进行了轴承的弯曲疲劳试验,试验结果显示,该疲劳寿命模型计算得到的理论值与试验值的误差在10%以内,验证了模型的正确性。     

Monte Carlo Simulation of Sudden Death Bearing Testing

Monte Carlo simulations combined with sudden death testing were used to compare resultant bearing lives to the calculated bearing life and the cumulative test time and calendar time relative to sequential and censored sequential testing. A total of 30,960 virtual 50-mm bore deep-groove ball bearings were evaluated in 33 different sudden death test configurations comprising 36, 72, and 144 bearings each. Variations in both life and Weibull slope were a function of the number of bearings failed independent of the test method used and not the total number of bearings tested. Variations in L ₁₀ life as a function of number of bearings failed were similar to variations in life obtained from sequentially failed real bearings and from Monte Carlo (virtual) testing of entire populations. Reductions up to 40% in bearing test time and calendar time can be achieved by testing to failure or the L ₅₀ life and terminating all testing when the last of the predetermined bearing failures has occurred. Sudden death testing is not a more efficient method to reduce bearing test time or calendar time when compared to censored sequential testing.     

Design of Accelerated Life Test for Sleeve Bearing of Construction Equipment Based on Wear Prediction

Joint bearings of attachments play a key role in the reliability of construction equipment. These joint bearings operate in very harsh environments with strongly varying dynamic impact loads and oscillating under low sliding speeds. The bearings therefore operate in boundary lubrication, which means that direct metal-to-metal contact inevitably renders the sleeve bearing highly prone to wear. The assessment of durability for sleeve bearings is carried out using a test bench with oscillatory motion. However, estimating a quantitative accelerated factor considering the actual operating conditions is limited. The aim of this work is to determine the experimental conditions of the accelerated life test and to analyze the quantitative accelerated factor considering the wear limits of bearings. The wear limits are determined by the analysis of dimensional management that simulates the dispersion of a bucket end position by using 3DCS dedicated software. The accelerated factor is obtained by the comparing the times required to reach the wear limits. This test duration is calculated by the prediction methodology of wear depth based on the correlation between wear rate and film parameter. After the wear tests are performed using a test bench with actual bearings, the wear depth is measured to verify the estimated bearings. The proposed methodology is useful to design an accelerated life test under periodically changed lubrication condition caused by oscillatory motion.     

A new accelerated zero-failure test model for rolling bearings under elevated temperature conditions

A method for accelerated zero-failure testing was proposed for rolling bearings at high operational temperature. The life-load relationship of rolling bearings is combined with the Arrhenius model based on a life-temperature relationship on bearing lubricants to take the temperature effect on bearing life into consideration. Testing duration was calculated to demonstrate at least 90% reliability at a designed rating life of rolling bearings with a given confidence level under the service load and temperature conditions. A step by step procedure for calculating equivalent bearing load and speed was also proposed using a data of load distribution duration of bearings. Finally, an example was given for the case of a deep-groove ball bearing.