Dynamic recrystallization behavior and microstructural evolution in SPHC steel

The dynamic recrystallization(DRX) behaviors in SPHC steel were investigated with hot compression tests at deformation temperatures of 950-1 150,strain rates of 0.1-15 s-1,and initial austenite grain sizes of 86-232 μm.The effects of deformation temperature,strain,strain rate and the initial austenite grain size on the microstructural evolution during DRX were studied in detail.The results show that DRX is observed under the condition of the Zener-Hollomon parameter being less than 1.07×10 13 s-1.The deformation activation energy for SPHC steel is calculated to be 299.4 kJ/mol by regression analysis.Austenite grain size of DRX is refined with decreasing temperature and increasing strain rate under steady state conditions,but it is not influenced by the initial grain size.The mathematical equation of DRX grain size of SPHC steel is obtained.     

Studies on the Effect of Accelerated Thermal Aging on Electrical and Physicochemical Properties of XLPE Cable

The degradation of crosslinked polyethylene (XLPE) cable insulation during service, such as thermo-oxidation and water treeing may lead to a premature electrical breakdown of the XLPE insulation cables. Therefore, it is necessary to optimize the period of replacement to evenly distribute the replacement cost by ascertaining the deterioration degree. Estimation of the aging degree is at present the most important task for diagnosis of the residual lifetime of the power cable insulation. This paper presents a study on the changes in the dielectric properties of the thermally aged XLPE cables in the frequency range from 0.07～10 MHz. Based on electrical and physicochemical characterization, some new "dactylograms" for the thermally aged XLPE cable insulation have been proposed.     

基于Wiener退化对镁水泥混凝土中钢筋的锈蚀预测

镁水泥混凝土对钢筋的腐蚀限制了其广泛的推广应用,为解决这一难题,提出利用涂层来缓解其对钢筋的腐蚀,确保镁水泥钢筋混凝土建筑满足设计规定的使用年限要求. 根据西部盐渍土地区的自然环境,采用溶液浸泡加速锈蚀的试验方法对氯氧镁涂层钢筋混凝土进行快速腐蚀试验;运用电化学工作站周期性地对氯氧镁涂层钢筋混凝土试块进行电化学试验;以表征涂层钢筋锈蚀的电化学参数（腐蚀电流密度）作为退化指标,在Wiener退化过程的基础上进行可靠度建模并且对涂层钢筋进行锈蚀预测. 研究结果表明:利用涂层钢筋腐蚀电流密度作为耐久性退化指标可以得到镁水泥涂层钢筋混凝土中的涂层钢筋锈蚀的可靠度函数,并确定出涂层钢筋在30 000 d左右达到中等腐蚀.      

基于首次穿越破坏的TMD体系频域可靠性分析

为了研究可靠度的频域特性及TMD(tuned mass damper)体系减震特性,基于首次穿越破坏准则,推导了结构在随机激励下关于谱矩截止频率的概率分布计算公式,采用向前差分方法求解关于频域的概率密度,利用概率分布计算公式分析了TMD结构体系可靠度的频域概率信息.结果表明:可靠度的频域概率密度为负值,且随着频带变宽频域可靠度趋近于直接按照首次穿越破坏准则的计算值;结构无控时前两阶频率处的可靠度下降比例为59.23%和35.45%, TMD结构体系的相应比例为34.54%和55.92%,从频域可靠度的角度表明了TMD结构体系主要控制一阶振型,并体现了减震的可靠性.      

Comparison analysis of efficiency between double-synchronous step-down-stress and step-up-stress accelerated life tests

Double-crossed-step-stress (DCSS) accelerated life test (ALT) method is widely used for estimating the lifetime of products with high reliability and long lifetime. In order to further reduce the test time and test cost, a double-synchronous-step-stress (DSSS) ALT method which combines a double-synchronous-step-down-stress (DSSDS) ALT method and a double-synchronous-step-up-stress (DSSUS) ALT method is proposed. The accelerated stresses decrease and increase in a synchronous way with one step in the DSSDS-ALT and DSSUS-ALT methods, respectively. Monte Carlo method is adopted to simulate the two methods, and the validity and efficiency of them are demonstrated by the simulation results. In addition, a comparison analysis of efficiency between DSSDS-ALT method and DSSUS-ALT method is carried out. The result shows that the DSSDS-ALT method compared with the DSSUS-ALT method can significantly improve the test efficiency under the same test condition.     

Bayesian reliability assessment and degradation modeling with calibrations and random failure threshold

A degradation model with a random failure threshold is presented for the assessment of reliability by the Bayesian approach. This model is different from others in that the degradation process is proceeding under pre-specified periodical calibrations. And here a random threshold distribution instead of a constant threshold which is difficult to determine in practice is used. The system reliability is defined as the probability that the degradation signals do not exceed the random threshold. Based on the posterior distribution estimates of degradation performance, two models for Bayesian reliability assessments are presented in terms of the degradation performance and the distribution of random failure threshold. The methods proposed in this paper are very useful and practical for multi-stage system with uncertain failure threshold. This study perfects the degradation modeling approaches and plays an important role in the remaining useful life estimation and maintenance decision making.     

基于KDE及Markov的高速列车传动系振动评价及可靠性分析

为研究高速列车运行过程中传动系的振动情况及可靠性，对CRH3型高速列车传动系关键部件的振动加速度数据进行实车采集，采用核密度估计（KDE）法对采集数据统计处理，得出各关键部件在各方向上振动响应的概率密度函数近似曲线，据此对传动系的关键部件进行振动评价；通过MATLAB计算各关键部件振动加速度的最优置信区间；对传动系及传动系的关键部件定义“安全”和“故障”两种状态，建立关键部件的威布尔比例失效率模型及传动系的Markov状态转移模型，以传动系当前状态为初始状态，基于实时故障率及维修率分析传动系可靠性的变化. 研究结果表明:传动系中轴箱轴承、齿轮箱以及电机轴承的垂向振动最强，振动加速度集中分布在25倍、20倍、10倍重力加速度范围内，概率99.75%的均方差值分别在20.5026倍、17.6712倍、11.4693倍重力加速度内；计算得到各关键部件振动加速度概率为99.75%的最优置信区间，为系统的振动监测阈值优化及故障评估提供参考；故障率及维修率是影响传动系统状态概率的关键因素，当故障率增加30%时，系统的状态概率约下降10%，当维修率由0.05提升至0.10时，可使系统的可靠性提高20%.      

Experimental study on frictional and sealing performances of packing rings in an oil-free gas compressor

To enhance the reliability and to extend service life of packing rings, tribological and sealing performances are investigated based on the experimental results. Friction force, leakage rate and power consumption of three materials of pressure packing seals are measured in a refitted vertical gas compressor. The rings are made of common filled polytetrafluroethylene (Filled PTFE), PTFE reinforced with 30% mass fraction carbon fiber (30%CF+PTFE), and carbon-carbon composites infiltrated with PTFE (C/C+PTFE), respectively. It is found that packing rings will periodically vibrate with the periodic vibration of pressure packing after the travel direction of motion abruptly turns to the reverse direction. Furthermore, the amplitude of vibration slows down with the increasing crank angle. Approximate value of friction force is available by multiple-point fast Fourier transformation (FFT) employed to process the experimental results by reducing the impact of vibration to a great extent. Of three materials of rings employed in experiments, Filled PTFE presents minimal leakage rate accompanied with maximum power consumption. And 30%CF+PTFE exhibits minimum friction power and moderate leakage rate. As for C/C+PTFE, its high mechanical and thermal properties are favorable factors to enhance the ability of operating under high pressure and velocity and to improve the wear resistance. Unfortunately, this also leads to a large leakage rate. Comprehensive consideration should be taken into to evaluate the availability, reliability and service life for a type of packing ring under dry running conditions.     

轮胎侧偏特性对过桥车辆行车舒适性评价的影响

侧风作用下桥上通行车辆因同时受到轮胎侧偏特性产生的侧偏力作用和桥梁振动响应的影响,驾驶员和乘客极易遭受行车舒适性问题,根据Dugoff非线性轮胎模型在车轮横向振动方程中引入轮胎侧偏力表达式,建立了考虑轮胎侧偏特性的车辆动力学分析模型.考虑自然风、车辆和桥梁三者之间的相互作用,构建了风-汽车-桥梁耦合振动分析框架,分析了不同影响因素下轮胎侧偏特性对车辆行驶舒适性评价的影响.结果表明:考虑轮胎侧偏特性后,车辆的横向振动状态得到了一定程度的改善,在风速25m/s及路面等级非常好的情况下,考虑轮胎侧偏特性时车辆行车舒适程度提高了20.6%.      

A Novel Model of Failure Rate Prediction for Circular Electrical Connectors

The reliability of electrical connectors has critical impact on electronic systems. It is usually characterized by failure rate prediction value according to standard MIL-HDBK-217(or GJB-299 C in Chinese) in engineering practice. Given to their limitations and mislead results, a new failure rate prediction models needs to be presented. The presented model aims at the mechanism of increase of film thickness which leads to the increase of contact resistance. The estimated failure rate value can be given at different environmental conditions,and some of the factors affecting the reliability are taken into account. Accelerated degradation test(ADT) was conducted on GJB599 III series electrical connector. The failure rate prediction model can be simply formed and convenient to calculate the expression of failure rate changing with time at various temperature and vibration conditions. This model gives an objective assessment in short time, which makes it convenient to be applied to the engineering.     

非线性随机振动分析的概率密度演化方法

为深入探讨概率密度演化方法对于非线性随机振动分析的适用性,考察了随机地震动作用下一类硬弹簧Duffing振子的非线性响应,对概率密度演化方法与经典非线性随机振动分析进行了比较研究.结果表明:在弱非线性水平,概率密度演化方法与混沌多项式展开、Monte Carlo模拟的解答一致;在强非线性水平,数值求解误差、人为截断误差放大,概率密度演化方法与混沌多项式展开解答在Monte Carlo模拟解附近上下波动,表明概率密度演化方法与经典非线性随机振动解答在均方特征意义上是等价的.      

机场道面高频振捣密实混凝土弯曲疲劳性能演化特征

为了验证高频振捣滑模摊铺工艺的可靠性及其对含大粒径骨料(最大粒径为40 mm)干硬性混凝土疲劳演化特征的影响, 分别采用小型机具施工工艺(低频振捣)和滑模施工工艺(高频振捣)在郑州新郑机场摊铺40 cm厚混凝土道面板; 对现场切割试件与室内相同配比成型的试件(尺寸均为150 mm×150 mm×550 mm)进行了弯拉强度与疲劳试验, 测量了跨中梁底应变和竖向位移; 根据可靠度理论分析了不同工艺成型混凝土小梁的弯曲疲劳寿命概率分布特征, 建立了弯曲疲劳方程, 进一步分析了试件的弹性模量衰减特征和梁底残余拉伸应变演变规律。研究结果表明: 高频振捣工艺能使混凝土更加致密, 试件平均疲劳寿命较低频振动成型试件长约27%;双对数疲劳方程能够很好地表征含大粒径骨料道面混凝土的疲劳行为; 高应力水平下高频振捣成型混凝土疲劳寿命比室内成型混凝土长4%, 低应力水平下高频振捣成型混凝土疲劳寿命比室内成型混凝土长18%以上; 混凝土抗弯拉弹性模量随加载循环比的增加基本呈线性衰减特征, 试件临近破坏时的抗弯拉弹性模量为初始模量的50%~80%;在重复荷载作用下, 梁底轴向残余应变随加载次数的增加而增大; 提出的4种典型演化形态可表征不同应力水平下混凝土残余应变的复杂增长趋势; 骨料粒径增大是导致试件疲劳性能演变规律离散性的主要原因, 疲劳荷载作用下的累积损伤和骨料依次失效过程是混凝土残余应变演化曲线出现明显台阶特征的主要原因。研究结果为进一步通过足尺环道加速加载试验建立室内试验与现场足尺道面板性能关联方程奠定了基础。      

Wind turbine gearbox reliability analysis based on the system level stress-strength model

In order to estimate the reliability of wind turbine gearbox based on the system level, a generalized stress-strength model is introduced. Considering that the system works properly under a variety of random stresses which affect every component, the total stress on the system is given by a known linear combination of the stresses of all components. Then the strength of the system can be viewed as a linear combination of the strengths of relative components. In this model, stress and strength are independent of each other. Reliability of the system is the probability that strength exceeds stress. Finally, the reliability of wind turbine gearbox is estimated by the multivariable reliability calculation method. The corresponding result is compared with the results of reliability in the extreme cases(completely dependent and completely independent) by the traditional evaluation method.     

结构动力抗震可靠度理论的研究进展

从状态变量模型、基本变量模型和实用简化模型3个方面,对结构动力抗震可靠度理论的研究进展系统地进行了总结与评述.针对状态变量模型,结合随机振动理论,将随机振动分析方法分为两类:第1类是面向数字特征的方法,主要解决结构的随机反应从基本随机变量空间到状态变量空间的统计矩演化问题;第2类是面向概率密度的方法,主要解决结构的随机反应从基本随机变量空间到状态变量空间的概率密度演化问题.分别评述了两类方法中的代表性方法:等价线性化方法和概率密度演化方法.针对基本变量模型,分别总结了考虑系统参数随机性的结构动力抗震可靠度分析方法,以及将动力可靠度问题转化为静力可靠度问题的理论和方法,对近年来提出的尾部等效线性化方法、子集模拟法、等价极值法等进行了对比分析.针对实用简化模型,总结评述了3种方法:基于随机地震动模拟-确定性时程分析的直接方法、基于一致危险性反应谱和等效非线性体系的简化方法、基于可靠度简化解析表达式与数值模拟的半解析方法.最后,对新近提出的结构整体抗震可靠度理论及其存在的问题进行了归纳分析,并从地震作用的输入模型、主要失效模式的搜索、结构的破坏准则、结构失效模式的多重性、结构的整体极限状态方程等方面给出了研究建议.      

Study on the thermal stability of Cu-14Fe in situ composite without and with trace Ag

The thermal stability of Cu-14Fe and Cu-14Fe-0.07Ag in situ composites is investigated. The evolution of Fe filaments in two composites is analyzed detailedly by annealing at high temperature. The results indicate that the Cu-14Fe in situ composite exhibits two kinds of evolution of Fe filament, the longitudinal splitting of Fe filaments at low temperature (below 600°C) and spheroidization of Fe filaments at high temperature (above 600°C). With the addition of trace Ag, the longitudinal splitting of Fe filaments at low temperature is accelerated, while spheroidization of Fe filaments at high temperature inhibited. The microstructure evolution procedure of Cu-14Fe without and with trace Ag has been modeled. This work would promote the understanding of the microstructure evolution of Cu-Fe in situ composite.     

Reliability Prediction Method Based on State Space Model for Rolling Element Bearing

Reliability analysis based on equipment’s performance degradation characteristics is one of the significant research areas in reliability research. Nowadays, many researches are carried on multi-sample analysis. But it is limited for a single equipment reliability prediction. Therefore, the method of reliability prediction based on state space model(SSM) is proposed in this research. Feature energy of the monitored signals is extracted with the wavelet packet analysis and the associated frequency band energy with online monitored data. Then,degradation feature is improved by moving average filtering processing taken as input pair model parameter of SSM to be estimated. In the end, state space predicting model of degradation index is established. The probability density distribution of the degradation index is predicted, and the degree of reliability is calculated. A real testing example of bearing is used to demonstrate the rationality and effectiveness of this method. It is a useful method for single sample reliability prediction.     

Understanding Spray Coating Process: Visual Observation of Impingement of Multiple Droplets on a Substrate

Spray coating is a facile deposition process with numerous existing and emerging applications. However, spray coating is a stochastic process comprising impingement of many droplets which upon impact on a heated substrate may dry or solidify individually or coalesce first to form a thin liquid film and then dry to yield a thin solid film. There is very limited knowledge on how this process occurs; therefore in this work, high speed imaging is used to visualize the spray coating process. Two model solutions including food-dye with properties like those of water, and poly (3, 4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS), a polymeric solution, are sprayed onto permeable glossy paper and regular impermeable glass substrates. Substrates are kept at room temperature and 80 °C elevated temperature. In some cases, a vertical ultrasonic vibration is imposed on the substrate to study its effect on the coating process. It is observed that the spray coating process is highly random and stochastic. A higher substrate temperature results in a better coating process in that a more uniform and defect-free coating forms. Imposed vibration in the case of glossy paper substrates results in better droplet spreading and more uniform coating. The results also show that under the conditions of these experiments, impinged droplets dry individually or as islands of multiple coalesced droplets to form a coating. In other words, at used spray flow rate and spray droplet size, a continuous thin liquid film does not form prior to drying even at room temperature. Further systematic studies and high magnification lenses are required to visualize and understand the details of the process.     

基于Copula函数的高速列车转向架故障特征提取

为了实时监测高速列车转向架关键部件的工作状态,提出了一种基于Copula函数的特征提取方法.以某型高速列车转向架正常、抗蛇形减振器失效、空气弹簧失效、横向减振器失效4种工况的振动信号为研究对象,将信号进行聚合经验模态分解,针对得到的本征模态函数,使用Gaussian Copula函数构建它们的联合概率密度函数.提取边缘分布的Kullback-Leibler Distance值,及联合概率密度函数的均值和方差作为特征,采用支持向量机进行识别.实验结果表明,在200 km/h速度下,故障平均识别率在95%以上,表明了该特征提取方法的有效性.      

Bivariate Constant-Stress Accelerated Degradation Model and Inference Based on the Inverse Gaussian Process

Modern highly reliable products may have two or more quality characteristics (QCs) because of their complex structures and abundant functions. Relations between the QCs should be considered when assessing the reliability of these products. This paper conducts a Bayesian analysis for a bivariate constant-stress accelerated degradation model based on the inverse Gaussian (IG) process. We assume that the product considered has two QCs and each of the QCs is governed by an IG process. The relationship between the QCs is described by a Frank copula function. We also assume that the stress on the products affects not only the parameters of the IG processes, but also the parameter of the Frank copula function. The Bayesian MCMC method is developed to calculate the maximum likelihood estimators (MLE) of the model parameters. The reliability function and the mean-time-to-failure (MTTF) are estimated through the calculation of the posterior samples. Finally, a simulation example is presented to illustrate the proposed bivariate constant-stress accelerated degradation model.     

室温下不锈钢的多轴时相关循环变形行为

对1Cr18Ni9不锈钢在室温下的非比例多轴时相关循环应变特征和棘轮行为进行了试验研究，以考察应变率、应力率和加载路径对其循环变形行为的影响．结果表明，1Cr18Ni9不锈钢的循环应变行为和棘轮行为对应变率、应力率很敏感，具有时相关特点：在多轴应变循环下，其最大等效应力随应变率增大而增大；在棘轮试验中，其轴向棘轮应变则随着应力率减小而增大．此外，加载路径对1Cr18Ni9不锈钢的循环粘塑性变形行为也有较大影响：多轴应变循环下，在所采用的直线、菱形和圆形3种加载路径中，圆形路径引起的非比例附加硬化程度最高，其次是菱形路径．然而，试验发现，在多轴棘轮试验中，圆形路径产生的棘轮应变高于菱形路径.