Spectroscopy of betatron radiation emitted from laser-produced wakefield accelerated electrons

X-ray betatron radiation is produced by oscillations of electrons in the intense focusing field of a laser-plasma accelerator. These hard x-rays show promise for use in femtosecond-scale time-resolved radiography of ultrafast processes. However, the spectral characteristics of betatron radiation have only been inferred from filter pack measurements. In order to achieve higher resolution spectral information about the betatron emission, we used an x-ray charge-coupled device to record the spectrum of betatron radiation, with a full width at half maximum resolution of 225 eV. In addition, we have recorded simultaneous electron and x-ray spectra along with x-ray images that allow for a determination of the betatron emission source size, as well as differences in the x-ray spectra as a function of the energy spectrum of accelerated electrons.     

氨氮水质监测仪步进应力加速退化试验研究

针对氨氮水质监测仪如何快速评定其可靠性问题,通过分析氨氮水质监测仪的失效机理,建立了以其对标准试样的示值误差为退化量的退化轨迹模型,并利用反应动力学理论建立了其温度应力下的加速退化方程;通过步进应力加速退化试验获取了退化数据,并利用加速退化方程实现了步进应力加速退化数据向恒定应力加速退化数据的折算,利用伪失效寿命评估方法对氨氮水质监测仪进行了可靠性评估。研究结果表明,利用步进应力加速退化试验可以在较短的试验时间和较少的样本量情况下,实现对氨氮水质监测仪的可靠性评估。     

基于定时测试的综合应力加速寿命试验方案优化设计

针对定时测试综合应力加速寿命试验设计问题,就恒定应力加速寿命试验方法,根据所提出的加速寿命试验方案优化设计的准则和方法,以产品在正常工作应力水平时寿命估计值的方差最小为目标,在确定了每个应力水平组合下定时测试时间获取方式后,以各加速因子的试验应力水平、各次试验的试样分配比例及各次试验的截尾时间为设计变量,应用极大似然估计理论,建立了定时测试综合应力加速寿命试验方案优化设计的数学模型.对航天电连接器的定时测试综合应力加速寿命试验方案优化设计的结果表明,经过优化以后的定时测试试验方案不仅可以提高试验数据的估计精度、减少试验次数,而且还可以在相同置信度下减少试验所需的样本数量,并能够缩短试验时间.     

Reliability evaluation according to the results of accelerated testing in alternating mode under increasing load

The determination of reliability characteristics with a piecewise load function based on available characteristics under constant load is considered. Also, the related reverse problem is considered, that is, to evaluate product reliability characteristics under constant load during accelerated testing under an alternating monotonically increasing load.     

随机道路谱作用下的汽车响应特性

针对驱动桥壳在随机道路谱作用下的响应特性问题,建立了汽车振动的7自由度动力学方程,应用随机振动理论求解出了汽车在路面不平度下的频率响应(FR),利用Matlab得到了不同速度下的后桥垂向振动加速度功率谱密度(PSD)。研究结果表明该随机道路谱作用下的汽车响应特性研究对驱动桥的动态设计具有一定的参考和应用价值。     

Life of threaded joints under the action of variable flexural stress

The life of 40Kh steel bolt-nut joints under the action of variable flexural stress is estimated. The limiting number of cycles for cut and rolled screw thread is determined from the change in electrical conductivity of the metal in the thread.     

Prediction of remaining useful life under different conditions using accelerated life testing data

Prognostics methods model the degradation of system performance and predict remaining useful life using degradation data measured during service. However, obtaining degradation data from in-service systems in practice is either difficult or expensive. Therefore, accelerated life testing (ALT) is instead frequently performed for validating designs using considerably heavy loads. This work discusses the methods and effectiveness of utilizing ALT degradation data for the prognostics of a system. Depending on the degradation model and loading conditions, four different ways of utilizing ALT data for prognostics are discussed. A similar transformation method used in ALT is adopted to convert accelerated loading conditions to field loading conditions. To demonstrate the proposed approach, synthetic data are generated for crack growth under accelerated loading conditions; these data are used for training a neural network model or identifying model parameters in a particle filter. The applied example shows that the use of ALT data increases the accuracy of prognostics in the early stages in all four cases and compensates for the problem posed by data insufficiency through the proposed method.     

换热器对气动发动机效率影响的研究

为提高气动发动机能量利用率不高的问题,在气动发动机系统中的二级膨胀往复式结构以及容积减压装置中引入换热器,对气体进行加热,利用气体膨胀做功吸热以及传热学的原理来提高工作气体的温度,进而提高整个气动发动机的能量利用率问题。选取纵向翅片管壳式换热器,通过对减压、换热、阻力、热扩散、能耗、效率等的计算,对比不用换热器和使用换热器时两种情况气动发动机的效率,同时借助AMESim软件对两级气动发动机系统热交换模型进行模拟仿真,得到仿真结果。对比仿真结果和实际实验结果,得出合理使用换热器可以使气动发动机的效率提升29.83%。     

冲击载荷作用下板壳结构的可靠性研究

根据振动方程得到了板壳结构在冲击载荷作用下的响应及其数字特征,基于首次超越破坏机制,建立了板壳结构在冲击载荷作用下的极限状态方程,采用泊松分布方法分析了动力可靠性.最后以某舰局部甲板承受随机冲击为工程背景,对其板壳结构进行了振动可靠性分析.     

碳效率目标下的铣削切削参数优化研究

为了提高数控铣削加工过程的能量利用率,降低铣削加工过程中的碳排放量,基于铣削加工能耗分析的基础,建立了数控铣床能耗模型,并基于铣削工艺输入输出特性提出了铣削工艺碳排放评估函数,结合材料去除率提出碳效率概念,以此作为优化目标,并以机床主轴转速和进给量作为优化变量,考虑机床各项性能参数和工件的加工质量等约束,建立了基于碳效率的数控铣削切削参数优化模型,并通过案例,采用遗传算法对模型进行优化求解,验证了该模型的有效性。     

腐蚀应力加速寿命试验条件下滚动轴承的可靠性评估

为了缩短轴承可靠性评估试验时间,用逆幂律Weibull加速寿命试验方法分析了腐蚀条件下滚动轴承的可靠性。用加权最小二乘法和极大似然法给出了评估模型参数的点估计,结合信息矩阵法给出了评估模型参数及轴承平均寿命、可靠度、可靠寿命等可靠性指标的区间估计。解决了常见轴承可靠性评估中只有可靠性指标点估计而缺少区间估计的问题,使评估结果更加全面。分析了具体实例,基于Akaike信息准则(AIC)、贝叶斯信息准则(BIC)原理,用最佳模型给出了腐蚀条件下轴承的可靠性评估结果。计算结果表明所提方法具有较高的评估精度,且当腐蚀应力提高1倍时,轴承的平均寿命缩短8.75%,可靠度减小16.83%。     

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.     

Surface-stiffened elastic halfspace under the action of a horizontally directed Mindlin force

This paper presents an analytical solution to the problem of the interaction between a thin plate that is adhesively bonded to the surface of an isotropic elastic halfspace and a concentrated Mindlin-type force that acts parallel to the bonded surface. The model is an idealization of a surface-stiffened region that has potential applications ranging from mechanics of thin films, thermal barrier coatings, layering created by attrition and wear of surfaces and functionally graded materials. The solution also illustrates the influence of the flexural plate model in mitigating the development of unbounded displacements during the application of localized loading directly at the bonded plate.     

Deformation of thin-walled rings under the action of n concentrated and distributed forces

Equations for displacement of the elastic line of the cross-section of a ring under the action of n lumped forces with allowance for radial displacements due to bending and compression (tension) and to n forces applied over arcs are derived. The maximum displacement values and the associated shape deviations and possibilities of their reduction are presented. Application of the obtained results in design and in technological calculations is illustrated by examples.     

轴向柱塞泵在不同工况下的效率

该文分析并通过试验验证了液压轴向柱塞泵在不同温度、压力、转速及摆角工况其效率的变化情况。     

Complex screw joint under the action of the separation force and a skew torque

The influence of pliability of the rough contact layer on the load distribution over the screws in a complex joint under the action of a separation force and a skew torque is investigated experimentally.     

水下装备挖掘过程的动力学研究

文中用多体动力学方法对海底机器人挖掘过程的动力学进行了研究.基于海底土壤特征建立了挖掘过程中工具-土壤之间相互作用的土动力学模型,利用莫里斯理论建立了铲斗等水阻力学模型,然后,将上述模型融合到整体挖掘动力学模型中,并采用机械动力学模拟软件ADAMS进行了仿真.     

交变载荷作用下Cymbal换能器的压电性能

Cymbal换能器具有较高等效压电常数的特点,使其可能成为开辟新能源的一条有效途径。采用有限元方法对该换能器共振和非共振交变载荷作用下的电耦合场进行分析。计算结果表明,Cymbal换能器在共振交变载荷作用下所产生的开路电压很高,但由于此时所产生的应力较高,使得换能器工作失效;而在低频非共振交变载荷作用下该换能器能够正常工作,并产生与载荷同频率的具有一定幅值的交变电压。仿真结果表明,Cymbal换能器在非共振低频状态下,可以产生与载荷力同周期的具有一定大小的电压,可作为收集常见低频振动将机械能转化为电能的压电换能元件。