电阻应变数据采集系统传递函数的评价

提出了电阻应变数据采集系统传递函数的一种辨识方法,给出了详细技术过程,包括:电阻应变阶跃激励源的构建与赋值,电阻应变阶跃信号波形的获取,应变放大器恒定时间延迟的测量估计,用等效采样方式获取电阻应变数据采集系统的阶跃响应序列,激励序列和响应序列的时序统一与合成,用一种特殊白化滤波器的最小二乘法进行电阻应变数据采集系统传递函数辨识等。在一组实验中的传递函数辨识应用,证明了该方法的有效性及可行性。该方法可用于电阻应变数据采集系统动态特性的计量校准,及其传递函数辨识。     

Thermal shock resistance analysis methodology of ceramic coating/metal substrate systems

The paper establishes a methodology for the study of thermal shock resistance behavior of ceramic coating/metal substrate systems, based on multiple cracking analysis. The stress criterion and the toughness criterion are used to predict the failure behavior of the system. Multi-scale analysis of the thermal shock resistance of the system is made and variations of the thermal shock resistance of the system with crack density are displayed for different values of coating to substrate thickness ratio. Some critical size parameters, which control the applicability of the stress-based criterion and the fracture mechanics-based criterion for the determination of the thermal shock resistance of the coating/substrate systems, are explored.     

Quality estimation of resistance spot welding by using pattern recognition with neural networks

A quality estimation system of resistance spot welding has been developed using a dynamic resistance pattern. Dynamic resistance is monitored in the primary circuit of the welding machine and is mapped into a bipolarized vector for pattern recognition. The Hopfield neural network classifies the pattern vectors and utilizes them to estimate weld quality. Weld strength measurements have been made to examine the performance of the estimation system. Good agreement is obtained between the classified results and tensile-shear strengths. For a better understanding of the estimation process of the network, an example in which the dynamic resistance is classified into the stored pattern is also illustrated.     

疲劳寿命计电阻变化的灰色建模研究

疲劳寿命计具有电阻-疲劳记忆特性，是一种新型的无损检测元件。其电阻值随疲劳而增加，载荷卸除后电阻变化值保留。它可用于多种目的的疲劳测试和结构疲劳检测。在给定载荷下，循环数和电阻变化量具有本征性的灰色关系，运用灰色系统的理论和方法，通过对循环数数列的一次累加，生成一个光滑离散函数。据此建立GM模型，并求解灰色系统微分方程。运用还原模型，可由测得的电阻变化量计算循环次数，进而推算结构的剩余寿命。     

基于主动学习Kriging模型的直立锁缝屋面系统抗风揭可靠度分析

直立锁缝屋面系统由于自重轻、柔性大,在强风作用下常发生风揭破坏。为减少风揭破坏的发生,进行直立锁缝屋面系统抗风揭可靠度分析极为必要。鉴于此,该文提出了基于主动学习Kriging模型的Monte Carlo法(AK-MCS)的直立锁缝屋面系统抗风揭可靠度分析方法。建立直立锁缝屋面系统力学模型以分析其破坏模式,并推导其失效准则对应的极限状态函数;结合AK-MCS法和推导的极限状态函数建立了直立锁缝屋面系统抗风揭可靠度分析方法;以典型实际工程的直立锁缝屋面系统为例进行了抗风揭可靠度分析。分析结果表明:该文方法兼顾精度与效率,与拉丁超立方抽样的Monte Carlo法(LHS-MCS)相比,其计算的可靠度指标的相对误差为3.74%,而计算成本仅为LHS-MCS法的25.1%;该文方法计算所得的直立锁缝屋面系统可靠度指标β=2.7703,相比规范要求的可靠度指标偏低,建议在支座与屋面板锁缝处采取相应的加强措施。     

水中脉冲电晕放电测试系统

建立了一套水中电晕放电测试系统．由高速摄影系统、电参数测量系统和压力测量系统组成．高速摄影系统由GSJ转镜式高速摄影仪和德国产Pentazet35型摄影仪等组成,最高拍摄频率分别为250万幅／s和4万幅／s．电参数测量系统由高压表、电阻分压器、同轴分流器和Tektronix THS730A示波器组成．详细分析了整个系统的敏感设备、干扰源及其传播途径,并提出了相应的控制措施．压力测试系统主要有压电式传感器等组成．     

汽车制动钳滑移阻力检测系统研制

依据国家汽车制动系统行业相关标准研制汽车制动钳滑移阻力检测系统.以行业标准和企业测试要求为依据,制定活塞滑动阻力测试方案,引入高精度数据采集、伺服精密加载控制、测量系统分析等技术,设计基于伺服运动控制的精密加载机构的测量装置、采用真空泵用来对系统抽真空实现系统自动可调节的真空源,利用气液增压器、电气比例阀来满足对气液源...     

10GΩ在片高值电阻溯源实验

为解决在片高值电阻参数的溯源问题,组建了一套可溯源的在片高值电阻测量系统,并提出针对该系统的量值溯源方案,实现了在片高值电阻到常规同轴形式标准高值电阻的溯源。组件的测量系统通过额外的探针和线缆将同轴形式的标准电阻器接口延伸至探针末端,使用在片直通对接线将对应探针短接,形成同轴-在片-同轴形式的测量回路,从而将在片测量值与同轴端测量值联系起来,同时给出了保守的不确定度评估方法。使用组建的测量系统进行在片高值电阻溯源实验,实验数据显示在10GΩ点的相对扩展不确定度为0.3%(k=2)。     

工业雷管抗弯性能试验装置与方法设计

为了研究工业雷管的抗弯性能,设计了一种测试工业雷管抗弯性能的试验装置及试验方法,研究了国内部分生产企业的工业雷管的抗弯性能。结果表明:设计的试验装置安全、可靠、操作简单,能够满足工业雷管抗弯性能测试要求;我国工业雷管的抗弯性能整体质量能够满足欧盟有关技术标准和规范的要求,抗弯性能质量达到了国外发达国家同类产品的水平。     

一种超长杆铂电阻温度计校准装置

核电站所用的铂电阻温度计总长度超过3m,温度计的感温元件长度接近3m,常规的校准系统不能用于此类超长杆温度计的性能评估。介绍了一种用于核电站的超长杆铂电阻温度计的校准实验装置,通过实验验证,该系统的温度稳定性优于±0.015℃,水平和垂直温度均匀性分别优于0.05℃和0.02℃,标准不确定度和扩展不确定度分别为0.016℃和0.032℃,该实验系统可有效地评估长杆铂电阻温度计的性能。     

碳/碳复合材料SiC/MoSi_2/ZrO_2涂层体系氧化烧蚀性能

抗氧化涂层技术是解决碳/碳复合材料高温抗氧化性的最有效技术途径之一。为了提高材料在1 800℃以上的高温抗氧化性能,首次采用包埋法、涂刷法和等离子喷涂法在碳/碳复合材料表面制备出SiC/MoSi_2/ZrO_2梯度抗氧化涂层体系。采用SEM/EDS、结合力和粗糙度测试对涂层表面及断面形貌进行微观分析,利用等离子风洞对整个涂层体系进行氧化试验。结果表明:基体、过渡层和高温抗氧化层之间结合力良好,高温抗氧化层厚度均匀、结构致密。经等离子风洞氧化600s后,涂层表面温度达到1 850℃,氧化质量失重速率仅为3.15×10~(-6) g/(cm~2·s)。表明SiC/MOSi_2/ZrO_2梯度抗氧化涂层体系在1 800℃以上的高温环境下具有很好的抗氧化性能。     

Environmental air pollution management system: Predicting user adoption behavior of big data analytics

This study has a dual purpose: to explore the novel phenomenon of a big data analytics-environmental air pollution (BDA-EAP) management system, and to propose a research model of factors influencing adoption of such a system. The research model is based on task-technology fit (TTF) and unified theory of acceptance and use of technology (UTAUT) concepts. A comprehensive BDA-EAP management system is proposed and the potential adoption speed of such a system evaluated by sending structured questionnaires to the employees of relevant environmental agencies, yielding 412 valid responses, using the structural equation modeling approach. The results of the study predict that factors of TTF including task characteristics and technology characteristics are strong influencers of TTF, and TTF is a strong predictor of the behavioral intention of users to adopt a BDA-EAP management system. The results demonstrated that the combination of TTF and UTAUT is a stronger predictor of behavioral intention than either TTF or UTAUT alone. Furthermore, resistance to change negatively moderates and extrinsic motivation positively moderates the significant positive relationship between behavioral intention and adoption of a BDA-EAP management system. Meanwhile, behavioral intention, resistance to change, and extrinsic motivation have a significant three-way interaction impact on adoption of a BDA-EAP management system such that an increase in users’ extrinsic motivation will decrease the negative impact of resistance to change during the process of adoption. The study findings contribute to the literature regarding the use of BDA to manage EAP, and provide a basis for future research in this area.     

Current-injection-based 12-pulse rectifier using a single three-phase diode bridge

A three-phase rectifier that applies current injection to reduce the input current total harmonic distortion (THD) is proposed. The rectifier injects rectangular current, which results in the waveforms of the input currents the same as in the case of 12-pulse rectifiers, with the THD equal to 15.22%. The current injection system applies a voltage-loaded resistance emulator. To simplify the rectifier analysis, an equivalent circuit of the rectifier is derived, which significantly reduces the number of nonlinear elements. Analytical optimisation of the resistance emulator transformer turns ratio is performed for the case when the losses in the current injection system can be neglected. Influence of the losses in the current injection system is analysed numerically, and it is shown that they considerably affect the rectifier performance and design. Numerical optimisation of the resistance emulator turns ratio in the presence of losses is performed. Analytical results are experimentally verified on a rectifier with a rated power of 3 kW     

Improved thermal resistance network model of motorized spindle system considering temperature variation of cooling system

In the motorized spindle system of a computer numerical control (CNC) machine tool, internal heat sources are formed during high-speed rotation; these cause thermal errors and affect the machining accuracy. To address this problem, in this study, a thermal resistance network model of the motorized spindle system is established based on the heat transfer theory. The heat balance equations of the critical thermal nodes are established according to this model with Kirchhoff's law. Then, they are solved using the Newmark-β method to obtain the temperature of each main component, and steady thermal analysis and transient thermal analysis of the motorized spindle system are performed. In order to obtain accurate thermal characteristics of the spindle system, the thermalconduction resistance of each component and the thermalconvection resistance between the cooling system and the components of the spindle system are accurately obtained considering the effect of the heat exchanger on the temperature of the coolant in the cooling system. Simultaneously, high-precision magnetic temperature sensors are used to detect the temperature variation of the spindle in the CNC machining center at different rotational speeds. The experimental results demonstrate that the thermal resistance network model can predict the temperature field distribution in the spindle system with reasonable accuracy. In addition, the influences of the rotational speed and cooling conditions on the temperature increase of the main components of the spindle system are analyzed. Finally, a few recommendations are provided to improve the thermal performance of the spindle system under different operational conditions.The full text can be downloaded at https://link.springer.com/article/10.1007/s40436-018-0239-4     

一等铂电阻温度计标准装置智能检定系统

一等铂电阻温度计标准装置主要用于检定二等标准铂电阻温度计,检定程序繁琐、计算量大,迫切需要改进目前的装置,实现标准铂电阻温度计的智能检定。本文系统是对传统一等铂电阻温度计标准装置的智能升级,优化了标准铂电阻温度计的检定过程,能自动采集数据、自动处理数据,能生成证书内页及分度表。     

Comparison of the quantized Hall resistance and ohm NRC

A report is given of the progress towards the establishment of a quantized Hall resistance (QHR) measurement system suitable for maintaining the NRC (National Research Center of Canada) representation of the ohm. A system using a cryogenic current comparator bridge is described and compared to the previously reported 15 T, 20-mK potentiometric system. General problems concerning the use of the quantized Hall resistance to realize a representation of the ohm are discussed     

Simultaneously Enhanced Cryogenic Tensile Strength,Ductility and Impact Resistance of Epoxy Resins by Polyethylene Glycol简

Rubbers have been well accepted for modifying brittle epoxies but rubber modified epoxies usually posses lowered tensile strength though enhanced ductility and fracture resistance. In this work, a polyethylene glycol （PEG-4000） is used to modify diglycidyl ether of bisphenol A/methyltetrahydrophthalic anhydride system for enhancing cryogenic tensile strength, ductility and impact resistance. The results display that the cryogenic tensile strength, ductility （failure strain） and fracture resistance （impact strength） are all enhanced for the modified epoxy system at proper PEG contents. The maximum tensile strength （127.8 MPa） at the cryogenic temperature （77 K） with an improvement of 30.1% is observed for the modified system with the 15 wt% PEG content. The ductility and impact resistance at both room temperature and cryogenic temperature are all improved for the modified epoxy system with proper PEG-4000 contents. These observations are explained by the positron annihilation lifetime spectroscopy results and scanning electron microscopy results. Moreover, the glass transition temperature decreases slightly with increasing PEG content.     

A semi-analytical simulation method for reliability assessments of structural systems

A semi-analytical simulation method is proposed in this paper to assess system reliability of structures. Monte Carlo simulation with variance-reduction techniques, systematic and antithetic sampling, is employed to obtain the samples of the structural resistance in this method. Variance-reduction techniques make it possible to sufficiently simulate the structural resistance with less runs of structural analysis. When resistance samples and its moments determined, exponential polynomial method (EPM) is used to fit the probability density function of the structural resistance. EPM can provide the approximate distribution and statistical characteristic of the structural resistance and then the first-order second-moment method can be carried out to calculate the structural failure probability. Numerical examples are provided for a structural component and two ductile frames, which illustrate the method proposed facilitates the evaluation of system reliability in assessments of structural safety.     

Wireless detection of internal delamination cracks in CFRP laminates using oscillating frequency changes

It is difficult to detect delamination of rotating composite components like helicopter and wind turbine blades while in-service with a wired system. In the present study, a wireless system using a tiny oscillation circuit for detecting delamination of carbon/epoxy composites is proposed. In this system, a tiny oscillation circuit is attached to the composite component. When delamination of the component occurs, electrical resistance changes, which causes a change in the oscillating frequency of the circuit. Since this system uses the composite structure itself as a sensor and the oscillating circuit is very small, it is applicable to rotating components. The electrical resistance change and oscillating frequency change due to delamination is experimentally measured using carbon/epoxy specimens. The effects of temperature changes are also measured. The wireless method is found to successfully detect embedded delamination, and to estimate the size of the delamination. The effect of temperature change is minimized by means of a temperature compensation circuit.     

A practical structural health monitoring system for carbon fibre reinforced composite based on electrical resistance

A practical structural health monitoring system based on measuring changes in the electrical resistance of a carbon fibre composite structure is presented. Electrical contact with the fibres is provided by flexible printed circuit boards which are interleaved with the carbon fibre plies during the lamination of the composite. The resistance between opposite pairs of contacts was measured before and after an impact load which caused barely visible impact damage (BVID) in the panel. It was found that even low levels of impact damage produced measurable changes in resistance in the vicinity of the damage. Therefore was demonstrated that electrical resistance measurements are a practical means of locating BVID. Various parameters were studied in order to better understand the mechanisms involved and optimise the system for improved sensitivity and accuracy. The location of the contacts in the through thickness direction, the spacing and orientation of the contacts and the residual thermal stress of the laminate were all investigated and recommendations made. A structural health monitoring system for composites based on electrical resistance has several important potential benefits over acoustic, ultrasonic or optical methods; it adds little parasitic mass, causes no reduction in mechanical integrity, can be carried out on structures either in or out of service conditions and is very simple in concept, implementation and data interpretation.