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A closed-loop electrohydraulic fatigue apparatus was constructed for testing from above room temperature to 77 K. Several important improvements in the electronics of the reference function generator and the servo controller over previous apparatus are described. The electronics allows cool-down of the specimen to 77 K at zero stress, correction for thermal contraction, and then cyclic fatigue testing under strain control, all without interruption of hydraulic power. 相似文献
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Rech I Labanca I Armellini G Gulinatti A Ghioni M Cova S 《The Review of scientific instruments》2007,78(6):063105
This article reports a complete characterization of single photon avalanche diodes (SPADs) at temperatures down to 120 K. We show that deep cooling of the device by means of a compact liquid-nitrogen Dewar brings several advantages, such as extremely low dark counting rates (down to 1 counts/s), better time resolution, and higher quantum efficiency in the visible range. By using a special current pick-off circuit, we achieved a time resolution of 20 ps full width at half maximum at 120 K for a 50 mum diameter SPAD. Afterpulsing effects are avoided by using a sufficiently long hold-off time (microseconds). 相似文献
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提出并设计了一种用于低温环境下测量温度的光纤布拉格光栅(FBG)双头管式封装结构,探究了涂覆层材料和封装形式对光纤Bragg光栅传感器低温传感稳定性和精度的影响。同时,试验研究了封装长度对双头管式传感器中心波长与温度的关系,通过多次重复试验测定了传感器低温灵敏度和重复性误差。研究结果表明:由于高折丙烯酸酯涂覆层具有较高的热膨胀系数,因此在77~273 K液氮环境中其增敏效果相对于聚酰亚胺和裸光纤更为显著;采用双头管封装后,FBG中心波长与温度具有高度线性关系,且能有效解决无封装裸FBG易受荷载扰动特性;适当提高封装长度有利于提高封装体系灵敏度系数。重复试验结果表明,所设计的双头管式封装FBG低温传感器灵敏度可达14~20 pm/K,测试误差和灵敏度优于传统FBG低温传感器。 相似文献
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Bernd Eichenhueller Emil Egerer Ulf Engel 《The International Journal of Advanced Manufacturing Technology》2007,33(1-2):119-124
Manufacturing of metallic parts by forming methods is industrially widespread due to several advantages like good surface
quality, high accuracy and good efficiency at concurrent high quantity. As a result of the steady miniaturisation of products,
large quantities of smallest metallic parts with the above mentioned attributes are needed. Despite the advantages of forming
methods, microparts are mainly produced by machining, because of problems caused by so-called size-effects. These effects
occur by scaling down geometry and process parameters, leading to the fact that the existing know-how for conventional processes
cannot be transferred unrestrictedly to microscale. One reason for the difference between macro- and microscale is the number
of grains within the forming area. At microscale only a small number of grains are directly involved in the forming process,
so that the single grain, characterised by its individual size, orientation and position, gains influence on the process.
The stochastic distribution of the grain characteristics leads to an inhomogeneous material behaviour and causes an increased
scatter of the process parameters. To minimise the effect of inhomogeneous material behaviour, microforming at elevated temperature
is applied. Experiments with different materials at elevated temperature show a homogenising effect which leads to a reduced
process scattering. This indicates that elevated temperatures are suitable to minimise and control the size-effects at microforming
processes. Additionally an enlargement of the forming limits by microforming at elevated temperature is observable. 相似文献
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Intumescent mat material is widely used to support ceramic substrates in catalytic converters and behaves very much like hyper-foam material under compressive loading. Experiments show that compressive loading curves depend on the ram speed and the number of cycles. The unloading curves show different slopes and paths that depend less on the ram speed and number of cycles. The slopes of the unloading curves decrease as the plastic strain increases; this is referred to as “softening” in this study. The effects of rate, softening, and plastic deformation must be considered to model the mechanical response of intumescent mat material. Finite deformation theory is applied with a multiplicative decomposition of the deformation gradient tensor. The developed theory is implemented as an implicit finite element algorithm in ABAQUSTM/STANDARD. The necessary material parameters are extracted from experiments. Numerical simulations show good agreement with experiments. 相似文献
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The automation of the temperature elevation test is outlined here for both the oil temperature elevation and the determination of the winding temperature elevation. While automating this test it is necessary to use four thermometers, one three-phase wattmeter, a motorized voltage variator and a Kelvin bridge to measure the resistance. All the equipments must communicate with a microcomputer, which will have the test program implemented. The system to be outlined here was initially implemented in the laboratory and, due to the good results achieved, is already in use in some transformer manufacturing plants. 相似文献
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空间低温辐射计中的精密电压测量系统 总被引:1,自引:0,他引:1
为了基于测温电阻实现空间低温辐射计的腔温测量,研究了系统的电子学测量精度和测量稳定度。结合实际电子学需求,进行方案设计和器件选型,提出了一种新型的基于超低噪基准源LTZ1000ACH,四线制柱状锗电阻GR1400-AA和24位模数转换器LTC2400的对偶相消式精密电压测量系统。对于整个链路信噪比进行了逐级理论计算和分析,并通过电路仿真软件TINA-TI对系统幅频特性和温度响应特性进行了仿真分析,最后在77K液氮环境下对该系统进行了测温精度和长期稳定性测试。实验结果表明:锗电阻实际采样电压值在100μV内波动,长期测量稳定度达到1×10-5;在77K液氮环境下,系统测温精度达到4mK,长期稳定性达到1×10-5。得到的结果基本满足空间低温辐射计电子学部分的设计指标要求。 相似文献
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Tribological properties of nickel-based self-lubricating composite at elevated temperature and counterface material selection 总被引:3,自引:0,他引:3
Solid lubricating materials are necessary for development of new generation gas turbine engines. Nickel-based self-lubricating composites with graphite and molybdenum disulfide as lubricant were prepared by powder metallurgy (P/M) method. Their tribological properties were tested by a MG-2000 high-temperature tribometer from room temperature to 600 °C. The structure of the composite was analyzed by XRD and worn surface morphologies were observed by optical microscope. The effects of counterface materials on tribological behavior of composites were investigated. It was found that chromium sulfide and tungsten carbide were formed in the composite by adding molybdenum disulfide and graphite, which were responsible for low-friction and high wear-resistance at elevated temperatures, respectively. The average friction coefficients (0.14–0.27) and wear rates (1.0–3.5 × 10−6 mm3/(N m)) were obtained for Ni–Cr–W–Fe–C–MoS2 composite when rubbed against silicon nitride from room temperature to 600 °C due to a synergetic lubricating action of graphite and molybdenum disulfide. The optimum combination of Ni–Cr–W–Fe–C–MoS2/Ni–Cr–W–Al–Ti–C showed lower friction than other counter pairs. The graphite played the main role of lubrication at room temperature, while sulfides were responsible for low friction at high temperature. 相似文献
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With the growing interest in liquefied natural gas (LNG) in the energy market, Coriolis mass flowmeters have been applied to many applications in the distribution of LNG. Since Coriolis flowmeters are normally calibrated at around room temperatures, measurements for LNG at cryogenic temperatures present a challenging condition. Firstly, a theoretical analysis for Coriolis mass flow sensors is provided considering the major changes of material properties (Young’s modulus and thermal expansion) at cryogenic temperatures. Then, a practical approach which can be used to correct the flow calibration factor obtained at a reference condition is presented. Finally, flow test results obtained from NIST’s cryogenic calibration facility are provided. Based on the results, it can be concluded that if a Coriolis flowmeter is calibrated at a reference condition and the flow calibration factor is corrected considering the non-linearity of Young’s modulus and thermal expansion change with temperature, it can still provide very accurate mass flow measurement even at cryogenic temperatures. 相似文献
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I. Valiente-Blanco E. Diez-Jimenez J. A. Cervantes-Montoro J. L. Perez-Diaz 《Instruments and Experimental Techniques》2013,56(6):665-671
Electronic components which are able to work at cryogenic temperatures are demanded in cryogenic instruments, high sensitivity measurement systems, space missions, medical diagnosis among other applications. Different non-cryogenic commercial electronic components have been characterized between room temperature and ?196°C. A simple measurement technique, taking advantage of the temperature gradient inside a partially empty LN2 Dewar vessel has been used. The results of the electrical characterization show that some of these components can be used at cryogenic temperatures with a reasonable performance even if their specifications datasheets state the contrary. 相似文献
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This article presents results of investigations of the cryogenic thermometers which can operate under high radiation environment. To clarify the temperature shifts due to gamma irradiation up to 1 MGy, the platinum (two types), carbon-glass, and TVO temperature sensors have been tested. Before the irradiation run, the selected sensors were calibrated and a series of experiments was carried out under irradiation of the sensors at 77.3 and 293 K when their readings were taken in situ. Afterwards, the postirradiation evolution (short and long time) of the sensors was measured at 4.2, 77.3, and 293 K. The results, depending on the type of the sensor, can be optimistic or pessimistic. Some comparisons with analogous data for fast neutron treatment have also been made. 相似文献
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Nanoscopic voltage distribution of operating cascade laser devices in cryogenic temperature
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A nanoscopic exploratory measurement technique to measure voltage distribution across an operating semiconductor device in cryogenic temperature has been developed and established. The cross‐section surface of the terahertz (THz) quantum cascade laser (QCL) has been measured that resolves the voltage distribution at nanometer scales. The electric field dissemination across the active region of the device has been attained under the device's lasing conditions at cryogenic temperature of 77 K. 相似文献
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阀门的工作温度,不仅与阀门主体材料有关,还与阀门使用的辅助材料有关。根据相关标准和资料,对阀门常用辅助材料的适宜工作温度作了介绍。 相似文献
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This paper presents investigations on the tribological behaviour of PTFE composites against steel at cryogenic temperatures. The results showed that the friction coefficient decreases with temperature down to 77 K, but did not follow a linear evolution further down to extreme low temperatures. It can be stated that the cryogenic environment has a significant influence on the tribological performance of the polymer composites. The effect of low temperatures was more clearly detected at low sliding speed, where friction heat is reduced. A change in wear mechanism from adhesive to abrasive was observed in this case. SEM and AFM analyses showed that the PTFE matrix composites investigated under these experimental conditions have transferred material onto the disc down to very low temperatures. Chemical analyses indicate the presence of iron fluorides. 相似文献
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The thermal properties of cutting tools have a dominant effect on metal cutting because of their influence on the length of the contact between the tool and the chip and on chip curvature. Low thermal conductivity of the tool is generally considered desirable.Experiments show that tools made from materials of high thermal conductivity but coated with layers of material of low conductivity have a cutting performance similar to that obtained when the whole tool is made from the material of low thermal conductivity even when the thickness of the coating is of the order of 5–10μm.A theoretical explanation of this behavior based on a discrete (i.e. non-continuum) model of the tool surface and on transient heat conduction considerations is presented. 相似文献
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In a cryogenic environment components with interacting surfaces in relative motion (tribosystems) like bearings, seals and valves often generate undesired heat and experience high wear. Because conventional lubricants like oils or greases cannot be used in this temperature range, solid lubricants or materials with good frictional properties in unlubricated operation must be used. To test the suitability of conventional and advanced materials for tribosystems in this extreme environment and to obtain reliable materials data, model friction tests at low temperatures are performed. In most of the tests the samples are in ball-on-disc-configuration but various methods for cooling, loading, and measurement are applied. As an example the test results for amorphous carbon coatings in the temperature range 10–77 K are presented. These coatings can be suitable for cryogenic tribosystems, but their behaviour strongly depends on the composition and deposition method. 相似文献
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A new type of apparatus for material tests using an internal loading system in high-pressure gas up to 100 MPa at room temperature without conventional material testing equipment was developed. The apparatus consists of a high-pressure control system and a pressure vessel, in which a piston is installed in the cylinder of the pressure vessel. The load caused by the pressure difference between spaces separated by the piston in the vessel cylinder is applied on the specimen connected to the piston in the vessel cylinder. The actual load on the specimen is directly measured by an external load cell and the displacement of the specimen is also measured by an external extensometer. As an example of the application of the apparatus, a tensile test on SUS316 stainless steel the Japanese Industrial Standard (JIS) G4303, which is comparable to the type 316 stainless steel ASTM A276, was conducted in 90 MPa hydrogen and argon. Hydrogen showed a marked effect on the tensile property of the material. The hydrogen gas embrittlement of the material was briefly discussed. 相似文献