公路桥梁规范中温度自应力计算方法误差的理论分析

基于弹性力学中三个不同方向的应力通过泊松比耦合在一起的性质,理论分析《公路钢筋混凝土及预应力混凝土桥涵设计规范》(JTG 3362-2018)及《公路桥涵设计通用规范》(JTG D60-2015)中规定的桥梁结构的温度自应力简化计算方法中的误差,并基于热弹性力学中温度应力的Duhamel相似定理,分析温度荷载作用于桥梁结构中的作用方式,即温度自应力的荷载模式,并基于这种思路分析桥梁规范中对温度荷载形式简化的合理性,进一步分析这种简化所可能导致的误差及今后可能的研究方向与解决方案。

综合离心环境试验系统中辅助设备的设计

介绍了以离心机为主体的各种综合环境模拟试验的具体内容,叙述了各种综合环境试验中辅助设备的设计情况,根据使用情况对辅助设备的原理进行分析,并对辅助设备在使用时的注意事项进行了说明。

Pyrolysis of Huadian oil shale by electrical heating on different heating rates

The electrical heating experiments on oil shale sample from Huadian of Jilin were carried out by the pyrolysis method at three different heating rate 2℃/min, 5 ℃/min and 10 ℃/min in the temperature range of 30℃ -750℃. Heating rate 2 ℃/rain is considered low, while intermediate one covers the range 5 ℃/min and high heating rate is 10℃/min. The controlling parameters studied were the final pyrolysis temperature and the influence of the heating rate as well as type. The heating rate has an important effect on the pyrolysis of oil shale and the amount of residual carbon obtained therefore. It is found that increasing the heating rate and py- rolysis temperature also increases the production of oil and the total weight loss. Higher heating rates resulted in higher rates of accumulation. The rate of oil and water collection passed through the maximum of different heat- ing rates at different pyrolysis temperatures. Heating rate affected density, oil conversion and oil yield.

Performance of Dual-throat Supersonic Separation Device with Porous Wall Structure

In this paper, a dual-throat supersonic separation device with porous wall has been proposed to solve the starting problem of supersonic separator, and the feasibility of the proposed device has been tested numerically and experimentally. Its flow characteristics have been investigated and the effect of some important parameters includ-ing nozzle pressure ratio(RNP), inlet temperature and swirl intensity were examined. In the device, the supersonic flow state and strong centrifugal acceleration of 240000g can be obtained, which are necessary for the condensation and separation of water vapor. The supersonic region in the device enlarged and the shock wave shifted downstream along with the increasing RNP. The separation performance was improved with the increasing RNP and the inlet temperature. The best separation performance in this study was obtained with ΔTd? 28 K.

Change in Aggregate Shape of Heat Treated Carbon Nanoparticles

To better understand the fusion mechanism of heated carbon black, heat treatment is conducted for carbon black produced by benzene pyrolysis. The effects of （a） heating time, （b） heating temperature and （c） heating rate on the aggregate shape and mean primary particle diameter of the carbon black are investigated using TEM （transmission electron microscopy）. The mean primary particle diameter does not change significantly when carbon black is heat treated. For short heating times and low heating temperatures, the aggregate shapes become simple when compared with those of non-heated carbon black, and shapes become complex with an increase in the heating time. Also, for low heating rates, the aggregate shapes become significantly simple when compared with those of non-heated carbon black. The results of this study suggest that sintering between primary particles is promoted under relatively low heating temperatures, and Ostwald ripening among aggregates is promoted under relatively high heating temperatures.

Brazing behavior of ultrafine cemented carbide with stainless steel

In order to investigate the effects of brazing temperature, heating rate and cooling methods on shear strength, hardness, magnetic saturation and coercivity of the ultrafine cemented carbide, the ultrafine cemented carbide was fabricated according to conventional powder metallurgical procedures, and then brazed to the stainless steel with silver-based filler alloy by supersonic frequency induction brazing. The microstructure was observed using scanning electron microscope （SEM）, energy dispersive spectroscopy （EDS） and the magnetic properties were tested utilizing coercimeter and cobalt magnetism instrument. The results show that no micro-crack is found in the cemented carbide after brazing because of silver-based sandwich compound used as filler alloy. In the melted silver layer, there is more carbon in the region adjacent to the cemented carbide. Varied shear strengths, hardnesses, magnetic saturations and coercivities are present under different brazing temperatures, heating rates and coolings. This phenomenon is correlated with some factors such as wettability and fluidity of filler alloy, brazing stress, oxidation of cemented carbide, and allotrope transition of cobalt. Shear strength reaches the maximum of 340 MPa and hardness of ultrafine cemented carbide remains 1879 HV at the brazing temperature of 730℃. The carbon increases with the of increase of the heating rate. What＇s more, and there is no r/phase found under this condition. content decreases with the increase of brazing temperature, and it the lowest magnetic saturation reaches 81.8% of the theoretic value,

A combined modulated feedback and temperature compensation approach to improve bias drift of a closed-loop MEMS capacitive accelerometer

The bias drift of a micro-electro-mechanical systems （MEMS） accelerometer suffers from the l/f noise and the tem- perature effect. For massive applications, the bias drift urgently needs to be improved. Conventional methods often cannot ad- dress the l/f noise and temperature effect in one architecture. In this paper, a combined approach on closed-loop architecture modification is proposed to minimize the bias drift. The modulated feedback approach is used to isolate the l/f noise that exists in the conventional direct feedback approach. Then a common mode signal is created and added into the closed loop on the basis of modulated feedback architecture, to compensate for the temperature drift. With the combined approach, the bias instability is improved to less than 13 μg, and the drift of the Allan variance result is reduced to 17 μg at 100 s of the integration time. The temperature coefficient is reduced from 4.68 to 0.1 mg/℃. The combined approach could be useful for many other closed-loop accelerometers.