Extrusion process and property of AZ31 magnesium alloy

The microstructure and mechanical properties of extruded AZ31 magnesium at different extrusion temperature were investigated.The results show that,at 380 ℃,when the extrusion ratio is 23,the AZ31 magnesium alloy has a dense recrystallized microstructure and good mechanical properties.On one hand,if the extrusion ratio is too small,grain crushing effect is not obvious,and part of the grain is not dynamic recrystallization.On the other hand,larger extrusion ratio can lead to grain growth and banded structure.Tensile fracture characteristics of extruded AZ31 magnesium alloy is quasi-cleavage.     

Regulation of sensory nerve conduction velocity of human bodies responding to annual temperature variations in natural environments

The extensive research interests in environmental temperature can be linked to human productivity / performance as well as comfort and health; while the mechanisms of physiological indices responding to temperature variations remain incompletely understood. This study adopted a physiological sensory nerve conduction velocity (SCV) as a temperature‐sensitive biomarker to explore the thermoregulatory mechanisms of human responding to annual temperatures. The measurements of subjects’ SCV (over 600 samples) were conducted in a naturally ventilated environment over all four seasons. The results showed a positive correlation between SCV and annual temperatures and a Boltzmann model was adopted to depict the S‐shaped trend of SCV with operative temperatures from 5°C to 40°C. The SCV increased linearly with operative temperatures from 14.28°C to 20.5°C and responded sensitively for 10.19°C‐24.59°C, while tended to be stable beyond that. The subjects’ thermal sensations were linearly related to SCV, elaborating the relation between human physiological regulations and subjective thermal perception variations. The findings reveal the body SCV regulatory characteristics in different operative temperature intervals, thereby giving a deeper insight into human autonomic thermoregulation and benefiting for built environment designs, meantime minimizing the temperature‐invoked risks to human health and well‐being.     

Comparisons of adaptive fault‐tolerant insensitive control methods for a class of linear systems

In this paper, the problem of fault‐tolerant insensitive control is addressed for a class of linear time‐invariant continuous‐time systems against bounded time‐varying actuator faults and controller gain variations. Adaptive mechanisms are developed to adjust controller gains in order to compensate for the detrimental effects of partial loss of control effectiveness and bias‐actuator faults. Variations of controller gains arise from time‐varying and bounded perturbations that are supposed to always exist in adaptive mechanisms. Based on the disturbed outputs of adaptive mechanisms, three different adaptive control strategies are constructed to achieve bounded stability results of the closed‐loop adaptive fault‐tolerant control systems in the presence of actuator faults and controller gain variations. Furthermore, comparisons of convergence boundaries of states and limits of control inputs among adaptive strategies are developed in this paper. The efficiency of the proposed adaptive control strategies and their comparisons are demonstrated by a rocket fairing structural‐acoustic model.     

CO2 hydrogenation over differently morphological CeO2‐supported Cu‐Ni catalysts

Differently morphological CeO₂‐supported Cu‐Ni catalysts utilized for carbon dioxide hydrogenation to methanol were prepared by the method of impregnation. The 100‐ to 300‐nm CeO₂ nanorod‐supported catalyst dominantly exposed low‐energy (100) and (110) facets, and the Cu‐Ni supported on 10‐ to 20‐nm CeO₂ nanospheres and on irregular CeO₂ nanoparticles were both enclosed by (111) facets owning high energy. Besides, all CeO₂‐supported Cu‐Ni catalysts possess oxygen vacancies, which can active and absorb CO₂ and is further beneficial for the reaction. Most oxygen vacancies were generated from the Ce⁴⁺ reduction to Ce³⁺ with the ceria lattice cell expansion, and small amount of oxygen vacancies resulted from the Ce⁴⁺ replacement by Cu or/and Ni atom. Because of the exposed (100) and (110) facets and numerous oxygen vacancies, well‐defined CeO₂ nanorod‐supported Cu‐Ni alloy showed more superior catalytic performance than on CeO₂ nanospheres and nanoparticles.     

Exergy analysis of a 1.2 MW waste heat power generation project

According to systematic features, analysis method based on exergy balance is established. Basic indicators in the system, the subsystem, and facilities are put forward in this paper. By using this method to analyze the generation system of megawatt‐scale in one chemical enterprise, it is found that the objective exergy efficiency of the system is 35.67%, and exergy loss of organic Rankine cycle (ORC) is the highest. The thermal efficiency of the total system is 9.61%. For the condenser, the thermal efficiency is 91.18%, and the exergy efficiency is only 23.44%. The objective exergy efficiency of the evaporator is 74.04%. The influence coefficient of exergy loss of condenser is higher than that of pump and expander, but input exergy of the condenser is lower than that of the expander. It is revealed that ORC subsystem is the part which needs to be focused on, and the condenser is the most important component of ORC subsystem which should be optimized firstly.     

Formation and O2/CO2 combustion characteristics of real-environment coal char in high-temperature oxy-fuel conditions

Oxygen-fuel combustion is a promising technology for CO₂ emission reduction. The high-temperature entrained flow reactor and high-temperature drop tube furnace were used to analyses the formation and O₂/CO₂ combustion characteristics of real-environment coal char in high-temperature oxy-fuel conditions. It proposed “inflection point standard” of high-temperature flame method for the preparation of real-environmental oxy-fuel coal char according to the flame method. The results show that the ratios of C=O/C-O and C=O/C_ar increase in the coal char compared with the raw coals. The trend of C=O/C_ar in oxy-fuel condition is opposite to that in the inert atmosphere, due to the effect of high-concentration CO₂. To achieve the burnout rate similar to air combustion for coal char, with the increase of coal rank, the O₂ concentration should be enhanced. The optimal O₂ concentration for the oxy-fuel combustion of JC anthracite is 30%, while that of other low-rank coals could be lower than 30%. The combustion characteristic of JC anthracite is with the highest sensitivity to temperature and O₂ concentration.     

同步热分析法研究超级铝热剂Al/MnO2的热安定性

A型车动车转向架扭转阻力测试试验研究

谭富星,刘洪涛,刘诗慧,张镇川,张鹏

（中车长春轨道客车股份有限公司,长春 130062）

摘要：

转阻力系数是转向架重要的运行参数,直接影响着轨道车辆的动力学性能。A型轨道车辆动车转向架扭转阻力参数测试通过理论计算、动力学仿真和试验验证等手段进行研究。通过对不同的空簧状态、空簧刚度和扭转速度等工况的分析和试验表明,扭转阻力系数与车辆通过曲线时的曲线半径相关性强;扭转阻力系数随着空簧水平刚度变化而变化;同时扭转阻力系数随扭转速度的增长而逐渐增大。在不同空簧状态和不同扭转速度的工况下的试验检定表明：扭转阻力系数随着扭转速度的增加而上升;抗蛇行减振器产生作用于转向架上的扭转阻力矩,且该力矩随着扭转速度增加而上升。试验结果表明理论分析、动力学仿真与真实转向架台架试验验证结果相吻合,试验满足EN14363中的要求和车辆安全操作指导。

关键词：A型车辆,动车转向架,扭转角,扭转阻力系数,扭转转速