基于温度应力效应下大体积混凝土裂缝防控策略探析

温度应力效应是大体积混凝土裂缝形成的一个重要原因,应当引起施工技术人员的重视.在温度裂缝的防控措施中,应重视施工方案设计、优选原材料、施工中质量控制和养护等.施工技术人员应根据工程具体情况,结合多种预防处理措施,制定合理可行的大体积混凝土施工方案和周密的技术措施,从而确保工程质量.     

Measuring and modelling the thermal performance of the Tamar Suspension Bridge using a wireless sensor network

A study on the thermal performance of the Tamar Suspension Bridge deck in Plymouth, UK, is presented in this paper. Ambient air, suspension cable, deck and truss temperatures were acquired using a wired sensor system. Deck extension data were acquired using a two-hop wireless sensor network. Empirical models relating the deck extension to various combinations of temperatures were derived and compared. The most accurate model, which used all the four temperature variables, predicted the deck extension with an accuracy of 99.4%. Time delays ranging from 10 to 66 min were identified between the daily cycles of the air temperature and of the structural temperatures and deck extension. However, accounting for these delays in the temperature–extension models did not improve the models' prediction accuracy. The results of this study suggest that bridge design recommendations are based on overly simplistic assumptions which could result in significant errors in the estimated deck movement, especially for temperature extremes. These findings aim to help engineers better understand the important aspect of thermal performance of steel bridges. This paper also presents a concise study on the effective use of off-the-shelf wireless technology to support structural health monitoring of bridges.     

Water absorption,biodegradation, thermal and morphological properties of Spartium junceum fiber-reinforced polyvinylchloride composites: effects of fibers content and surface modification

In this study, we want to investigate the effects of fibers content and surface modification of Spartium junceum (SJ) fibers on the water absorption characteristics, thermal degradation, and morphological properties of SJ-reinforced poly (vinyl chloride) (PVC) composites. In addition, the change in mechanical proprieties of the composites after biodegradation test was evaluated by tensile strength. In order to improve the interfacial interactions between the PVC matrix and the SJ fibers, SJ fibers were modified by sodium hydroxide (NaOH), vinyltrimethoxysilane (VTMS) and treated with sodium hydroxide solution followed by VTMS (NaOH+VTMS). The results show that the water uptake of PVC/SJ fibers composites increases with the increase in the fibers’ content. However, the surface modification reduces water uptake. Moreover, the results indicate that the kinetics of water absorption of the PVC/SJ fibers composites approaches the Fickian diffusion mechanism. Also, the results indicate that the tensile strength of the composites is affected by the biodegradation test and chemical treatments. The atomic force microscope pictures of the composites illustrate the reduction of roughness via surface treatments of fibers.     

铝合金阳极氧化着黑色热控涂层工艺研究

介绍了一种铝合金阳极氧化着黑色热控涂层工艺,此工艺采用硫酸阳极氧化方法以及深黑32#有机染料着色,对LY12铝合金H112热处理状态材料进行了处理。通过正交试验对氧化时间、氧化温度、电流密度工艺参数进行优化,得到高发射率的最佳工艺参数。     

Effect of thermal treatment on energy dissipation of granite under cyclic impact loading

High temperature treatment causes thermal damage to rocks in deep mining. To study the thermal effect on the energy dissipation of rocks during the dynamic cyclic loading, cyclic impact loading experiments of heat-treated rocks were carried out using the splitting Hopkinson pressure bar (SHPB) experimental system. The correlations among the energy dissipation, energy dissipation rate, impact times, accumulated absorbed energy per volume, failure mode and temperature were analyzed. The results show that the reflected energy under the first impact increases and finally exceeds the absorbed energy when the temperature increases; however, the total reflected energy decreases above 200 °C. The absorbed energy under the first impact and the total absorbed energy all decrease as the temperature increases, the rates of which decrease accordingly. And the same phenomenon appears for the transmitted energy and the rate of the transmitted energy. On the contrary, the rate of the reflected energy increases with the rising temperature. When the temperature increases, the fewer impact times are needed to destroy the sample. In addition, the failure modes are different when the rock is treated at different temperatures; that is, when the temperature is high, even though the absorbed energy is low, the sample breaks into powder after several impacts.     

提高Φ2700×3600型湿式球磨机传动齿轮的使用寿命

对Φ2700×3600型湿式球磨机在实际使用中传动齿轮损坏的主要形式和原因分别作了介绍和分析，并提出了提高其使用寿命应采取的具体措施。     

工件热变形对加工精度影响的研究

通过分析工件在均匀受热和不均匀受热状态下的热变形 ,应用数学、传热学和力学方法推导出在这 2种情况下的热变形量计算公式 ,从而为减小工件的热变形提高工件的加工精度提供了理论上的依据     

轴向柱塞泵配流副润滑特性试验系统的建立及仿真研究

论述了轴向柱塞泵配流副润滑特性试验系统的组成和工作原理．该润滑特性试验系统用来测量压力、温度、转速和结构对配流副润滑膜厚度、承载力和泄漏流量等润滑特性参数的影响规律．润滑特性试验装置使用高精度电涡流位移传感器测量配流副间隙,以保证对润滑膜厚度的测量误差小于1μm,采用PID控制算法对微米级的润滑膜厚度进行反馈控制．利用MATLAB语言的SIMULINK软件包对精密位置反馈控制系统进行了动态仿真,得出参数V0/βe和Kce值的选取对该精密位置反馈控制系统的设计是非常重要的．     

HT-7U装置中的一种新波导阵天线的冷却研究

介绍了一种新的低杂波天线的冷却研究 ,在冷却的过程中 ,选择了加压去离子水作为冷却液体来消除微波通过时所遗留下的热损 ,并运用对流传热的方法对冷却进行了分析 ,从而为托卡马克实验中加热的顺利进行提供了理论基础     

A New Clearance Design Method for Reciprocating Fuel Pumps of Medium-Speed Diesel Engines

A new clearance design method is proposed for a reciprocating fuel pump. Structural and hydrodynamic lubrication analyses were conducted to design the clearance of the pump, and the former was used to evaluate the clearance reduction due to the deformation that results from applying maximum supply pressure. The reduction in the maximum clearance was used as the limit of the design, and the two-dimensional Reynolds equation is used to evaluate the lubrication characteristics of the pump with variations in the viscosity and clearance. The optimal clearance in the pump must be separately designed in both the stem and the head because the lubrication characteristics and the deformation patterns of the two parts are different. The validity of the numerical model was then verified by determining that the position of the wear was also similar to that of the minimum film thickness. Moreover, a rig test system was also used to verify the clearance of the proposed design method.