Study of a new type of self‐centering beam‐column joint in steel frame structures

A new type of self‐centering beam‐column joint with installed steel arc plates is proposed in this study. First, mechanical behavior of the self‐centering joint using prestressed steel strands to provide the centering force is theoretically analyzed in detail, followed by experimental validation. New joints with different arc plate parameters are designed and tested under cyclic loading. Test results show that the hysteretic curve of the new joint exhibits typical characteristic of self‐centering capacity. By parametric analysis of five design parameters of the arc plate, it is found that vector height has the greatest influence on the joint's moment‐rotation skeleton curve, which is consistent with experimental findings. A simplified model of the joint is built in OpenSees to simulate its hysteretic behavior, which agrees well with the tested results. To demonstrate the effectiveness of the new joint to improve the seismic performance of the overall structure, a series of nonlinear time history analysis on a steel frame structure with the new joint under earthquakes are conducted, which show that the joint is particularly effective in reducing the residual interstory drift response.     

深埋巷道围岩变形及支护技术研究

随着煤炭开采逐渐向深部转移,巷道围岩变形越来越严重。分析了深埋巷道围岩变形及支护技术,对研究巷道进行了三轴抗拉试验,得到煤和岩石力学参数,采用结构梁和弹性力学分析了巷道围岩变形,为模型分析提供了理论基础,然后采用FLAC^3D数值模拟软件,分析了巷道变形位移,与现场实测相比,数值模拟能够较好地模拟煤矿巷道实际变形情况。研究能够为巷道参数设计提供借鉴。     

Q235碳钢在静止和流动条件下的腐蚀不均匀性研究

目的研究Q235碳钢在静止和流动条件下腐蚀程度和主要腐蚀区域的差异。方法使用丝束电极(WBE)技术和电化学阻抗谱(EIS)技术分别研究了WBE在静止和流动条件下的电流密度分布、电荷转移电阻以及腐蚀形貌的变化和差异,同时分析了电极的极性转换现象。结果流动条件下Q235碳钢的电荷转移电阻明显降低。在静止条件下,Q235碳钢表面阳极电流区域所占的最大比例为47%,且阳极电流峰集中出现在WBE的中间区域,而四周边缘处的阳极电流峰较少。在流动条件下,Q235碳钢表面的阳极电流区域所占的最大比例为58%,阳极电流峰随机分布在整个WBE表面,且电流分布区间明显变窄。浸泡在静止条件下的58~#电极和流动条件下的39~#电极发生了多次极性转换现象。结论 Q235碳钢在静止和流动条件下均发生了明显的不均匀腐蚀现象。流动条件加剧了Q235碳钢的腐蚀且降低了腐蚀不均匀性。静止条件下Q235碳钢的腐蚀区域集中在中间区域,流动条件下Q235碳钢的腐蚀区域随机分布在整个碳钢表面。静止和流动条件下的钢电极均发生了电流的极性转换现象。     

ZL104铝合金连杆半固态挤压铸造工艺实验研究

研究了传统液态挤压铸造与半固态挤压铸造成形ZL104铝合金连杆的充填状态、微观组织及力学性能。结果表明:传统液态挤压铸造成形连杆充填饱满,但其抗拉强度及伸长率低于半固态挤压铸造成形连杆。对于半固态挤压铸造成形,浇注温度高于565℃时,铸件充填性能良好;平均晶粒尺寸及形状因子随浇注温度的升高而逐渐增大;连杆抗拉强度及伸长率先增加后减小。挤压压力高于25MPa时,铸件均充填饱满;挤压压力升高,平均晶粒尺寸不断减小且形状因子不断增大,连杆机械性能不断提高。模具预热温度升高,平均晶粒尺寸和形状因子不断增大,连杆机械性能逐渐提高。但当模具预热温度超过300℃时,平均晶粒尺寸进一步增大而其形状因子减小,导致连杆的机械性能下降。     

Effect of microstructure inhomogeneity on mechanical properties of different zones in TA15 electron beam welded joints

The effects of microstructure inhomogeneity on the mechanical properties of different zones in TA15 electron beam welded joints were investigated using a micromechanics-based finite element method. Considering the indentation size effect, the mechanical properties for constituent phases of the base metal (BM) and heat affected zone (HAZ) were determined by the instrumented nano-indentation test. The macroscopic mechanical properties of BM and HAZ obtained from the tensile test agree well with the numerical results. The incompatible deformation between the constituent phases tends to localize along the softer primary phase α where failure usually initiates in form of localized plastic strain. Compared with the BM, the mechanical properties of constituent phases in the HAZ differ substantially, leading to more serious strain localization behavior.     

轿车后轿横梁焊缝纵向开裂的原因分析

针对某轿车后梁焊缝纵向开裂情况，采用宏观观察、金相检验和扫描电镜分析等方法，对材质为CP-800高强钢，厚度为2 mm焊缝开裂原因进行了分析。扫描电镜发现裂纹起源于Cr的氧化物，以及其与Al、Si、Ca和Mn的复合氧化物处，且有疲劳辉纹形成，说明开裂是疲劳裂纹扩展到临界尺寸时在外载荷作用下发生快速扩展造成的。     

Modelling of electron energy absorption and backscattering during EBW

A three-dimensional heat flux model for deep-penetrating electron beam welding (EBW) is established to mathematically describe the physical heat generation process during interaction between electrons and the dynamic molten pool free surface. Monte Carlo method is used to determine the electron-target interaction, and random distribution of initial electrons, progressive trajectory tracing and electron backscattering models are used to describe the spatial distribution of electrons absorption. The model is verified in preset keyholes and applied in the simulation on electron beam welding process, and the calculated bead shape shows a good consistency with experimental results.     

Hydrogen annealing induced physical properties of ZnTe thin films

The ZnTe material has an unprecedented role in the fabrication of high efficiency CdTe thin film solar cells and optimization of hydrogen annealing induced physical properties of ZnTe films is next required step. Consequently, in the present work, the impact of Hydrogen annealing temperature on the structural, optical, electrical, topographical, morphological, and compositional properties of ZnTe films is explored. The ZnTe thin films (having 300 nm thickness) are grown via electron-beam evaporation technique on glass and ITO substrates followed by annealing at different temperatures under a Hydrogen atmosphere. The ZnTe films are found to crystallize in cubic phase with (111) predominant peak having crystallite size in the range of 19–28 nm, whereas annealed films demonstrated lower optical transmittance vis-à-vis to pristine films. The PL spectra exhibit two luminescence peaks with a stronger band at ～351 nm and a weaker band at ～450 nm. Ohmic behavior of ZnTe films is assured through I–V characteristics, while the AFM images revealed hill-like surface topographies. The FESEM image of pristine films demonstrated a homogeneous surface comprising spherical grains whereas annealed films have spherical, stone, and blisters like morphologies. The EDS patterns assured the Te element richness as well as successful ZnTe films deposition. The observed findings signify that the Hydrogen annealing at different temperatures notably modified the physical properties of ZnTe films.     

Polypyrrole and platinum deposited onto carbon substrate to enhance direct methanol fuel cell electrodes behaviour

The aim of this work is to study the ability of polypyrrole to reduce the platinum load of low temperature methanol fuel cell electrodes. Platinum was deposited onto carbon paper and a layer of polypyrrole electrodeposited onto carbon paper, using electron beam evaporation and electrodeposition by pulses. Subsequently, the morphology and electrochemical behaviour of the synthesised samples were analysed in sulphuric acid solution, determining their electrochemically active surface area; and in a solution of sulphuric acid and methanol, to analyse their catalytic performance. The electrochemical measurements showed that the electrochemically active surface area and the catalytic performance of the electrodes prepared by evaporating platinum are increased when prepared on the polypyrrole film. Electrodes prepared using the pulse electrodeposition technique presented fairly homogeneous coatings that led to the reduction of the oxidation potential of methanol and the increase of their resistance to CO poisoning.     

2195铝锂合金电子束焊接头的焊后热处理

采用光学显微镜、扫描电镜、能谱仪及X射线衍射仪等微观分析手段,研究不同热处理工艺条件下2195铝锂合金电子束焊接头焊缝区的显微组织演变,探讨接头的焊后热处理强化机制。结果表明,焊后热处理可显著改善接头区域的显微组织,促进强化相的析出,有利于提高接头的力学性能。经过焊后固溶+双级时效热处理,焊态下接头熔合线附近存在的等轴细晶区消失,β′、θ′和T₁等强化相在接头焊缝区析出,与单级时效处理工艺相比,双级时效处理的析出强化效果更为显著。力学性能测试表明,经过双级时效热处理后,接头的抗拉强度达到492.5 MPa,为母材强度的90.4%。接头拉伸断口表面存在许多小韧窝,并伴随出现解理面,接头呈韧-脆混合型断裂特征。