某340矫直机上辊快开机构裂纹原因分析及预防措施

340管线矫直机是太原重工成熟产品,在国内占有较大市场,并出口印度、印尼、缅甸、埃及等国际市场。出口印度矫直机在质保期内出现主缸裂纹问题,为探明问题原因并杜绝类似情况发生,快开机构设计静强度分析、疲劳强度分析及生产加工过程等方面探查裂纹原因并提出几点预防措施。     

An approach to measure infill matric suction of irregular infilled rock joints under constant normal stiffness shearing

Rock joints infilled with sediments can strongly influence the strength of rock mass. As infilled joints often exist under unsaturated condition, this study investigated the influence of matric suction of infill on the overall joint shear strength. A novel technique that allows direct measurement of matric suction of infill using high capacity tensiometers (HCTs) during direct shear of infilled joints under constant normal stiffness (CNS) is described. The CNS apparatus was modified to accommodate the HCT and the procedure is explained in detail. Joint specimens were simulated by gypsum plaster using three-dimensional (3D) printed surface moulds, and filled with kaolin and sand mixture prepared at different water contents. Shear behaviours of both planar infilled joints and rough joints having joint roughness coefficients (JRCs) of 8–10 and 18–20 with the ratios of infill thickness to asperity height (t/a) equal to 0.5 were investigated. Matric suction shows predominantly unimodal behaviour during shearing of both planar and rough joints, which is closely associated with the variation of unloading rate and volumetric changes of the infill material. As expected, two-peak behaviour was observed for the rough joints and both peaks increased with the increase of infill matric suction. The results suggest that the contribution of matric suction of infill on the joint peak normalised shear stress is relatively independent of the joint roughness.     

铜基化合物的可见光催化研究进展

与传统贵金属光催化剂相比，铜基光催化剂具有价格低廉、绿色环保、反应条件温和、光催化活性可调节等优势，受到合成化学家们广泛关注。本文简述了铜基催化剂的光催化历史，回顾了近五年来铜基化合物在可见光催化领域的研究成果与进展，总结了铜基催化剂的独立光催化机理与协同光催化机理；简要阐述了铜催化剂在不同类型反应中的应用，重点讨论了铜(Ⅰ)催化剂在烯烃官能化、碳-碳偶联、碳-杂偶联、原位催化等反应中的应用研究，表明铜基化合物在光催化合成领域具有很大的应用潜力。对未来的研究工作进行了展望，指出拓展催化剂的反应适用性、探索催化剂的氧化还原能力、进一步开发催化剂在手性合成中的应用将是该领域的研究重点。     

潮流能水平轴水轮机在剪切来流下的水动力分析

采用基于计算流体力学方法的全尺度数值模拟计算,建立了适用于潮流能水轮机模拟的剪切来流环境,通过数值计算结果,对潮流能水轮机随时间变化的宏观力和流场特征进行了系统分析,探索水轮机在复杂工况下的水动力特性规律。结果表明,水轮机整个叶轮的总体平均受力在剪切流工况中未受到明显影响; 单个叶片的瞬态轴向力系数和瞬态轴向扭矩系数在旋转周期内出现了明显的周期性变化,且周期性变化幅值随转速增大而增大; 非定常的瞬时轴向扭矩和力的周期性振荡容易引起单个叶片的结构性振动,可能对水轮机的机械结构造成影响。     

Strength and dilatancy behaviors of deep sands in Shanghai with a focus on grain size and shape effect

With rapid development of infrastructures like tunnels and open excavations in Shanghai, investigations on deeper soils have become critically important. Most of the existing laboratory works were focused on the clayey strata up to Layer 6 in Shanghai, i.e. at depth of up to 40 m. In this paper, Layers 7, 9, and 11, which were mostly formed of sandy soils at depth of up to 150 m, were experimentally investigated with respect to physico-mechanical behaviors. The stress–strain behaviors were analyzed by the consolidated drained/undrained (CD/CU) triaxial tests under monotonic loading. One-dimensional (1D) oedometer tests were performed to investigate the consolidation properties of the sandy soils. Specimens were prepared at three different relative densities for each layer. Also, the micro-images and particle size analyzers were used to analyze the shape and size of the sand grains. The influences of grain size, density, and angularity on the stress–strain behaviors and compressibility were also studied. Compared to the other layers, Layer 11 had the smallest mean grain size (D₅₀), highest compressibility, and lowest shear strength. In contrast, Layer 9 had the largest mean grain size, lowest compressibility, and highest shear strength. Layer 7 was of intermediate mean grain size, exhibiting more compressibility and less shear strength than that of Layer 9. Also, the critical state parameters and maximum dilatancy rate of different layers were discussed.     

Graph-based video fingerprinting using double optimal projection

A double optimal projection method that involves projections for intra-cluster and inter-cluster dimensionality reduction are proposed for video fingerprinting. The video is initially set as a graph with frames as its vertices in a high-dimensional space. A similarity measure that can compute the weights of the edges is then proposed. Subsequently, the video frames are partitioned into different clusters based on the graph model. Double optimal projection is used to explore the optimal mapping points in a low-dimensional space to reduce the video dimensions. The statistics and geometrical fingerprints are generated to determine whether a query video is copied from one of the videos in the database. During matching, the video can be roughly matched by utilizing the statistics fingerprint. Further matching is thereafter performed in the corresponding group using geometrical fingerprints. Experimental results show the good performance of the proposed video fingerprinting method in robustness and discrimination.     

Electrocatalytic Reduction of CO2 to Ethylene by Molecular Cu‐Complex Immobilized on Graphitized Mesoporous Carbon

The electrochemical reduction of carbon dioxide (CO₂) to hydrocarbons is a challenging task because of the issues in controlling the efficiency and selectivity of the products. Among the various transition metals, copper has attracted attention as it yields more reduced and C2 products even while using mononuclear copper center as catalysts. In addition, it is found that reversible formation of copper nanoparticle acts as the real catalytically active site for the conversion of CO₂ to reduced products. Here, it is demonstrated that the dinuclear molecular copper complex immobilized over graphitized mesoporous carbon can act as catalysts for the conversion of CO₂ to hydrocarbons (methane and ethylene) up to 60%. Interestingly, high selectivity toward C2 product (40% faradaic efficiency) is achieved by a molecular complex based hybrid material from CO₂ in 0.1 m KCl. In addition, the role of local pH, porous structure, and carbon support in limiting the mass transport to achieve the highly reduced products is demonstrated. Although the spectroscopic analysis of the catalysts exhibits molecular nature of the complex after 2 h bulk electrolysis, morphological study reveals that the newly generated copper cluster is the real active site during the catalytic reactions.     

基于3D打印技术复制砂浆节理的剪切试验及峰值抗剪强度模型

为进一步研究节理三维形貌特征与节理峰值抗剪强度的关系,首先采用巴西劈裂试验获取了自然劈裂岩石表面,通过三维扫描技术获取了节理面形态的高精度点云,通过逆向建模得到了自然岩石表面的立体模型,结合3D打印技术制作出了与自然岩石表面一致的PLA模具,以3D打印获得的底模通过水泥砂浆浇筑了含有自然结构面形貌的相似节理面试样。PLA模具与复制材料差异较大,复制材料在凝结过程中不易与PLA模具黏结,进而使脱模过程较为方便,不会破坏节理面。同时PLA模具可重复进行相似材料复制工作,具有可重复使用的优点。然后进行了具有5组形貌面的20个水泥砂浆节理面在4种不同法向荷载情况下的结构面剪切试验,得到了结构面剪切位移-荷载曲线。研究了结构面峰值抗剪强度、峰值位移、剪切刚度影响因素。节理经过剪切后形貌面出现不同程度的磨损,其磨损范围与等效高差分布范围基本一致,并且在等效高差为剪断破坏模式且成片的区域磨损较为严重。在新粗糙度指标基础上提出了新的峰值抗剪强度模型,经试验对比显示出新模型的有效性。在新模型基础上提出了一个简化模型。对比发现新模型简化后其计算精度较新模型有所降低但由于所需参数减小计算较为方便,新模型简化结果精度虽然有所下降但是还是比Barton公式精度高。     

Excellent Mechanical and Transparency Properties of Cationic Waterborne Polyurethane Films Modified by Boehmite Sol

The strategies for nanosol from metal alkoxide have enabled production of ultratransparent and mechanically robust polymer nanocomposites at extremely high loading. Herein, a simple approach to fabricate high‐performance polyurethane‐based nanocomposites via unmodified boehmite nanoparticles is reported. Evaluating their physical properties, the uniform dispersion of boehmite in the matrix caused nanocomposites retains ultrahigh transparency. Hydrogen bonding and intermolecular entanglement between boehmite and polyurethane brings about the mechanical properties of the nanocomposites material enhanced, i.e., strength, stiffness, and toughness. Optimized strength, stiffness, and toughness of Boehmite/Cationic waterborne polyurethane at 40 wt% (BNC40) are up to 58.1 MPa, 1096.7 MPa, 249.5 MJ m^?3, respectively. Furthermore, the feasibility and mechanism of polymer strengthening and toughening by inorganic rigid nanoparticles is explored from the aspects of crystallinity and micromorphology.