FRP strengthening of steel and steel-concrete composite structures: an analytical approach

A recent technique for strengthening steel and steel-concrete composite structures by the use of externally bonded Fiber Reinforced Polymer (FRP) sheets, to increase the flexural capacity of the structural element, is described. Several researches developed FRP strengthening of reinforced concrete and masonry structures, but few experimental studies about steel and steel-concrete composite elements are available. Some examples of guidelines for the design and construction of externally bonded FRP systems for strengthening existing metal structures are available, but the method used to predict the flexural behaviour of FRP strengthened elements is usually based on the hypothesis of elastic behaviour of materials and FRP laminate is mainly considered only under the tensile flange. In this paper, an analytical procedure to predict the flexural behaviour of FRP strengthened steel and steel-concrete composite elements, based on cross-sectional behaviour and taking into account the non-linear behaviour of the materials with any configuration of FRP reinforcement, is given. Analytical predictions are compared with some experimental results available in the literature on the flexural behaviour of FRP strengthened steel and steel-concrete composite elements, showing good agreement of the results, even in the non-linear phase, until failure.     

Coarsening kinetics and strengthening mechanisms of core-shell nanoscale precipitates in Al-Li-Yb-Er-Sc-Zr alloy

The tailored nanoparticles with a complex core/shell structure can satisfy a variety of demands, such as lattice misfit, shearability and coarsening resistance. In this research, core-shell nanoscale Al3(Yb, Er, Sc,Zr, Li) composite particles were precipitated in Al-2 Li-0.1 Yb-0.1 Er-0.1 Sc-0.1 Zr(wt%) alloy through the double-aging treatment, in which the core was(Yb, Er, Sc, Zr)-rich formed at 300°C and the shell was Li-rich formed at 150°C. The coarsening kinetics and precipitate size distributions(PSDs) of Al3(Yb, Er, Sc,Zr, Li) particles aged at 150°C previously aged at 300°C for 24 h showed a better fit to the relation of 2∝ kt and normal distribution, indicating that the coarsening of precipitates was controlled by interface reaction, not diffusion. The Orowan bypass strengthening was operative mechanism at 150°C.     

三峡升船机顶部机房钢屋架设计与施工

根据三峡升船机顶部机房钢屋架的使用要求,研究分析了钢屋架的结构形式,通过建立三维有限元模型验证了钢屋架结构形式及其设计方案在施工阶段的结构安全性。同时,通过对钢屋架施工方案的研究,制定了适合三峡升船机顶部机房钢屋架施工作业环境的施工程序以及施工设备选型,对钢屋架施工过程中钢桁架分段、格构支撑架的设置、钢桁架吊装、中控室屋面网架安装、屋面板安装等环节提出了针对性的施工方法。三峡升船机顶部机房钢屋架所采用的结构设计方法与施工方案确保了钢屋架的顺利安装与安全运行,对类似工程具有一定的参考价值。     

工业建筑预埋件三维快速装配设计方法

当前工业建筑结构预埋件设计主要采用二维CAD软件,效率较低且容易出错。为此提出基于广义参数化模板的三维预埋件快速装配设计方法。该方法建立包含三维参数化形状结构、安装定位方式和二维投影简图等各种信息的预埋件广义参数化模板;通过构建预埋件参数化模板库,采用基于历史的装配设计技术,实现预埋件的快速安装设计。该文方法已经集成到商品化工业建筑结构三维CAD软件InteRDS中,并在实际工程设计中得到应用。     

First-principle study on the segregation and strengthening behavior of solute elements at grain boundary in BCC iron

Grain boundary(GB)significantly influences the mechanical properties of metal structural materials,yet the effect of solutes on GB modification and the underlying atomic mechanisms of solute segregation and strengthening in iron-based alloys remain insufficiently explored.To address this research gap,we conducted a comprehensive investigation into the segregation and strengthening effect of 33 commonly occurring solutes in iron-based alloys,with a specific focus on the body-centered cubic(BCC)iron Σ5(310)GB,utilizing first-principle calculations.Our findings reveal a negative linear correlation between solute segregation energy and atomic radius,highlighting the crucial role of atomic radius and electronic structure in determining GB strength.Moreover,through analyzing the relationship between strength-ening energy and segregation energy,it was found that the elements Ni,Co,Ti,V,Mn,Nb,Cr,Mo,W,and Re are significant enhancers of GB strength upon segregation.This study aims to provide theoretical guidance for selecting optimal doping elements in BCC iron-based alloys.     

Failure analysis of threaded connections in large-scale steel tie rods

Steel tie rods are very important load-carrying components in applications where high levels of pre-stresses are required. The bearing capacity of a steel tie rod is determined not only by the strength of the rod body, but also by the strength of the threaded connection that resists force. Analysis of the strength of the threaded connection and determining the optimal number of turns of thread engagement is critical to ensure structural safety. This paper reports the results of full-scale tensile rupture experiments on two categories of large-scale steel tie rods provided by China JULI Corporation: (i) LG75-00 steel tie rods with triangle threaded connection, and (ii) LG100-00 steel tie rods with trapezoidal threaded connection. The full-scale tensile rupture experiments were carried out to test the maximum allowable axial working load under different numbers of turns of engaged threads. The results of these experiments suggest strong guidelines on the minimum number of turns of thread engagement for preventing the failure of thread teeth of steel tie rods in practical shear and bending applications.     

1Cr13不锈钢电火花表面强化层摩擦磨损性能研究

针对我国水轮机过流部件磨蚀严重这一问题,选用WC电极对水轮机叶片用1Cr13不锈钢材料进行电火花表面强化处理,对生成的强化层摩擦磨损性能进行了深入研究,并利用扫描电子显微镜和X射线衍射仪对强化层的金相组织、元素分布以及相结构进行了分析.结果表明,强化层的硬度和耐磨性明显高于工件基体,强化层的硬度在白亮层最高,而在强化层...     

浅埋深两硬条件下特厚煤层综放开采技术

针对平朔矿区4号煤层条件,采用理论分析方法研究了浅埋深两硬条件下4号煤层顶煤的冒放性及合理采煤方法。以提高顶煤冒放性为目标,采用数值模拟的方法进行了综放工作面参数及设备选型配套研究。实践表明,浅埋深两硬煤层条件下通过加大综放工作面长度与割煤高度,可以实现安全、高效、高回收率开采。     

Restricted randomization and multiple responses in industrial experiments

Two issues regarding designed experiments are discussed; restrictions on randomization and multiple responses. The former is typically related to hard‐to‐vary factors and factors appearing in separate stages of a process experiment. Randomization restrictions should be taken into account in the construction of the design as well as in the statistical modelling. In the paper, a case study of sausage production is discussed, having a split‐plot model with correlated multiple responses. Multiple responses are handled in two ways, by principal component analysis (PCA) followed by ANOVA of the principal components, and by a newly developed alternative, the ‘50–50 MANOVA’. Multiple tests of correlated response variables are also described. Practical aspects of the planning, performing, response measurements, and statistical analysis are emphasized throughout. Hence, the paper aims to extend the utility of statistical methods in industry by linking design of experiments to multivariate analysis of the responses. Copyright © 2007 John Wiley & Sons, Ltd.     

电磁感应传感器用铠装电缆在钢包中的应用

为满足电磁感应国产化的需要,研制了适合高温恶劣环境、结构简单、价格低廉的电磁感应传感器用铠装电缆。电缆利用传感器次级线圈感应初级线圈电流大小,来判断钢渣的位置,以生产出优质高效钢的特点进行研制。通过整机运行表明研制的铠装电缆绕制的电磁感应传感器能够准确可靠地判断钢渣的位置,满足了钢包除渣的要求。     

Association of microstructure and electric heterogeneity in BiFeO3

BiFeO₃ ceramics was synthesized by solid state reaction technique. Synchrotron X-ray diffraction analysis was employed to investigate the phase formation and structure determination. Rietveld refinement of the diffracted data confirmed the rhombohedrally distorted perovskite structure with space group R3c. Localized atomic structure determined from fitted X-ray data showed off centered displacement of Fe³⁺ cations with a magnitude of 0.397 Å along c-axis. The FeO₆ octahedron comprised of two types of Fe–O bonds with bond lengths of ∼1.935 Å and ∼2.131 Å. Impedance spectroscopic data collected in wide temperature (300–400 K) and frequency (200 Hz–2 MHz) ranges, demonstrated two relaxation phenomena corresponding to two heterogeneous phases. The best fits to the collected impedance data were achieved by employing an equivalent circuit model R_g(R_gbC_gb)(R_eQ_e). Grain boundaries showed only p-type small polaronic hopping conduction process assisted with the oxidation of Fe³⁺ to Fe⁴⁺ in measured temperature range of 300–400 K. Grains exhibited p-type small polaronic hopping conduction mechanism up to 375 K; however, above 375 K electronic conduction becomes prominent. Conduction is dominated by short range hopping of the polarons among Fe³⁺ and Fe⁴⁺ or through the first ionized oxygen vacancy bridge between Fe³⁺ and Fe²⁺ cations.     

浅谈民用建筑地下车库通风与机械排烟

本文根据工程设计经验对地下车库通风换气量和排烟量的确定，通风与排烟系统方案设计，提出自己的看法，供大家参考。     

难熔金属加工业现状及在真空炉行业中的应用

从资源、设备、产品及市场等方面简要阐述了我国难熔金属加工业发展的历程,现状及其在真空炉工业中的应用。     

XRD and TEM analysis of microstructure in the welding zone of 9Cr-1Mo-V-Nb heat-resisting steel

Under the condition of tungsten inert gas shielded welding (TIG) + shielded metal arc welding (SMAW) technology, the microstructure in the welding zone of 9Cr-1Mo-V-Nb (P91) heat-resisting steel is studied by means of X-ray diffractometry (XRD) and transmission electron microscopy (TEM). The test results indicate that when the weld heat input (E) of TIG is 8.5 ∼ 11.7 kJ/cm and the weld heat input of SMAW is 13.3 ∼ 210 kJ/cm, the microstructure in the weld metal is composed of austenite and a little amount of δ ferrite. The substructure of austenite is crypto-crystal martensite, which included angle. There are some spot precipitates in the martensite base. TEM analysis indicates that the fine structure in the heat-affected zone is lath martensite. There are some carbides (lattice constant, 1.064 nm) at the boundary of grain as well as inside the grain, most of which are Cr₂₃C₆ and a little amount of (Fe, Me)₂₃C₆.     

Strength and Failure of Synthetic Webbing of Unitizing Sling Assemblies in the Initial State and after Overloading

The results of full-scale tests of unitizing multiple-leg sling assemblies loaded with a trapezoidal waveform are considered. Mechanical behavior of the sling webbing material was evaluated by comparing its strength in the initial state and after overloading. A parameter to estimate the damage accumulated in the polymer material held under load is proposed, which makes it possible to determine the residual strength of the webbing at a known loading history. Under cyclic loading of slings the webbing strength markedly deteriorates, which leads to a decrease in the actual value of the sling safety factor. Design calculations of lifting capacity for unitizing sling assemblies should be performed with regard for the breaking force of their webbing tested after overloading.     

Redox ratio and optical absorption of polyvalent ions in industrial glasses

The changes in glass structure and redox ratio, R (reduced ion to oxidized ion) of Mn²⁺-Mn³⁺, Cu⁺-Cu²⁺, Cr³⁺-Cr⁶⁺, Ni²⁺-Ni³⁺ and Co²⁺-Co³⁺ couples and optical absorption due to Mn³⁺, Cu²⁺, Cr³⁺, Ni²⁺ and Co²⁺ ions in industrial soda-lime-silica glass were investigated as a function of Na₂O concentration in the range 11–19 mol%. With increasing Na₂O concentration in the experimental glasses, the basicity, expressed as calculated basicity, Λ_cal, increased. ²⁹Si NMR and X-ray diffraction were used to investigate the structural change in glasses. The NMR spectra showed high non-bridging oxygens (NBOs) when the basicity of glass was increased. The results were interpreted to be due to the tetrahedral networks; Q ⁴ species were depolymerized by replacing the bridging oxygens (BOs) with NBOs to Q ³ species. These results confirmed the shift of broadening peaks of XRD patterns. The redox reactions of the Mn²⁺-Mn³⁺, Cu⁺-Cu²⁺ and Cr³⁺-Cr⁶⁺ couples shifted more toward their oxidized ions due to the oxygen partial pressure, p(O₂), during melting and the oxide ion activity, a _O2−, increased with increasing glass basicity. These changes caused the redox ratio of these ion couples to decrease. The Ni²⁺-Ni³⁺ and Co²⁺-Co³⁺ couples were assumed to be present only in the Ni²⁺ and Co²⁺ ions in these glasses, respectively. The optical absorption bands due to Mn³⁺, Cu²⁺, Cr³⁺, Ni²⁺ and Co²⁺ ions were also investigated. Their spectra occurred at constant wavelengths with different optical densities or intensities as a function of glass basicity. The increase in the intensities of the absorption bands of these absorbing ions, except for Cr³⁺ ion, at the maximum wavelength, depends not only on the ion concentration but also on the increase of polarizability of oxide (−II) species, α _oxide(−II), surrounding the ions. This value affected directly the extinction coefficients of the ions, ɛ _ion. The increase of ɛ _ion caused the colour of glasses appearing in high intensity. In the case of Cr³⁺ ion, the results were reversed such that the lower the concentration, the higher the intensities of colour.     

Hydrogen gas-sensing with bilayer structures of WO3 and Pd in SAW and electric systems

A bi-layer sensor structure of WO₃ (~ 100 nm) with a very thin film of palladium (Pd~ 18 nm) on the top, has been studied for hydrogen gas-sensing application at ~ 80 °C and ~ 120 °C and low hydrogen concentrations (0.025-1%). The structures were obtained by vacuum deposition (first the WO₃ and then the Pd film) onto a LiNbO₃ Y-cut Z-propagating substrate making use of the Surface Acoustic Wave method and additionally (in this same technological processes) onto a glass substrate with a planar microelectrode array for simultaneous monitoring of planar resistance of the structure. A very good correlation has been observed between these two methods — frequency changes in SAW method correlate very well with decreases in the bi-layer structure resistance. The SAW method is faster at the lower interaction temperature such as 80 °C, whereas at an elevated temperature of 120 °C, the electrical planar method is also fast and has a lower limit of detection.     

Brownian motion and the drift of charged nanoparticles in laminar gas flow in a plane channel

Using two limiting cases (of adsorbing and reflecting channel walls), the influence of Brownian motion on the motion of nanoparticles in laminar gas flow under the action of an external electric field has been considered. Similarity criteria making it possible to classify experimental situations have been found. Numerical modeling of deposition from the flow has been carried out with the example of the motion of a monodisperse ensemble of spherical nanoparticles with a radius of 3 nm. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 82, No. 2, pp. 215–220, March–April, 2009.     

过冷对共析钢动态相变和组织演变的影响

将共析钢在600-700℃的过冷奥氏体状态下进行单轴热压缩,获得了亚微米级别等轴铁素体 纳米级别弥散分布球化渗碳体的复相组织,其组织演变经历动态相变、片层渗碳体球化、铁素体动态再结晶和纳米级别渗碳体颗粒析出等过程.随着形变温度的降低,过冷度增加,相变动力学过程加快.片层渗碳体的球化程度由球化时间和球化速度控制,形变温度升高使渗碳体球化速度加快,但是相变开始时间及动力学延迟使得用于渗碳体球化和熟化的时间相应缩短,导致球化程度降低.铁素体再结晶和等轴化过程则主要受位错迁移、渗碳体颗粒钉扎的影响,形变温度升高导致较高的等轴化发展速度.     

Enhancement of mechanical and tribological properties in AISI D3 steel substrates by using a non-isostructural CrN/AlN multilayer coating

Enhancement of mechanical and tribological properties on AISI D3 steel surfaces coated with CrN/AlN multilayer systems deposited in various bilayer periods (Λ) via magnetron sputtering has been studied in this work exhaustively. The coatings were characterized in terms of structural, chemical, morphological, mechanical and tribological properties by X-ray diffraction (XRD), electron dispersive spectrograph, atomic force microscopy, scanning and transmission electron microscopy, nanoindentation, pin-on-disc and scratch tests. The failure mode mechanisms were observed via optical microscopy. Results from X-ray diffraction analysis revealed that the crystal structure of CrN/AlN multilayer coatings has a NaCl-type lattice structure and hexagonal structure (wurtzite-type) for CrN and AlN, respectively, i.e., made was non-isostructural multilayers. An enhancement of both hardness and elastic modulus up to 28 GPa and 280 GPa, respectively, was observed as the bilayer periods (Λ) in the coatings were decreased. The sample with a bilayer period (Λ) of 60 nm and bilayer number n  =  50 showed the lowest friction coefficient (∼0.18) and the highest critical load (43 N), corresponding to 2.2 and 1.6 times better than those values for the coating deposited with n = 1, respectively. The best behavior was obtained when the bilayer period (Λ) is 60 nm (n = 50), giving the highest hardness 28 GPa and elastic modulus of 280 GPa, the lowest friction coefficient (∼0.18) and the highest critical load of 43 N. These results indicate an enhancement of mechanical, tribological and adhesion properties, comparing to the CrN/AlN multilayer systems with 1 bilayer at 28%, 21%, 40%, and 30%, respectively. This enhancement in hardness and toughness for multilayer coatings could be attributed to the different mechanisms for layer formation with nanometric thickness such as the Hall–Petch effect and the number of interfaces that act as obstacles for the crack deflection and dissipation of crack energy.