Hot-dip galvanized steel: surface structures and adhesion of paints

The surface structures of as-received, pretreated and painted hot-dip galvanized steel are studied. The hardness of six different paint systems and their adhesion to selected types of zinc coating are investigated before and after accelerated ageing. Both hardness and adhesion depend on the pretreatment and the chosen combination of zinc coating and paint system.     

LASER SURFACE TREATMENTS FOR PROMOTING CORROSION RESISTANCE OF A CARBON STEEL

The effect of laser treatment and laser alloying on corrosion resistance of 1045 steel has been studied. Various ways of surface alloying have been investigated by using continuous CO₂ laser beam: i) irradiation of chromium painted surfaces; ii) irradiation of Ni and Cr-electroplated surfaces; iii) direct injection of Ni and Cr powders into the melt pool. A high and uniform level of alloying in the surface layer can be achieved in the cases of electroplated surfaces and direct powder injection. It requires, however, an appropriate choice of irradiation conditions (such as beam power, beam traverse speed, beam defocusing and degree of overlapping) that provide remelted layer of a limited and fairly uniform thickness. It has been found that in order to achieve corrosion behavior of laser treated surfaces similar to that of austenite type 304 stainless steel chromium and nickel contents in the alloyed layer are to be higher than those of 304 steel.     

有机硅改性丙烯酸树脂夜光涂料

用有机硅改性丙烯酸树脂作为主要成膜物质,将稀土硫化锌夜光颜料和铝酸锶铕夜光颜料分散于有机硅改性丙烯酸树脂中制成夜光涂料。结果表明,所得有机硅改性丙烯酸树脂稀土硫化锌夜光涂料和有机硅改性丙烯酸树脂铝酸锶铕夜光涂料的涂抹性能好,耐水性、耐碱性、耐候性和耐沾污性强,夜光性能好,余辉亮度强且余辉时间长,为优质的夜光涂料。     

Modeling and Prediction of Thermal Cycle Induced Failure in Epoxy-Silica Composites

Epoxy resins filled with dielectric mineral particles are frequently used as insulating materials in power industry applications. Due to their excellent dielectric properties and relatively good thermal performance (resistance, ageing and conductivity) their usability is common and extensive. However, the mechanical performance of the resins is influenced by several factors such as resistance to crack propagation, especially in low temperature applications. This phenomenon is normally linked with appearance of two phase systems where particle filled epoxy material interacts with metallic inserts having significantly different thermal expansion coefficients. This kind of epoxy-metal interface can produce relatively high stresses in the product structure during thermal cycle loading. The paper deals with mechanical problems of power industry products and introduces the methodology for numerical modeling of failure in silica filled epoxy systems subjected to severe temperature gradients. Various aspects of material behavior modeling are covered in this article, including polymerization process, viscoelastic stress relaxation as well as stochastic cracking.     

Three Phase Composite Cylinder Assemblage Model for Analyzing the Elastic Behavior of MWCNT-Reinforced Polymers

Evolution of computational modeling and simulation has given more emphasis on the research activities related to carbon nanotube (CNT) reinforced polymer composites recently. This paper presents the composite cylinder assemblage (CCA) approach based on continuum mechanics for investigating the elastic properties of a polymer resin reinforced by multi-walled carbon nanotubes (MWCNTs). A three-phase cylindrical representative volume element (RVE) model is employed based on CCA technique to elucidate the effects of inter layers, chirality, interspacing, volume fraction of MWCNT, interphase properties and temperature conditions on the elastic modulus of the composite. The interface region between CNT and polymer matrix is modeled as the third phase with varying material properties. The constitutive relations for each material system have been derived based on solid mechanics and proper interfacial traction continuity conditions are imposed. The predicted results from the CCA approach are in well agreement with RVE-based finite element model. The outcomes reveal that temperature softening effect becomes more pronounced at higher volume fractions of CNTs.     

Element Analysis of Ceramic Coatings under Spherical Indentation with Metallic Interlayer:Part Ⅱ Ring Crack

Spherical indentation of ceramic coatings with metallic interlayer was performed by means of axisymmetric finite element analysis(FEA). Two typical ceramic coatings with relatively high and low elastic modulus deposited on aluminum alloy and carbon steel were considered. The fracture mechanics of the ceramic coatings mechanisms due to occurrence of surface ring cracks extending traverse the coating thickness under spherical indentation are investigated within the framework of linear fracture mechanics. The J-integral associated to such cracks was computed. The evolution of J-integral vs the crack length and the indentation depth was studied. The effects of the interlayer, the coating and the substrate on the J-integral evolution were discussed. The results show that a suitable metallic interlayer can improve the fracture resistance of the coating systems under the same indentation conditions through reducing the J-integral.     

Boundary element analysis of thermal stress intensity factors for interface griffith and cusp cracks

The thermal stress intensity factors for interface cracks of Griffith and symmetric lip cusp types under vertical uniform heat flow in a finite body are calculated by the boundary element method. The boundary conditions on the crack surfaces are insulated or fixed to constant temperature. The relationship between the stress intensity factors and the displacements on the nodal point of a crack-tip element is derived. The numerical values of the thermal stress intensity factors for an interface Griffith crack in an infinite body are compared with the previous solutions. The thermal stress intensity factors for a symmetric lip cusp interface crack in a finite body are calculated with respect to various effective crack lengths, configuration parameters, material property ratios and the thermal boundary conditions on the crack surfaces. Under the same outer boundary conditions, there are no appreciable differences in the distribution of thermal stress intensity factors with respect to each material property. However, the effect of crack surface thermal boundary conditions on the thermal stress intensity factors is considerable.     

Element Analysis of Ceramic Coatings under Spherical Indentation with Metallic Interlayer：Part Ⅱ Ring Crack

Spherical indentation of ceramic coatings with metallic interlayer was performed by means of axisymmetric finite element analysis （FEA）. Two typical ceramic coatings with relatively high and low elastic modulus deposited on aluminum alloy and carbon steel were considered. The fracture mechanics of the ceramic coatings mechanisms due to occurrence of surface ring cracks extending traverse the coating thickness under spherical indentation are investigated within the framework of linear fracture mechanics. The J-integral associated to such cracks was computed. The evolution of J-integral vs the crack length and the indentation depth was studied. The effects of the interlayer, the coating and the substrate on the J-integral evolution were discussed. The results show that a suitable metallic interlayer can improve the fracture resistance of the coating systems under the same indentation conditions through reducing the J-integral.     

A 3D fibre beam-column element with shear modelling for the inelastic analysis of steel structures

A force-based fiber beam-column element is proposed for the capacity assessment of frame structures under high shear. The proposed element is suitable for the performance assessment of large scale steel structures, which are not flexure-dominated. The element formulation follows the assumptions of the Timoshenko beam theory, while its kinematics are obtained through the natural-mode method. The element state-determination phase, instead of uniaxial material laws, typically associated with fiber elements, is based on a three-dimensional law taking into consideration the interaction between axial, bending, shear and torsion. Numerical examples are presented confirming the accuracy and the computational efficiency of the proposed formulation under monotonic, cyclic and dynamic/seismic loading. Compared to experimental results and the results of detailed finite element models, excellent agreement is achieved.     

纳米SiO2/环氧复合钢板涂层材料机械及耐腐蚀性能

研究了纳米SiO₂添加量对环氧复合钢板涂层硬度、 T弯和应变等机械性能的影响, 并通过盐雾试验和电化学交流阻抗技术对涂层的耐腐蚀性能进行了测试。研究表明, 纳米SiO₂添加量为2.0%时, 涂层性能有较大的提高, 铅笔硬度从H提高到2H, T弯从4T改善到2T, 涂层的耐盐雾时间也由720h增加到1030h, 提高了40％以上。从电化学交流阻抗谱图得出, 添加量为2.0%的纳米SiO₂复合涂层的阻抗值最大, 高于未添加纳米SiO₂涂层的阻抗值近2个数量级。另外, 涂层的SEM照片显示, 纳米SiO₂添加量为2.0%时, 颗粒较均匀地分散, 黏接紧密, 形成较为致密的复合涂层。      

Funktionale Oberflächen auf Duplex‐Stahl durch Laserfeinbeschichten

Functional surfaces on duplex stainless steel by lasercladding The product‐lubricated axial and radial bearings installed in multistage high‐pressure pumps inevitably encounter severe mixed friction conditions as the pumps start and stop. This leads to extremely high tribological loads on the bearing components, compounded by the effects of a highly corrosive pumped fluid. The present paper describes a laser cladding process which produces near‐net‐shape coatings of new, highly corrosion and wear resistant functional layers which can be deposited directly on high‐alloy stainless steels without requiring additional buffer layers and without affecting the mechanical properties and corrosion resistance of the substrate. The results cover the solidification behaviour of the coatings as well as the microstructure resulting from various heat treatment conditions. In addition, the technological properties of the coatings and the resulting composites are discussed. The coating systems are tested as to their corrosion resistance and tribological characterization in a pump‐specific tribological system.     

不锈钢复合钢材钢结构研究进展

不锈钢复合钢材兼具不锈钢优良的耐腐蚀性能和传统结构钢材的高强度、低成本特点,应用于钢结构工程中具有综合力学性能更优、施工简单周期更短、设计使用年限更长、全生命周期成本更低、综合社会效益更高等显著优势,尤其适用于对耐腐蚀性要求较高的工程结构。目前不锈钢复合钢材已在高层建筑幕墙和铁路钢桥面板中得到了成功应用,为了继续推广其在结构工程领域中的应用发展,亟需加强从相关基础力学性能和关键应用技术角度进行的研究与讨论。详细介绍了不锈钢复合钢材的生产制造和工程应用等产业基础,并对国内外学者针对不锈钢复合钢材在材料和构件层面力学性能开展的研究进展进行了全面综述,包括材料的拉伸性能、冷弯性能、高温性能、断裂与疲劳性能、滞回性能、动态力学性能、耐腐蚀性能、界面性能等基本力学性能和构件的稳定性能、残余应力、焊接接头性能、缺陷修复以及有限元模型的相关研究。该文可为进一步在结构工程领域开展不锈钢复合钢材的相关研究、设计与应用实践提供参考。     

Experimental research on bolted joint strength and dispersion in steel lattice transmission tower legs under low temperatures (−20°C to −45°C)

Cold regions with subzero temperatures (?20°C to ?45°C) have important impacts on the mechanical properties of structural steel used in lattice steel towers of overhead transmission line systems. The results from regular material tests are not appropriate for the accurate analysis of joint strength in cold weather conditions. This paper presents the tensile test results of 18 coupons of steel material and eight groups (18 specimens per group) of bolted joints with Q345 and Q420 steel under temperatures of 20°C, ?20°C, and ?45°C. The results show that the yield‐to‐ultimate strength ratio of the joints under low temperature conditions is beyond the range of 0.60 to 0.75 for Q420 structural steel. Suggestions are made on how to improve the accuracy of joint design for both the partial resistance factor and the design value of joint yield strength in cold regions.     

不同钢种离子渗硫层的抗擦伤性能研究

为改善高速钢，模具钢和45钢的抗擦伤性能，采用低温离子渗硫技术在这三种材料表面生成了FeS固体润滑渗硫层，在QP-100球盘式摩擦磨损试验机上对比研究了这三种材料渗硫层在油润滑条件下的抗擦伤及摩擦学性能。利用SEM与XRD观察分析了渗硫层截面，擦伤面形貌及表面相结构，利用AES及XPS分析了擦伤表面元素沿深度的分布及边界润滑膜化合物的价态，研究表明，渗硫后三种材料的抗擦伤及摩擦学性能都有明显改善，其中渗硫高速钢的抗擦伤性最好。其后依次为渗硫模具钢，渗硫45钢，分析认为，不同钢种渗硫层抗擦伤性能的差异主要由基体硬度，组织结构及耐蚀性三方面决定。     

二维机织复合材料弹性常数的有限元法预测

为了预测二维机织复合材料的弹性性能,建立了有限元力学分析模型。基于二维机织复合材料的几何特征,建立了参数化的单胞模型;考虑了织物纤维束呈现出的各向异性材料特征,将有限元中材料主方向转化到纤维屈曲方向,建立其力学分析有限元模型;分析了单胞边界面保持平面假设的不足,提出了对于二维机织复合材料通用的周期边界条件,获得了更为准确的二维机织复合材料的工程弹性常数。结果表明:织物衬垫单胞边界面,在单向拉伸载荷和纯剪切载荷下,呈凹凸翘曲变形,即为周期边界;应用给出的织物参数化几何建模方法与有限元求解方法,可以精确地获得工程弹性常数,数值计算结果与实验值吻合较好。      

基于ANSYS的模铸高碳钢凝固过程温度场数值模拟

为改善钢锭头部保温性能,利用有限元分析软件ANSYS对模铸高碳钢凝固过程的温度场进行了数值模拟。重点讨论了绝热板不同热导率值与不同宽面厚度值及发热板不同生热率值对钢锭头部保温性能的影响。结果表明,通过增加发热板生热率不能明显改善钢锭头部温度场;绝热板热导率数值符合保温材料性能指标,将其宽面厚度调整为35~40mm能满足钢锭头部保温要求。     

Carbon dioxide corrosion of carbon steel and corrosion inhibition by natural olive leaf extract

The corrosion of carbon steel in carbon dioxide saturated chloride carbonate solution with and without olive leaf extract at 25 °C and 65 °C has been studied by linear polarization resistance technique, electrochemical impedance spectroscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. In the absence of olive leaf extract, the corrosion products created under the testing conditions within 24 h at both testing temperatures have no significant protective properties. Measurements for uninhibited systems showed high corrosion current densities and low polarization resistances of carbon steel. Both linear polarization resistance technique and electrochemical impedance spectroscopy measurements reveal that olive leaf extract inhibits the carbon steel corrosion. The addition of a low‐concentration olive leaf extract decreases corrosion current densities, increases charge transfer and polarization resistance, resulting in more uniform and smoother steel surfaces. These effects are attributed to the adsorption of olive leaf extract on the carbon steel surface.     

Silver-nanoparticle-embedded antimicrobial paints based on vegetable oil

Developing bactericidal coatings using simple green chemical methods could be a promising route to potential environmentally friendly applications. Here, we describe an environmentally friendly chemistry approach to synthesize metal-nanoparticle (MNP)-embedded paint, in a single step, from common household paint. The naturally occurring oxidative drying process in oils, involving free-radical exchange, was used as the fundamental mechanism for reducing metal salts and dispersing MNPs in the oil media, without the use of any external reducing or stabilizing agents. These well-dispersed MNP-in-oil dispersions can be used directly, akin to commercially available paints, on nearly all kinds of surface such as wood, glass, steel and different polymers. The surfaces coated with silver-nanoparticle paint showed excellent antimicrobial properties by killing both Gram-positive human pathogens (Staphylococcus aureus) and Gram-negative bacteria (Escherichia coli). The process we have developed here is quite general and can be applied in the synthesis of a variety of MNP-in-oil systems.     

Numerical Solutions for Heat Transfer of An Unsteady Cavity with Viscous Heating

The mechanism of viscous heating of a Newtonian fluid filled inside a cavity under the effect of an external applied force on the top lid is evaluated numerically in this exploration. The investigation is carried out by assuming a two-dimensional laminar in-compressible fluid flow subject to Neumann boundary conditions throughout the numerical iterations in a transient analysis. All the walls of the square cavity are perfectly insulated and the top moving lid produces a constant finite heat flux even though the fluid flow attains the steady-state condition. The objective is to examine the effects of viscous heating in the fully insulated lid-driven cavity under no-slip and free-slip Neumann boundary conditions coupled with variations in Reynolds and Prandtl numbers. The partial differential equations of time-dependent vorticity-stream function and thermal energy are discretized and solved using a self-developed finite difference code in MATLAB^® environment. Time dependence of fluid thermodynamics is envisaged through contour and image plots. A commercial simulation software, Ansys Fluent^® utilizing a finite element code is employed to verify the finite difference results produced. Although the effect of viscous heating is very minimal, Neumann no-slip and free-slip boundary conditions are able to trap the heat inside the fully insulated cavity as the heat flux is constantly supplied at the top lid. A lower Reynolds number and a greater Prandtl number with free-slip effects reduce temperature distribution in the cavity with a faster velocity than in the no-slip condition as the free-slip behaves as a lubricant.