Numerical study on notched steel plate with center hole strengthened by CFRP

Steel members could be damaged and fail to fulfill the requirements of safety after long-term service. Carbon fiber reinforced polymer (CFRP) strengthening turns out to be an excellent method for prolonging its service life. The strengthening technique has been extensively studied in recent decades, however, few researchers concerned about the simulation of steel plates with center hole strengthened by CFRP. Therefore, its mechanical performance was investigated numerically in this study. The numerical results were compared with the experimental results and an acceptable agreement was reached, which verified the validity of the numerical model. A parametric study was conducted, in which the interfacial stress distribution change with CFRP elastic modulus, thickness and strengthening form was analyzed. For fully covered CFRP strengthening, increasing of elastic modulus and thickness of CFRP plates can enhance the stiffness of steel plates, however, it has insignificant effect on debonding load and obvious decrease on ultimate load. While the partially covered CFRP bonding strengthening can also upgrade the stiffness with CFRP elastic modulus and thickness, the effect to both of debonding load and ultimate load is minimal.     

Compressive behavior of post-heated circular CFST short columns externally strengthened with CFRP sheets

Due to the increasing usage of concrete-filled steel tube (CFST) members in structural engineering, there will be more chances of fire hazards on these structures in the near future. Externally bonding carbon fiber reinforced polymer (CFRP) composites has emerged as a popular method for repairing damaged steel-reinforced concrete members. However, limited research is available to evaluate the behavior of CFRP strengthened CFST members. This paper presents the results of an experimental investigation on the compressive behavior of the post-heated circular CFST short columns externally strengthened with CFRP sheets. A total of twenty-one specimens are tested to investigate the influence of temperature and the number of CFRP layers on the mechanical behavior of repaired specimens. The ultimate strength is obtained from monotone static tests. The extensometer technique based on gauge strain is used to measure strains of electric gauges glued to the external surface of specimens. The results indicate that the increase in the number of CFRP layers leads to a significant change in the mechanical properties of post-heated CFST columns. Furthermore, it is shown that increases in the number of CFRP layers remarkably enhance the ultimate strength and initial stiffness of specimens subjected to the same heat treatments, while deteriorate the ductility. Based on extensive experimental analysis, simplified formulae are proposed to estimate the compressive ultimate strength of all specimens tested, providing reasonably good correlation with the experimental results. Besides, the proposed formulae are compared with some existing empirical models, and validity of the proposed formulae is evaluated.     

Microstructures and mechanical properties of thin 304 stainless steel sheets by friction stir welding

Friction stir welding (FSW) was performed on 304 stainless steel sheets. The welding speed was varied from 30 to 70 mm/min. Because the FSW of thin plates is sensitive to heat input. The surface of the welds is smooth and without any macroscopic cracks and cavities only when the rotation speed is 50 mm/min. The stir zone had equiaxed grains with austentic structure due to dynamic recrystallization. There was not any evidence for the presence of sigma phases being found in this study. Meanwhile, there was a weak region in the advancing side because of the flow of plastic metals. However, compared with the base material, mechanical properties of the joint are maintained in a comparatively high level.     

碳纤维薄板与混凝土界面的粘结性能研究

采用试验与有限元分析相结合的方法,研究碳纤维薄板与混凝土界面的粘结力学性能及剥离破坏机理,结果表明,界面粘结强度比混凝土抗剪强度高,随着载荷的不断增加,界面剪应力的分布和峰值位置逐渐变化,最终导致混凝土在界面发生剥离破坏．     

Stainless steel coupled with carbon nanotube-modified epoxy and carbon fibre composites: Electrochemical and mechanical study

The aim of this work is the study of the electrochemical and mechanical behaviour of stainless steel (SS304) adhesively bonded with carbon nanotube (CNT)-reinforced epoxies to either SS304 or carbon-reinforced composites substrates. For metal to metal (MtM) joints, the shear strength of nano-reinforced adhesives was studied using single lap shear specimen geometries. The lap shear strength was improved by almost 50% and the highest shear strength appeared for 0.6% CNT weight content in the adhesive. The metal to composite joint performed altogether better compared to the MtM joint, although the CNT inclusion had an adverse effect on the lap shear strength attributed to the physical property change of the epoxy. Although the incorporation of CNTs was found to increase the galvanic effect, it also enhanced corrosion protection, as the modified adhesives exhibited increased resistance to uniform corrosion and localised corrosion and prevented the electrolyte from reaching the substrate.     

碳酸化预养护钢渣制备钢渣水泥的性能试验研究

应用碳酸化技术对比表面积287m2/kg的钢渣粗粉进行预养护,从而制备大掺量钢渣水泥,并对其性能进行了试验研究。试验结果表明,碳酸化钢渣的fCaO含量降低,水化活性提高。碳酸化预养护钢渣较未碳酸化的钢渣制备的钢渣水泥强度及安定性有显著提高;钢渣水泥的密度、比表面积、标准稠度用水量和凝结时间等基本物理量与碳酸化钢渣粗粉的掺入量有关;在满足水泥强度和压蒸安定性的条件下,碳酸化钢渣粗粉的掺量可达50%。     

NAFC、LCFC板及其与轻钢龙骨自攻螺栓连接性能

进行了 NAFC、L CFC板及其与轻钢龙骨自攻螺栓连接性能试验研究 ,得到了 NAFC、L CFC板的力学特性及其采用自攻螺栓与轻钢龙骨连接的承载力及荷载 -位移特征 ,结果表明 NAFC、L CFC板具有轻钢龙骨复合承载体系所需的结构性能 ,均可作为轻钢龙骨体系合适的结构板材 ;两种板材均有明显的方向性 ,纵向纤维受力结构性能明显好于横向纤维受力 ;板材与龙骨间自攻螺栓连接的性能与板的性能有明显对应关系 ,承载力主要由自攻螺栓孔边板的承压强度控制。     

An experimental study on the retrofitting effects of reinforced concrete columns damaged by rebar corrosion strengthened with carbon fiber sheets

This paper presents the results of an experiment study on the structural behavior of reinforced concrete (RC) columns damaged by rebar corrosion and the retrofitting effects of damaged RC columns strengthened with carbon fiber sheets (CFS). In the experiment, a cyclic horizontal loading test was carried out using RC columns damaged by different degrees of rebar corrosion and strengthened with CFS. As a result, it was revealed that the deterioration of their structural behavior was mainly caused by the decline in the confining effect due to the falling off of concrete cover and the reduction of mechanical properties of corrosion rebar. In addition, the test proved that shear strengthening using CFS is an very effective retrofit technique that prevents bond splitting cracks and shear cracks from growing and improves the ductility of RC columns with corroded rebars due to the confining effect of CFS.     

Experimental and theoretical study on amino acid derivatives as eco-friendly corrosion inhibitor on mild steel in hydrochloric acid solution

Amino acid derivatives, namely, 2-(2-oxo-2-phenothiazin-10-yl)ethylamino)-3-mercaptopropanoic acid (OPEM) and 2-(2-oxo-2-phenothiazin-10-yl)ethylamino)acetic acid (OPEA) were synthesized and investigated as inhibitors for mild steel corrosion in 15% HCl solution using the weight loss, polarization, and electrochemical impedance spectroscopy (EIS) techniques. The inhibition efficiency of both the inhibitors increased with increasing the temperature and concentration of inhibitor. The inhibitors OPEM and OPEA show corrosion inhibition efficiency of 97.5 and 95.8%, respectively, in 200?ppm concentration, at 333?K. Polarization studies showed that both studied inhibitors were of mixed type in nature. The adsorption of inhibitors on the mild steel surface obeys Langmuir adsorption isotherm and the surface of inhibited and uninhibited specimens were analyzed by scanning electron microscopy (SEM). The semiempirical AM1 method was employed for theoretical calculations and the obtained results were found to be consistent with the experimental findings.     

自转清洗包塑钢丝螺旋的动力学特性试验研究

本文围绕自转清洗包塑钢丝螺旋的动力学特性进行实验研究。钢丝螺旋的自转动力矩特性,与管内流速的关系呈现为随流速增大而增大的抛物线曲线;开始自转需要的管内流速与钢丝螺旋自身的螺旋角大小关系,则是先随着螺旋角增大而减少、后来随着螺旋角增大而增大,并且以44°螺旋角为最低;管内沿程阻力与钢丝螺旋螺距大小的关系,则是随着螺距增大而显著减少。     

利用钢渣微细粉制备高强度混凝土的试验研究

利用粉磨至不同比表面积的转炉钢渣微细粉取代部分水泥进行了C60混凝土的早期和后期强度及坍落度试验，考察了钢渣微细粉的比表面积及掺入量、水胶比和减水剂掺入量对混凝土性能的影响，并用PoreMaster——60孔测定仪测定了硬化混凝土的孔分布。试验结果表明，钢渣微细粉的比表面积为487m^2／kg、掺入量为15％-20％时，可获得令人满意的混凝土3d和28d抗压强度；随着水胶比的增大，混凝土3d和28d抗压强度显著降低，坍落度急剧增大；减水剂掺入量对混凝土坍落度影响明显，但对混凝土强度影响不大。     

Polybithiophene and its bilayers with polyaniline coatings on stainless steel by electropolymerization in aqueous medium

For the first time, electrosynthesis of polybithiophene (PBTh) and its bilayers with polyaniline (PAni) coatings on stainless steel (SS) in aqueous oxalic acid solutions containing monomer and sodium dodecyl sulfate (SDS) was carried out by potentiodynamic synthesis technique. Smooth and adherent films were obtained on the steel surfaces. Homopolymers and bilayers were characterized by cyclic voltammetry, FTIR, UV–vis spectroscopies and SEM. Homopolymers were also characterized by means of conductivity and the number average molecular weight measurements. The effects of the scanning potential limits on electrosynthesis of PBTh and its bilayer coatings were investigated. The test for corrosion protection of the polymer coated and uncoated SS substrates were performed in highly aggressive 0.5 M NaCl and 0.5 M HCl solutions by linear potentiodynamic polarization and Tafel test technique, respectively. Corrosion test revealed that among the protective coatings obtained, PBTh as homopolymer and PAni/PBTh as bilayer exhibited the most effective anticorrosive properties. According to linear potendynamic polarization test, the dissolution current of these coatings at 1.6 V decreased to 99.8% and 99.6% in NaCl solution, respectively, when compared to that of uncoated SS surfaces.     

430不锈钢表面微纳多孔结构阳极氧化膜的制备及疏水性研究

利用扫描电镜(SEM)研究了阳极氧化工艺对SUS430不锈钢在由氟化铵、水及乙二醇(Eg)组成的电解液中制备微纳多孔结构氧化膜的影响,通过能谱仪(EDS)对阳极氧化膜微孔内部和未成孔位置的组成进行了分析,测试了阳极氧化前后不锈钢表面的水接触角。适当降低电解液含水量有利于提高不锈钢表面的微孔密度,可形成微纳多孔结构的氟化铵浓度以0.15 mol/L最好,氧化电压过大以及氧化时间过长都会导致阳极氧化膜发生过度腐蚀。在氟化铵含量为0.15 mol/L、含水量小于0.4 mol/L的电解液中,保持电解液温度为20°C,采用氧化电压50~60 V阳极氧化15~30 min,不锈钢表面可制备出孔径为3~5μm的多孔结构,微米级孔洞内部形成有序的蜂窝状纳米多孔结构(孔径约为100 nm)。阳极氧化后不锈钢表面形成了氧化物和氟化物,与水的接触角为138.2°,具有较好的疏水性。     

高压脉冲介质阻挡放电协同臭氧溶气降解聚丙烯酰胺模拟废水

利用高压脉冲介质阻挡放电与臭氧联用的上流式反应器,考察了高压脉冲介质阻挡放电、臭氧和二者协同处理聚丙烯酰胺的降解情况以及COD和BOD5/COD的变化趋势;另外研究了反应器内加入TiO2催化剂对处理效果的影响,并探讨了其作用机理。结果表明,停留时间为10min时,放电协同臭氧溶气对聚丙烯酰胺的降解率可达51%,比单独放电和单独臭氧分别提高了27%和4%。加入TiO2催化剂后,COD去除率达到65%,BOD5/COD提高到0.37。     

Experimental study on the auto-ignition and combustion characteristics in the homogeneous charge compression ignition (HCCI) combustion operation with ethanol/n-heptane blend fuels by port injection

This article investigates the auto-ignition, combustion, and emission characteristics of homogeneous charge compression ignition (HCCI) combustion engines fuelled with n-heptane and ethanol/n-heptane blend fuels. The experiments were conducted on a single-cylinder HCCI engine using neat n-heptane, and 10%, 20%, 30%, 40%, and 50% ethanol/n-heptane blend fuels (by volume) at a fixed engine speed of 1800 r/min. The results show that, with the introduction of ethanol in n-heptane, the maximum indicated mean effective pressure (IMEP) can be expanded from 3.38 bar of neat n-heptane to 5.1 bar, the indicated thermal efficiency can also be increased up to 50% at large engine loads, but the thermal efficiency deteriorated at light engine load. Due to the much higher octane number of ethanol, the cool-flame reaction delays, the initial temperature corresponding the cool-flame reaction increases, and the peak value of the low-temperature heat release decreases with the increase of ethanol addition in the blend fuels. Furthermore, the low-temperature heat release is indiscernible when the ethanol volume increases up to 50%. In the case of the neat n-heptane and 10% ethanol/n-heptane blends, the combustion duration is very short due to the early ignition timing. For 20–50% ethanol/n-heptane blend fuels, the ignition timing is gradually delayed to the top dead center (TDC) by the ethanol addition. As a result, the combustion duration prolongs obviously at the same engine load when compared to the neat n-heptane fuel. At overall stable operation ranges, the HC emissions for n-heptane and 10–30% ethanol/n-heptane blends are very low, while HC emissions increase substantially for 40% and 50% ethanol/n-heptane blends. CO emissions show another tendency compared to HC emissions. At the engine load of 1.5–2.5 bar, CO emissions are very high for all fuels. Beside this range, CO emissions decrease both for large load and light load. In terms of operation stability of HCCI combustion, for a constant energy input, n-heptane shows an excellent repeatability and light cycle-to-cycle variation, while the cycle-to-cycle variation of the maximum combustion pressure and its corresponding crank angle, and ignition timing deteriorated with the increase of ethanol addition.