Arc welding induced residual stress in butt-joints of thin plates under constraints

The purpose of this work is to assess the effect of welding fixtures on distributions and values of residual stresses during Gas Tungsten Arc Welding (GTAW). The butt-joint GTAW of AA5251 plate is investigated using a transient thermo-mechanical analysis performed by the finite element program, ABAQUS. The model considers two different welding conditions including unconstrained and perfectly constrained conditions while macro examination and residual stress measurements by implementing hole drilling techniques are utilized to evaluate the predictions. The results show that the utilizing of a welding fixture alters the temperature field within the plate being welded and the depth of the weld pool decreases by about 21% in this case. In addition, the application of a welding fixture effectively changes both distributions and maximum values of transverse and longitudinal residual stresses.     

A comparative study on the effect of GTAW processes on the microstructure and mechanical properties of P91 steel weld joints

Modified 9Cr-1Mo (P91) steel is widely used in the construction of power plant components. In the present study, a comparative study on influence of activated flux tungsten inert gas (A-TIG), and gas tungsten arc (GTA) welding processes on the microstructure and the impact toughness of P91 steel welds was carried out. P91 steel welds require a minimum of 47 J during the hydrotesting of vessels as per the EN1557: 1997 specification. Toughness of P91 steel welds was found to be low in the as-weld condition. Hence post-weld heat treatment (PWHT) was carried out on weld with the objective of improving the toughness of weldments. Initially as per industrial practice, PWHT at 760 °C – 2 h was carried out in order to improve the toughness of welds. It has been found that after PWHT at 760 °C – 2 h, GTA weld (132 J) has higher toughness than the required toughness (47 J) as compared with A-TIG weld (20 J). The GTA weld has higher toughness due to enhanced tempering effects due to multipass welding, few microinclusion content and absence of δ-ferrite. The A-TIG weld requires prolonged PWHT (i.e. more than 2 h at 760 °C) than GTA weld to meet the required toughness of 47 J. This is due to harder martensite, few welding passes that introduces less tempering effects, presence of δ-ferrite (0.5%), and more alloy content. After PWHT at 760 °C – 3 h, the toughness of A-TIG weld was improved and higher than the required toughness of 47 J.     

Combined effects of adsorption and photocatalysis by hybrid TiO2/ZnO-calcium alginate beads for the removal of copper

The use of nanosized titanium dioxide(TiO_2) and zinc oxide(ZnO) in the suspension form during treatment makes the recovering and recycling of photocatalysts difficult.Hence,supported photocatalysts are preferred for practical water treatment applications.This study was conducted to investigate the efficiency of calcium alginate(CaAlg) beads that were immobilized with hybrid photocatalysts,TiO_2/ZnO to form TiO_2/ZnO-CaAlg.These immobilized beads,with three different mass ratios of TiO_2:ZnO(1:1,1:2,and 2:1) were used to remove Cu(Ⅱ) in aqueous solutions in the presence of ultraviolet light.These beads were subjected to three cycles of photocatalytic treatment with different initial Cu(Ⅱ) concentrations(10-80 ppm).EDX spectra have confirmed the inclusion of Ti and Zn on the surface of the CaAlg beads.Meanwhile,the surface morphology of the beads as determined using SEM,has indicated differences of before and after the photocatalytic treatment of Cu(Ⅱ).Among all three,the equivalent mass ratio TiO_2/ZnO-CaAlg beads have shown the best performance in removing Cu(Ⅱ) during all three recycling experiments.Those TiO_2/ZnO-CaAlg beads have also shown consistent removal of Cu,ranging from 7.14-52.0 ppm(first cycle) for initial concentrations of10-80 ppm.In comparison,bare CaAlg was only able to remove 6.9-48 ppm of similar initial Cu concentrations.Thus,the potential use of TiO_2/ZnO-CaAlg beads as environmentally friendly composite material can be further extended for heavy metal removal from contaminated water.     

两种纳米颗粒对沸石吸附环丙沙星的影响

为了探明纳米颗粒（NPs）共存对抗生素在黏土矿物上的吸附的影响,以沸石为供试黏土矿物,环丙沙星（CIP）为目标污染物,研究了不同温度、 pH值和离子强度条件下,纳米氧化锌（ZnO NPs）和纳米二氧化钛（TiO₂ NPs）这2种NPs对沸石吸附CIP的影响,并结合沸石的表面特征探讨不同类型NPs对CIP吸附的影响机制.结果表明,除5 mg·L^-1ZnO NPs共存时,轻微促进了CIP的吸附,其他NPs浓度均对CIP产生不同程度的抑制,抑制程度表现出TiO₂ NPs>ZnO NPs的顺序;随温度升高,NPs的存在增强了沸石对CIP吸附的增温正效应;当离子强度由0.001mol·L^-1增加到0.01mol·L^-1时,CIP的吸附量下降,但2种NPs的存在均减弱了离子强度的负效应;溶液pH会影响CIP的存在形态和NPs的性质,进而影响CIP的吸附.沸石对单一CIP的吸附存在静电引力、氢键和孔径填充作用,ZnO NPs主要通过静电引力竞争吸附位点对CIP吸附产生影响,而TiO     

Minimization of methabenzthiazuron residues in leaching water using amended soils and photocatalytic treatment with TiO2 and ZnO

In the present work, potential groundwater pollution by methabenzthiazuron （MTBU） and the effect of three different amendments （composted sheep manure, composted pine bark and spent coffee grounds） on its mobility were investigated under laboratory conditions. The efficiency of ZnO and TiO2 suspensions in the photocatalytic degradation of MTBU in leaching water was also investigated. The relative and cumulative breakthrough curves were obtained from disturbed soil columns. The presence and/or addition of organic matter drastically reduced the movement of the herbicide. On other hand, photocatalytic experiments showed that the addition of ZnO and TiO2 strongly enhances the degradation rate of this herbicide compared with the results of photolytic experiments under artificial light. ZnO appeared to be more effective in MTBU oxidation than TiO2. The results obtained point to the interest of using organic wastes and heterogeneous photocatalysis for reducing the pollution of groundwater by pesticide drainage.     

Metal-cored arc welding process for joining of modified 9Cr-1Mo (P91) steel

In the present work, metal-cored arc welding process was used for joining of modified 9Cr-1Mo (P91) steel. Metal-cored arc welding process is characterized by high productivity, slag-free process, defect-free weldments that can be produced with ease, and good weldability. Toughness is essential in welds of P91 steel during hydro-testing of vessels. There is a minimum required toughness of 47 J for welds that has to be met as per the EN1557:1997 specification. In the present study, welds were completed using two kinds of shielding gases, each composition being 80% Argon + 20% CO₂, and pure argon respectively. Microstructural characterization and toughness evaluation of welds were done in the as – weld, PWHT at 760 °C – 2 h and PWHT at 760 °C – 5 h conditions. The pure argon shielded welds (‘A2’ and ‘B2’) have higher toughness than 80% argon + 20% CO₂ shielded welds (‘A1’ and ‘B1’). Pure argon shielded welds show less microinclusion content with low volume fraction of δ-ferrite (<2%) phase. Themo-calc windows (TCW) was used for the prediction of equilibrium critical transformation points for the composition of the welds studied. With increase in post-weld heat treatment (PWHT) duration from 2 h to 5 h, there was increase in toughness of welds above 47 J. Using metal-cored arc welding process, it was possible to achieve the required toughness of more than 47 J after PWHT at 760 °C – 2 h in P91 steel welds.     

Experimental investigation on mechanical and metallurgical properties of super duplex stainless steel joints using friction welding process

Friction welding is one of the most economical and highly practicable methods in joining similar and dissimilar metals. In this study, high-quality welds are produced in the super duplex stainless steel by continuous drive friction welding successfully. Design of experiment was done using central composite design of response surface methodology. In the present work, the microstructure and mechanical properties of friction welded super duplex stainless steel (UNS S32760) were examined. The base material has a microstructure consisting of the ferrite matrix with austenite islands. Ferrite content was analyzed through the phase analyzer software and found that it is in the range of 42–55% in all weld metals. The phases were further analyzed through X-ray diffraction method. All the weld metals have higher hardness than the base metals. Weld transverse tensile failures consistently occurred away from the weld zone and exhibit more hardness, yield and ultimate tensile strengths than the base material. The austenite content increases with nitrogen concentration. Nitrogen could enhance the yield stress and ultimately tensile strength of super duplex stainless steel. Secondary phase precipitation is not observed in the welded joint probably due to the shorter heating times.     

光催化氧化法处理染料中间体H酸水溶液

为了去除水中难氧化的有害染料中间体Ｈ酸,研究以ＴＩＯ２、ＺｎＯ、ＣｄＳ和Ｆｅ２Ｏ３为催化剂,采用低压汞灯为光源,对Ｈ酸水溶液进行光催化氧化实验．结果表明：ＴｉＯ２和ＣｄＳ的催化效果最好．采用ＴｉＯ２作催化剂,光催化氧化５ｈ后,Ｈ酸分解率可达９０％,反应速率遵从Ｌａｎｇｍｕｉｒ－Ｈｉｎｓｈｅｌｗｏｏｄ方程,Ｋ＝１２．３Ｌ／ｍｍｏｌ,ｋ＝２５．２×１０－６ｍｏｌ／ｈ．溶液中投加１０ｍｇ／Ｌ的Ｆｅ３＋或Ａｇ＋,可使反应时间缩短２—３ｈ．研究探讨了ｐＨ、ＴｉＯ２投加量和Ｈ酸浓度对催化氧化过程的影响．     

Determination of the mechanism of photoinduced toxicity of selected metal oxide nanoparticles (ZnO, CuO, Co3O4 and TiO2) to E. coli bacteria

Cytotoxicity of selected metal oxide nanoparticles(MNPs)(ZnO,CuO,Co 3 O 4 and TiO 2)was investigated in Escherichia coli both under light and dark conditions.Cytotoxicity experiments were conducted with spread plate counting and the LC 50 values were calculated.We determined the mechanism of toxicity via measurements of oxidative stress,reduced glutathione,lipid peroxidation,and metal ions.The overall ranking of the LC 50 values was in the order of ZnO < CuO < Co 3 O 4 < TiO 2 under dark condition and ZnO < CuO < TiO 2 < Co 3 O 4 under light condition.ZnO MNPs were the most toxic among the tested nanoparticles.Our results indicate depletion of reduced glutathione level and elevation of malondialdehyde level correlated with the increase in oxidative stress.Released metal ions were found to have partial effect on the toxicity of MNPs to E.coli.In summary,the dynamic interactions of multiple mechanisms lead to the toxicity of the tested MNPs to E.coli.     

Metallurgical and mechanical characterization of electron beam welded super-duplex stainless steel UNS 32750

This paper addresses the weldability of 6 mm thick plates of super-duplex stainless steel by electron beam welding (EBW) process. Microstructure investigations conducted using optical and SE microscopy showed the presence of large ferrite grains with intra- and inter-granular austenite. Ferrite content studies on the weld zone estimated that there is no significant element partitioning between austenite and ferrite phases. Hardness studies portrayed that the weld hardness is found to be greater than the parent metal which is acquainted due to the solid solution strengthening effect. Tensile results corroborated that the joints obtained by EB welding process have better strength than the base metal. A detailed structure–property relationships has also been carried out through point and line mapping EDAX analysis across the weldment to substantiate the discussions.     

Comparative cytotoxicity of nanoparticles and ions to Escherichia coli in binary mixtures

The objective of this study was to understand toxicity of mixture of nanoparticles (NPs) (ZnO and TiO₂) and their ions to Escherichia coli. Results indicated the decrease in percentage growth of E. coli with the increase in concentration of NPs both in single and mixture setups. Even a small concentration of 1 mg/L was observed to be significantly toxic to E. coli in binary mixture setup (exposure concentration: 1 mg/L ZnO and 1 mg/L TiO₂; 21.15% decrease in plate count concentration with respect to control). Exposure of E. coli to mixture of NPs at 1000 mg/L (i.e., 1000 mg/L ZnO and 1000 mg/L TiO₂) resulted in 99.63% decrease in plate count concentration with respect to control. Toxic effects of ions to E. coli were found to be lesser than their corresponding NPs. The percentage growth reduction was found to be 36% for binary mixture of zinc and titanium ions at the highest concentration (i.e., 803.0 mg/L Zn and 593.3 mg/L Ti where ion concentrations are equal to the Zn ions present in 1000 mg/L ZnO NP solution and Ti^+ 4 ions present in 1000 mg/L TiO₂ NP solution). Nature of mixture toxicity of the two NPs to E. coli was found to be antagonistic. The alkaline phosphatase (Alp) assay indicated that the maximum damage was observed when E. coli was exposed to 1000 mg/L of mixture of NPs. This study tries to fill the knowledge gap on information of toxicity of mixture of NPs to bacteria which has not been reported earlier.     

Welding processes for wear resistant overlays

This paper presents a comprehensive survey of welding processes used to deposit wear resistant overlays. It is based on both literature review and research work performed at the Canadian Centre for Welding and Joining. The focus is on the two most popular material systems used for wear resistant overlays: nickel-base with the addition of tungsten carbide particles, and iron-base in which chromium carbides of the form M₇C₃ nucleate during solidification. The processes surveyed in detail are plasma transfer arc welding, submerged arc welding, laser beam welding, gas metal arc welding-related processes using tubular wires, oxy-acetylene flame brazing, and the still-experimental applications of friction stir processing. Cost and market are key factors influencing technical decisions on wear protection overlays, but the information is scarce and often tightly guarded. An informal survey from our industrial partners is included.     

7A52铝合金及25CrMnSiA钢焊接件海洋大气应力腐蚀试验研究

目的研究7A52铝对接焊拉伸试样、25CrMnSiA钢对接焊拉伸试样的海洋大气应力腐蚀行为。方法利用自行设计制作的恒载荷大气应力腐蚀试验装置,在海南万宁站海洋大气环境中,分别采用7A52铝对接焊拉伸试样、25CrMnSiA钢对接焊拉伸试样进行海洋大气应力腐蚀试验研究。对试验中断裂的试样和未断裂的试样,进行表面腐蚀形貌、断口形貌、显微组织、显微硬度分布等分析。结果 7A52铝焊接件断裂在焊接部位,Cl-富集于SCC部分的含钙或含硫的第二相质点,促进了7A52铝焊接件应力腐蚀开裂。海洋大气应力腐蚀试验的25CrMnSiA钢焊接件断裂在母材部位,而实验室拉伸试验断裂在焊接部位。结论两种焊接件在海南海洋大气环境下均存在应力腐蚀开裂,裂纹萌生、扩展于朝向海洋方向的试样表面,存在"风脆"现象。     

Rubber sheet strewn with TiO2 particles:Photocatalytic activity and recyclability

A new method for the preparation of rubber sheet strewn with titanium dioxide particles (TiO₂-strewn sheet) is presented. This simple and low cost method is based on the use of TiO₂ powder (Degussa P25) being strewn onto the sheet made from rubber latex (60% HA) through a steel sieve. The characteristic of the TiO₂-strewn sheet was studied by using scanning electron microscopy/energy dispersive X-ray spectrometer (SEM/EDS) and X-ray diffractometer (XRD) techniques. The photocatalytic activity of TiO₂-strewn rubber sheet was evaluated using Indigo Carmine (IC) dye as a model for organic dye pollutant in water. The results showed that the TiO₂-strewn sheet could degrade IC dye solution under UV light irradiation. The effects of pH, initial concentration, and the intensity of UV light on the photodegradation were also investigated. Kinetics of the photocatalytic degradation was of the first-order reaction. The used TiO₂-strewn sheet can be recovered and reused. The recycling uses did not require any cleaning between successive uses and no decline in the photodegradation efficiency was observed compared with freshly prepared TiO₂-strewn sheet.     

Influence of organic ley–arable management and afforestation in sandy loam to clay loam soils on fluxes of N2O and CH4 in Scotland

Assessment of the sustainability of alternatives to conventional uses of agricultural land, viz. organic systems and afforestation should include consideration of any effects on trace gas budgets. Nitrous oxide (N₂O) and methane (CH₄) fluxes and controlling soil properties were measured in an organic ley–arable rotation in north-east Scotland on a sandy loam. N₂O fluxes were monitored in the ley and arable phases and in organic permanent grass (Lolium perenne) located nearby throughout the 3-year phase duration. Gas fluxes in woodland that had been converted from arable for 1 or 6 years were also measured in both north-east and south-east Scotland on sandy loam to clay loam soils. The climate is maritime and variable with annual rainfall between 800 and 900 mm. Within the organic rotation, differences in N₂O fluxes between the ley and arable phases were less marked than in conventional agriculture. Although this was mainly because grassland emissions were low, some losses from the arable component were also relatively high. Seasonal rainfall had a major influence on cumulative emissions of N₂O, including the first year after conversion from ley to arable. In the short term, changing land use from arable to woodland increased CH₄ oxidation rates and decreased N₂O emissions, though both these rates were also influenced by seasonal weather. Afforestation of agricultural land appears to be more beneficial to trace gas exchange than conversion to organic production.     

基于HSPF及回归模型的淡水河流域非点源负荷计算

应用分布式水文模型HSPF结合回归模型,对广东省东江流域中淡水河流域的非点源负荷进行计算.研究结果显示,模型较好地再现了悬浮泥沙(SS)、CODCr、NO3--N及TP在2010年内的通量随时间的变化过程.统计结果表明,淡水河流域的SS、CODCr、NO3--N及TP在汛期的通量对年通量的贡献十分显著,分别占年通量的86.81%、77.56%、69.83%和73.08%;NH4+-N和TN的计算结果与实测值之间拟合程度较弱,可能是由于这两类污染物与人类活动的点源排放关系密切,而本研究中所用回归方程只考虑了径流量与污染物通量之间的关系,并没有更多地考虑与人类活动相关的因素.     

纳米氧化物粒子对PVDF中空纤维膜结构与性能的影响

采用相转化法制备纳米氧化物/聚偏氟乙烯复合中空纤维膜,讨论了纳米氧化钛和氧化铝粒子对PVDF膜结构和性能的影响.应用牛血清白蛋白截留实验、扫描电子显微镜、傅立叶红外光谱分别对不同膜的分离性能、微观结构和晶相组成进行了分析.结果表明,复合膜的性能与纯PVDF膜相比有显著地改善,其中纯PVDF膜、Al₂O₃/PVDF和TiO₂/PVDF复合膜对牛血清白蛋白的截留率分别为3.27%、67.20%和86.67%,复合膜的水通量则较纯PVDF膜分别提高2.3倍和2.6倍.氮气吸附实验测定的孔径分布进一步表明复合膜的孔径分布变窄,孔径变小.     

Experimental analysis of friction stir forming for dissimilar material joining application

Mass reduction of automotive body structures is a critical part of achieving reduced CO₂ emissions in the automotive industry. There has been significant work on the application of ultra high strength steels and aluminum alloys. However, the next paradigm is the integrated use of both materials, which poses a challenge of how to join the dissimilar materials. Friction stir forming is a new manufacturing process for joining dissimilar materials. The concept of this process is stir heating one material and forming it into a mechanical interlocking joint with the second material. In this research the process was experimentally analyzed in a position controlled robotic friction stir welding machine between aluminum and steel workpieces. New tool geometries were evaluated toward the goal of optimizing joint strength. The significant process parameters were identified and their optimized settings for the current experimental conditions defined using a design of experiments methodology. A scanning electron microscope was used to characterize the bonding and joint structure for single and multi-pin configurations. Two failure modes, aluminum sheet peeling and bonding delamination, i.e. braze fracture, were identified. It was found that the presence of zinc coating on the steel and overall joint geometry greatly affected the joint strength. The aluminum–zinc braze joint appears to be the largest contributor to joint strength for the single-pin joint configuration. The multi-pin geometry enabled a distribution of load to the four pins following fracture of the braze for increased joint toughness and ductility. Thus, the FSF method has been shown to exhibit potential for joining of aluminum to steel.     

不同肥料施用对设施菠菜地NH3挥发和N2O排放的影响

以湖南设施菠菜地为研究对象,采用通气法和静态箱-气相色谱法研究了设施菠菜生长季施用工厂化堆肥(SC)、农民传统堆肥(SS)和单施化肥(FC)对土壤NH_3和N_2O排放的影响.结果表明在同等施氮水平下,与FC相比,SC处理能减少NH_3和N_2O排放量,分别减少52.9%和95.12%(P0.01);SS处理则增加NH_3挥发量24.8%,减少N_2O排放量48.8%.不同处理NH_3损失率分别为SS(10.97%)FC(4.19%)SC(2.74%);N_2O排放系数分别为FC(4.50%)SC(2.21%)SS(0.60%);与FC处理相比,SC处理条件下菠菜产量和作物吸氮量分别降低19.61%和13.20%,差异不显著;SS处理则显著降低27.9%和40.0%(P0.05).在该地区冬季设施菠菜田中,影响NH_3和N_2O排放的主要因素为土壤水分,环境温度不是此研究中影响气体排放的主要因素.因此,畜禽养殖固体废弃物经过不同处理后作为有机肥施入菠菜田,SC处理的菠菜可保证产量的同时,减少NH_3挥发和N_2O排放损失.