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.     

Modeling of the influence of sample preparation sequences when measuring selectively induced residual stress depth profiles

The selective introduction of compressive residual stresses is gaining increasing importance as design tool in today's manufacturing process chains. Manufacturing processes such as shot peening or hydraulic autofrettage are used to improve the surface integrity, and hence the fatigue life of the components. However, measuring the corresponding residual stress depth profiles is a challenging task as the results will always include the manufacturing and preparation history of the components. In this paper, results of residual stress measurements with X-ray diffraction and optical hole-drilling after autofrettage and sample preparation are presented and compared to a finite element analysis for two representative geometries. The presented approach can be used to predict the influence of the mandatory sample preparation procedure. As a consequence, the effectiveness of the manufacturing process to improve the surface integrity can be predicted more precisely and wrong interpretations of the measured residual stress depth profiles can be avoided.     

Analytical modelling of residual stresses in orthogonal machining of AISI4340 steel

Residual stress profile in a component is often considered as the critical characteristic as it directly affects the fatigue life of a machined component. This work presents an analytical model for the prediction of residual stresses in orthogonal machining of AISI4340 steel. The novelty of the model lies in the physics-based approach focusing on the nature of contact stresses in various machining zones and the effect of machining temperature. The model incorporates: (i) stresses in three contact regions viz. shear, tool-nose-work piece and tool flank and machined surface, (ii) machining temperature, (iii) strain, strain rate and temperature dependent work material properties, (iv) plastic stresses evaluation by two algorithms, S-J and hybrid, (v) relaxation procedure and (iv) cutting conditions. The model benchmarking shows (86–88%) agreement between the experimental and predicted residual stresses in the X- and Y-directions. On the machined surface, the tensile residual stresses decrease with an increase the edge radius and increase with an increase the cutting speed. However, below the surface, the compressive residual stresses increase with an increase the depth of cut. Further, it is observed that the proposed model with hybrid algorithm gives better results at a lower feed rate, whereas with the S-J algorithm, at a higher feed rate.     

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.     

3D numerical investigation of thermally assisted high efficiency ductile machining of nanocrystalline hydroxyapatite

This study investigates the effects of four different variables (initial workpiece temperature, side rake angle, edge radius/feed rate, and nose radius/depth of cut) on ductile regime machining of a bioceramic material known as nanohydroxyapatite (nano-HAP) using 3D numerical simulation. AdvantEdge FEM Version 5.9 is used to conduct turning simulations of the nano-HAP workpiece. Tecplot 360 is used to analyze the results of the simulations. Because the workpiece is thin, the entire workpiece is set to a uniform initial temperature to simulate laser preheating of the material. Initial workpiece temperature, rake angle (side rake angle), edge radius, and nose radius are varied, and the effects of these operating conditions on critical feed are investigated. It is found that critical feed increases as initial workpiece temperature increases, and also as negativity of rake angle increases. For the edge radius, it is concluded that an initial increase causes an increase in critical feed – however, at some value of edge radius, critical feed shows no further increase; for the nose radius, critical feed appears to show no significant dependence.     

甲醛致核酸损伤作用的实验研究

应用单细胞凝胶电泳技术(SCGE)和液相色谱-电化学检测法(HPLC-EC)研究了典型环境污染物甲醛对DNA分子的损伤效应．结果表明：甲醛不仅可诱导人外周血淋巴细胞DNA发生链断裂,还可引起DNA-DNA,DNA-蛋白质交联;甲醛与小牛胸腺DNA的体外作用较弱,但在铁离子介导下对DNA的氧化能力增强,可产生一定量的8-羟基脱氧鸟苷(8-OHdG)加合物：动物实验表明甲醛诱导大鼠肺组织DNA氧化损伤生成8-OHdG,提示甲醛较强的遗传毒性．     

Experimental investigation and characterization of nano-scale dry electro-machining

This paper presents an experimental investigation and characterization of a novel technique of nanoscale electro-machining (EM) in atmospheric air, named dry nano-EM, by using scanning tunneling microscopy (STM) as the platform for nanomachining. The electro-machining has been conducted in near field by maintaining a gap distance of 1–2 nm between the Platinum–Iridium [Pt–Ir (80:20)] tool electrode and atomically flat gold substrate with the air as dielectric medium. An in situ process of evaluating the tool quality before and after machining has been used by monitoring the current–displacement (I–Z) spectroscopy curves. The mechanism of dry nano-EM has been presented as well as the machining performance of the process has been evaluated. Based on the observations, it has been established that field induced evaporation due to intense heat generated at the gap width is the primary mechanism of material removal in dry nano-EM. The experimental results show that dry nano-EM is capable of fabricating consistent nano-features with good repeatability. The volume of material removal increases almost linearly with increasing number of features machined and machining time, indicating the consistency in the dimensions of the nano-features. Finally, dry nano-EM is established as a technique capable of machining 50–100 features in a pre-defined manner with average feature size of 7.5–10 nm in a single pass, thus suitable for nano-patterning in atomically flat electrically conducting surfaces.     

液柱喷射湿法脱硫产物处理实验研究

本实验系统中 ,液柱喷射湿法脱硫在脱硫产物的处理上采用就地强制氧化CaSO3 ,真空带式过滤机脱水的方式 .实验通过塔内氧化速度测试 ,对不同脱水效果的石膏、浆液进行了分析比较 ,发现氧化不完全的残余CaSO3 是影响脱水效果的一个重要因素 .改善氧化效果 ,降低残余CaSO3 的量 ,是提高石膏品质的一种重要方法 .     

Thermal cracking of waste printed wiring boards for mechanical recycling by using residual steam preprocessing

Mechanical waste-processing methods, which combine crushing and separation processes for the recovery of valuable materials, have been widely applied in waste printed wiring board (PWB) treatment. However, both the high impact toughness and the tensile and flexural strengths of whole PWB with a laminated structure result in great energy consumption and severe abrasion of the cutters during multi-level crushing. In addition, the high temperatures occurring in continual crushing probably cause the decomposition of the polymer matrix. A thermal-crack method using residual steam as the heating medium has been developed to pre-treat waste PWBs. This treatment reduces the mechanical strength in order to improve the recovery rate of valuable materials in subsequent mechanical recycling. The changes of the PWBs’ macro-mechanical properties were studied to evaluate thermal expansion impacts associated with changes in temperature, and the dynamic dislocation micro-structures were observed to identify the fracture mechanism. The results showed that thermal cracking with steam at the temperature of 500 K can effectively attenuate the mechanical properties of waste PWBs, by reducing the impact, tensile and flexural strengths respectively, by 59.2%, 49.3% and 51.4%, compared to untreated PWB. Thermal expansion can also facilitate the separation of copper from glass fiber by reducing peel resistance by 95.4% at 500 K. It was revealed that the flexural fracture was a transverse cracking caused by concentrated stress when the heating temperature was less than 500 K, and shifted to a vertical cracking after exceeding 500 K.     

Rotary ultrasonic machining of potassium dihydrogen phosphate (KDP) crystal: An experimental investigation on surface roughness

Potassium dihydrogen phosphate (KDP) crystal, widely used for important electro-optic parts, is a typical hard-to-machine material because of its soft, brittle, and anisotropic properties. High quality is usually required for machined surfaces on KDP parts. Reported machining methods for KDP crystal include diamond turning, grinding, magnetorheological finishing, and polishing. Each of these methods has its limitations. Therefore, it is desirable to develop new machining methods for KDP crystal. This paper presents an experimental investigation on surface roughness in rotary ultrasonic machining (RUM) of KDP. It was found that the surface roughness obtained when using a tool with a chamfered corner was lower than that obtained using tools with right-angle corners. Other process variables (spindle speed, feedrate, and ultrasonic power) also affected the surface roughness obtained.     

汽油机燃用乙醇和汽油的混合燃料的试验研究

对摩托车汽油机进行了燃用乙醇 汽油混合燃料的试验,并与燃用汽油时的结果进行了对比分析.结果显示,汽油机燃用乙醇和汽油的混合燃料,当混合燃料中乙醇比例为10%和15%时,即使发动机的结构不变、燃油系统和点火系统不作任何调整的时候,发动机的全负荷输出不受影响,发动机的能耗率得到改善,HC和CO排放有所降低,但是NOx排放会有显著增加.     

Insights into the mechanism of the deterioration of mainstream partial nitritation/anammox under low residual ammonium

Residual ammonium is a critical parameter affecting the stability of mainstream partial nitritation/anammox (PN/A), but the underlying mechanism remains unclear. In this study, mainstream PN/A was established and operated with progressively decreasing residual ammonium. PN/A deteriorated as the residual ammonium decreased to below 5 mg/L, and this was paralleled by a significant loss in anammox activity in situ and an increasing nitrite oxidation rate. Further analysis revealed that the low-ammonium condition directly decreased anammox activity in situ via two distinct mechanisms. First, anammox bacteria were located in the inner layer of the granular sludge, and thus were disadvantageous when competing for ammonium with ammonium-oxidizing bacteria (AOB) in the outer layer. Second, the complete ammonia oxidizer (comammox) was enriched at low residual ammonium concentrations because of its high ammonium affinity. Both AOB and comammox presented kinetic advantages over anammox bacteria. At high residual ammonium concentrations, nitrite-oxidizing bacteria (NOB) were effectively suppressed, even when their maximum activity was high due to competition for nitrite with anammox bacteria. At low residual ammonium concentrations, the decrease in anammox activity in situ led to an increase in nitrite availability for nitrite oxidation, facilitating the activation of NOB despite the dissolved oxygen limitation (0.15–0.35 mg/L) for NOB persisting throughout the operation. Therefore, the deterioration of mainstream PN/A at low residual ammonium was primarily triggered by a decline in anammox activity in situ. This study provides novel insights into the optimized design of mainstream PN/As in engineering applications.     

降雨淋滤条件下淄河滩陈化残油释放试验

淄河滩陈化油污土层是引起大武水源地东部地区地下水污染的主要污染源之一，通过对油污土层采取原壮土桩样，在室内进行了旨在模拟大气降水作用时的残油释放试验研究，结果表明，平面上油污土层多年平均可淋出油量1449.26mg/m^2,油污土层的存在不仅使大量的地下水遭到石油物质污染，而且将是一个长期的污染源。     

紊流作用下泥沙释放磷的试验及数值模拟

为研究水体紊动对泥沙释放污染物的影响,引入近似均匀紊流模拟装置,开展不同强度紊动作用下泥沙运动释放磷动态过程及基本规律的试验,研究表明:紊动扩散作用对泥沙解吸释放磷有着十分重要的影响,紊动较弱时,泥沙尚未起动,床面泥沙颗粒吸附的磷元素解吸至孔隙水中,在垂向紊动扩散作用下输送至上覆水中,将使得上覆水中溶解态磷浓度增大;紊动作用较强时,泥沙逐渐悬扬至水体中,悬浮泥沙颗粒吸附的磷元素直接解吸至上覆水中,泥沙浓度越高,溶解态磷含量增长速率越大,达到平衡的时间越短.通过耦合紊流模型、水流泥沙数学模型、污染物对流扩散模型和Langmuir吸附动力学方程建立了紊动作用下泥沙释放磷的垂向一维数学模型,针对试验条件进行数值模拟,模拟结果与试验数据吻合较好,平均相对误差低于10%,可为模拟天然水体中泥沙悬浮释放磷的时空演化提供参考.     

废弃印刷线路板热解过程传热特性实验研究

为了改善印刷线路板热解过程中的传热性能、提高废弃印刷线路板热解效率和产率、减少热解过程对环境的二次污染,本文设计并搭建了一套固定床热解实验装置,在高温氮气渗流条件下对3种不同尺寸废弃印刷线路板颗粒料层的热解过程进行了对比实验;测试了颗粒料层热解过程沿轴向和径向的温度分布,分析了线路板颗粒尺寸对物料层温度场和对热解区域迁移速度的影响,阐明了沿热解炉高度方向物料温度参数随时间的变化特征,揭示了热解区域和热解状态对于沿轴向的温升速率和温度梯度的影响规律.结果表明:较大颗粒料层的热解区域纵向迁移速度要快于小颗粒料层,当颗粒尺寸分别为1.5、2.5和3.5 cm时,热解区域的纵向迁移速度分别为0.47、0.50和0.63 m·h~(-1);热解区域和热解状态对于沿轴向的温升速率和温度梯度有显著影响;废弃印刷线路版热解过程的能源利用效率较低,只有29.50%～37.13%,主要损失为热解装置和物料的蓄热损失.研究结果对印刷线路板热解装置的设计和运行具有重要的指导意义.     

内质网应激和氧化应激通路对DINP诱发Allergic March的介导作用

为了研究增塑剂邻苯二甲酸二异壬酯（diisononyl phthalate,DINP）致Allergic March的作用机制,以雄性BALB/c小鼠为受试动物,随机分为5组,包括空白对照组（生理盐水）、20 mg·kg^-1 DINP组、OVA组、20 mg·kg^-1 DINP+OVA组和4-苯基丁酸（4-PBA）拮抗组（20 mg·kg^-1 DINP+OVA+4-PBA）,染毒周期为47 d.以肺组织匀浆测定活性氧（reactive oxygen species,ROS）、还原型谷胱甘肽（glutathione,GSH）、丙二醛（malondialdehyde,MDA）和一氧化氮（nitric oxide,NO）.采用ELISA试剂盒检测血清中总免疫球蛋白E（T-IgE）、OVA特异性免疫球蛋白E（OVA-IgE）和白细胞介素-33（IL-33）评价机体的炎症因子,并同时观察肺组织的病理变化结果.与生理盐水组比较,OVA组的肺功能、Th2免疫系统功能亢进的分子、氧化应激指标和肺组织病理学损伤都有所加重.与OVA组比较,20 mg·kg^-1 DINP+OVA组的肺功能、Th2免疫系统功能亢进的分子、氧化应激指标和肺组织病理学损伤同样也有所加重.而4-PBA拮抗组（20 mg·kg^-1 DINP+OVA+4-PBA）与20 mg·kg^-1 DINP+OVA组相比较,其各项指标都有了明显的减轻.实验结果表明,20 mg·kg^-1的DINP能加重小鼠的Allergic March,内质网应激拮抗剂4-PBA可使Allergic March症状减轻,对小鼠肺组织起保护作用,说明内质网应激通路可能通过调节氧化应激介导了DINP所致的Allergic March.     

Environmental investigation of bio-modification of steel slag through microbially induced carbonate precipitation

Steel slag (SS) is one of byproduct of steel manufacture industry. The environmental concerns of SS may limit their re-use in different applications. The goal of this study was to investigate the leaching behavior of metals from SS before and after treated by microbially induced carbonate precipitation (MICP). Toxicity characteristic leaching procedure, synthetic precipitation leaching procedure and water leaching tests were performed to evaluate the leaching behavior of major elements (Fe, Mg and Ca) and trace elements (Ba, Cu and Mn) in three scenarios. The concentrations of leaching metals increased with the content of SS. After it reached the peak concentration, the leaching concentration decreased with the content of SS. The leachability of all elements concerned in this study was below 0.5%. The carbonate generated from the MICP process contributed to the low leachability of metals. After bio-modified by MICP process, the leaching concentrations of Ba from TCLP, SPLP and WLT tests were below 2.0 mg/L, which was the limit in drinking water regulated by U.S. EPA. The concentrations of Cu leached out from MICP-treated SS-sand samples were below 1.3 mg/L which is the limit regulated by national secondary drinking water. Compared with the regulations of U.S.EPA and Mississippi Department of Environment Quality (MDEQ), MICP-treated samples were classified as non-hazardous materials with respects to the leaching of metals. Meanwhile, maximum contaminant limits regulated by U.S.EPA states that MICP-treated SS are eco-friendly materials that can be reused as construction materials.     

钢筋混凝土偏心受压短柱尺寸效应研究

现行钢筋混凝土结构设计方法是基于小尺寸构件的试验研究建立起来的,大尺寸构件的设计的科学性和合理性有待进一步研究.本文制作2组4根钢筋混凝土偏心受压短柱,偏心距为0.6h0,试件的截面几何尺寸分别为200 mm×200 mm、400 mm × 400 mm.研究相同偏心距下,不同尺寸的钢筋混凝土偏心受压短柱的破坏特征,极...     

亚致死剂量氯吡嘧磺隆胁迫对斑马鱼典型肝脏代谢物的影响

为获知水环境中亚致死剂量的氯吡嘧磺隆对斑马鱼肝脏的影响,将斑马鱼暴露在亚致死剂量的氯吡嘧磺隆药液中8 d,采用超高效液相色谱与四级杆-轨道离子阱质谱串联对斑马鱼的肝脏代谢物进行分析,采用SIEVE软件将图谱信息转换为含有保留时间、质荷比和相对峰面积的二维数据阵.同时,结合mz Cloud、Human Metabolome Database(HMDB)数据库共鉴定出33种代谢物,包括氨基酸、糖、有机酸等物质.最后,采用SIMCA软件对正离子和负离子模式下的检测结果进行主成分、偏最小二乘法和正交校正的偏最小二乘法分析.主成分和偏最小二乘法结果表明,对照组与处理组在2种检测模式下均存在差异代谢物.为了寻找造成对照组与处理组之间差异的代谢物,对代谢物进行S-Plot分析,结果表明,肌酸酐、牛磺酸、多巴胺和5b-胆甾醇硫酸酯组间差异最大(p0.01).4种代谢产物可作为斑马鱼在氯吡嘧磺隆亚致死剂量胁迫下肝脏代谢异常的潜在标记物.