Influence of interpass temperature on the properties of duplex stainless steel during welding by submerged arc welding process

Duplex stainless steels are materials that present high corrosion resistance with high values of mechanical strength, therefore motivating their use in various components in the offshore industry. However, there are major challenges in the welding of these materials in terms of the productivity and quality of the joint produced, considering its extensive use for components of small thickness, such as umbilicals, to those of large thickness, such as salt water injection pipelines. In relation to pipes of small thickness, the gas tungsten arc welding process is successfully used. In thick-walled pipes, the automatic process of submerged arc welding (SAW) has been recently implemented in lines of pre-assembled piping, and this has considerably increased the productivity of the joints produced, though, a great deal of time is required to perform a new weld pass, due to the fact that the maximum interpass temperature needs to be lower than 150 °C. This work presents the results of characterization and the evaluation of corrosion resistance of a welded joint corresponding to DSS UNS S31803, with a wall thickness of 21.4 mm, welded by the gas metal arc welding process in the root and SAW process in the filling and cap passes, employing an interpass temperature between 150 and 290 °C. The results of the characterization of the mechanical properties, chemical composition and corrosion resistance in different regions of the welded joint were compared with those obtained for the base metal of the pipe, as well as with the minimum values required by the project standards. Therefore, this study has made an evaluation of the influence of the interpass temperature in the properties of the joints produced, motivated by a possible increase in productivity in pipe welding.     

Performance evaluation and mathematical modelling of granular activated carbon biofiltration in wastewater treatment

Biological filtration is an effective technique for removing organic matter from wastewater. The performance of a biofilter can be influenced by a range of operational conditions. In this study the performance of biofilters was investigated for the influence of filter media depth, influent concentrations, filtrations rates and backwashing. The results show that performance of GAC filters decreased with shallower filter bed depths. In addition, the GAC performed better at lower influent concentration and lower filtration rates. The daily backwash adopted to avoid the physical clogging of the biofilter did not have any significant effect on the organic removal efficiency of the filter. The concentration, activity and characteristics of the biomass are quantified and described. A mathematical model was developed to simulate the organic removal of the GAC biofiltration system. The performance of the GAC filter under different influent organic concentration levels, filtration rates and filter bed depths was adequately simulated by the mathematical model developed for this study.     

金刚石砂轮双端面磨削氧化铝陶瓷

本研究涉及双端面磨削技术应用于用两片陶瓷结合剂金刚石砂轮同时磨削圆柱形氧化铝陶瓷工件两个端面的技术评价。精细陶瓷(advanced ceramics),例如氧化铝(Al2O3),由于具有高的硬度、抗压强度、耐腐蚀性、导电性、磁导率和脆性而应用广泛。本试验为四因子试验,评价被磨工件的表面粗糙度Ra,采用重量法测定材料去除率,采用激光折射技术测定的平均比例系数来评价被磨工件平面度。本文的研究结果表明,双端面磨削可以在很短的加工时间内获得极高的表面光洁度、高的精度和高的磨除率。     

Interference‐resilient spectrum sharing with collision detection and data recovery for cognitive radio networks

Data recovery under collision of primary/secondary users in cognitive radio networks is largely an unaddressed problem. Existing approaches require either (a) retransmissions, (b) interference‐free alignment of transmission parameters, or (c) prior knowledge for data recovery. In contrast to the existing approaches, the paper proposes estimation of channel state information based on received collided frames and recommends techniques for spectrum sharing, collision detection, and data recovery. Specifically, based on estimated channel vector, interference‐resilient spectrum‐sharing protocol and techniques are proposed for (a) identification of primary user (PU) activity before (or during) secondary user's (SU's) transmission, (b) MIMO channel estimation under collision, (c) optimal pilot permutation, and (d) interference cancellation (with/without receiver diversity). Results are reported for different baseband modulation techniques under frequency selective/flat fading channel scenarios that demonstrate the efficacy of a proposed work.     

Intelligent optimization methodology of battery pack for electric vehicles: A multidisciplinary perspective

Past studies focused on proposing new materials for batteries components, state of health (SOH) prediction, thermal design, equivalent circuit modeling, and so on. Those studies have been implemented on individual basis on a single battery or battery pack. However, there is hardly any research found that encompasses all the multidisciplinary aspects (such as materials, SOH, intelligent configuration [assembly], thermal design, mechanical safety, and recycling of materials and pack) simultaneously for the battery pack design of electric vehicles. This research article proposes a synthetic methodology for an advanced design of battery pack and its components by incorporating optimal scenario of materials selection for battery electrodes, SOH estimation, configurations (assembly) of cells, thermal (air and liquid cooling) design, battery pack casing mechanical safety, and recycling aspects of battery and battery pack. The problem is divided into the several parts and methodology for each is proposed. Cumulative advantages of the methodology with six future critical directions are discussed in the end.     

Sensing electrochemical activity in polymer coated metals during the early stages of coating degradation–Effect of the polarization of the substrate

Eventual limitations in the applicability of the SECM in the SG-TC mode to in situ monitor electrochemical activity in the proximity of a sub-centimeter defect (holiday) through the coating applied to protect a metal against the corrosive environments has been explored. The possible occurrence of chemical interferences between the chemical species involved in the corrosion reactions, as well as the formation of reactive secondary products, have been investigated because they would influence the faradaic signals registered at the SECM tip. In order to separate the contributions of the half-cell processes, polarization of the substrate was performed in this work, both negative and positive with respect to the corrosion potential of the sample in the test environment, and the signals detected at the tip were analyzed. By selecting different values for the potential applied to the tip, the local concentrations of Fe(II) ions, hydrogen peroxide and oxygen could be monitored. It has been observed that the oxygen reduction reaction occurring at the cathodic sites on the corroding steel surface can be accompanied by the formation of hydrogen peroxide as intermediate, and this species will interfere with the detection of dissolved metal at the tip.     

Multi-functional multi-walled carbon nanotube-jute fibres and composites

Jute fibres and corresponding epoxy based composites with sensing abilities could be realized by depositing multi-walled carbon nanotubes (MWCNTs) on the surfaces of jute fibres or fabrics using simple and scalable dip coating. The formation of electrically semiconducting MWCNT networks on jute fibre surfaces was confirmed, which in turn caused the formation of jute/epoxy interphases with highly concentrated MWCNTs. The sensing behaviour of the MWCNT coated jute fibres and jute/epoxy composites for temperature, relative humidity and stress/strain was further established in detail, which were strongly influenced by the intrinsic physical and chemical features of the fibres. In addition, a significant improvement in dielectric properties of the MWCNT-jute/epoxy composites was observed compared to neat jute/epoxy composites. Based on this approach, the electrically insulating natural fibres along with semiconducting MWCNTs on surface will stimulate and realize a broad range of multi-functional applications.