The influence of the bevel angle on the micro-mechanical behaviour of bonded scarf joints

In this work, both experimental and theoretical analyses are presented of the influence of the scarf angle (α) on the micro-mechanical behaviour of a scarf-joint bonded structure loaded in uniaxial tension. The specimens studied were made of mild steel for the adherends and of an epoxy resin for the adhesive. This study not only considers the ultimate strength of the specimens, but also characterizes the various stages of the gradual adhesive damage and takes into account the threshold for the initiation of the first microcracks and the threshold for the start of flaw propagation as the fundamental parameters. These thresholds were determined by two experimental methods used simultaneously: extensometry with electrical strain gauges, and acoustic emission. Some of the experimental results are also compared with some theories that the authors have developed previously in this field, in order to determine their limits of application.     

Thermal contact resistance and adhesion studies on thin copper films on alumina substrates

A new photothermal method for measuring the thermal contact resistance in the interfacial area is presented. Copper thin films were prepared on alumina substrates by physical vapour deposition. On the basis of a mathematical model developed here, thermal contact resistance was determined in samples of various thicknesses and processed under various argon pressures. The effects of these parameters on the films and interface properties are discussed. A correlation between the thermal contact resistance and the adhesion, as determined by the scratch test, is found. In order to understand the origin of the mean critical load and the thermal contact resistance evolution, observations were made by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results obtained have shown that the change in stress level in the copper film and the formation of a new compound in the interfacial area seem to be the main reasons for the enhancement of heat transfer.     

FEM stress analysis and sealing performance improvement of box-shaped bolted flanged joints using silicone sealant under internal pressure and thermal conduction conditions

Interface stresses and sealing performance of thin-wall box-shaped bolted flanged joints using silicone sealant under internal pressure and thermal conduction conditions are analyzed by the thermo-elastic finite element method. The flexible flanges were fastened by M8 bolts and nuts with an initial clamping force (bolt preload) after being joined with the silicone sealant. In the elastic and thermo-elastic Finite Element Method (FEM) calculations, the effects of the bolt pitch distance, flange rigidity and flange thickness were examined on the interface stress distributions. In addition, the effects of the linear thermal expansion coefficient and Young's modulus of the silicone sealant in the steady temperature state were also examined from a design standpoint. In the experiments, leakage pressure was measured when the silicone sealant was applied between an aluminum flexible flange with 1 mm thickness and an aluminum flange (body) with 10 mm thickness. Measurements of sealing performance with the silicone sealant and a sheet gasket were also conducted. In addition, strains in the joint in steady temperature states were also measured by strain gauges to understand the effect of the operative temperature on the sealing performance. The experimental results were found to be in fairly good agreement with the calculated results. From the results, it was found that the effect of the thermal conduction condition was greater than that of the internal pressure on both the interface stress distributions and the sealing performance. In addition, the sealing performance was found to be better in the joint with the silicone sealant than that with the sheet gasket.     

Development and characterization of a lignin–phenol–formaldehyde wood adhesive using coffee bean shell

In the present study, the possibility of development of a wood adhesive using coffee bean shell lignin (Cbsl) has been explored. Cbsl-modified phenolic adhesive has been prepared by replacing phenol with lignin at different weight percents. The optimization of weight percent lignin incorporation was carried out with respect to mechanical properties. It was found that up to 50 wt% of phenol could be replaced by Cbsl to give lignin–phenol–formaldehyde adhesive (LPF) with improved bond strength in comparison to control phenol–formaldehyde (CPF). Optimized LPF and CPF adhesives were characterized by IR, DSC and TGA. The IR spectrum of LPF showed structural similarity to CPF. Thermal stability of LPF adhesive was found to be lower as compared to that of CPF. DSC studies revealed a higher rate of curing in the LPF adhesive.     

Investigation of coating failure on the surface of a water ballast tank of an oil tanker

The current crude oil tanker is constructed as a double-hull structure which consists of an oil tank and a water ballast tank whose surface is coated with epoxy paint to prevent corrosion. Since the cracks that developed in the epoxy coating have caused corrosion of the interface of the water ballast tank, the identification of the parameters for crack development is important. In addition, the moisture absorption by the epoxy coating can cause deterioration of bond strength, which results in delamination of the coating and accelerates the corrosion at the interface. In this study, after the mechanical and thermo-mechanical properties of epoxy paints were measured, the residual stresses induced by the temperature change and cure shrinkage were calculated by the finite element analysis, which were compared with the experimental results. Also, the pull-off tests were performed to investigate the deterioration of the bond strength of epoxy coatings due to moisture absorption. It was found that the thermo-mechanical properties such as the coefficient of thermal expansion and glass transition temperature of the coating materials had dominant effects on the crack resistance rather than the cure shrinkage; the moisture penetration to the bonding interface caused interfacial failure and a significant deterioration of bond strength.     

Hot cracking of welds on heat treatable aluminium alloys

Abstract

The Spot Varestraint test was used to evaluate the hot cracking susceptibility of several aluminium alloys namely 6061-T6, 6061-T6 (H), 7075-T6, 7075-T6 (H). The effects of augment strain, the number of thermal cycles and cold working (rolling) on the cracking susceptibility were investigated, and the total crack length was used to evaluate the hot cracking susceptibility. The results indicate that the number of thermal cycles is irrelevant to the hot cracking susceptibility in the weld fusion zone, but does affect this susceptibility in the heat affected zone (HAZ). More thermal cycles correspond to larger hot cracks in the HAZ, especially in the weld metal HAZ. The hot cracking susceptibility of materials increased with augment strain in both the fusion zone and the HAZ. Cold working of the materials can reduce their hot cracking susceptibility. The hot cracking susceptibility of 7075-T6 aluminium alloys is higher than that of 6061-T6. There was significant Cu segregation in the HAZ of 7075-T6 aluminium alloy, resulting in a higher susceptibility to hot cracking in this zone.     

Simulation of GMAW thermal process based on string heat source model

Abstract

A 3-D string heat source model was developed to simulate the thermal process for gas metal arc welding (GMAW) with a new transient solution of heat transfer. Reflection heat sources, the imaginary heat source and the imaginary heat sink were introduced to make the solution more reliable. The moving welding heat input during GMAW welding process was presented with a moving 3-D string heat source model made up of a group of elementary point heat sources along the moving coordinate axes. Using established models, the whole process from arc starting, quasi-steady state (QSS), to arc extinguishing during welding Q195 steel has been simulated. Meanwhile, some calculations and experiments for JG590 steel have also been made. The predicted weld cross-sections and welding thermal cycles show a good agreement with experimental measurements.     

Thermal and metal transfer behaviours in pulsed current gas metal arc weld deposition of Al–Mg alloy

Abstract

The control of pulsed current gas metal arc (GMA) welding is highly critical owing to the simultaneous influence of the pulse parameters on thermal and metal transfer behaviours of the process. An analytical model has been developed to provide a theoretical understanding of the influence of pulse parameters on the behaviour of metal transfer and thermal characteristics in pulsed current GMA welding using Al–Mg filler wire. The variations in thermal and metal transfer behaviours with changes in pulse parameters have been satisfactorily analysed considering a summarised influence of pulse parameters defined by a dimensionless factor &phis; = (I _b/I _p)ft _b, proposed previously. A large number of process parameters have been considered, as a result of using four different GMA welding power sources. The hypothesis has been verified using some previously reported experimental results. The theoretical model may be useful in the control of pulse parameters to achieve desired behaviours of thermal and metal transfer under different conditions of weld fabrication, thereby facilitating more universal application of GMA welding.     

Inorganic,physicochemical, and microbial aspects of copper corrosion: literature survey

Abstract

A literature survey on the corrosion of copper in aqueous solutions, with particular relevance to potable water, is presented. Coverage is of inorganic and physicochemical aspects of copper corrosion, namely those dealing with the thermodynamics of copper corrosion reactions, oxygen reduction at copper surfaces, and the photoelectrochemistry of the copper-copper oxide-electrolyte, system. Microbially induced pitting corrosion and transport in associated biomembranes are also considered.     

Progress of electroless amorphous and nanoalloy deposition: a review – Part 1

Abstract

The progress and longitudinal history of electroless plating from its discovery to its present development, from published research reports and, particularly, patents are discussed and reviewed in this paper. The progress of electroless plating can be divided into five stages: the discovery of electroless plating; the early stage of development; the period of slow growth; the period of rapid development; and the period of deeper, more fundamental development and nanoelectroless plating. The contents of each stage are described and discussed in detail. Investigating and understanding the history of electroless plating can not only make clearer the process of development and characteristics of electroless plating, but also clarify to some degree the scientific and technical direction of the process and its applications. In the current Part 1, the authors review the first three stages noted above and some details from the period of fast development including the wealth of information gathered from numerous studies on the properties of electroless deposits. Part 2, to be published in a forthcoming issue of Transactions, will deal with further studies from the period of rapid development, including large scale applications, ternary and multicomponent alloys and composites, the impressive developments in China, now the world’s biggest market in electroless nickel plating, and development of electroless Fe–B alloy plating, again much of which took place in Chinese laboratories. In addition, in Part 2, the authors will discuss what they consider to be a period of sustained deep and fundamental research into the theory and mechanism of electroless plating, and development of nanoelectroless plating.