No description available.

Thermite reactions were well studied in the past few decades; however, implementation of these reactions with nanoscale components is a new interest for today’s researchers both for military and civil industries. Nanothermites are mixtures of a metal fuel and a metal oxide, undergoing a redox reaction while heated, and generating a large amount of energy (heat/thrust) which can reach combustion temperatures above 3000K. Aluminum is commonly used as the fuel because of its abundance, easy handling, high reactivity and benign products. By using nano-sized components, the surface energy, contact area, and mixing homogeneity increase. These properties result in greatly improved reactivity and propagation rate as well as easier ignition compared to traditional thermites, which make them attractive as advanced propellants, pyrotechnics, and heat and thrust generators. They also find civil applications such as joining. Here, the application of nanothermites for joining metal to ceramic/glass is investigated. To approach this goal, composites of nanothermite modified by Copper powder were developed for the first time and their related properties were studied to find the best composition for joining. These energetic composites can be applied where a localized heat source is required. The advantage of using nanothermite for joining is its fast reaction, high energy density and liquid products that can wet surfaces. In this research, the reaction products were studied by X-Ray Diffraction spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy. The overall thermite reaction corresponding to the Al-NiO nanothermite was found producing the AlNi phase in a fuel-rich mixture. The microstructures of these reaction products showed the formation of a composite made from copper, AlNi and AlNi/Al2O3 spheres in an Al2O3 matrix. On the other hand, the influences of the fuel (Al) to oxidizer (NiO or CuO) mass ratio and the amount of Cu additive, on the ignition temperature and energy release were characterized using Differential Scanning Calorimetry. It was found that both parameters do not affect the ignition temperature significantly but change the energy release dramatically. Furthermore, according to these results, (Al-33%NiO)-50%Cu was selected and applied to join dissimilar materials such as copper, alumina-silica and glass. As a proof of concept, joint cross-sections were studied by SEM-EDAX revealing that the alumina phase produced by this reaction was joined to the glass/ceramic, while the metal phase wetted the metallic surfaces. Therefore, this composite was introduced as a good interlayer for dissimilar metal/ceramic surfaces.

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The main objective of the project was to conceptually design a friction stir welding machine for joining rails. The applicability of friction stir welding types and its application in rail joining was investigated. A number of machine concepts for joining rail using friction stir welding techniques were developed and a final workable concept was laid out. In addition, the existing methods and machines for joining rails were considered, including arc welding, exothermic welding, flash butt welding and manual joining (rails joined by means of splice plate). After comparing different methods of joining rails, an optimized method was selected. The capabilities of the new conceptual machine, such as its ability to accommodate various rail profiles, were demonstrated through designs and various calculations. The development cost analysis was performed and a comparison was made with the other three methods of joining rails. Consequently, it was concluded that friction stir welding concept could be applied in rail joining and the costs associated with it could be lowered

This master thesis is written to examine the influence of different low carbon steel sheet materials on the GMAW welding process. During welding the properties of the base material influence the productivity of the welding process. The purpose of this thesis is to examine how the choice of material and welding speed affect the welding process and the productivity. A literature survey was performed to describe the welding technique and the differences in manufacturing for the sheet materials as well as the effect of alloying and welding on the sheet material. Defects in the weld and methods used to determine them are explained. Test pieces of the different sheet materials were welded with the GMAW process and examined. The result shows that there is a variation in the welding process regarding weld penetration. Measurements also show that welding speed and gap have little influence on the hardness of the weld and heat-affected zone and that the S355MC is more likely to suffer from a narrower toe transition radius than S355NL and S355MC Si. This and the higher area in the Y2 region for the S355MC could indicate a stronger inward flow in the weld pool during welding possibly a result of surface active agents such as oxygen and sulphur. / Denna uppsats skrevs för att undersöka hur olika lågt legerade kolstål påverkar svetsprocessen för gasmetallbågsvetsning. Under svetsning påverkar materialets egenskaper produktiviteten för svetsprocessen. Syftet med denna uppsats är att undersöka hur svetshastighet och materialval påverkar svetsprocessen och produktivitet. En litteraturstudie genomfördes för att beskriva svetsprocessen och olikheter i tillverkningen av de olika plåtkvaliteterna samt hur olika legeringsämnen påverkar plåtkvaliteten. Dessutom beskrivs Svetsdefekter samt metoder för detektering av svetsdefekter förklaras. Testbitar av de olika plåtkvaliteterna svetsa samman genom gasmetallbågsvetsning och undersöks sedan. Resultatet visar på att variationer i svetsprocessen förekommer vid mätning av inträningen. Resultat visar även på att svetshastigheten och förekomsten av en spalt har liten inverkan på hårdheten i svetsen eller den värmepåverkade zonen samt att S355MC i större utsträckning lider av en snävare övergångsradie an S355NL och S355MC Si. Detta tillsammans med en större area i Y2 regionen av svetsen tyder på att S355MC kan leda av ett starkare inåtgående flöde i smältan vilken kan påverkas av ytaktiva ämnen som syre och svavel.

This study investigated the bonding technique for the joining together of tubular sections which are under axial loading. In particular the yielding of polymers was studied and the criterion which was eventually used in the analyses was a modification of the Von Mises one. The Paraboloidal criterion accommodates differences in tensile and compressive yield strengths and accounts for any dependence of yielding on the hydrostatic component of the applied stress state. The yielding behaviour of the thin layer of the adhesive epoxy resin was analysed and it has been shown that the prediction of the adhesive strength is affected by the progress of the yield. Comparisons between the Paraboloidal and the Von Mises yield criteria have also been applied to a modified tubular joint involving threads within the bonded region. It is suggested that the prediction of the stresses at yield, using the modified criterion have a greater credibility compared with those of the Von Mises. The paraboloidal yield criterion has been implemented correctly in a standard finite element package ABAQUS. The author has made use of the "user subroutine" facility which allows a user of ABAQUS to write a sub-program defining the material constitutive relations to be used in an analysis.

Joining of dissimilar metals is a process that is of interest in many fields, especially the automotive industry where lightweighting of the body structure is important. However, creating strong joints between dissimilar metals can be challenging. Friction bit joining (FBJ) is a solid-state method that uses a consumable bit to create a strong joint between dissimilar metals such as aluminum and steel. The purpose of this research is to gain understanding of how adjusting FBJ parameters affects the heating and pressure at the weld interface using a modeling approach, in order to better understand the bonding process. The questions guiding this research are: (1) What is the effect of spindle speed, plunge rate, and plunge depth on joint strength? (2) Can the proposed model be developed with enough fidelity to correlate the effect of these parameters on joint strength, within 10%? (3) What is the effect of the simulated vertical load profile on heating at the interface? (4) Does the load profile/heating relationship correlate to experimental joint strength to within 10%? A design of experiments approach found that the effect of spindle speed on joint strength is significant. Plunge rate did not have a significant effect, but the interaction between plunge rate and spindle speed was significant. A model was created, and multiple simulations were run to study these interactions. Initial simulations were run based on the input parameters used for the experiments. The simulation data was used to run a full second order regression was run which found that spindle speed had a significant effect on the experimental Z load. The data also revealed that spindle speed and plunge rate have a strong correlation between bonded area and temperature. Simulated versus experimental Z loads have a good correlation. Experimental bonded area had a slight correlation to joint strength trending in the correct direction. The shape of the simulated cross section did not fully match the experimental cross sections but was reasonable. Simulated bonded area and experimental bonded area also have a positive correlation. Despite some weaknesses, the current model does appear to be predictive enough that it can provide insight into other FBJ design configurations and material combinations in terms of temperature profiles and welding loads.

No description available.

Carbon nanotubes (CNTs) discovered at 1991 have attracted great interest for applications in Nano-Electro-Mechanical-Systems (NEMS). However, the search for methods to join CNTs with metallic parts has been a worldwide challenge. Many efforts have been devoted to manipulating individual CNTs and joining them to each other. Joining processes so far attempted are premature and fall short of efficiency for joint quality evaluation. Thus, it has been found necessary to work on macro CNTs strands which are easy to handle via macro joining techniques. In this study, vacuum brazing technology has been developed for joining macro CNTs strands with Ni using a Ti-Ag-Cu alloy. The brazing mechanism has been confirmed as due to TiC formation at the CNTs/Ti-Ag-Cu interface. To evaluate this novel vacuum brazing technique for CNTs joining, the temperature effect on the brazing mechanism, microstructure and stoichiometry at joint interface needed to be understood. Firstly, the influence of temperature (from room temperature to 1000C) on mechanical behaviour of CNTs was well examined. The ultimate tensile strength (UTS) of CNTs was measured to be a maximum at 900C. Then, the mechanical performance of the joints was investigated from 850C to 1000C, and the fracture modes of the joints were identified. The UTS of joint also achieves maximum at 900C. Below 900C, due to little TiC formation, the bonding is weak thus leading to interfacial fracture. Above 900C, due to much TiC formation, the bonding is strong thus resulting in CNTs fracture. Furthermore, the vacuum brazing technique was applied to join CNTs to Ni contact wires used as a lamp filament. Compared to the filament joined by Ag paste or mechanical connection, the illumination of the brazed CNTs filament was stronger. The current density of the brazed filament was superior to the Ag paste connected filament. This may represent a promising way to produce energy saving lamps.

Carbon nanotubes (CNTs) discovered at 1991 have attracted great interest for applications in Nano-Electro-Mechanical-Systems (NEMS). However, the search for methods to join CNTs with metallic parts has been a worldwide challenge. Many efforts have been devoted to manipulating individual CNTs and joining them to each other. Joining processes so far attempted are premature and fall short of efficiency for joint quality evaluation. Thus, it has been found necessary to work on macro CNTs strands which are easy to handle via macro joining techniques. In this study, vacuum brazing technology has been developed for joining macro CNTs strands with Ni using a Ti-Ag-Cu alloy. The brazing mechanism has been confirmed as due to TiC formation at the CNTs/Ti-Ag-Cu interface. To evaluate this novel vacuum brazing technique for CNTs joining, the temperature effect on the brazing mechanism, microstructure and stoichiometry at joint interface needed to be understood. Firstly, the influence of temperature (from room temperature to 1000C) on mechanical behaviour of CNTs was well examined. The ultimate tensile strength (UTS) of CNTs was measured to be a maximum at 900C. Then, the mechanical performance of the joints was investigated from 850C to 1000C, and the fracture modes of the joints were identified. The UTS of joint also achieves maximum at 900C. Below 900C, due to little TiC formation, the bonding is weak thus leading to interfacial fracture. Above 900C, due to much TiC formation, the bonding is strong thus resulting in CNTs fracture. Furthermore, the vacuum brazing technique was applied to join CNTs to Ni contact wires used as a lamp filament. Compared to the filament joined by Ag paste or mechanical connection, the illumination of the brazed CNTs filament was stronger. The current density of the brazed filament was superior to the Ag paste connected filament. This may represent a promising way to produce energy saving lamps.