Master of Science / Department of Computing and Information Sciences / Doina Caragea / The evolution of the World Wide Web has resulted in extremely large amounts of information. As a consequence, users are faced with the problem of information overload: they have difficulty in identifying and selecting items of interest to them, such as books, movies, blogs, bookmarks, etc. Recommender systems can be used to address the information over-load problem by suggesting potentially interesting or useful items to users. Many existing recommender systems rely on the collaborative filtering technology. Among other domains, collaborative filtering systems have been widely used in e-commerce and they have proven to be very successful. However, in recent years the number of users and items available in e-commerce has grown tremendously, challenging recommender systems with scalability issues. To address such issues, we use canopy/clustering techniques and Hadoop MapReduce distributed framework to implement user-based and item-based recommender systems. We evaluate our implementations in the context of movie recommendation. Generally, standard rating prediction schemes work by identifying similar users/items. We propose a novel rating prediction scheme, which makes use of dissimilar users/items, in addition to the similar ones, and experimentally show that the new prediction scheme produces better results than the standard prediction scheme. Finally, we engineer two new approaches for clustering-based collaborative filtering that can make use of movie synopsis and user information. Specifically, in the first approach, we perform user-based clustering using movie synopsis, together with user demographic data. In the second approach, we perform item-based clustering using movie synopsis, together with user quotes about movies. Experimental results show that the movie synopsis and user demographic data can be effectively used to improve the rating predictions made by a recommender system. However, user quotes are too vague and do not produce better predictions.

In order to meet the increasing fuel efficiency requirements, the automotive industry has strived for component weight reduction in order to improve the performance of automotive vehicles through the use of light Al and Mg alloys. Resistance spot welding (RSW) currently is the primary joining method in the manufacturing of automotive assemblies. With the increased use of Al and Mg, there is a pressing need for a technology to produce dissimilar Al/Mg joints, and preferably by RSW since this technology is already prevalent in the industry. Direct welding of Al to Mg usually results in formation of hard and brittle intermetallic compounds and poor quality of the welds. Employing an interlayer is a promising approach to overcome this problem. Current literature, however, does not consider the effects of different interlayers on RSW of Al to Mg. This thesis examines effects of different interlayers on microstructure and mechanical properties of Al/Mg joints made by RSW. Effects of three types of interlayers, specifically pure Ni foil, Au-coated Ni foil and Zn-coated were investigated in details. While only brief investigation of joints made with Sn-coated steel, Zn foil, and Cu foil interlayers was conducted. No joints were achieved with a bare Ni interlayer during Al to Mg alloy resistance spot welding, as coupons separated without applying any force. The Ni interlayer remained intact and Al-Mg intermetallic compounds did not form. Addition of Au coating on Ni surface greatly contributed to the metallurgical bonding at the interfaces and welds easily met requirements of the AWS D17.2 standard. Average lap-shear strength reached 90% of that in similar AZ31B resistance spot welds. Acceptable welds were also produced using galvanised Zn-coated steel interlayer, which easily met strength requirements of the AWS D17.2 standard. Average failure load reached 74% of same size similar AZ31B joints. The steel interlayer was not melted which prevented mixing of Al and Mg. The Zn coating on the steel interlayer was melted and squeezed to the nugget periphery, providing a clean steel surface for welding-brazing in the center and acting as a solder metal at the periphery. A feasibility study of Al/Mg RSW with Sn-coated steel, Zn foil and Cu foil interlayers was also conducted. Mechanical properties of welds made with Sn-coated steel interlayer were very similar to those made with Zn-coated steel interlayer. While welds made with only a Zn foil interlayer were much weaker. The Zn foil completely melted during the welding which resulted in formation of brittle Al-Mg-Zn phases. None of the welds made with Zn foil interlayer met requirements of the AWS D17.2 standard. RSW of Al to Mg with Cu foil interlayer also could not produce welds with acceptable strength.

The interface crack branching phenomena, including thermal effects, has been investigated by using complex variable method and Stroh's dislocation theory, extended to thermo-elasticity in matrix notation. As one of the most catastrophic failure modes in structures like laminated and sandwich composites in aerospace and marine construction, thin film in electronic packaging, rotators in high speed engine of aircraft and reactor in nuclear power station, the study of interface crack branching has become a topic not only having theoretical importance, but also having practical significance. A unified approach is presented to address the thermoelastic interface crack problems in dissimilar anisotropic bimaterial composites, and a compact closed form solution is formulated by analytical continuation principle of complex analysis. Employing the contour integral method, an explicit solution to the interaction between the dislocations and the interface crack is obtained. By modeling the branched portion as a continuous distribution of the dislocations, the thermoelastic interface crack branching problem is then converted to a set of semi-coupled singular integral equations and solved by Gauss-Jacobi integration schemes. The influence of material property mismatches between the two constituents and the thermal loading effects on the interface crack branching are demonstrated by extensive numerical simulation. Some useful criteria for predicting the interface crack branching growth and guidance for optimal composites design are suggested. Further, a contact model to eliminate the overlapping between the two surfaces of an interface crack is also proposed and some new parameters which could influence the interpenetrating phenomena are also discovered. The technique to extend the current method to three dimensional problems is also outlined. Furthermore, the C++ source code has been implemented to manipulate the complicated complex operations for numerically solving the singular integral equations in complex matrix form.

A three-Dimensional deflection of the electron-beam resulting a missed joint due to thermoelectric magnetism generated in welding dissimilar metal is experi- mentally and analytically investigated. In theoretical analyisis a narrow welding cavity is assumed to be a paraboloid of revolution. Applying a three-dimensional analytical solution of thermolectric currents, magnetic fiux densities, and deflections of the electron beam are determined from Maxwell's electromagnetic equations. The computed magnetic fields,thermoelectric currents and beam deflection will be compared to experimental results. Factors affect-ing deflection are discussed. The major advantage of welding with a high-power-density-electron-beam is the ability to weld dissimilar metals, unfortunately, can be missed. when the beam from the electron gun is properly aligned with the joint, subsequent deflection of the beam can result in nonsymmetric fusion along a joint, or the fusion zone may miss the joint .One reason responsible for the beam deflection is due to thermoelectric magnetic fields. Since temperature gradients exist between the top and bottom and in front and be-hind the deep and narrow cavity ,thermoelectric currents due to the Seebeck effect are produced in dissimilar metals. The induced magnetic field above and below the top surface therefore deflects the electron-beam and induces a missed joint in S-shaped. In this study, experiments will be conducted to measure missed joints. A three-dimensional thermoelectric and heat conduction model is also to predict deflection of an electron-beam From the surroundings and to bulk workpieces, the entire trajectory of the beam can be determined.a more systematical and realistic understanding on missed joint parameters.

In order to meet the increasing fuel efficiency requirements, the automotive industry has strived for component weight reduction in order to improve the performance of automotive vehicles through the use of light Al and Mg alloys. Resistance spot welding (RSW) currently is the primary joining method in the manufacturing of automotive assemblies. With the increased use of Al and Mg, there is a pressing need for a technology to produce dissimilar Al/Mg joints, and preferably by RSW since this technology is already prevalent in the industry. Direct welding of Al to Mg usually results in formation of hard and brittle intermetallic compounds and poor quality of the welds. Employing an interlayer is a promising approach to overcome this problem. Current literature, however, does not consider the effects of different interlayers on RSW of Al to Mg. This thesis examines effects of different interlayers on microstructure and mechanical properties of Al/Mg joints made by RSW. Effects of three types of interlayers, specifically pure Ni foil, Au-coated Ni foil and Zn-coated were investigated in details. While only brief investigation of joints made with Sn-coated steel, Zn foil, and Cu foil interlayers was conducted. No joints were achieved with a bare Ni interlayer during Al to Mg alloy resistance spot welding, as coupons separated without applying any force. The Ni interlayer remained intact and Al-Mg intermetallic compounds did not form. Addition of Au coating on Ni surface greatly contributed to the metallurgical bonding at the interfaces and welds easily met requirements of the AWS D17.2 standard. Average lap-shear strength reached 90% of that in similar AZ31B resistance spot welds. Acceptable welds were also produced using galvanised Zn-coated steel interlayer, which easily met strength requirements of the AWS D17.2 standard. Average failure load reached 74% of same size similar AZ31B joints. The steel interlayer was not melted which prevented mixing of Al and Mg. The Zn coating on the steel interlayer was melted and squeezed to the nugget periphery, providing a clean steel surface for welding-brazing in the center and acting as a solder metal at the periphery. A feasibility study of Al/Mg RSW with Sn-coated steel, Zn foil and Cu foil interlayers was also conducted. Mechanical properties of welds made with Sn-coated steel interlayer were very similar to those made with Zn-coated steel interlayer. While welds made with only a Zn foil interlayer were much weaker. The Zn foil completely melted during the welding which resulted in formation of brittle Al-Mg-Zn phases. None of the welds made with Zn foil interlayer met requirements of the AWS D17.2 standard. RSW of Al to Mg with Cu foil interlayer also could not produce welds with acceptable strength.

Friction joining techniques, such as Friction Stir Spot Welding (FSSW) and high power Ultrasonic Welding (USW), could offer a solution for joining dissimilar materials combinations, such as aluminium (Al) to magnesium (Mg), where high intermetallic reaction rates make the use of conventional joining techniques problematic. Ultrasonic welds have been produced between 1 mm gauge Al 6111-T4 and Mg AZ31-H24 sheets, and the interfacial reaction has been studied as a function of welding time. For this welding system, the mechanical properties of the joints were optimised when a double reed welding system was employed to join materials that had been prepared using 800 grit SiC paper under a clamping force of 1.9 kN, and when the materials were oriented with the rolling direction parallel to the vibration direction. Welds produced between Al and Mg achieved similar peak lap shear strengths to those produced between Mg and Mg at welding times of 0.4 s, but the failure energy of the Al-Mg welds was less than half that of the parent material. In addition, the Al-Mg welds always failed at the interface between the sheets, rather than the desirable, and more energy intensive, pullout mechanism. The inferior mechanical properties were attributed to the rapid formation of a brittle intermetallic layer that initially formed as islands of the γ-Al12Mg17 phase. These islands rapidly spread and became continuous within 0.3 s of welding time, at which point a second sublayer of the β-Al3Mg2 phase began to form on the Al side of the intermetallic reaction layer. The combined layers reached a total thickness of 20 µm within 0.9 s of welding time, with the β-Al3Mg2 sublayer becoming the thicker of the two by this point. At longer welding times, interface liquation was observed at temperatures below the recognised lowest temperature eutectic reaction in the Al-Mg binary phase diagram. This was the result of the alloying elements present in the system and there was no depression in the melting point as a result of the high strain rate associated with this process, as has been proposed elsewhere. The rate of growth of the intermetallic layer during welding was higher than in static heat treatments, which was most likely due to the deformation causing microcracking in the brittle intermetallic layer, allowing short circuit diffusion to occur, and enhancing the growth rate by a factor of approximately 2. Finally, attempts were made to limit the rate of intermetallic compound (IMC) formation by applying coatings to the Mg sheet. The effect of the coatings was to reduce the overall IMC layer thickness by 50 %.

The following report conducted by the theoretical research and experimental study in the University of Halmstad. The focus of the project is experimental investigation on weld characteristics for shield metal arc welding with SS304 & SS409. Welding is a joining process of similar metals but nowadays it is also joined dissimilar metals by the application of heat. The different types of welding process are available in industry. Welding can be done with or without the application of pressure and filler materials in shielded metal arc welding (SMAW), an arc between a covered electrode and a weld pool is used to accomplish a weld. As the welder steadily feeds the covered electrode into the weld pool, the decomposition of the covering evolves into gases that shield the pool. Austenitic stainless steel and Martensitic chrome alloys is widely used materials in the current industrial area including higher and lower temperature applications such as storage tanks, pressure cups, furnace equipment’s etc. This paper concentrated to the investigate the dissimilar material joining by using shield metal arc welding and study the welding characteristics and do the mechanical tests. The aim of this study performance of steel and maximum hardness of welded material, microstructure of steel on next phase of project. The results will be used to character of dissimilar material performance.

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.

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