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Thesis on Electron beam welding of ODS materials is divided into theoretical and experimental part. In the first part the theoretical research work focuses on the accurate description of the candidate materials in a research fusion reactor ITER. Following are detailed constructional ODS materials and tungsten alloy as a material of the first wall. The second part of the theoretical research deals with various possibilities of joining high-melting dissimilar materials such as brazing or electron beam welding as well, which will be established in the experimental section. The experimental part of the thesis deals with a joining ODS steel MA 956 with sintered carbide WC-Co and ODS tungsten. These materials are welded by electron beam. Individual samples are distinguished used filler material, preheating or welding parameters. This thesis contains photographic documentations of microstructure the welding samples, results from scanning electron microscopy, and measurements of microhardness across the weld metal.

The primary contributor to greenhouse gases emissions in the European Union is the road transport sector, accounting for over 70% of total emissions. In response to this environmental concern, the EU is working on implementing strict regulations aimed at reducing emissions by 45% by the year 2030, compelling manufacturers of heavy-duty vehicles to produce emission free alternatives. While vehicle electrification is a promising solution,it introduces a new challenge: the need for lighter vehicles becomes more increasing with the incorporation of powerful yet heavy battery systems. This work aims to study the possibility of substituting the steel bus frames with composite material frames with the dual objectives of reducing the overall weight of the bus and minimising its environmental footprint throughout the life cycle of the part. The most suitable composite materials, manufacturing processes and joining methods for the studied frames were investigated based on literature review and a list of requirements. Composite finite element analysis was performed to study the behaviour of the composite assembly when it is inserted into the steel bus model to simulate the real-life environment.  The analysis performed showed that composite frames can facilitate a mass reduction of over half of the steel frames weight. An unfailing structural behaviour of the laminate can be achieved using adhesive bonding as the joining method between the two distinct materials. At the same time, two significant needs were highlighted: the importance of laminate optimisation (in terms of different material properties, number of layers and orientations) both to reduce costs and to maximise the structural strength through effective and efficient material distribution and the importance of partitioning the composite structure in a cost beneficial way (when it comes to scrap levels and moulds complexity). / Den huvudsakliga bidragande faktorn för utsläpp av växthusgaser inom den Europeiska Unionen är vägtransportsektorn som står för över 70% av alla utsläpp. Som gensvar på detta bekymmer för klimatet jobbar EU på att implementera stränga regler som syftar till att minska utsläppen med 45% till år 2030, vilket tvingar tillverkare av tunga fordon att producera utsläppsfria alternativ. Fastän fordonselektrifieringen är en lovande lösning, introducerar den en ny utmaning: behovet av lättare fordon ökar i takt med införandet av kraftfulla men tunga batterisystem.  Syftet med detta arbete är att studera möjligheten att ersätta bussars stålramar med kompositmaterialramar med det dubbla målet att minska bussarnas totala vikt samt minimera deras klimatvtryck under ramarnas livscykel. Tillverkningsprocessen och sammanfogningsmetoderna för de studerade ramarna undersöktes baserat på litteraturgenomgång och en kravlista för att ta fram de mest lämpliga kompositmaterialen. Kompositfinit elementanalys genomfördes för att studera beteendet hos ihopsättningen av kompositen när det sattes in i stålbussmodellen för att simulera den verkliga miljön. Den genomförda analysen visade att kompositramar kan leda till en massreduktion på över hälften av stålramarnas vikt. Ett osvikligt strukturellt beteende hos laminatet kan uppnås genom att använda adhesiv bindning som sammanfogningsmetod mellan de två distinkta materialen. Samtidigt lyftes två betydande behov: vikten av att optimera laminatet (vad gäller olika materialegenskaper, antal lager och orienteringar) både för att minskakostnader och för att maximera den strukturella styrkan genom effektiv materialfördelning och vikten av att dela upp kompositens struktur på ett kostnadseffektivt sätt (när det kommer till avfallsniv ̊aer och gjutningskomplexitet).

This thesis explores new methods for achieving load-carrying joints between the dissimilar materials of continuous fibre reinforced polymer matrix composites and structural metals. The new composite-to-metal joining methods investigated in this work exploit the metal-to-metal joining techniques of arc micro-welding, resistance spot welding, and metal filler brazing, to form novel micro-architectured metal adherends that can be used for enhanced composite-to-metal joining. Through a combination of equipment instrumentation and metallographic inspection of fabricated prototype joints, understanding is gained of how materials respond when processed by manufacturing techniques that have not previously been exploited for dissimilar material joining. Mechanical testing of prototype joints; both to ultimate loading strength and partial failure states, with subsequent inspection of specimens and comparative performances evaluation enabled joining performance characterisation of the new joining methods. Key results include: the identification of micropin reinforced adhesive joints to exhibit pseudo-ductile failure characteristics, resistance spot weld reinforcement of adhesive joints to boost bonding performance, and the use of a polymer infused metal foam to overcome difficulties of thermoplastic to metal adhesion. Through this work knowledge of how novel micro-architectures reacted under mechanical loading enabled insights to be gained into how perceived manufacturing defects can benefit joining performance. Such examples include, localised material weakness that lead to global pseudo-ductile failure behaviour, and low-strength secondary joining mechanisms boosting primary load transfer systems. By comparison of the diverse joining methods investigated in this work, trends were identified that suggest joining performance between the two dissimilar materials is improved by increasing the direct interaction between the composite reinforcement fibres and the metal structure. It is demonstrated that joining improvements are gained by forming mechanical connections between metals and composite precursory material before the final manufacturing process of the composite.

During the assembly process of battery packs for electric vehicles, it is crucial to ensure that the cell-to-busbar joints can be produced with high quality, good reliability, and with minimal impact on the individual battery cells. This thesis project investigates the influence of different process parameters on the joint quality for laser welded dissimilar material cell-to-busbar joints. Nickel plated copper and steel plates, joined in an overlap configuration, are used as a simplified geometry, representing a cell-to-busbar joint. By the utilization of artificial neural network-based meta models, trained on numerical results from computational fluid dynamics simulations of the laser welding process, the joint quality is predicted and evaluated. The present thesis investigates how a set of optimized process parameters can be identified for the considered laser welded dissimilar material cell-to-busbar joints, in order to simultaneously maximize the interface width for the joints, and minimize the formation of undercuts and resulting in-process temperatures. NSGA-II is used to efficiently search for trade-off solutions, in an meta model-based multi-objective optimization approach, where the meta models are used to approximate the objectives, corresponding to the joint quality obtained from computational fluid dynamics simulations. With this, the time for one objective evaluation is reduced from approximately 9 hours, when the objectives are evaluated directly from computational fluid dynamics simulations, to only tenths of a second. With the proposed optimization approach, the Pareto-optimal front of trade-off solutions is identified, leading to the selection of three optimal solutions for validation. The validity of the proposed optimization approach, and the selected optimal solutions, are confirmed by means of both physical laser welding experiments and computational fluid dynamics simulations. It is shown that the selected optimal solutions, corresponding to three parameter setups, can be used to produce joints with large interface width and low in-process temperatures, without achieving a full penetration in the lower plate of the joint.

Electromagnetic welding is an innovative, high-speed technology to manufacture mixed material joints. In this dissertation, an experimental-numerical method is presented to identify robust process windows of aluminum-copper and aluminum-steel compounds. The microstructural characteristics of these joints were investigated in detail. Moreover, an evaluation of the joint quality is presented and different numerical models were introduced for the simulation of macroscopic and microscopic effects. To improve the accuracy of the simulations, the strain rate sensitivity of the materials must be considered. For this purpose a high-speed setup for the identification of relevant viscoplastic material parameters, comprising an inverse evaluation strategy, was developed.

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