This thesis work intended to verify an analysis method for welded, thin-walled geometries. Guidelines for stress evaluation in welded structures exist and are standardised, but they are often verified for structures with higher plate thicknesses, such as those found in the offshore industry. Thinner structures are commonly analysed using the hotspot method, but questions still exist wherever the method is valid and can provide conservative results in thin-walled geometries.  One goal of the thesis work was to create a test plan to experimentally verify the results given by FE models of welded structures, as well as to investigate the strain gradient close to the weld toe. The plan, as well as two different welded specimens were designed and manufactured on which future analysis can be performed.  The hotspot method was also evaluated using FE analysis on geometries where two tubes were welded together with a T-joint with varying diameter, thickness and applied loads. A total of 13 different models were created using solid elements where hotspot stress extrapolation was evaluated using different extrapolation points and evaluation paths. In conclusion, it was found that the method provides a correct extrapolation of the geometric stress when stress extrapolation points at a distance of 0,4t and 1,0t from the weld toe are used (t=plate thickness). It was also found through the analysis that the geometric stress can be harder to differentiate from the non-linear part of the stress gradient for some profiles with a thickness of 0,89 mm. In some cases, this resulted in a small part of the non-linear stress being included in the extrapolation which increased the extrapolated hotspot stress. Comparisons between the hotspot stress and geometric parameters showed that stress concentration factors can be created which reduce the need for time-consuming FE models.

The majority of Refill Friction Stir Spot Welding (RFSSW) is used to join two materials together oriented in a lap joint configuration. In this study, RFSSW was investigated and tested using an unconventional configuration setup, a hole/plug insertion approach. RFSSW was tested as a means of repairing a cracked rivet hole due to excessive use conditions. This was done by inserting a plug into a hole and using the RFSSW process to bond the plug to the base material. Machine and tool limits were investigated to determine if a refilled plug repair was possible and if complete mixing between plug/hole interface was attainable. Plug/hole homogenization was assessed via metallographic polishing of weld cross sections. Properties of the repaired aluminum alloy including both dynamic and and quasi-static tensile tests were also evaluated.

An experimental program was developed to test various unreinforced RHS-to-RHS 90° T-connections subject to branch in-plane bending moment with the objective of determining the effectiveness of the welded joint. Twelve unique test specimens were designed to be weld-critical and the results from the full-scale tests revealed that the current equation for the effective elastic section modulus for in-plane bending, S_ip, given in Table K4.1 of ANSI/AISC 360 (2010) is conservative. A modification to the current requirements that limit the effective width of the transverse weld elements is proposed, resulting in a safe and more economical weld design method for RHS-to-RHS T-, Y- and X- connections subject to branch axial load or bending moment. It is also concluded that the fillet weld directional strength enhancement factor, (1.00 + 0.50sin1.5Ө), should not be used for strength calculations of welded joints to square and rectangular hollow structural sections.

An experimental program was developed to test various unreinforced RHS-to-RHS 90° T-connections subject to branch in-plane bending moment with the objective of determining the effectiveness of the welded joint. Twelve unique test specimens were designed to be weld-critical and the results from the full-scale tests revealed that the current equation for the effective elastic section modulus for in-plane bending, S_ip, given in Table K4.1 of ANSI/AISC 360 (2010) is conservative. A modification to the current requirements that limit the effective width of the transverse weld elements is proposed, resulting in a safe and more economical weld design method for RHS-to-RHS T-, Y- and X- connections subject to branch axial load or bending moment. It is also concluded that the fillet weld directional strength enhancement factor, (1.00 + 0.50sin1.5Ө), should not be used for strength calculations of welded joints to square and rectangular hollow structural sections.

Le soudage à électrode réfractaire, plus souvent appelé TIG (Tungsten Inert Gas), est un procédé dans lequel un arc électrique est généré entre une électrode en tungstène et les pièces à souder sous un flux gazeux inerte. Le transfert d'énergie entre l'arc et l'anode donne naissance à un bain métallique et à la production de vapeurs. La qualité des soudures obtenues est directement liée au comportement du plasma et aux phénomènes physiques présents dans le bain métallique (effets Marangoni, force de traînée, gravité, forces de Laplace, conduction thermique...). L'objectif de ces travaux de thèse est de mettre en place des méthodes de diagnostic permettant une meilleure compréhension des mécanismes impliqués dans le transfert d'énergie lors de l'interaction arc-matériau sur une configuration de soudage TIG. Il s'agit également d'évaluer et d'analyser l'influence de certains paramètres opératoires impliqués dans le procédé (nature du gaz, intensité du courant, longueur de l'arc...) sur ces mécanismes. Plusieurs axes de recherche ont été dégagés : - l'étude de la colonne plasma pour estimer sa température selon les paramètres opératoires utilisés ; - l'étude de l'interface arc-liquide pour la compréhension des phénomènes de brassage et d'écoulement dans le liquide ainsi que l'influence des vapeurs métalliques issues de l'érosion du matériau sur le plasma ; - l'étude du matériau après son interaction avec l'arc pour faire le lien entre le brassage dans le bain durant le procédé et les caractéristiques de la zone fondue observée après solidification. L'équipe Arc Électrique et Procédés Plasmas Thermiques (AEPPT) du laboratoire LAPLACE s'intéresse à ces phénomènes d'interaction arc-matériau par le biais de la modélisation et de l'expérience. Un modèle 3D a été récemment développé au sein de notre équipe sur cette thématique. La caractérisation expérimentale du procédé devrait permettre également d'apporter des éléments de validation aux modèles déjà existants. / TIG (Tungsten Inert Gas) welding process is achieved by the creation of an electric arc between a tungsten cathode and a piece of metal. This process uses a shielding gas as argon, helium or mixtures at atmospheric pressure. The heat transfer between the arc and the work piece leads to a metallic weld pool and metallic vapours production. Weld quality is related to the plasma behavior and the molten zone motion (Marangoni force, Laplace force, drag force and gravity...).during the process. The aim of this work is to develop diagnostic methods leading to a better understanding of mechanisms involved in heat transfer in TIG welding. The aim is also to evaluate the influence of different experimental conditions (gaz nature, current intensity, arc length...) on theses mechanisms. Several lines of research were defined: - the study of the plasma temperature under different experimental conditions; - the study of the arc-liquid interface to understand the weld pool flow behavior and the impact of metallic vapor on the arc plasma ; - the study of the work piece after interaction to determine the dimension of the melted zone and link it to the flow behavior during the process. Arc-material interaction phenomena can be studied through modeling and experience. A 3D model has recently been designed in our team. The experimental characterization of the process developed in this work should provide a set of data to validate it.

This thesis is focused on application samples with the inner insert used for Charpy impact test. This insert is welded to additional material by electron beam with pre-selected welded parameters. These parameters were chosen from data of performed experiments on homogenous welds. Resulting heterogenous weld was performed of evaluation of the microstructure, chemical composition and microhardness. Experimental materials were used austenitic steel 17 240 and ferritic steel 17 153 used on high-temperature applications.

CE-märkta stålbalkar byggdes in i två konstruktioner innan det upptäcktes att det fanns porer i hattbalkarnas svets. Den defekta svetsen innebar att byggnadernas bärförmåga inte kunde garanteras. Kunskapen kring inbyggt stål stommaterial med defekt svets är liten. Det är dessutom svårt att reparera och undersöka stålbalkarnas svets när de är inbyggda i konstruktionen. Syftet med examensarbetet är att hitta förstärkningsmetoder och därmed främja kortare hanteringstid vid händelse av att defekta stålbalkar byggs in i en konstruktion. Metoden består av litteraturstudie och intervjuer. Först granskas litteratur för att förstå problematiken med defekt svets i stål stommaterial. Därefter utförs intervjuer med personer erfarna inom stål och byggteknik. Examensarbetets resultat är ett flertal förstärkningsmetoder för inbyggda stålbalkar med defekt svets. Några av förstärkningsmetoderna är möjliga att utföra med den kunskap som finns idag medan andra behöver undersökas och värderas innan de kan implementeras. Förstärkningsmetoderna som är möjliga att utföra med dagens kunskap är: att svetsa om balken från insidan eller att placera en balk/fackverksbalk under den befintliga balken. De metoder som behöver undersökas och värderas vidare är: skruvförband genom balken, efterspänna balken med vajrar eller GWS-stag och sedan fylla den med betong, föra in en balk inne i balken och fylla balken med betong och att kolfiberförstärka svetsen. Slutsatsen är att den här studien kan ligga till grund för framtagning av åtgärder för inbyggda stålbalkar med defekt svets med mål att uppnå den dimensionerade hållfastheten och en lösning som är tidseffektiv, kostnadseffektiv och har låg klimatpåverkan. / Before the discovery of pores in the weld, CE-certified steel beams were embedded in two constructions. Since the weld was defective, the carrying capacity of the two buildings was questioned. There is a lack of knowledge about embedded steel beams with a damaged weld. It is difficult to repair and analyze the weld when the beams are embedded in the construction. The aim of the study is to find reinforcement methods for steel beams. The expectation is to shorten time in the production in case that defective steel beams are detected in the construction. The method consists of a literature study complemented by interviews. Literature is examined to understand the problem of defective welding in the steel framework. Subsequently, interviews are conducted with professionals within steel and building technology. The result of the report is multiple reinforcement methods for embedded steel beams with a defective weld. Some of the methods are possible to implement with the knowledge available today. Other methods need to be examined and assessed before executed. The reinforcement methods that are possible to perform are: weld the beam from the inside or place a beam underneath the existing beam. The methods that need further analysis are: drill a screw joint through the beam, strain the beam with steel-wires and fill the inside with concrete, place a beam inside the existing beam and fill the inside with concrete and last to reinforce the weld with carbon fibers. The conclusion is that this study can be used when reinforcement methods are needed for embedded steel beams with a defective weld. The objective with these methods is to restore the load-bearing capacity as well as finding a solution that is time efficient, economic and has low climatic influence.

The use of recommended S-N curves, presented in current literature, to analyse and determine the fatigue life of a part is common practice in, inter alia, the construction industry.However, the recommended S-N curves are generally created for larger components used in mainly the construction industry. Hence, the use of S-N curves for the evaluation of smaller parts, may result in over-dimensioning of such parts. For this reason, evaluation and designing of smaller parts could benefit from the development of an in house S-N curve specific for the part. The purpose of this thesis is to generate and validate an in-house method for creating a S-N curve, for a specific part to be compared with recommended S-N curves in the literature. The specific part used for the generating of the method is a welded steel joint with the geometry of two steel pipes, welded together in a t-formation and which has been provided by Thule AB for the purpose of the thesis. The method presented uses the results from 1) physical fatigue tests using a fatigue testing machine and 2) static FEA to derive a S-N curve for the specific part using the least squares method. A fatigue testing rig enables the gathering of data of the number of cycles to failure when the part is subject to a given cyclic load. The rig uses pneumatics to control the forces applied onto the part with the use of a cylinder. Furthermore, the fatigue testing rig was designed to be controlled by the applied force, meaning, that the rig ensured a homogeneous load cycle by measuring the force from a load cell and alternating the direction of the cylinder with an electrically controlled pressure valve. The performance of static FEA evaluations aim at locating stresses in the part. For this thesis the stresses were evaluated using the hot spot method due to the part's welded geometry. The data gathered from the physical fatigue tests and the static FEA evaluations are subsequently combined deriving S-N curves applicable to the part. From the fatigue tests and FEA evaluations for the t-shaped welded steel part, four S-N curves were derived of which two curves showed the results of a linear fitted curve whereas the other curves used the recommended slope of $-1/3$. The results showed that the S-N curves derived, using a set slope, resulted in similar curves to the recommended S-N curve provided by the literature. However, the linear fitted S-N curve showed that the part, according to the S-N curve, had a higher fatigue resistance than recommended.  Due to limitations in the thesis work, the S-N curves derived within the framework of this thesis should be regarded as theoretical and have been strictly used to identify whether the method generated is applicable for deriving of S-N curves.

Welds play a crucial role in the product portfolio of GKN Aerospace. For ease of manufacturing and repairability, butt welds are preferred in the aerospace industry. Weld regions undergo local distortions during manufacturing due to the external heat-input, and the resulting local geometries are complex and stochastic in nature. Under operational loads, the distorted geometry affects the local stress field around the weld region, and this has a significant impact on the fatigue life. Traditional design calculations of welds resort to idealization of the local weld geometry. In this thesis, the influence of real weld geometry on the computed fatigue life is investigated. Linear elastic fracture mechanics principles are utilized to calculate the fatigue life of a weld starting from a pre-defined initial crack. The influence of important weld geometric parameters, namely, – edge offset and weld toe radii, on the fatigue life is investigated in detail. A statistical analysis approach, using transfer functions and Monte Carlo simulation, is devised to study the effect of variation in the different weld geometric parameters. Different edge offset measures from a real geometry are identified and these measures are investigated as potential candidates to obtain conservative life estimates using the idealized geometry. Investigations in this thesis show that the real geometry has a significant effect on the weld fatigue life. In all cases of local weld geometry, the edge offset has the largest influence on life. For a real weld geometry, the root toe radius has a significant influence on life. In an idealized geometry, for the same normalized edge offset, an increase in the plate thickness leads to a decrease in life. A new edge offset measure is proposed that leads to conservative life estimates when used in conjunction with the idealized geometry, thus enabling computationally efficient design calculations. / Svetsar spelar en avgörande roll i GKN Aerospace produktportfölj. För att underlätta vid tillverkning och reparationer föredras stumsvetsar inom flygindustrin. Svetsområden genomgår lokala deformationer under tillverkningen på grund av extern värmepåverkan, och de resulterande lokala geometrierna är komplexa och stokastiska till sin natur. Vid termisk och mekanisk belastning i drift påverkar den deformerade geometrin det lokala spänningsfältet runt svetsområdet vilket har en betydande inverkan på utmattningslivslängden. Vid traditionell dimensionering av svetsar idealiseras den lokala svetsgeometrin. Denna avhandling undersöker inverkan av verklig svetsgeometri på den beräknade utmattningslivslängden. Linjärelastisk brottmekanik används för att beräkna utmattningslivslängden för en svets med utgångspunkt från en fördefinierad initial spricka. Inverkan av viktiga svetsgeometriska parametrar, nämligen - kantförskjutning och svetsradie, på utmattningslivslängden undersöks i detalj. En statistisk analysmetod, med hjälp av överföringsfunktioner och Monte Carlo simulering, är framtagen för att studera effekten av variation i de olika svetsgeometriska parametrarna. Olika kantförskjutningsmått från en verklig geometri identifieras och dessa mått undersöks som potentiella kandidater för att erhålla konservativa livslängdsuppskattningar med hjälp av den idealiserade geometrin. Undersökningar i denna avhandling visar att den verkliga geometrin har en signifikant effekt på svetsutmattningslivslängden. I alla fall av lokal svetsgeometri har kantförskjutningen den största inverkan på livslängden. För en riktig svetsgeometri har svetsradien vid svetsens rotsida en betydande inverkan på livet. I en idealiserad geometri, för samma normaliserade kantförskjutning, leder en ökning av plåttjockleken till en minskning av livslängden. Ett nytt kantförskjutningsmått föreslås som leder till konservativa livslängdsuppskattningar när de används i kombination med den idealiserade geometrin, vilket möjliggör beräkningseffektiva designberäkningar.

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