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A push towards more energy-efficient transport solutions has led to an increasing lightweight trend in structural design, requiring new materials, manufacturing, and assembly processes. The development of solid-state welding techniques, such as friction-stir welding (FSW), and the continuous improvement of adhesive technology, has created opportunities for new structural design concepts. Although FSW is capable of producing sound defect-free welds with high tensile strength efficiency in butt joint configuration, in the case of lap joints, the formation of a “hook”-like defect results in worse properties than base material. The combination of adhesive bonding (AB) with FSW aims to overcome this issue and create a hybrid joining technique. This work aims to develop a hybrid technique combining FSW and AB aggregating static strength testing and numerical modelling efforts. AB joints showed a 60% higher strength than FSW lap joints, but when combining FSW with adhesive, the hybrid joint managed to match the adhesive joints strength. Finite elements method (FEM) models developed for both AB and FSW lap joint showed some level of agreement, but when attempting to combine both models to discretize the hybrid joints the developed model failed to mimic the more complex failure mode. [ABSTRACT FROM PUBLISHER]

Building lightweight structures is one of the key strategies to guarantee an efficient, competitive, safe and sustainable public transport system. The implementation of reliable and optimized lightweight structures needs to achieve high levels of performance, cost effectiveness and sustainability. The expected weight saving will significantly reduce fuel consumption and therefore CO 2 emission per passenger-kilometer. Friction Stir Welding (FSW) is a solid state process enabling to develop new design concepts for lightweight metallic materials, where previously conventional manufacturing processes as riveting or classical welding were used. This study was conducted within the LighTRAIN project that aims to improve the life cycle costs of the underframe of a passenger railway car, with a novel lightweighted solution. The major objective of the research was to study the fatigue behaviour of dissimilar welded joints based on two different aluminium alloys: AA6082 and AA5754. The paper presents the experimental results obtained in two different structures: AA6082-T6 2 mm and AA5754-H111 2 mm thick joints, and AA6082-T6 2 mm thick joints. Fatigue tests were carried out on lap joints specimens with a constant amplitude loading with a stress ratio R = 0.1. The results of the fatigue tests are presented as well as detailed metallographic characterization of the weld zone and also the hardness distribution at the weld region. Fatigue tests performed on similar and dissimilar joints show low fatigue strength when compared with base materials AA5754 and AA6082, which is associated with the typical “hook” defect inherent to this welding process. The fatigue performance of AA6082 and AA5754 FSW welded joints suggests a shallower S–N curve than for the similar AA6082 FSW welded joints with an improvement in fatigue performance for lower applied stress ranges. [ABSTRACT FROM AUTHOR]

The push towards lightweight efficient structural design has led to an increasing interest in joining technologies for aluminum alloys. Although the use of these alloys has previously been restrained by production difficulties associated with their poor welding properties, friction stir welding and adhesive bonding allowed for a larger flexibility in lightweight structural design. In this work a combined joining process of this welding technique with adhesive bonding (friction stir weldbonding) is presented. Quasi-static mechanical properties, fatigue behavior and other properties of the friction stir weldbonding joints were assessed and compared with adhesive only and welded only joints. Friction stir welding (FSW) is a revolutionary joining method that allowed welding of previously unweldable alloys with excellent characteristics, and has an enormous potential for application in a large array of industries. Even though friction stir welding presents several advantages over other welding techniques when regarding joining of aluminum alloys, it also presents its share of challenges. For example, in the case of overlap configuration joints, which are very common in structural design, the presence of a hook defect reduces the static and fatigue strength as this defect acts like crack initiation point. In certain alloys the question of chemical corrosion is also a factor requiring good sealant measures to avoid degradation. The combination of FSW with adhesive bonding (AB), forming friction stir weldbonding may present itself as a solution for these concerns. The development of this new joining technology aims at incorporating properties and characteristics of both joining technologies, as well as improving damage tolerance. FSW is able to produce consistent joints with high static strength, while the adhesive will not only allow improved vibration damping and fatigue strength but may also serve double duty as a sealant, isolating the weld from the environment. Damage tolerance is improved, by having to failure mechanisms, cohesive rupture in the adhesive and ductile and shear failure in the aluminum. [ABSTRACT FROM AUTHOR]

Abstract: Railways passenger transportation seeks weight reductions as a means to reinforce its sustainability. The use of aluminium alloys for the vehicle car bodies is a possible alternative, but difficulties are foreseen concerning the fatigue behaviour of the connection of heavy equipment to the underside of the structural floor panels. This study was conducted within the LighTRAIN project, involving two universities, two industrial companies and one research centre, that aims to improve the life cycle of the underframe of a passenger railway car, with a novel light-weighted solution. The main objective of present work was to study the fatigue behaviour of 2.0mm thick aluminium AA6082-T6 welded joints based on two different welding processes: Friction Stir Welding (FSW) manufactured at Instituto Superior Tecnico (IST) and Laser Beam Welding (LBW) manufactured at QUANTAL. The paper presents the experimental results obtained in tensile and fatigue tests of welded lap joints. The specimen types include the loading condition applied to the specimen in a transverse or longitudinal direction to the weld bead. The fatigue tests were carried out under a constant amplitude loading with a stress ratio R=0.1 for a wide range of applied stress. The mechanical behaviour, including microstructural, microhardness, tensile and fatigue tests results of AA6082 2.0mm thick FSW welded joints are compared with LBW welded joints in the framework of the aforementioned QREN project. Moreover, details of fracture surfaces obtained with optical microscopy are also presented. [Copyright &y& Elsevier]