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In this article, friction stir welded lap joints of innovative dissimilar aluminum alloys have been produced and tested to investigate the feasibility of using this joining technique in this configuration. The introduction of both this new welding technique alloys, such as AA 2198, could allow making lighter and stronger structures. Some experiments, carried out previously, have shown that the fixturing device, the tool geometry, and the tilt angle play a significant role in the joint soundness. A wide experimental characterization has been carried out on friction stir welded lap joints of AA 7075T6 extrudes to AA 2198T351 rolled plates. The results attained are allowed to put in evidence some critical issues on the investigated configuration and can be considered as a further acquired knowledge in the understanding and the design of friction stir process.

The effect of welding parameters on the mechanical properties of friction stir-welded dissimilar aluminium alloys in overlap joint configuration was studied. Both the welding configuration and the materials chosen were a typical skin-stringer configuration, widely used for aeronautical fuselage panels. Mechanical properties were evaluated by means of both hoop stress and T-pull test. Results show that there is a great dependence of the hoop stress resistance from welding parameters; conversely, T-pull tests do not show the same dependence. The present work demonstrates the suitability of the x in lap configuration for joining dissimilar aluminium alloys.

Friction-stir welding (FSW) is a solid-state joining process where, in contrast to the fusion welding, the material to be welded does not reach the melting point. Due to its interesting features, a lot of research activities have been carried out on FSW of different materials. In particular, FSW of AA 2198 aluminium alloy has gained wide interest for the fabrication of lightweight structures requiring a high strength-to-weight ratio and a good corrosion resistance. In this study, rolled plates of AA 2198 T3 aluminium alloy are friction-stir welded in butt configuration varying two fundamental process parameters: rotational and welding speeds. An empirical model based on regression analysis is developed to predict the mechanical strength, in particular yield and tensile strength, of the joints as function of the process parameters under investigation. For the development of the empirical model, a 32 full factorial designs with the yield and tensile strength as observed responses is used. Statistical tools such as analysis of variance, F tests, Mallows' CP, coefficient of determination etc. are used to build and to validate the developed models. By using the desirability function approach, the optimum process parameters to simultaneously obtain maximum possible yield and tensile strength are found within the investigated range. The developed models can be effectively used to predict the stationary forces and the mechanical proprieties of the joints at 95% confidence level. Finally, to validate the possible use of FSWof 2198 in the in the aerospace industry, joints welded using the optimum process parameters before identified are tested under stress corrosion cracking and fatigue. Results show that, unlike the base material, the optimized joints are not attacked by pitting if subjected to a tensile stress in a corrosive environment; furthermore, their fatigue life is comparable to that of the base material and longer than that showed by joints welded using traditional techniques, as MIG or TIG.

The bending behavior of hybrid sandwich panels, with aluminum foam core, and carbon fiber reinforced thermoset resin face sheets, have been investigated. The effect of core and face sheets thickness and span , on 3-point bending test, has been evaluated for the sandwich panels . Core yielding and indentation failure modes, influenced by the core properties, have been identified and analytical models to evaluate the maximum load have been applied. The failure mode map has been constructed, which illustrates the dominant failure mode for practical beam design. In order to simulate the different failure modes, FE analysis has been pointed out.

Nel presente lavoro sono stati studiati giunti FSW di testa in lega innovativa AA 6156, di cui sono state valutate sia le proprietà meccaniche che le tensioni residue indotte dal processo di saldatura stesso. Per lo studio delle tensioni residue è stata utilizzata una tecnica innovativa denominata QNA che si basa sull’interpretazione di immagini termografiche che ritraggono l’oggetto in esame, opportunamente sollecitato, attraverso il software matlab ed in particolare l’utilizzo della trasformata Wavelet.

Laminates of high density polyethylene (HDPE) reinforced with wood flour and long hemp fibres have been manufactured adopting a process consisting of two steps. In the first step, pellets of wood flour/HDPE composite, i.e. wood plastic composite (WPC), were compounded by extrusion; in the second step, laminates of WPC and WPC reinforced with hemp fibres were manufactured by compression molding. The properties of the obtained composite materials, measured by means of flexural tests, dynamic mechanical analysis (DMA) and creep tests, have been compared with the matrix (HDPE) properties. Mechanical properties of the WPC increase with the weight percent of wood flour, but WPC reinforced by unidirectional long hemp fibres present the best properties also at high temperature.

Magnesium alloys are attractive for lightweight structural applications in the transportation industry because of their low density and high specific strength and stiffness [1]. With an ultrafine-grained microstructure, they exhibit superplasticity at relatively low temperatures and high strain rates [2]. Friction stir processing (FSP) was used to obtain a microstructure with ultrafine grains in the magnesium alloy AZ31. In this project, microstructures obtained using different rotational speeds are studied. Free bulge forming of the FSP processed AZ31 sheets are carried out to evaluate the superplastic behaviour [3]. The model and the evolution equations have been implemented into a commercial finite element modeling (FEM) code and different simulations are conducted to correlate the experimental and numerical results for the model validation [4]. The purpose of this study is to investigate the effect of the microstructure on the superplastic forming behaviour using free bulge forming and FE simulations.

The influence of welding speed and laser power on weld quality of 1.6 mm thick Ti − 6Al − 4V sheets autogenously laser beam welded in butt configuration using a Nd-YAG laser was studied. The joint quality was characterized in terms of weld morphology, microstructure and mechanical properties. An underfill defect, controlling the whole weld geometry, was observed both at the weld face and root surface. In dependence of the specific heat input, this defect showed a maximum, which separates two different welding regimes: keyhole welding, at low heat input, and a welding regime where heat conduction around the keyhole is predominant, at high heat input. Influence of the underfill radius on the weld fatigue life was also assessed.