On the FSW of AA2024-T4 and AA7075-T6 T-joints: an industrial case study

The paper presents an artificial neural network-optimization hybrid model to predict and optimize penetration depth of CO₂ LASER-MIG hybrid welding used for 5005 Al–Mg alloy. The input welding parameters are power, focal distance from the work piece surface, torch angle, and the distance between the laser and the welding torch. The model combines single hidden layer back propagation artificial neural networks (ANN) with Bayesian regularization for prediction and quasi-Newton search algorithm for optimization. In this method, training and prediction performance of different ANN architectures are initially tested, and the architecture with the best performance is further used for optimization. Finally, the best ANN architecture is found to show much better prediction capability compared to a regression model developed from the experimental data.     

Structural analysis and electronic properties of a homodinuclear erbium(III) complex bridged by the polyazine ligand 2,2′-bipyrimidine

Structural analysis of the previously reported homodinuclear complex [Er(tfa)₃]₂bpm (where tfa = 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione and bpm = 2,2′-bipyrimidine) synthesized by reaction of two equivalents of ErCl₃ with six equivalents of tfa and one equivalent of bpm in a basic ethanol solution is presented. X-ray quality crystals were grown by slow evaporation of concentrated methanol solution containing the complex. The complex crystallizes in the monoclinic space group P2₁/n, with a planar bpm ligand. The erbium…erbium distance is 6.715(5) Å. Each erbium center is eight coordinate from six tfa oxygens and two bpm nitrogens. Electronic transitions of concentrated solutions of the complex reveal three sharp lines corresponding to the 4f–4f1 transitions at 486 nm, 520 nm and 657 nm with the lowest energy transition corresponding to ⁴I_15/2 → ⁴F_9/2.     

Thermal stress in the Apuan marbles: Relationship between microstructure and petrophysical characteristics

Apuan marbles originating from different zones of the Apuan Metamorphic Complex have been characterized from the chemical, petrographical, microstructural and physical points of view. All samples were subjected to accelerated ageing by thermal cycling and their petrophysical parameters evaluated. After accelerated ageing, all samples show an increase in total open porosity and/or porosity evaluated with Hg porosimeter in the range of pore sizes between 0.0037 and 150 μm. The greatest variations were recorded in the coarse and fine-grained marbles with straight grain boundaries. Two trends were observed in variation of the ratio of Hg-porosity to total open porosity after thermal cycling: either an increase in total open porosity not followed by a proportional increase in Hg-porosity or an increase in Hg-porosity proportional to an increase in total open porosity.During total immersion tests, an increase of the water absorption was observed for those samples characterised by a high ratio Hg-porosity/total open porosity with a unimodal distribution of Hg-porosity. In the case of water absorption through capillarity, the samples that suffer a higher increase are those characterised by a bimodal pore size distribution, even if they possess low Hg-porosity. This behaviour underlines that in the aged samples, subjected to the two different mechanisms of water absorption, the pore size distribution plays an important role.     

On the material flow in FSW of T-joints: Influence of geometrical and tecnological parameters

Friction stir welding (FSW) now definitively reached a large interest in the scientific community and what is more in the industrial environment, due to the advantages of such solid state welding process with respect to the classic ones. The latter aspects are relevant also with reference to joints characterized by a complex geometry. What is more, advanced FEM tools permit to develop effective engineering of the processes; quantitative results can be acquired from numerical simulations once basic information, as the process mechanics and the material flow, are certain. Material flow plays a fundamental role in FSW since it determines the effectiveness of the joints or, in turn, the insurgence of defects. In the paper, the material flow in the FSW of aluminum alloys T-joints is investigated at the varying of the most relevant technological and geometrical parameters with numerical simulations and experiments. In particular, to investigate the metal flow, a wide campaign of experimental tests and observations was developed utilizing a thin foil of brass as marker, placed at the interface of the two blanks to be welded. Some relevant conclusions on the process mechanics and on the actual material flow determining the material bonding are outlined, permitting an insight of the FSW of T-joints.     

Interferometric radar vs. accelerometer for dynamic monitoring of large structures: An experimental comparison

Interferometric radar has been recently proposed as a measurement instrument for dynamic testing/monitoring of large structures, such as bridges, towers, buildings, and dams, which is currently performed by networks of accelerometers. In this paper, the authors report a direct comparison between the two measurement techniques (radar interferometer vs. accelerometers) both employed during a field test on a bridge. As different quantities, displacement and acceleration are measured by the two techniques, a preliminary discussion about signals and noise has been necessary. Finally, the experimental results are critically discussed.     

In-service testing of wind turbine towers using a microwave sensor

A remote-sensing technique based on microwave interferometry is applied to dynamic testing of wind turbine towers for power generation. A high-speed interferometric radar is able to sample the structure at a rate high enough for modal and transient analysis. An experimental campaign is reported carried out on wind turbine towers of a power plant in north Sardinia, Italy.     

Detection of vertical bending and torsional movements of a bridge using a coherent radar

Interferometric radar has been recently proposed as a measurement instrument for static and dynamic testing of large structures, such as bridges, towers, dams. At the state of the art, the equipment has been demonstrated able to follow the displacements of a bridge provided that vertical bending movements are predominant with respect to torsional ones. In this paper, the authors propose and experimentally test an advancement of the interferometric technique able to overcome the previous assumption and to retrieve the effective displacement of each single section of a bridge in case of both vertical bending and torsional movements.     

Remote sensing of building structural displacements using a microwave interferometer with imaging capability

Phase interference of microwave images has been experimented for remote submillimeter-accuracy detection of structural displacements of a real-scale building, subject to tensional stress. The images are obtained by a synthetic-aperture interferometric radar, making use of continuous-wave step-frequency waveform. Phase information of the synthesized microwave images is exploited for detecting displacements of the illuminated structure.     

Control of silver-polymer aggregation mechanism by primary particle spatial correlations in dynamic fractal-like geometry

Silver nanocrystals have been prepared by reacting silver nitrate with ascorbic acid in aqueous solution containing a low concentration of a commercial polynaphthalene sulfonate polymer (Daxad 19). Various crystalline morphologies have been obtained simply by tuning the reaction temperature. We have investigated the nanoparticle formation mechanism at three different temperatures by in situ and time resolved small angle X-ray scattering measurements. By modeling the scattering intensity with interacting spherical particles in a fractal-like polymer-Ag matrix, we found signatures of nucleation, growth and assembly of primary particles of about 15-20 nm. We observed how the time evolution of both spatial correlations between primary particles and the dynamic fractal geometry of the polymer-Ag matrix could influence and determine both the aggregation mechanism and the morphology of forming nanostructures in solution.