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In the present paper the Continuous Friction Stir Extrusion process (CFSE), derived from the already known Friction Stir Extrusion (FSE), is proposed for effective solid-state recycling of metal scraps. A new dedicated machine tool was designed and developed. A Lagrangian implicit thermomechanical numerical model was set up and used to determine the proper ranges of the most relevant process parameters. An effective case study is proposed, involving the actual extrusion of a recycled wire in a continuous way. Metallurgical observations and mechanical characterization tests were carried out on the obtained specimen showing the potential of the process and its industrial feasibility.(c) 2023 CIRP.

Aluminum Lithium alloys are recuperating substantial interest from automotive and aerospace industries owing to their extraordinary specific strength as compared to conventional aluminum (2xxx, 6xxx, and 7xxx) alloys. The goal of the present investigation is to study AA 8090 joints produced with the unique solid-state welding technique friction stir welding (FSW). Tool pin profile induces remarkable influence on friction and further plastic deformation during FSW. Therefrom, the influences of three distinct but constant dynamic area conditioned tool pin geometries namely, square trapezoidal, hexagonal trapezoidal, and threaded taper on the resulting material flow patterns, mechanical properties, and the microstructure have been studied and discussed in detail. The FSW joint produced with hexagonal trapezoidal pin geometry delivered the highest joint resistance owing to grain refinement and almost flawless microstructure.

Simple Summary The Alps are among the most vulnerable ecosystems to climate change, as these modifications take place at a faster pace at higher elevations. Since butterflies are ideal model systems to investigate species responses to climate and habitat changes, we monitored a butterfly community of the Valasco valley in the Maritime Alps (NW Italy) by three sampling events covering a period longer than 40 years. We observed an overall increase in mobile, tolerant and thermophilous species, which eventually might cause an overall loss of community distinctiveness. The variations observed in the butterfly community can be explained by the notable increase in maximum temperatures and the reduction of grasslands, along with the increase of woodlands, supporting the hypothesis that local warming and land-use changes have ultimately affected the butterfly community composition. Abstract Our work aims to assess how butterfly communities in the Italian Maritime Alps changed over the past 40 years, in parallel with altitudinal shifts occurring in plant communities. In 2019, we sampled butterflies at 7 grassland sites, between 1300–1900 m, previously investigated in 2009 and 1978, by semi-quantitative linear transects. Fine-scale temperature and precipitation data elaborated by optimal interpolation techniques were used to quantify climate changes. The changes in the vegetation cover and main habitat alterations were assessed by inspection of aerial photographs (1978–2018/1978–2006–2015). The vegetation structure showed a marked decrease of grassland habitats and an increase of woods (1978–2009). Plant physiognomy has remained stable in recent years (2009–2019) with some local exceptions due to geomorphic disturbance. We observed butterfly ‘species substitution’ indicating a general loss in the more specialised and a general gain in more tolerant elements. We did not observe any decrease in species richness, but rather a change in guild compositions, with (i) an overall increased abundance in some widespread and common lowland species and (ii) the disappearance (or strong decrease) of some alpine (high elevation) species, so that ‘resilience’ could be just delusive. Changes in butterfly community composition were consistent with predicted impacts of local warming.

Transcatheter mitral valve replacement (TMVR) is an emerging alternative treatment for those patients not qualified for surgery. However, TMVR can determine an obstruction of the left ventricular outflow tract (namely, neo-LVOT) induced by the transcatheter heart valve (THV) displacing the native mitral valve leaflet towards the myocardial wall. This condition can lead to haemodynamic impairment and ultimately patient death. We sought to predict the neo-LVOT obstruction by first developing patient-specific simulations of the THV deployment and then comparing predictions with post-TMVR diagnostic images and 3D printed human models. Using pre-TMVR computed-tomography (CT) imaging, patient-specific anatomies of two patients were reconstructed and then meshed with ABAQUS/Explicit solver. The latter was used to simulate the crimping and deployment of SAPIEN 3 THV (Edwards Lifesciences, Irvine, CA) and then simulate the cardiac beating. The neo-LVOT cross sectional area was then computed. For both patients, rigid heart models were printed with SLS rapid prototyping technology while the SAPIEN 3 device was printed with flexible resin to manually positioning the device in the human host. Numerical predictions and 3D printed model measurements of neo-LVOT area agreed well with those obtained by post-TMVR CT imaging. Both computational modelling and 3D printing revealed a comprehensive assessment of the TMVR feasibility, which is not readily conferred by conventional CT imaging. Particularly, the realistic printed models could become an efficient and indispensable tool to help the heart team visualizing the LVOT obstruction to anatomical scale, in a life-size replica of patient-specific cardiac anatomy.

Titanium alloy Ti6Al4V is one of the most utilized alloys in the field of additive manufacturing due to the excellent combination of mechanical properties, density and good corrosion behavior. These characteristics make the use of this material particularly attractive for additively manufacturing components with complex geometry in sectors such as aeronautics and biomedical. Selective Laser Melting (SLM), by which a component is fabricated by selectively melting of stacked layers of powder using a laser beam, is the one of most promising additive manufacturing technologies for Ti6Al4V alloy. Although this technique offers numerous advantages, it has some critical issues related to the high thermal gradients, associated with the process, promoting the formation of a metastable martensitic microstructure resulting in high tensile strength but poor ductility of the produced parts. The formation of microstructural defects such as balling and porosity can occur together with the presence of residual stresses that may significantly affect the mechanical characteristics of the component. Specific process parameters and geometries can determine heat accumulation phenomena that result in a progressive decrease in thermal gradients between layers. These heat accumulation phenomena are influenced by the number of layers deposited, but also by the building orientation that, for a given geometry, determines a variation of the deposited surface for each layer. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

Laser powder bed fusion is one of the additive manufacturing technologies which has developed more rapidly in recent years as it enables the production of very complex geometries. Titanium alloys are among the most popular materials in the aerospace industry thanks to excellent mechanical and corrosion resistance. The corrosion behavior and mechanical properties of samples made of Ti6Al4V and characterized by the geometrical features typical of brackets were investigated taking into account the effects of process parameters on porosity and microstructure. A comparison between the corrosion resistance of samples with complex geometry (3D) and specimens characterized by simple geometry (FLAT) was carried out to understand the role of the part geometry in the passive film formation mechanism, also highlighting the effect of the lack of passivation film formed naturally by exposure to air. Finally, the samples with complex geometry were anodized in a fluoride-free aqueous solution and the corrosion resistance was evaluated.

The progressively more demanding needs of emissions and costs reduction in the transportation industry are pushing engineers towards the use of increasingly lightweight structures. This goal can be achieved only if dissimilar and/or new materials, including polymers and composites, are joined together to create complex structures. Conventional fusion welding processes have often been proven inadequate to this task because of the high heat input reducing the joint mechanical properties or even making the joining process impossible. Joining by forming technologies take advantage on the plastic deformation to create sound joints out of even very dissimilar materials. Over the last 25 years, several new processes, with increasing potential in effectively joining virtually every structural material, have been invented and developed. In the paper, a comprehensive overview of the most utilized joining by forming processes is given. For each process, an analysis of the current research trends and hot topics is provided, highlighting strengths and weaknesses for industrial applications.

It is well known that the processing parameters of selective laser melting (SLM) highly influence mechanical and physical properties of the manufactured parts. Also, the energy density is insufficient to detect the process window for producing full dense components. In fact, parts produced with the same energy density but different combinations of parameters may present different properties even under the microstructural viewpoint. In this context, the need to assess the influence of the process parameters and to select the best parameters set able to optimize the final properties of SLM parts has been capturing the attention of both academics and practitioners. In this paper different hybrid prediction-optimization approaches for maximizing the relative density of Ti6Al4V SLM manufactured parts are proposed. An extended design of experiments involving six process parameters has been configured for constructing two surrogate models based on response surface methodology (RSM) and artificial neural network (ANN), respectively. The optimization phase has been performed by means of evolutionary computations. To this end, three nature-inspired metaheuristic algorithms have been integrated with the prediction modelling structures. A series of experimental tests has been carried out to validate the results from the proposed hybrid optimization procedures. Also, a sensitivity analysis based on the results from the analysis of variance was executed to evaluate the influence of the processing parameter and their reciprocal interactions on the part porosity.

Ever since its inception, friction stir welding (FSW) is being validated by scientific investigations as an effective substitution for fusion-based conventional joining technologies. One of the main strengths of FSW is the possibility to produce dissimilar joints, even using materials extremely different in terms of thermal and mechanical properties. The goal of the present research is to investigate the feasibility of both Al-Ti skin-stringer and reversed Ti-Al skin-stringer joints, highlighting the effect of joint configuration and main process parameters on material flow and joint mechanical properties. During the investigation, the essentiality of the proper heat input through balancing

Friction Stir Welding is nowadays an established technique successfully used by many industries. However, most of the research and, consequently, most of the applications regard aluminum alloys and butt joints. T-joints are of high interest for different industrial sectors as aeronautical, aerospace, naval and ground transportation, for which joint integrity and low residual stress are extremely important. In this study, an experimental and numerical approach is proposed with the aim to study the peculiarities of the residual stress distribution and material flow occurring in FSW of CP-Ti T-joints. Experiments were carried out to assess the feasibility of the process and to acquire the temperature data needed for the validation of a specifically set-up numerical model. Peculiar numerical strategies have been defined in order to calculate the residual stress with affordable CPU time and to highlight the bonding surface between the skin and the stringer. Main findings include a longitudinal residual stress profile different from the one usually found for butt joints. The reasons for this behavior were explained through a deep investigation on the temperature distribution in space and evolution in time. Finally, the bonding surface between skin and stringer was highlighted together with the possibility of flow defects in the fillet area.

Explosion welding (EXW) is a solid-state joining process used to produce lap joints out of metal plates of dissimilar materials. During the process, a controlled explosive detonation results in a pressure wave pushing one of the plates to be welded, called flyer, against the other with high velocity. The high pressure and temperature generated, because of the impact energy decaying into heat, create the conditions for solid bonding phenomenon to take place. Due to the complexity of experimental tests, numerical simulation is considered a fundamental design tool for the process. Different approaches are found in literature to simulate the process. In this paper, a dual step Lagrangian–Eulerian approach is proposed to evaluate the effect of different explosives on the final quality of the weld. The numerical model was developed using the commercial software ABAQUS. A three dissimilar materials joint is considered, made of two outer plates of AA5083 aluminum alloy and A516 steel, respectively, and an intermediate layer made of AA1050 aluminum alloy. The model was first validated by comparing the wavy profile of the intermediate layer after the weld, and then used to evaluate the effect of different explosive by analyzing the distribution of the main process parameters as well as the presence of voids.

In recent decades, the focus of research has shifted towards new production technologies with the aim of optimizing production and reducing costs. These innovative technologies include additive manufacturing processes as Selective Laser Melting (SLM). The analysis of the literature on the identification of optimal building orientation to maximize the mechanical properties and minimize porosity of the final products highlights contrasting results, denoting that the thermomechanical complexity of the process, as associated with the variation of the building orientation, has not been fully clarified. A study in which the building orientation effect was evaluated together with the geometry of the sample and characterized as a function of the preferentially active heat exchange phenomena was carried out with the aim to provide guidelines for the choice of the orientation angle. Heat accumulation phenomena observed in SLM were taken into account to define three geometrical parameters able to identify the causes of the decrease of mechanical properties due to incorrect choice of the orientation angle.