Progresses in multi-materials billet manufacturing out of metal scraps through friction stir consolidation

The evolution of Friction Stir Consolidation (FSC) from recycling towards upcycling technique proved to be one of the excellent solid-state methods for manufacturing functionally graded billets. Multi-material Functional Graded Materials (FGMs) represent a novel class of materials characterized by a gradual change in properties and functions which can be tailored to enhance components performance. Manufacturing techniques play a critical role in achieving the designed compositional and microstructural distribution. Specifically, FSC allows the manufacturing of FGM billets out of metallic chips; the mixing of different metallic chips offers mutually exclusive mechanical properties like high hardness and good ductility in a single FSC billet with excellent formability. The present research further explores some challenges while combining dissimilar aluminum alloys chips in different percentages and spatial order, especially in the radial direction. The mechanical and metallurgical properties were assessed through the Vickers hardness measurements and microstructure analysis. The results revealed that new strategies are needed for a better exploitation of FSC as a solid-state method for fabrication of Functionally Graded Materia

Towards the implementation of circular economy in the water softening industry: A technical, economic and environmental analysis

To reduce the environmental impact of the industrial sectors, circular strategies should be implemented to purify the effluents and recover raw materials. In this context, a novel integrated methodological approach is proposed to identify the most suitable strategy to improve the sustainability of the water softening industry via the treatment and recycling of the produced wastewater. Different concentration technologies and energy supply systems are compared to find economically feasible and environmentally friendly treatment systems. The investigated chains present the same pre-treatment step (nanofiltration and crystallization) and different concentration technologies: Multi-Effect Distillation (MED), Membrane Distillation (MD) and the coupling of Reverse Osmosis and Membrane Distillation (RO-MD). In the case of electricity supplied by the grid, the MED and the RO-MD chain are economically competitive with the state of the art (Levelized Brine Cost (LBC) between 4 and 6$/m3, lower than the regenerant solution cost, equal to 8$/m3). Moreover, the specific CO2 emissions due to the energy required by the treatment processes (10.8 kgCO2/m3regenerant for the MED chain and 16.7kgCO2/m3regenerant for the RO-MD chain) are lower than those produced by the current system (19.7kgCO2/m3regenerant). Varying the feed flow rate, the MED-chain is more feasible at larger plant sizes for its lower energy demand, while the chain including RO-MD shows lower costs at smaller plant sizes for its lower investment costs. When a photovoltaic-battery system is coupled, both the MED-chain and RO-MD-chain show a CO2 emission reduction of more than 75% with respect to the state of the art. Furthermore, their LBC values are very competitive, especially if the plant is located in a region with high solar potential

In-stent restenosis of superficial femoral artery: use all arrows in the quiver.

In-stent restenosis (ISR) is a common superficial femoral artery (SFA) stenting complication, occurring in more than one third of patients within 2-3 years after the index procedure. Moreover, there is no standard treatment for ISR, and although many options are available, there is still limited data regarding its optimal management. We report a paradigmatic case report of a patient complaining of symptomatic peripheral arterial disease, underwent multiple endovascular revascularizations for recurrent femoro-popliteal ISR. A step-by-step approach was followed. At the time of the first presentation, the ISR was treated by drug-eluting balloon (DEB) angioplasty. The repeated ISR was treated by laser debulking, achieving a good angiographic result. Finally, after the third repeated restenosis, a combined approach with laser debulking and DEB angioplasty guaranteed a good acute angiographic result. Long-term duplex-scan follow-up demonstrated the good patency of the femoro-popliteal target lesion

Right anterior mini-thoracotomy vs. conventional sternotomy for aortic valve replacement: A propensity-matched comparison

Background: Right anterior mini-thoracotomy (MIAVR) is a promising technique for aortic valve replacement. We aimed at comparing its outcomes with those obtained in a propensity-matched group of patients undergoing sternotomy at our two high-volume centers. Methods: Main clinical and operative data of patients undergoing aortic valve replacement between January 2010 and May 2016 were retrospectively collected. A total of 678 patients were treated with a standard full sternotomy approach, while MIAVR was performed in 502. Propensity score matching identified 363 patients per each group. Results: In-hospital mortality was not significantly different between the propensity-matched groups (1.7% in MIAVR patients vs. 2.2% in conventional sternotomy patients; P=0.79). No significant difference in the incidence of major post-operative complications was observed. Post-operative ventilation times (median 7, range 5-12 hours in MIAVR patients vs. median 7, range 5-12 in conventional sternotomy patients; P=0.72) were not significantly different between the two groups. Cardiopulmonary bypass time (61.0±21.0 vs. 65.9±24.7 min in conventional sternotomy group; P < 0.01) and aortic cross-clamping time (48.3±16.7 vs. 53.2±19.6 min in full sternotomy group; P < 0.01) were shorter in MIAVR group. EuroSCORE (OR 1.52, 95% CI, 1.12-2.06; P < 0.01) was found to be the only independent predictor of intra-hospital mortality in the whole propensity-matched population. Conclusions: Our experience shows that mini-access isolated aortic valve surgery is a reproducible, safe and effective procedure with similar outcomes and no longer operative times compared to conventional sternotomy

Characterization of shape and dimensional accuracy of incrementally formed titanium sheet parts with intermediate curvatures between two feature types

Single point incremental forming (SPIF) is a relatively new manufacturing process that has been recently used to form medical grade titanium sheets for implant devices. However, one limitation of the SPIF process may be characterized by dimensional inaccuracies of the final part as compared with the original designed part model. Elimination of these inaccuracies is critical to forming medical implants to meet required tolerances. Prior work on accuracy characterization has shown that feature behavior is important in predicting accuracy. In this study, a set of basic geometric shapes consisting of ruled and freeform features were formed using SPIF to characterize the dimensional inaccuracies of grade 1 titanium sheet parts. Response surface functions using multivariate adaptive regression splines (MARS) are then generated to model the deviations at individual vertices of the STL model of the part as a function of geometric shape parameters such as curvature, depth, distance to feature borders, wall angle, etc. The generated response functions are further used to predict dimensional deviations in a specific clinical implant case where the curvatures in the part lie between that of ruled features and freeform features. It is shown that a mixed-MARS response surface model using a weighted average of the ruled and freeform surface models can be used for such a case to improve the mean prediction accuracy within ±0.5 mm. The predicted deviations show a reasonable match with the actual formed shape for the implant case and are used to generate optimized tool paths for minimized shape and dimensional inaccuracy. Further, an implant part is then made using the accuracy characterization functions for improved accuracy. The results show an improvement in shape and dimensional accuracy of incrementally formed titanium medical implants

Evaluation of strain and stress states in the single point incremental forming process

Single point incremental forming (SPIF) is a promising manufacturing process suitable for small batch production. Furthermore, the material formability is enhanced in comparison with the conventional sheet metal forming processes, resulting from the small plastic zone and the incremental nature. Nevertheless, the further development of the SPIF process requires the full understanding of the material deformation mechanism, which is of great importance for the effective process optimization. In this study, a comprehensive finite element model has been developed to analyse the state of strain and stress in the vicinity of the contact area, where the plastic deformation increases by means of the forming tool action. The numerical model is firstly validated with experimental results from a simple truncated cone of AA7075-O aluminium alloy, namely, the forming force evolution, the final thickness and the plastic strain distributions. In order to evaluate accurately the through-thickness gradients, the blank is modelled with solid finite elements. The small contact area between the forming tool and the sheet produces a negative mean stress under the tool, postponing the ductile fracture occurrence. On the other hand, the residual stresses in both circumferential and meridional directions are positive in the inner skin of the cone and negative in the outer skin. They arise predominantly along the circumferential direction due to the geometrical restrictions in this direction.The authors would like to gratefully acknowledge the financial support from the Portuguese Foundation for Science and Technology (FCT) under project PTDC/EMS-TEC/1805/2012. The first author is also grateful to the FCT for the postdoctoral grant SFRH/BPD/101334/2014.info:eu-repo/semantics/publishedVersio

Review on the influence of process parameters in incremental sheet forming

Incremental sheet forming (ISF) is a relatively new flexible forming process. ISF has excellent adaptability to conventional milling machines and requires minimum use of complex tooling, dies and forming press, which makes the process cost-effective and easy to automate for various applications. In the past two decades, extensive research on ISF has resulted in significant advances being made in fundamental understanding and development of new processing and tooling solutions. However, ISF has yet to be fully implemented to mainstream high-value manufacturing industries due to a number of technical challenges, all of which are directly related to ISF process parameters. This paper aims to provide a detailed review of the current state-of-the-art of ISF processes in terms of its technological capabilities and specific limitations with discussions on the ISF process parameters and their effects on ISF processes. Particular attention is given to the ISF process parameters on the formability, deformation and failure mechanics, springback and accuracy and surface roughness. This leads to a number of recommendations that are considered essential for future research effort