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Residual stresses are one of the major issues in welded parts, since they could be detrimental to the integrity of components and structure. Their determination is rather complex and could be an arduous task, both when it is based on experimental methods and on numerical simulations. The proposed work presents a theoretical approach to the prediction of the longitudinal residual stress distribution, based on a parameterized multi-source model for thermal field simulation in laser welding previously introduced. Reference is made to the case of “keyhole” full penetration welding mode obtained by CO2 laser beam single pass on butt-positioned AISI 304L plates. The resolution of the thermal field allows the analytical calculation of the distribution of the longitudinal residual stresses in two ways: one makes use of a simplified formulation of the distribution well-known in the literature; a second modality makes use of a procedure for residual stress generation, which is based on a combined processing of thermal profiles and the corresponding heating–cooling cycles calculated in single points as their distance from the welding axis varies, and provides a complete characterization of the distribution of longitudinal residual tensile stresses. After the introduction of thermal field modeling, both the proposed residual stress calculation procedures are detailed, applied to the analyzed case, and validated, highlighting the differences in the approaches and results.

Abstract The objective of the work is to present a new approach to the simulation of the thermal field in laser beam welding, based on an experimentally-fitted analytical model, applied to investigate the weldability of AISI 304L austenitic steel. Reference is made to the welding trial in a single pass of two 10 mm thick butt-positioned plates. Welding was performed under the keyhole full penetration mode, which is characteristic of high-power laser beam, and simulated by an analytical model based on a multipoint-line thermal source system and fitted on the experimental fusion zone profile. The model was applied to simulate the effects of welding speed changes on thermal fields and cooling rates, in order to determine how they can affect the weld composition, the solidification mode and the possible formation of a sensitized zone in the heat affected zone. A limit value of welding speed, which allows the weld formation without lack of fusion, was identified. For all the welding speeds considered, the formation of a sensitized zone can be excluded. The contribution of welding speed on cooling rate, not significant near the welding axis, results to be determinant at the boundary of the fused zone with base metal. The combined choice of the filler material and the welding speed, which in all cases gives rise to primary ferrite solidification modes, affects the content of residual ferrite, which must be balanced to enhance the resistance to solidification cracking, avoiding the adverse effects due to too high contents. As a conclusion, the model proves to be a valid support in investigating the thermal effects, which result from the setup of welding parameters, on the weldability of the base metal-filler system. Graphic Abstract

Curcumin is a natural active principle with antioxidant, antibacterial and anti-inflammatory properties. Its use is limited by a low water solubility and fast degradation rate, which hinder its bioavailability. To overcome this problem, curcumin can be delivered through a carrier, which protects the drug molecule and enhances its pharmacological effects. The present work proposes a simple one-pot sol–gel synthesis to obtain a hybrid carrier for curcumin delivery. The hybrid consists of a mesostructured matrix of amorphous silica, which stabilizes the carrier, and hexadecyltrimethylammonium (CTA), a surfactant where curcumin is dissolved to increase its water solubility. The carrier was characterized in terms of morphology (FESEM), physicochemical properties (XRD, FTIR, UV spectroscopy) and release capability in pseudo-physiological solutions. Results show that curcumin molecules were entrapped, for the first time, in a silica-surfactant mesostructured hybrid carrier. The hybrid carrier successfully released curcumin in artificial sweat and in a phosphate buffer saline solution, so confirming its efficacy in increasing curcumin water solubility. The proposed drug release mechanism relies on the degradation of the carrier, which involves the concurrent release of silicon. This suggests strong potentialities for topical administration applications, since curcumin is effective against many dermal diseases while silicon is beneficial to the skin.

In the last decades, great attention has been focused on the characterization of cellular foams, because of their morphological peculiarities that allow for obtaining effective combinations of structural properties. A predictive analytical model for the compressive behavior of closed-cell Al foams, based on the correlation between the morphology of the cellular structure and its mechanical response, was developed. The cells’ morphology of cylindrical specimens was investigated at different steps of compression by X-ray computed tomography, in order to detect the collapse evolution. The structure, typically inhomogeneous at local level, was represented by developing a global virtual model consisting of homogeneous cells ordered in space, that was fitted on the experimentally detected structure at each deformation step. As a result, the main parameters characterizing the two-dimensional cells morphology (equivalent diameter, circularity), processed by the model, allowed to simulate the whole compression stress–strain curve by enveloping those obtained for each step. The model, fitted on the previous foam, was validated by comparing the simulated stress–strain curve and the corresponding experimental one, detected for similar foams obtained by different powder compositions. The effectiveness in terms of an accurate prediction of the compression response up to the final densification regime has been confirmed.

The thermal effects of the “keyhole” full penetration welding mode, which is characteristic of high-power CO2 laser, are simulated introducing a multipoint-line thermal source model based on heat conduction, parameterized by the distribution of the laser beam power, and the setting of the source system layout, and to be fitted on experimentally detected cross sections of the heat-affected or fusion zones of the weld. The proposed model allows to express the thermal field according to the moving reference system fixed on the overall heat source, and to analyze the temperature profiles that develop in some detection points fixed on the workpiece, as time varies during the welding process. By this way, it can be useful in evaluating the thermal effects that result from the variation of the main welding parameters (beam power, welding speed, plate thickness), with the aim of simplifying the selection of the optimal process conditions. As an application, reference is made to a cross section of a joint between plates of AISI 304 L austenitic steel. The fitting procedure allows to set the power distribution and layout parameters of the most suitable source combination (obtained by superposition of a line and two point sources). The value of the absorption coefficient also is assumed as fitting variable, so to overcome the complex problem of evaluating the beam power actually absorbed by the material on keyhole mode welding. Finally, the fitted model is applied to carry out a detailed thermal field analysis in the welded plates.

This paper analyzes the causes and effects of the COVID-19 crisis, with a specific focus on the food system. Food consumption and production has not only been impacted by the crisis, but it may have also contributed to causing the pandemic. After providing a brief introductory framework, the paper presents the results of a pilot study on the link between COVID-19 and the food system, as indicated by the social media activity of selected European Union (EU) Twitter accounts, measured using an original &ldquo, theme popularity&rdquo, metric. Thereafter, a systematic review of the literature is proposed to identify the causes of the rise in popularity of a sustainable food system theme, the potential consequences of the COVID-19 crisis for the food system (targeting the production, consumption and waste disposal phases) and possible solutions, focusing on the circular economy. Challenges and opportunities for policymakers in the short and long term are discussed. A holistic approach is advocated, as the global food system is intimately connected with society and requires deep cooperation among nation states and economic actors.

The present paper proposes an environmental sustainability-oriented Design for Additive Manufacturing approach, which takes into account material, shape, and additive process, in order to guide the designer towards environmentally conscious choices in terms of component characteristics, correlating them with the peculiarities of the additive process and its main parameters. In its formulation, the approach has been developed with reference to the specific class of "powder bed fusion" additive processes for metallic materials, in which the volume growth by stratified fusion of powder layers, takes place by means of power beams. As a reference process, that of Electron Beam Melting has been considered. The quantification of the environmental impact of built components focuses on the estimation of the intrinsic energy consumption of the additive process, correlating it to the main process parameters, and to some significant features that characterize the shape of the component. To analyze the dependence of the energy impact on the material and shape characteristics, the case of Ti6Al4V components is studied.

An integrated experimental-theoretical approach to the metallurgical characterization of the interfaces in steel plates clad by hot rolling is proposed. Three different couplings of materials have been studied: ASTM A 515 Gr.60 low carbon steel clad with austenitic stainless steel AISI 304L, extra low carbon steel ASTM A283 clad with high Ni content Alloy 59, and, low carbon steel AISI 1010 clad with Cu-Ni Monel 400. Experimental investigations, which are addressed to analyse the microstructural changes near the interfaces and identify the present phases, have been carried out through scanning electron microscopy (SEM) observations, microanalytical measurements by energy dispersive spectroscopy (EDS), and Vickers microhardness tests. In all of the cases examined, the zones that are affected by detrimental microstructural changes results in being considerably less thick than the overall cladding layer. Simulations that are based on theoretical diffusion modelling have been integrated to the experimental characterization by introducing a cladding parameter that acts on the diffusion bonding efficiency, in order to evaluate the effects of process temperature and time variations on diffusion bonding efficiency and stability. In particular, this analytical investigation has shown how the shorter is the duration of the diffusion transient and the higher the temperature, the lower results the sensitivity of the diffusion processes to temperature fluctuations.

Additive manufactured Ti6Al4V alloy has become a widely used metallic material in many structural applications including aerospace components and medical implants, where its balance of mechanical performance and flexibility in assuming complex shapes is very appreciated. As a consequence, extensive efforts have been directed towards its mechanical characterization and extended data collections are reported in the literature. However, in the basic characterization, some prominent aspects related to “true” stress-strain behaviour and strain rate effects appear to have been substantially neglected. In this work the tensile behaviour of a Ti6Al4V alloy produced by Electron Beam Melting is investigated at static and dynamic rates together with the torsion response at static rates, in order to evaluate the effects of the strain rate and the Lode stress-state parameter on the elastoplastic response and the fracture initiation. The experimental procedure adopted here relied on enhanced true stress-true strain measurements based on optical measurements of the necking cross section of the specimen, continuously acquired by video recordings, as an alternative to the traditional elongation-based approach to the true stress-true strain evaluation. In the case of static torsion tests, the Nadai method has been used, delivering the equivalent stress-strain curves directly from the torque-rotation experimental data. Moreover, the real stress amplification due to high strain rates has been obtained subtracting the thermal softening effect from the flow curves of the dynamic tests. In addition to the mechanical characterization, micrographic analyses allowed to relate the microstructural properties to the additive process conditions and the fracture morphology to the various test conditions imposed to different specimens. Finally the stress-strain results from experiments are compared with literature data for Ti6Al4V alloy, manufactured by the same or different production processes, evidencing how not only manufacturing technique and process conditions, but also the approach used in the characterization affects the results of material behaviour assessment.

In the present paper a Design for Additive Manufacturing approach is proposed, with the aim to outline a generalized method and define an energy consumption model that allow, during the development of component design, to evaluate the effects of the different solutions on the energy efficiency of the additive process that will build the component. For this purpose the concept of building energy is introduced, that is the real energy of the heat source during the phases of the building process, and can be directly correlated to key properties of the component (material, geometry and shape, volumetric distribution). For the detailed formulation of the energy consumption model, the Electron Beam Melting technology has been considered. Two parameters are identified to effectively characterize each design solution, combining the geometric and volumetric properties of components in the most significant way, and taking into account also the efficiency in build volume packing. The application of the model to the fabrication of components characterized by different shape classes is detailed, highlighting how a different spatial distribution of the same volume affects the building energy. The outcomes in terms of energy consumption, due to alternative design choices, can be assessed and simulated. The analysis of critical points in the design solutions presents an heuristic potential, as it can guide the designer in effective improvement interventions. The accuracy in the evaluation of the process energy consumption due to the proposed approach, also suggest limiting the use of simplifications, that may not be fully suitable to correlate energy efficiency and component properties in a Design for Additive Manufacturing perspective.

Inside a research program agreed with the AIAS-MEAS Energy Methods Group, this preliminary study starts defining the fatigue parameters of a commercial steel in static and cyclic loading conditions. The final purpose of the research is to define the fatigue limits in different loading conditions using different energetic methodologies and comparing them with those derived by several tests performed by the other researchers of the Group. This first step was carried out using the thermographic methods already proposed in literature, determining the values of the fatigue limit for R=0. At the same time, the thermal response in static tests were derived in order to correlate the limit of the totally thermoelastic behavior, corresponding with the phase of the crack nucleation, with the fatigue limit.

The paper is focused on the study of fatigue materials, using an energy approach, with the support of two different non-destructive techniques. Indeed, the analysis of the energy behavior was conducted by the simultaneous application of Acoustic Emission (AE) and Thermography (TH). The purpose of the paper was to compare and integrate the results obtained by the two methodologies to assess the fatigue behavior of materials. The experimental tests were carried out on flat steel specimens of steels commonly used for metal carpentry either under static loading or under sequences of increasing cyclic loading. The results allow to define the fatigue limit either by the thermography or by the acoustic emission and they are encouraging to continue the comparison and the integration between the two energetic methodologies.

Most of the research on materials selection has been characterized by a basic approach to the problem, isolating material choice from the other design variables, and focusing on single components. Instead, a complete approach aimed at optimizing material selection cannot be set aside from component sizing, and the analysis of constraints between components, that characterize the sub-assemblies or the whole system, and can influence the material choice itself. In this paper, a structured method to approach the simultaneous materials selection and sizing optimization of multi-component assemblies is proposed. It is based on a modeling of the problem, fully generalized in its formalization, so as to be applicable to the various cases, and formulated in order to take into account the systemic vision that must have the optimal choice in a multi-component perspective, and its close connection with the sizing of geometric variables, to effectively meet the required performances. In this regard, an efficiency criterion, which provides for the choice of material and variables sizing gauged on real needs, is also introduced. After presenting the framework and formalization of the method, the problem of searching for the best solution has been discussed. With regard to this, a genetic algorithm has been specifically developed according to the peculiarities of the generalized formulation, with the aim of enhancing the heuristic potential of the concurrent material choice and sizing approach in multi-component environment, in the search for the optimal solution. The application to a sub-system of a widely used plant device is reported in detail, so that use and capacity of the structured method are detailed and discussed.

In the degenerative disc disease, an alternative treatment to the traditional arthrodesis, consisting in the fusion of the two adjacent vertebral bodies, is the artificial intervertebral disc. The advantage of an artificial intervertebral disc is that the d.o.f. of the vertebral segment can be saved and the mobility of the spine could be almost restored. Many solutions were proposed in the last decades, most of them consisting in metallic rigid joints able to assure the mobility and to maintain the correct distance between the vertebrae but subject to corrosion, wear and interface problems due to the different stiffness with the biological tissues. Purpose of this paper is the design of a prosthetic device substituting the disc to be placed in the intervertebral zone. Different types of artificial prostheses have been proposed by the authors, based on similarity with physiological discs, then with a central part (nucleus) made of hyperelastic material and an outer containment frame (annulus) consisting of a plastic material with a stiffness high enough to assure the reaction force and to avoid large radial displacements. In our solutions, the external parts (annulus and plates) were modeled by HDPE and the inner part (nucleus) by silicone and hydrogel. All the materials are highly biocompatible. The intention of the authors, moreover, is to permit an easier surgical technique. The prosthesis, in fact, could be mounted void of the nucleus, allowing an easier placement, and filled only after the frame insertion, by injecting the silicone through a syringe. The nucleus was modeled by the Mooney-Rivlin parameters related to elastomers, being the disc subject to large deformations that the materials have to be able to withstand in elastic conditions. The discs are subjected to compressive loads either in the mounting phase or, after the silicone filling, due to the physiological loads.

The energetic methods to determine the fatigue limit, proposed by various researchers in the last decades, are based on the evidence that fatigue is an energy dissipation process, and most of the dissipated energy is converted into heat, which manifests itself in the form of temperature change. The study of fatigue behaviour through the determination of the heat quantity released during the fatigue tests, and the analysis of the temperature variation of material under fatigue loading, by mean of thermography-based methods, constitutes a well-established approach. Reaching very high temperature in the specimen is a critical aspect of this phenomenon of conversion of the dissipated energy into heat, particularly with regards to materials characterized by high thermal releases, that could be subject to microstructural changing and behaviour decay. This effect can be exalted by the use of ultrasonic fatigue testing systems for the characterization of very high cycle fatigue behaviour of material. To highlight the influence of the fatigue test frequency on the specimen temperature that already occurs at low frequencies, in this paper a study of the thermal behaviour of AISI 304 stressed by fatigue loads in high cycle fatigue testing at different frequency values, based on energetic method to determine the fatigue curve, is presented.

Seidel intramedullary humeral nail is locked distally by a spreading device and proximally by transverse cross locking screws. The main problems found in its use are: the loosening of the distal anchorage, even after X-ray verification of the correct expansion of the device; the formation of distal fractures, occurring even 1 month after the operation; the system's low stability. The problems noted can be ascribed to the behaviour of the spreading device for distal fixing. The present study, therefore, was directed at analysing the contact between the spreading mechanism and the medullary canal in relation to the geometric parameters of the mechanism itself. The main objective was to define the correct regulation of the expansion in the operating theatre, and to delimit the more appropriate conditions of use, allowing the surgeon to evaluate the suitability of this particular device for the type of fracture under treatment. Numerical and experimental techniques were used to perform an analysis of the implant behaviour. This investigation, referred to immediate post-operative condition, allowed to evaluate the stability to traction of the system, to define the typology and properties of the bone-implant contact zone and to quantify the stresses produced, all as a function of the parameter on which the surgeon intervenes in the operating theatre: the number of turns used to tighten the spreading screw. The results obtained confirm and explain the disadvantages associated with the distal expansion system: the bone-implant contact turns out to be inefficient, as revealed by the distribution of the pressure on the inner wall of the medullary canal. On the basis of the results, it is possible to define the optimal conditions of use of the nail, and to formulate a simple solution for the improvement of its performance.

The choice of materials takes on strategic importance in design aimed at harmonising the performance characteristics and eco-compatibility of products in line with the Life-Cycle Design approach. The objective of the present study is the development of a systematic method which introduces environmental considerations in the selection of the materials used in components, meeting functional and performance requirements while minimising the environmental impact associated with the product's entire life-cycle. The proposed selection procedure elaborates data on the conventional and environmental properties of materials and processes, relates this data to the required performance of product components, and calculates the values assumed by functions which quantify the environmental impact over the whole life-cycle and the cost resulting from the choice of materials. As shown in the case study presented, the results can then be evaluated using multi-objective analysis techniques.

The evaluation of the temperature rising during a fatigue test is extremely important to define the energy method to be used. In order to define the best load program and the more appropriate test frequency, it is necessary to estimate the surface temperature of the material, in particular when it's needed to arrange some tests on mechanical components. With regards to the energetic approach to the study of fatigue phenomena, in the past the internal damping factor was considered an important parameter to define the fatigue quality of the material used for the mechanical application. In the present paperthe role of another important work parameter ishighlighted, when linked to the plastic strain caused by the high number of fatigue tests. An approach to the detection of first microplasticization and crack beginning is also proposed, with a model for the estimation of the crack propagation during the last cycles of fatigue test.

With the aim of investigating the applicative possibilities of chiral blade turbines in obtaining energy from water conduits with low velocity of flow, the present study traces a design procedure, defining analytical tools and identifying various expedients which can guide the effective choice of the functional parameters of the device and allow a preliminary estimation of the quantities in play, confirming their suitability by the construction of a prototype and its functional characterisation as a real device.

This article proposes a methodological statement and a design procedure based on an integrated approach combining finite element analysis (FEA) tools, and an instrument oriented at improving the design solutions in terms of ease of production, according to the principles of design for manufacture and assembly (DFMA). The result of an overview on product development theoretical models, with particular regard to the evolutionary mechanisms for converging on the final solution which characterize the design process, and of a review on the implementation of concurrent engineering principles, the proposed approach was expressly devised to introduce integrated and simultaneous interventions into design practice, in a way that makes the use of FEA and DFMA instruments as proactive as possible, consequently favoring the effectiveness of design choices, in order to limit the iterative processes of improvement and thereby reduce the burden they present. As evidenced by the results of a case study, this approach can allow the principal constructional characteristics of the preliminary design to be redefined in a way which simplifies manufacture and assembly processes, while guaranteeing and sometimes improving the structural functionality of the product, to the full advantage of product quality and the containment of production times and costs.