17 research outputs found
Combined effect of process variables on the plastic behaviour of 316L stainless steel printed by L-PBF
No full textThe metal additive manufacturing (AM) is a technology that is rapidly spreading in the industrial sector with its enormous potential in making components with complex shapes and low weight, ensuring a high structural strength. However, the mechanical properties of the components depend on the printing process, and the interactions between the process variables and the final material behaviour is still not totally understood. In this work, 12 different types of tensile specimen were built by AM using the laser powder bed fusion (L-PBF) technique; the used material is the 316L stainless steel. The specimens have the same geometry and the same process parameters in terms of layer thickness, hatch space, laser power, spot diameter, scanning speed and platform preheating temperature, while different laser scan strategies and building orientations are evaluated. The scope is to characterize the plastic behaviour of such specimens and study the differences due to distinct printing strategies. Stereo digital image correlation (stereo-DIC) was used to evaluate the deformation state and analyse the material anisotropy. Finally, the microstructure and presence of defects were investigated through the optical microscopy (OM) and the scanning electron microscopy (SEM). The analysis shows how the plastic behaviour and the formation of defects are remarkably influenced by the laser scan strategy and by the building orientation
Integrated Thermomechanical Characterization of Metals Using the Virtual Fields Method
No full textIn this paper, the possibility of characterizing the thermomechanical behavior of metals using the virtual fields method (VFM) and suitable specimens with heterogeneous strain and temperature fields was demonstrated using simulated experiments. The used geometry is a double-notched tensile test with a Gaussian distribution of temperature over the surface. The chosen constitutive model is the Johnson-Cook hardening law coupled with the Hill48 anisotropic yield criterion. First the VFM strategy and the simulated experiments are described. Then the results are presented showing three case studies, (i) only the effect of the temperature is identified, (ii) the whole set of constitutive parameters is identified at the same time, (iii) a two-step identification is performed. The potentiality of the method as well as the main problems are discussed extensively.</jats:p
Influence of Core Cellular Structures on Collapse Mechanisms Maps of Sandwich Beams
No full textThe main advantage of 3D printing is manufacturing complex and innovative shapes which guarantee high mechanical properties. Therefore, it is necessary easily figure out the most suitable structure for the required design requirements. The well-known strategy to design sandwich panels is evaluating collapse maps as they determine the panel performances based on their geometrical features. The aim of this study is to update the traditional collapse maps by showing how the core shape can improve the sandwich beam performance. The collapse maps proposed are based on advanced analytical models than the traditional Gibson theories. The analytical modelling of the indentation phenomenon is based on Vlasov’s model. The analytical modelling of the bending phenomenon is based on the First Shear Order Theory. The overall panel stress and strain maps are computed superposing both effects. A composite sandwich panels with Gyroid core based are analyzed to verify the proposed model consistency. A core failure criterion is chosen by experimental testing evidence on the representative core structure. Once the computed stress state overtakes failure criterion ones, the critical load is defined. In the end, the model is exploited to compare the performances of four sandwich panels with cores based on different lattice structure
Towards Material Testing 2.0: thermomechanical characterization of steels through inverse methods
No full textIl Material Testing 2.0 (MT2.0) rappresenta la nuova frontiera nella caratterizzazione delle proprietà termomeccaniche dei materiali, specialmente degli acciai. Nel MT2.0, i metodi inversi, come ad esempio il metodo dell’aggiornamento del modello agli elementi finiti e il metodo dei campi virtuali, vengono applicati a prove sui materiali con provini specificamente studiati per generare, in maniera simultanea, stati eterogenei di deformazione, tensione e temperatura. Questo approccio massimizza le informazioni ottenibili da una singola prova e permette di calibrare in modo efficace i parametri di modelli costitutivi anche avanzati in grado di descrivere il comportamento del materiale testato. Durante la prova, i campi di deformazione e temperatura eterogenei sul provino vengono monitorati utilizzando tecniche di misura a campo intero come la correlazione digitale di immagini e la termografia ad infrarossi. La conoscenza dei campi di deformazione e temperatura riveste infatti un ruolo fondamentale nella procedura d’identificazione dei parametri costitutivi del materiale. Il MT2.0 grazie alle sue potenzialità è quindi ragionevolmente candidato a sostituire in futuro le prove standard basate su stati omogenei di tensione, deformazione e temperatura sul provino.
L’attività di ricerca presentata in questa tesi di dottorato lavora nella direzione di estendere l’applicazione del MT2.0 alla caratterizzazione avanzata degli acciai ed è divisa in tre parti che corrispondono ad altrettanti campi di applicazione: (i) prove di rigonfiamento per studiare, con stati di tensione e deformazione eterogenei, le proprietà meccaniche delle lamiere, (ii) prove di trazione eterogenee ad alta temperatura per caratterizzare il comportamento termomeccanico degli acciai e (iii) prove combinate di trazione-torsione per studiare il comportamento plastico degli acciai prodotti mediante manifattura additiva. Nella prima parte, è stata sviluppata una macchina per realizzare prove di rigonfiamento e prove Nakajima. A differenza di soluzioni commerciali rigide e costose, la macchina progettata offre elevata flessibilità all’utilizzo con diverse geometrie di premilamiera e punzone. Inoltre, è pensata per essere integrata facilmente con la correlazione digitale di immagini stereo come sistema di misura a campo intero della deformazione. Nella seconda parte, è stata disegnata una nuova geometria di provino per prove di trazione ad alta temperatura da eseguire con il sistema di test Gleeble. La geometria è stata studiata attraverso simulazioni multifisiche agli elementi finiti elettro-termo-meccaniche realizzate con il software commerciale ABAQUS/Standard®. L’obiettivo era generare sul provino stati eterogenei di deformazione, tensione e temperatura tali da consentire di caratterizzare, mediante l’applicazione di metodi inversi, il comportamento termomeccanico di acciai in un ampio intervallo di temperatura con una singola prova. La geometria “eterogenea” di provino così definita è stata successivamente validata con prove sperimentali sull’acciaio laminato a freddo DC05EK per calibrare i parametri della legge di incrudimento di Johnson-Cook accoppiata al criterio di snervamento di Hill48. Il metodo dei campi virtuali è stato utilizzato come strategia di identificazione inversa. Infine, nella terza parte, è stato condotto uno studio approfondito per analizzare l’effetto combinato di diverse strategie di scansione laser e orientamenti rispetto alla piattaforma di stampa sul comportamento plastico dell’acciaio inossidabile 316L prodotto mediante manifattura additiva con la tecnologia di fusione laser selettiva a letto di polvere. La forte influenza di queste variabili di stampa sulle proprietà meccaniche del materiale è stata rilevata conducendo prove standard di trazione e indagata attraverso la microscopia ottica e la microscopia elettronica a scansione. In seguito, sono stati condotti test di torsione pura e trazione su provini cilindrici dello stesso materiale al fine di calibrare un modello di plasticità per diversi orientamenti rispetto alla piattaforma di stampa. Il metodo dell’aggiornamento del modello agli elementi finiti è stato impiegato per l’identificazione inversa dei parametri di diversi modelli di plasticità. Lo studio dimostra i limiti dei modelli di plasticità tradizionali nel descrivere il comportamento torsionale osservato durante le prove.Material Testing 2.0 (MT2.0) represents the new frontier in characterizing the thermomechanical properties of materials, especially steels. Inverse methods, e.g. Finite Element Model Updating (FEMU) and Virtual Fields Method (VFM), can be applied to specimens specifically designed to generate heterogeneous strain, stress, and temperature states simultaneously. Such approach maximizes the information that can be obtained from a single test and allows to calibrate efficaciously the parameters of advanced constitutive models. The heterogeneous strain and temperature fields are measured using suitable full-field techniques, e.g. Digital Image Correlation (DIC) and InfraRed Thermography (IRT), which play a key role for the success of the identification procedure. Thanks to their flexibility and potentialities, heterogeneous tests coupled with inverse methods (i.e. MT2.0) are reasonable candidates in the future to replace standard tests based on homogeneous stress, strain, and temperature states on the specimen.
The research activity presented in this doctoral thesis works in the direction of extending the application of MT2.0 to advanced characterization of steel and it is divided in three parts that correspond to different experimental procedures: (i) heterogeneous bulge tests to study the mechanical properties of sheet metals, (ii) heterogeneous hot tensile test for characterizing the thermomechanical behavior of steels and (iii) combined tension-torsion tests to study the plastic behavior of steels produced by Additive Manufacturing (AM). In the first part, a machine was developed to conduct bulge and Nakajima tests. Unlike rigid and expensive commercial solutions, this machine offers flexibility in using various die and punch geometries. Additionally, it is specifically designed for an easy integration with stereo-DIC as full-field strain measurement system. In the second part, a novel specimen geometry for hot tensile tests was studied in ABAQUS/Standard® through multiphysics electro-thermo-mechanical simulations to be tested using the Gleeble system. The heterogeneous specimen geometry was then validated with a real test on the DC05EK cold-rolled steel to calibrate the parameters of the Johnson-Cook hardening law coupled with Hill48 anisotropy yield criterion. The non-linear Virtual Fields Method (VFM) was used as inverse identification strategy. Finally, in the third part, a detailed study was conducted to analyze the combined effect of different laser scan strategies and orientations with respect to the build platform on the plastic behavior of the 316L stainless steel printed by Laser Powder Bed Fusion (L-PBF) additive technology. The strong influence of these variables on the mechanical properties of the material was detected through standard tensile tests and investigated through optical microscopy (OM) and scanning electron microscopy (SEM). Subsequently, pure torsion and tensile tests were conducted on cylindrical specimens of the same material in order to calibrate a plasticity model for different orientations with respect to the build platform. The Finite Element Model Updating method (FEMU) was employed as strategy for the inverse identification of the parameters of different plasticity models. The study demonstrates the limits of the classical plasticity models in describing the torsional behavior observed during the tests
Combined effect of process variables on the plastic behaviour of 316L stainless steel printed by L‐PBF
No full textEffectiveness of remote monitoring of CIEDs in detection and treatment of clinical and device-related cardiovascular events in daily practice: The HomeGuide Registry
No full textAimsThe HomeGuide Registry was a prospective study (NCT01459874), implementing a model for remote monitoring of cardiac implantable electronic devices (CIEDs) in daily clinical practice, to estimate effectiveness in major cardiovascular event detection and management.Methods and resultsThe workflow for remote monitoring [Biotronik Home Monitoring (HM)] was based on primary nursing: each patient was assigned to an expert nurse for management and to a responsible physician for medical decisions. In-person visits were scheduled once a year. Seventy-five Italian sites enrolled 1650 patients [27% pacemakers, 27% single-chamber implantable cardioverter defibrillators (ICDs), 22% dual-chamber ICDs, 24% ICDs with cardiac resynchronization therapy]. Population resembled the expected characteristics of CIED patients. During a 20 ± 13 month follow-up, 2471 independently adjudicated events were collected in 838 patients (51%): 2033 (82%) were detected during HM sessions; 438 (18%) during in-person visits. Sixty were classified as false-positive, with generalized estimating equation-adjusted sensitivity and positive predictive value of 84.3% [confidence interval (CI), 82.5-86.0%] and 97.4% (CI, 96.5-98.2%), respectively. Overall, 95% of asymptomatic and 73% of actionable events were detected during HM sessions. Median reaction time was 3 days [interquartile range (IQR), 1-14 days]. Generalized estimating equation-adjusted incremental utility, calculated according to four properties of major clinical interest, was in favour of the HM sessions: +0.56 (CI, 0.53-0.58%), P < 0.0001. Resource consumption: 3364 HM sessions performed (76% by nurses), median committed monthly manpower of 55.5 (IQR, 22.0-107.0) min × health personnel/100 patients.ConclusionHome Monitoring was highly effective in detecting and managing clinical events in CIED patients in daily practice with remarkably low manpower and resource consumption. © 2013 The Author
Manpower and outpatient clinic workload for remote monitoring of patients with cardiac implantable electronicc devices data from the HomeGuide Registry
No full textDizionario biografico degli Italiani, vol. 76: Montauti -- Morlaiter
No full textHo curato la redazione -- e in qualche caso la radicale revisione -- delle voci relative ai seguenti musicisti: Giovanni Domenico Montella, Italo Montemezzi, Claudio Monteverdi, Giulio Cesare Monteverdi, Monti (famiglia di cantanti e attori), Giacomo Monti, Angelo Maria Monticelli, Monticini (famiglia di danzatori), Carlo Monza, Carlo Ignazio Monza, Tebaldo Monzani, Pietro Maria e Giovanni Morandi, Roberto Moranzoni, Antonio Morari, Sebastiano Moratelli, Paolo Morellato, Angelo Moreschi, Morettini (famiglia di organari), Napoleone Moriani, Anna Morichelli Bosello, Angelo Morigi, Pietro Morigi, Francesco Morlacch
ANMCO Position paper. From acute to chronic disease: The needs of complex cardiac patients
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