8,930 research outputs found
Influence of residual stresses on the fatigue life of welded joints
No full textA deep knowledge of the production process is needed, in order to achieve quality and safety requirements in a structural component. As a matter of fact, manufacturing processes can introduce defects such as residual stresses, internal and superficial imperfections. Together with the inherent geometric variations, such as notches, cracks or defects in general, it is often difficult to precisely characterise the structural strength of such parts. In this context, residual stresses play an important role, especially in welded structures. The evaluation of residual stresses is typically performed using both experimental and numerical methods. Both present strengths and drawbacks which demand their combined usage to achieve a consistent and meaningful evaluation of the residual stresses. Within this scope, this PhD thesis presents an evaluation of residual stresses in a pipe-to-plate welded joint and studied their influence on the fatigue life of torsionally and bending loaded components. In the first part, the finite element method was used to assess the capability of different thermal methods used to simulate a single pass of the gas metal arc welding process in reproducing the temperature distribution around the weld bead. Results of the simulations were compared to experimental measurements of the surface temperature close to the weld region. The considered thermal techniques adopted different levels of complexity, from the basic implementation of a constant initial temperature assigned to a given material volume, to the more comprehensive and widespread Goldak's double-ellipsoid model. The study shows that, close to the weld seam, very similar thermal behaviours can be achieved by employing each one of the analysed methods. Secondly, considering the constant initial temperature method, the comparison between experimental measurements and numerical simulations showed a fairly good agreement, suggesting that a relatively simple method (i.e., requiring the setting of only one parameter) can be used to efficiently reproduce the thermal history of a welding process. In the second part, the study of residual stresses for a S355JR carbon steel pipe-to-plate welded joint is presented. Numerical simulations and experimental tests were both employed in order to gain wide-ranging knowledge. Numerical simulations were performed with the software Ansys through uncoupled thermal-structural simulations in order to evaluate the stresses, strains and temperature at each node of the finite element model for each phase of the simulation. Temperature-dependent elastic-plastic material properties were adopted in combination with the \textit{element birth \& death} method to simulate the welding process. Two different numerical approaches were implemented for reproducing the weld seam solidification process. The obtained results were discussed and compared with experimental data, in terms of relaxed radial strains measured nearby the seam weld, due to a material removal procedure. The third part investigates the influence of residual stresses on the fatigue life of the welded joints. Influencing factors such as geometric discontinuities and the material heterogeneous microstructure were considered. Experimental tests on as-welded and stress relieved specimens with fully reversed torsion and bending loading conditions were carried out. Experimental results showed how residual stresses exhibited an influence mainly on torsionally loaded components. Numerically, the uncoupled thermal-structural finite element simulation presented in the chapters before was used to assess the complete residual stress field within the specimens. Secondly, residual stresses were mapped and included as initial condition in numerical models intended for fatigue damage factors calculation. Finally, experimental results were then used to corroborate numerical models and verify their efficacy in assessing fatigue endurance. In the last part of this work, a preliminary numerical study of a notched specimen geometry is presented. The work attempts to reproduce residual stress conditions comparable to those found on the welded joint critical notch section on notched specimens thus in order to explain the results observed on welded specimens. Indeed, by varying notch radius and opening angle of a cylindrical specimen, it is possible to obtain a stress gradient similar to that obtained after the welding process at the weld notches. The use of simplified geometry allows easier analysis and a possible improved understanding of the processes taking place within the material
Francesco Zugno (1707-1787): da allievo di Giambattista Tiepolo a protagonista della pittura veneta del Settecento.
No full textLa ricerca condotta per la tesi di dottorato ha permesso di ricostruire la biografia e l’attività di Francesco Zugno, esponente di spicco della bottega di Giambattista Tiepolo (1696-1770) e protagonista della stagione settecentesca della pittura veneta.
L’obiettivo della ricerca è stato quello, dunque, di ricostruire il profilo di Francesco Zugno, operazione che non poteva prescindere dalla redazione di un catalogo ragionato delle opere realizzate dal pittore in modo da ripercorrere tutta la sua attività professionale.
Tenendo sotto controllo tutti i diversi ambiti di attività di Francesco Zugno – compresi la ritrattistica e la partecipazione in più articolate dinamiche di bottega, in particolare il sodalizio con Battaglioli – lo studio ha aspirato a ridefinire i caratteri della personalità artistica del pittore, nel tentativo di misurarne il ruolo nella stagione pittorica settecentesca. Ne è risultata la figura di un artista che ha saputo essere interprete in maniera personalissima e riconoscibile della lezione di Tiepolo e che ha cercato di raccoglierne l’eredità al momento della partenza definitiva di Giambattista per la Spagna, soprattutto, ma non soltanto, per quel che riguarda la grande decorazione ad affresco in un mercato sempre più affollato di seguaci e imitatori. Il suo ruolo chiave all’interno del panorama lagunare è testimoniato inoltre dalla carica pluriennale ricoperta all’interno dell’Accademia.
A completare il lavoro si è proceduto a redigere il corposo catalogo delle opere pittoriche e a seguire un puntuale regesto
Schede (Palazzo Dotto de’ Dauli, ora Da Rio - Palazzo Dotto, ora Vigodarzere - Palazzo Savonarola - Palazzo Maffetti, ora Manzoni - Palazzo Trento, poi Papafava, poi Vigodarzere, ora Papafava - Palazzo Buzzacarini - Palazzo Mussato - Loggia del Consiglio o della Gran Guardia - Palazzo Belloni - Palazzo Obizzi - Palazzo Abriani - Palazzo del Capitanio - Palazzo Dondi dall’Orologio, via Dondi - Palazzo Capodilista, ora Emo Capodilista)
No full textImmissione e compilazione schede nel database sulla "Grande decorazione profana" del Sei e Settecento all'interno dei palazzi di Padova per il Centro di ricerca “Rossana Bossaglia” in occasione del PRIN 2010-2011 – La pittura profana dall’età barocca all’età neoclassica nell’Italia settentrionale, con particolare attenzione alla presenza dei pittori veneti e veneziani
Scheda 160. Tiziano e bottega, Ritratto di Giulia Varano Della Rovere
No full textIl catalogo celebra nel 500enario della sua nascita, Eleonora di Toledo, la consorte spagnola di Cosimo I de’ Medici.Arrivata a Firenze nel 1539 portò con sé un bagaglio culturale notevolissimo per l’epoca. Sostenitrice di artisti del calibro di Bronzino, di letterati e poetesse come Laura Battiferri e la discussa cortigiana Tullia d’Aragona, ma anche di religiosi come il nuovo ordine dei Gesuiti. Una sovrana illuminata che trasferì la corte medicea da Palazzo Vecchio (riadattato e decorato da alcuni dei maggiori pittori dell’epoca per ospitare i suoi appartamenti) al Giardino di Boboli e a Palazzo Pitti, acquistati nel febbraio1550 dalla duchessa con le proprie finanze, trasformati secondo i suoi personali ideali progettuali e da lei amministrati attivamente, da vera e propria manager del patrimonio. Un catalogo di una mostra che prende in esame un’epoca d’oro non solo per l’arte ma anche per l’abbigliamento, il campo musicale e l’arredamento come l’arazzeria.Curato da uno dei più importanti studiosi della materia Bruce Edelstein e da Valentina Conticelli, responsabile del Tesoro dei Granduchi che ospita la mostra fino al 14 maggio
Scheda 54. Anonimo napoletano, Ritratto di Don Pedro de Toledo
No full textIl catalogo celebra nel 500enario della sua nascita, Eleonora di Toledo, la consorte spagnola di Cosimo I de’ Medici.Arrivata a Firenze nel 1539 portò con sé un bagaglio culturale notevolissimo per l’epoca. Sostenitrice di artisti del calibro di Bronzino, di letterati e poetesse come Laura Battiferri e la discussa cortigiana Tullia d’Aragona, ma anche di religiosi come il nuovo ordine dei Gesuiti. Una sovrana illuminata che trasferì la corte medicea da Palazzo Vecchio (riadattato e decorato da alcuni dei maggiori pittori dell’epoca per ospitare i suoi appartamenti) al Giardino di Boboli e a Palazzo Pitti, acquistati nel febbraio1550 dalla duchessa con le proprie finanze, trasformati secondo i suoi personali ideali progettuali e da lei amministrati attivamente, da vera e propria manager del patrimonio. Un catalogo di una mostra che prende in esame un’epoca d’oro non solo per l’arte ma anche per l’abbigliamento, il campo musicale e l’arredamento come l’arazzeria.Curato da uno dei più importanti studiosi della materia Bruce Edelstein e da Valentina Conticelli, responsabile del Tesoro dei Granduchi che ospita la mostra fino al 14 maggio
Representative structure elements for the fatigue assessment of additively manufactured components
No full textThe fatigue life estimation of additively manufactured structures can be a very challenging task, because the component behaviour will be influenced by many parameters, such as surface roughness, imperfections and inhomogeneous properties. Furthermore, the loading conditions and the component geometry have to be taken into account. The problem of considering the singular influences adequately is intensified by their interactions, which invokes a simultaneous treatment of all relevant influencing factors. Without predefinition of the fatigue approach, properties to describe the cyclic aspects of component behaviour and the fatigue life are required. Even in the case of using small sized specimens, it is not possible to produce a defect-free material for studying the behaviour of sound material in order to derive cyclic material properties as a requirement for the local strain-based fatigue concept, or in order to derive a reference SN-curve and knock-down factors for load-based concepts
Schwingfestigkeitsbewertung von additive gefertigten metallischen Bauteilen
No full textA wide range of evaluation concepts exists for assessing the fatigue strength of metallic components produced in classical processes such as casting or welding. In these concepts, the mechanical and geometric properties can be taken into account for the fatigue assessment.
In this paper, approaches for the transfer of known evaluation methods for the fatigue assessment of additively manufactured metallic samples are discussed. Therefore, the influencing variables relevant for the fatigue strength are shown. This is followed by a discussion how these variables can be taken into account for a fatigue assessment
Evaluation of residual stresses in a pipe-to-plate welded joint by means of uncoupled thermal-structural simulation and experimental tests
No full textA deep knowledge of the production process is needed, in order to achieve quality and safety requirements in a component. In this context, residual stresses play an important role, especially in welded structures. The present work deals with the assessment of residual stresses in a S355JR carbon steel pipe-to-plate welded joint. Both numerical simulations and experimental tests were employed in order to gain wide-ranging knowledge. Numerical simulations were performed with the software Ansys through an uncoupled (one-way coupling) thermal-structural simulation in order to evaluate the stress, strain and temperature at each node of the finite element model for each phase of the simulation. Temperature-dependent elastic-plastic material properties were adopted in combination with the element birth & death method, necessary to simulate the welding process. Two numerical weld seam solidification methods were employed and discussed, in terms of expected results and simulation performances. The obtained numerical results were compared with experimental data of relaxed radial strains measured nearby the weld seam
Closed‐form solution for the Fatemi‐Socie extended critical plane parameter in case of linear elasticity and proportional loading
No full textFatigue damage remains a significant issue for both metallic and non-metallic components, being the main cause of in-service failures. Among the different assessment methodologies, critical plane methods have gained significance as they enable identifying the critical location and the early crack propagation orientation. However, the standard plane scanning method used for calculating critical plane factors is computationally intensive, and as a result, it is usually applied only when the component's critical region is known in advance. In the presence of complex geometries, loads, or constraints, a more efficient method would be required. This work presents a closed-form solution to efficiently evaluate a critical plane factor based on the Fatemi-Socie criterion, in the case of isotropic linear-elastic material behavior and proportional loading conditions. The proposed algorithm, based on tensor invariants and coordinate transformation laws, was tested on different case studies under various loading conditions, showing a significant reduction in computation time compared to the standard plane scanning method
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