Representative structure elements for the fatigue assessment of additively manufactured components

The 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

Closed‐form solution for the Fatemi‐Socie extended critical plane parameter in case of linear elasticity and proportional loading

Fatigue 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

Fatigue assessment of a FSAE car rear upright by a closed form solution of the critical plane method

Material fatigue is extensively discussed and researched within scientific and industrial communities. Fatigue damage poses a significant challenge for both metallic and non-metallic components, often resulting in unexpected failures of in-service parts. Within multiaxial fatigue assessment, critical plane methods have gained importance due to their ability to characterize a component's critical location and detect early crack propagation. However, the conventional approach to calculate critical plane factors is time-consuming, making it primarily suitable for research purposes or when critical regions are already known. In many real-world scenarios, identifying the critical area of a component is difficult due to complex geometries, varying loads, or time limitations. This challenge becomes particularly crucial after topological optimization of components and in the context of lightweight design. Recently, the authors proposed an efficient method for evaluating critical plane factors in closed form, applicable to all cases that necessitate the maximization of specific parameters based on stress and strain components or their combination. This paper presents and validates the proposed methodology, with reference to a rear upright of a FSAE car, which is characterized by a complex geometry and is subjected to non-proportional loading conditions. The efficient algorithm demonstrated a substantial reduction in computation time compared to the standard plane scanning method, while maintaining solution accuracy

Dataset of dimensionless operating conditions for welding and metal additive manufacturing

The present dataset contains the dimensionless operating conditions obtained by processing a wide range of welding and metal Additive Manufacturing (AM) process parameters through a unified theoretical framework based on the Rosenthal solution [1]. The exploratory data analysis covered Arc and Beam Welding (AW and BW, respectively) on various materials, joint types, and bead sizes ranging from 0.5 to over 10 mm. As for AM, we considered Laser Metal Deposition (LMD) and Selective Laser Melting (SLM) on steel, Al, Ni, Ti, Cu, and Co-Cr alloys by limiting the research to the last five years of published literature

Technological implications of the Rosenthal solution for a moving point heat source in steady state on a semi-infinite solid

This paper introduces a theoretical framework for the analysis and optimization of melting processes that use focused moving heat sources. Specifically, we consider the Rosenthal solution for a moving point heat source in steady state on a semi-infinite solid. Firstly, we analyze the feasibility of the thermal problem while constraining the melt pool size and aspect ratio. We then express the maximum allowable velocity and the corresponding power as explicit functions of the constraints and material properties. Finally, we examine a wide range of melting processes within a dimensionless framework derived from the above solution. The paper concludes with an application example concerning lack of fusion porosity in powder bed fusion additive manufacturing, which shows the reliability of analytical estimates despite the complexity of the underlying physics. This makes it possible to outline a direct procedure for optimizing the main process parameters given a few basic requirements. Ultimately, the proposed methods are not intended to replace other modeling and experimental approaches, but rather to complement their capabilities and encourage more efficient use of available resources. In addition, reframing seemingly different problems within a common perspective can improve understanding, reveal new levels of similarity, and sometimes even allow for global solutions

Schede (Palazzo Dotto de\u2019 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\u2019Orologio, via Dondi - Palazzo Capodilista, ora Emo Capodilista)

Immissione e compilazione schede nel database sulla "Grande decorazione profana" del Sei e Settecento all'interno dei palazzi di Padova per il Centro di ricerca \u201cRossana Bossaglia\u201d in occasione del PRIN 2010-2011 \u2013 La pittura profana dall\u2019et\ue0 barocca all\u2019et\ue0 neoclassica nell\u2019Italia settentrionale, con particolare attenzione alla presenza dei pittori veneti e veneziani

Analysis of the interaction and propagation of multiple cracks in weldments.

This thesis is the result of a five-months work at the Fraunhofer LBF research centre. This thesis explores the recent field of fracture mechanics about the study of interaction and coalescence´of multiple cracks. The work will be focused on propagation of multiple cracks in a butt welded joint specimen intended for heavy industrial application. The thesis is based on previous research carried forward by Fraunhofer LBF group for Numerical Method and Component Design and all the groups belonging to the IBESS project. The study takes place on short cracks regime in which the use of elastic material hypothesis through the stress intensity factor loses its validity. Instead, an elastic plastic material behaviour is necessary with the introduction of the J-integral parameter, calculated through the use of FEM simulations of interacting and coalescing cracks’ models. This leads to the definition of two factors necessary for a more accurate study of the propagation of fatigue cracks, the interaction and coalescence factors. A research is conducted to compare the crack growth between experimental results and the IBESS computational algorithm. Also, an improvement of the coalescence factor is required, to solve a singularity problem in the function. The work showed that the simulations with heat affected zone material behaviour leads to results closer to reality respect the base material behaviour. Furthermore, the new implemented coalescence formula solved the problem of singularity at the beginning of coalescence, maintaining the behaviour of the function close to the experimental results

Influence of residual stresses on the fatigue life of welded joints

SOMMARIO Per ottenere elevati standard di qualità e sicurezza in un componente strutturale, occorre una notevole familiarità con il processo di produzione. Di fatto, i processi di produzione tendono a generare difetti quali tensioni residue, imperfezioni interne e superficiali, e considerando anche le variazioni geometriche intrinseche, come intagli, cricche o difetti in generale, è spesso complesso caratterizzare con precisione la resistenza strutturale di tali parti. In questo contesto, le tensioni residue giocano un ruolo importante, specialmente nelle strutture saldate. La stima delle tensioni residue è tipicamente effettuata tramite metodi sperimentali e numerici. Entrambi presentano punti di forza e svantaggi che ne richiedono l'uso combinato in modo da ottenere una valutazione coerente e significativa delle tensioni residue. La presente tesi di dottorato si inserisce in tale ambito. Il lavoro presentato nel seguito propone uno studio sulla generazione delle autotensioni e analizza il loro effetto sulla vita a fatica di giunti saldati tubo-piastra caricati in torsione e in flessione. Nella prima parte, viene valutata la capacità di diversi metodi termici nel riprodurre la distribuzione della temperatura intorno al cordone di saldatura, utilizzando simulazioni agli elementi finiti. I risultati delle simulazioni sono stati successivamente confrontati con misure sperimentali della temperatura superficiale calcolata in prossimità al cordone di saldatura. I modelli termici considerati presentano diversi livelli di complessità, partendo da quello base, che implementa una temperatura iniziale costante degli elementi appartenenti al cordone di saldatura, al più completo e diffuso modello a doppia ellissoide di Goldak. Lo studio mostra come i diversi metodi termici impiegati, presentino comportamenti termici simili in prossimità del cordone di saldatura. In secondo luogo è stato ottenuto un buon accordo tra le misure sperimentali e quelle numeriche utilizzando un metodo semplificato (cioè che richiede l'impostazione di un solo parametro). Il seguente modello può essere utilizzato per riprodurre efficacemente la storia termica durante un processo di saldatura. Nella seconda parte, viene presentato lo studio sulle autotensioni per un giunto saldato tubo-piastra in acciaio al carbonio S355JR. Per ottenere una conoscenza più ad ampio raggio sono state utilizzate sia simulazioni numeriche che prove sperimentali. Il software Ansys è stato utilizzato per effettuare simulazioni termo-strutturali disaccoppiate e valutare così le sollecitazioni, deformazioni e la temperatura in ogni nodo del modello. Per simulare correttamente il processo di saldatura agli elementi finiti sono state implementate proprietà del materiale elasto-plastiche e dipendenti dalla temperatura mentre, per riprodurre il processo di solidificazione del cordone, sono stati analizzati due diversi approcci numerici. I risultati ottenuti sono stati discussi e confrontati con dati sperimentali di deformazioni radiali rilassate misurate vicino al cordone di saldatura e ottenute tramite una tecnica di foratura incrementale. Nella terza parte del lavoro è stata studiata l'influenza delle autotensioni sulla vita a fatica dei giunti saldati. Nell'analisi sono stati considerati fattori critici quali discontinuità geometriche e la microstruttura eterogenea del materiale. Sono state eseguite prove sperimentali sui giunti saldati in condizioni as-welded e rilassati, sottoposti a carichi di torsione e flessione. I risultati sperimentali hanno mostrato come le tensioni residue abbiano un'influenza principalmente sui componenti caricati in torsione. In questo contesto il modello termo-strutturale presentato nei capitoli precedenti è stato usato per valutare il campo completo delle sollecitazioni residue all'interno del provino, così da poterle mappare e includerle come condizioni iniziali nei modelli numerici destinati al calcolo dei fattori di danno a fatica. Infine, l'efficacia dei modelli numerici nel descrivere il danneggiamento a fatica è stata valutata tramite confronto con risultati sperimentali. Nell'ultima parte di questo lavoro viene presentato uno studio numerico preliminare su un provino con intaglio acuto. Il lavoro si pone lo scopo di riprodurre nel provino intagliato condizioni di stress residuo paragonabili a quelle riscontrate sulla sezione critica del giunto saldato. Infatti, è possibile ottenere un gradiente di stress simile a quello ottenuto dopo il processo di saldatura variando il raggio e l'angolo di apertura dell'intaglio. L'uso di una geometria semplificata permette un'analisi più accessibile e migliora la comprensione dei processi che avvengono all'interno del materiale in presenza di autotensioni e carichi affaticanti. ABSTRACT A 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

Influence of residual stresses on the fatigue life of welded joints

A 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

MEASURING FAIR AND SUSTAINABLE WELL-BEING FOR ECONOMIC POLICY PLANNING AND EVALUATION

openL'Indice del Benessere Equo e Sostenibile (BES) è un importante strumento di valutazione che va oltre il tradizionale focus sul PIL, valutando l'impatto economico e sociale delle politiche. Esso considera una vasta gamma di indicatori che misurano il benessere delle persone, la qualità dell'ambiente e la sostenibilità a lungo termine. L'implementazione del BES può avere un impatto significativo sulle decisioni politiche ed economiche, promuovendo politiche più inclusive, sostenibili e orientate al benessere delle persone e del pianeta.The Well-being, Equity, and Sustainability Index (BES) is an important evaluation tool that goes beyond the traditional focus on GDP, assessing the economic and social impact of policies. It considers a wide range of indicators that measure people's well-being, environmental quality, and long-term sustainability. The implementation of the BES can have a significant impact on political and economic decisions, promoting more inclusive, sustainable, and people- and planet-centered policies