Steel structures are often subject to aesthetic requirements and challenging environmental conditions. They require complex structural nodes having expensive design and verification, high weight and fabrication labour content. Metal Additive Manufacturing is an opportunity for improving the efficiency of nodes by optimizing them for function, producing with additive processes, and assembling them to conventional beams and columns. The typical advantages and weaknesses of metal additive manufacturing are already known, but the key factors for design and user-friendly methods for assessing its favourability in the construction sector are not yet available. This work investigated the weldability of metal additive manufacturing steel with conventional steel profiles, which induced limited modifications in the additively manufactured steel. The performed analyses identified a 15mm long heat affected zone with deletion of weld pool boundaries, unstable microhardness, and a 10% reduction of the elongation at break. The typical anisotropy of additively manufactured components has been analysed in case studies redesigned for additive manufacturing. The nodes demonstrated that anisotropy has a relevant role in assessing the stress and strain distributions in complex shapes, and in defining the failure location in welded joints. These are relevant aspects to be considered when outlining the design rules for using additive manufacturing for structural components. Indeed, one of the first steps of structure design is the definition of the failure mechanism, and the material anisotropy is an important factor to be considered together with joint detailing and geometrical features. Steel structures are also frequently subject to cyclic loads, and the fatigue life of the welded samples made by an additively manufactured part and a conventional one was experimentally evaluated. It showed compatible values to the design provisions of Eurocode3, even though the fatigue life was strongly determined by the quantity and orientation of the internal defects of the additively manufactured component, which depends on the build direction of the components. A design solution’s suitability is due also to the economic and environmental costs. A cost model based on well-established formulations proved the sustainability of additively manufactured nodes in steel structures in a 10 years scenario when the technologies and its market will be mature. Our environmental impact model quantified a 45% reduction of input steel by designing the node for additive manufacturing. In terms of CO2 emissions, 40% is saved from transportation, while the energy input for additively manufactured nodes is 7% higher than for the traditional solution. Although metal additive manufacturing is not yet a sustainable solution to complement traditional manufacturing in steel structures, its performances are promising; therefore pointing the research to outlining proper design tools for industrial application will build a favourable scenario for exploiting all its advantages.
Le strutture in acciaio sono spesso soggette a specifici requisiti estetici ed estreme condizioni ambientali. Queste strutture possiedono nodi strutturali complessi, con progettazione e verifiche costose, grandi quantità di materiale e ore di lavoro. La Manifattura Additiva di Metalli è un'opportunità per migliorare l'efficienza dei nostri strutturali in acciaio ottimizzandoli in relazione alla loro funzione, producendoli con metodi additivi e assemblandoli con travi e colonne prodotte convenzionalmente. I tipici vantaggi e debolezze della manifattura additiva di metalli sono ormai noti, ma tuttora non sono ancora disponibili i principali fattori per la progettazione e metodi per la valutazione dell’efficienza di questa tecnologia per l’ambito delle costruzioni. Questa ricerca ha studiato la saldabilità di acciaio prodotto con tecniche additive con acciai convenzionali. Le analisi condotte hanno identificato una zona termicamente alterata pari a 15mm in cui sono state rilevate microdurezza instabile e una riduzione di deformazione a rottura pari al 10%. L’anisotropia tipica dei prodotti da manifattura additiva di metalli è stata analizzata in casi di studio riprogettati per le tecniche di produzione additive. I nodi hanno dimostrato che l’anisotropia assume un ruolo rilevante nel determinare le distribuzioni di sforzi e deformazioni quando questi hanno una geometria complessa e quando sono presenti giunti saldati. Questi aspetti devono essere considerati nel definire regole di progettazione. Infatti, uno dei principali fattori nella progettazione strutturale è la definizione del meccanismo di frattura, insieme all’anisotropia dei materiali e alle proprietà geometriche dei nodi. Le strutture in acciaio sono anche frequentemente sottoposte a carichi ciclici, infatti la vita a fatica di componenti ibridi saldati è stata valutata sperimentalmente. Sono stati osservati valori paragonabili a quelli forniti dall’Eurocodice 3, anche se i risultati hanno dimostrato che la vita a fatica è fortemente determinata dalla quantità e dell’orientamento dei difetti interni presenti dei componenti da manifattura additiva. Perché una soluzione progettuale sia competitiva deve avere anche costi contenuti e basso impatto ambientale. L’analisi di costi e impatto ambientale è stato sviluppato su solide formulazioni analitiche a banche dati, dimostrando la sostenibilità di nodi prodotti con manifattura additiva in uno scenario futuro di 10 anni. Il modello definito ha quantificato una riduzione del 45% dell’acciaio necessario per la produzione del nodo da manifattura additiva. In termini di emissioni di CO2, il 40% verrebbe risparmiato nei trasporti, mentre l’energia necessaria per la produzione è risultata essere maggiore del 7% rispetto alla produzione con metodi tradizionali. Nonostante la manifattura additiva di metalli non sia ancora una soluzione sostenibile come tecnologia complementare ai metodi convenzionali nell’ambito delle costruzioni, le sue prestazioni sono promettenti. Infatti, indirizzando la ricerca per definire strumenti specifici per l’ambito delle costruzioni si può costruire uno scenario favorevole per sfruttare appieno le potenzialità della manifattura additiva di metalli.
Additively manufactured steel nodes for optimising performance and material efficiency in steel structures
CHIERICI, MARTINA
2023/2024
Abstract
Steel structures are often subject to aesthetic requirements and challenging environmental conditions. They require complex structural nodes having expensive design and verification, high weight and fabrication labour content. Metal Additive Manufacturing is an opportunity for improving the efficiency of nodes by optimizing them for function, producing with additive processes, and assembling them to conventional beams and columns. The typical advantages and weaknesses of metal additive manufacturing are already known, but the key factors for design and user-friendly methods for assessing its favourability in the construction sector are not yet available. This work investigated the weldability of metal additive manufacturing steel with conventional steel profiles, which induced limited modifications in the additively manufactured steel. The performed analyses identified a 15mm long heat affected zone with deletion of weld pool boundaries, unstable microhardness, and a 10% reduction of the elongation at break. The typical anisotropy of additively manufactured components has been analysed in case studies redesigned for additive manufacturing. The nodes demonstrated that anisotropy has a relevant role in assessing the stress and strain distributions in complex shapes, and in defining the failure location in welded joints. These are relevant aspects to be considered when outlining the design rules for using additive manufacturing for structural components. Indeed, one of the first steps of structure design is the definition of the failure mechanism, and the material anisotropy is an important factor to be considered together with joint detailing and geometrical features. Steel structures are also frequently subject to cyclic loads, and the fatigue life of the welded samples made by an additively manufactured part and a conventional one was experimentally evaluated. It showed compatible values to the design provisions of Eurocode3, even though the fatigue life was strongly determined by the quantity and orientation of the internal defects of the additively manufactured component, which depends on the build direction of the components. A design solution’s suitability is due also to the economic and environmental costs. A cost model based on well-established formulations proved the sustainability of additively manufactured nodes in steel structures in a 10 years scenario when the technologies and its market will be mature. Our environmental impact model quantified a 45% reduction of input steel by designing the node for additive manufacturing. In terms of CO2 emissions, 40% is saved from transportation, while the energy input for additively manufactured nodes is 7% higher than for the traditional solution. Although metal additive manufacturing is not yet a sustainable solution to complement traditional manufacturing in steel structures, its performances are promising; therefore pointing the research to outlining proper design tools for industrial application will build a favourable scenario for exploiting all its advantages.| File | Dimensione | Formato | |
|---|---|---|---|
|
2023_12_Chierici.pdf
non accessibile
Descrizione: Tesi di dottorato completa
Dimensione
134.46 MB
Formato
Adobe PDF
|
134.46 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/214764