Shape Memory Alloys (SMAs), and in particular NiTi, are functional materials with unique thermo-mechanical behaviors that make them attractive for various applications in fields such as aerospace, automotive, and biomedical engineering. NiTi can serve multiple functions, ranging from damping to actuation. However, one of the main limitations to the broader adoption of NiTi is its poor machinability. This thesis focuses on investigating the functional behavior of NiTi structures fabricated using Laser Powder Bed Fusion (LPBF) technology, with the aim of exploring the feasibility of designing geometries more complex than those achievable with conventional manufacturing techniques. Both functional effects of NiTi were investigated: the pseudoelastic effect for damping applications and the shape memory effect for shape recovery and actuation upon heating. The first phase of this work focused on optimizing the printing parameters to achieve good functionality, particularly a well-defined pseudoelastic response, while also minimizing the presence of defects. The outcomes of this initial phase enabled the definition of the manufacturing process. This was subsequently applied to fabricate the more complex structures analyzed in the later stages of the study: octahedral cells and origami-inspired structure. The octahedral cell was investigated for damping applications, with the subsequent goal of integrating the cell design into a damping plate. It was studied by varying its dimensions and optimizing its mechanical response through numerical analyses. The thermo-mechanical responses of the initial and optimized cells were compared, focusing on their damping capabilities and performance under cyclic loading. Finally, a preliminary version of the damping plate was tested. The origami structure instead showed a more complex geometry and was tested to evaluate its pseudoelastic, shape memory, and actuation performances. The results showed that, despite the increased geometrical complexity, the structure exhibited promising performance, demonstrating a high capability to recover imposed deformations both under load and in unloaded conditions. This thesis confirmed the high potentiality of L-PBF processes for manufacturing NiTi complex structures capable of efficiently exploiting the material functionality and lay the foundations for deeper research that may allow a broader adoption of the material in different fields.
I materiali a memoria di forma (SMA), e nello specifico il NiTi, sono materiali che presentano un comportamento termo-meccanico unico, rendendoli particolarmente interessanti per diverse applicazioni, tra cui quelle in ambito aerospaziale, dell’automotive e biomedico. Tuttavia, una delle limitazioni principali ad una più ampia diffusione degli SMA è la loro ridotta lavorabilità tramite l’utilizzo di tecnologie tradizionali. Questa tesi si focalizza sullo studio della funzionalità di strutture prodotte in NiTi con la tecnologia Laser Powder Bed Fusion (L-PBF). Lo scopo è quello di esplorare la possibilità di realizzare strutture con una complessità maggiore rispetto a quelle tipicamente ottenute con tecniche tradizionali. Entrambi gli effetti che caratterizzano il NiTi sono stati investigati: l’effetto pseudoelastico per lo smorzamento e l’effetto a memoria di forma per l’attuazione. Nella prima fase del lavoro sono stati ottimizzati i parametri di processo allo scopo di ottenere una buona funzionalità del materiale, in particolare studiando la risposta pseudoelastica, e minimizzando allo stesso tempo la presenza di difetti. I parametri risultanti sono stati utilizzati nella parte successiva della tesi per realizzare strutture più complesse, concentrandosi su celle ottaedriche e su una struttura origami. Lo studio della cella ottaedrica è stato intrapreso allo scopo di progettare una piastra smorzante, costituita dalla combinazione di più celle. La singola cella è stata caratterizzata e successivamente analizzata tramite test numerici, cercando di ottimizzarne la funzionalità. La geometria ottimizzata è stata poi stampata e testata, confrontando le risposte termomeccaniche ottenute con quelle della cella iniziale, concentrandosi in particolare, sulle proprietà smorzanti. A conclusione di questa parte dello studio, un prototipo di piastra smorzante è stato realizzato e testato. La struttura ad origami infine, ha permesso di verificare la funzionalità del materiale su una geometria con una complessità maggiore. La struttura è stata testata per gli effetti pseudoelastico, a memoria di forma e per l’ attuazione. I risultati hanno mostrato come, nonostante l’incremento della complessità della geometria, il comportamento della struttura continui ad essere promettente, con elevate capacità di recupero della forma iniziale. In conclusione, questa tesi conferma le elevate potenzialità dei processi L-PBF per la produzione di strutture in NiTi caratterizzate da geometrie complesse e capaci di sfruttare efficacemente la funzionalità del materiale, ponendo le basi per estenderne l’utilizzo in diversi ambiti.
3D Printing of shape memory alloys for complex architectures
Biasutti, Tiziana
2024/2025
Abstract
Shape Memory Alloys (SMAs), and in particular NiTi, are functional materials with unique thermo-mechanical behaviors that make them attractive for various applications in fields such as aerospace, automotive, and biomedical engineering. NiTi can serve multiple functions, ranging from damping to actuation. However, one of the main limitations to the broader adoption of NiTi is its poor machinability. This thesis focuses on investigating the functional behavior of NiTi structures fabricated using Laser Powder Bed Fusion (LPBF) technology, with the aim of exploring the feasibility of designing geometries more complex than those achievable with conventional manufacturing techniques. Both functional effects of NiTi were investigated: the pseudoelastic effect for damping applications and the shape memory effect for shape recovery and actuation upon heating. The first phase of this work focused on optimizing the printing parameters to achieve good functionality, particularly a well-defined pseudoelastic response, while also minimizing the presence of defects. The outcomes of this initial phase enabled the definition of the manufacturing process. This was subsequently applied to fabricate the more complex structures analyzed in the later stages of the study: octahedral cells and origami-inspired structure. The octahedral cell was investigated for damping applications, with the subsequent goal of integrating the cell design into a damping plate. It was studied by varying its dimensions and optimizing its mechanical response through numerical analyses. The thermo-mechanical responses of the initial and optimized cells were compared, focusing on their damping capabilities and performance under cyclic loading. Finally, a preliminary version of the damping plate was tested. The origami structure instead showed a more complex geometry and was tested to evaluate its pseudoelastic, shape memory, and actuation performances. The results showed that, despite the increased geometrical complexity, the structure exhibited promising performance, demonstrating a high capability to recover imposed deformations both under load and in unloaded conditions. This thesis confirmed the high potentiality of L-PBF processes for manufacturing NiTi complex structures capable of efficiently exploiting the material functionality and lay the foundations for deeper research that may allow a broader adoption of the material in different fields.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/239098