Additive manufacturing technologies have opened a world of possibilities in the production of structures, such as lattices, in a wide range of materials with high geometrical freedom. Lattice structures have been widely used in lightweight energy absorption applications, applied in a range of industrial sectors (automotive, body protection, biomedical fields…). Scientists and engineers are seeking novel and optimized systems for which nature can be a source of innovation: the purpose of this project lies in designing bioinspired structures, capable of providing resistance to compression. The freedom of shape made possible by the manufacturing process, blended with the biomimetic approach, gave the possibility to define innovative lattices. The objectives of the project were two: to define morphological features that characterise some structures found in nature, which make them resistant to different types of loads, and to generate novel bio-inspired structures (BLSs) thought for energy absorption applications. In this context, bamboo was a source of inspiration: its diaphragm allows the plant to resist compression and bending loads. Two unit cells were developed: almost identical to each other, but the second with a slightly more slender profile. For each of the unit cells, a periodic lattice structure was made; then, some dimensional variations were introduced to the original lattices (the height of the unit cells was doubled, halved, or the fillets dimension was varied) in order to analyse the role of individual geometrical aspects on the mechanical performance of the designed lattices. The project was based on the collaboration with the Department of Mechanical and Industrial Engineering of NTNU. They offered the manufacturing and experimental instruments to deepen the topic of the project, contributing to 3D printing of the novel structures. The lattices were manufactured with FDM technology made of PLA and subsequently, quasi-static compressive tests were carried out. Detailed numerical finite elements (FE) simulations were developed to further analyse the performance and deformation behaviour of the structures; the results of these experiments were compared with the elastic stage obtained with FE. Lattice structures based on original unit cell were found to have better performance in terms of energy absorption compared to the structures based on the unit cell with a more slender profile. In general, the best results were shown by the lattice with halved height of unit cell and by the structure composed of the original unit cell with increased dimension of fillets. A hypothetical application for this structure could be in the biomedical field, with the possibility of introducing this lattice for the development of prosthetic feet.
La natura, fonte di ispirazione pressoché inesauribile per scienziati e ingegneri alla ricerca di sistemi nuovi e ottimizzati, è alla base di questo lavoro di ricerca che mira alla progettazione di strutture bio-ispirate resistenti a compressione. Le tecniche di additive manufacturing hanno aperto un mondo di possibilità nella produzione di strutture lattice, in un'ampia gamma di materiali e con un'elevata libertà geometrica, consentendo applicazioni di assorbimento di energia in vari settori industriali (automotive, protezione del corpo, campo biomedicale...). Pertanto, la libertà di forma resa possibile dal processo produttivo, unita all'approccio biomimetico, ha dato la possibilità di definire strutture lattice innovative. Gli obiettivi del progetto erano due: definire le caratteristiche morfologiche di alcune strutture presenti in natura resistenti a diversi tipi di carichi; generare nuove strutture bio-ispirate (BLS) pensate per applicazioni di assorbimento di energia. L’ispirazione è partita dal bambù. Il suo diaframma, che permette alla pianta di resistere ai carichi di compressione e di flessione, ha consentito lo sviluppo di due unit cells quasi identiche tra loro: la seconda ha un profilo leggermente più sottile. Per ognuna delle unit cells è stata realizzata una struttura lattice periodica; in cui successivamente sono state introdotte alcune variazioni dimensionali (l'altezza delle unit è stata raddoppiata, dimezzata, o è stata variata la dimensione dei raggi di raccordo) al fine di analizzare il ruolo dei singoli aspetti geometrici sulle prestazioni meccaniche delle strutture lattice progettate. Il lavoro è stato svolto in collaborazione con il Dipartimento di Ingegneria Meccanica e Industriale di NTNU che ha messo a disposizione tecnologie di stampa 3D per la produzione delle strutture fabbricate con la tecnologia FDM in PLA e successivamente sottoposte a prove di compressione quasi statiche. Dettagliate analisi FEM sono state condotte per analizzare ulteriormente le prestazioni e il comportamento a compressione delle strutture; i risultati dei test sperimentali sono stati confrontati con la fase elastica ottenuta dalle analisi FEM. Le strutture lattice basate sulla unit cell originale sono risultate migliori in termini di assorbimento di energia rispetto alle strutture dal profilo leggermente più sottile. In generale, i risultati migliori sono stati conseguiti con la struttura con unit cell con altezza dimezzata e con la struttura composta dalla unit originale con dimensione aumentata dei raggi di raccordo. Un ipotetico campo di applicazione per questa struttura potrebbe essere quello biomedicale, approfondendone l’utilizzo per lo sviluppo di piedi protesici.
Analysis and development of additive manufactured novel bio-inspired lattice structures
Greco, Lucrezia
2020/2021
Abstract
Additive manufacturing technologies have opened a world of possibilities in the production of structures, such as lattices, in a wide range of materials with high geometrical freedom. Lattice structures have been widely used in lightweight energy absorption applications, applied in a range of industrial sectors (automotive, body protection, biomedical fields…). Scientists and engineers are seeking novel and optimized systems for which nature can be a source of innovation: the purpose of this project lies in designing bioinspired structures, capable of providing resistance to compression. The freedom of shape made possible by the manufacturing process, blended with the biomimetic approach, gave the possibility to define innovative lattices. The objectives of the project were two: to define morphological features that characterise some structures found in nature, which make them resistant to different types of loads, and to generate novel bio-inspired structures (BLSs) thought for energy absorption applications. In this context, bamboo was a source of inspiration: its diaphragm allows the plant to resist compression and bending loads. Two unit cells were developed: almost identical to each other, but the second with a slightly more slender profile. For each of the unit cells, a periodic lattice structure was made; then, some dimensional variations were introduced to the original lattices (the height of the unit cells was doubled, halved, or the fillets dimension was varied) in order to analyse the role of individual geometrical aspects on the mechanical performance of the designed lattices. The project was based on the collaboration with the Department of Mechanical and Industrial Engineering of NTNU. They offered the manufacturing and experimental instruments to deepen the topic of the project, contributing to 3D printing of the novel structures. The lattices were manufactured with FDM technology made of PLA and subsequently, quasi-static compressive tests were carried out. Detailed numerical finite elements (FE) simulations were developed to further analyse the performance and deformation behaviour of the structures; the results of these experiments were compared with the elastic stage obtained with FE. Lattice structures based on original unit cell were found to have better performance in terms of energy absorption compared to the structures based on the unit cell with a more slender profile. In general, the best results were shown by the lattice with halved height of unit cell and by the structure composed of the original unit cell with increased dimension of fillets. A hypothetical application for this structure could be in the biomedical field, with the possibility of introducing this lattice for the development of prosthetic feet.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/183857