This dissertation work focused on the investigation of solutions to improve the mechanical performance of manufactured products in composite material. Several approaches were employed to achieve this goal. For what concerned the first approach, performance improvement was pursued through the dispersion of graphene-based nanofillers in the polymer matrix. In the second approach, high-performance lattice structures in fibre-reinforced composite materials wereinvestigated using additive manufacturing techniques. The study of nanofilled composites initially focused on analysing the effect of the type, content (0.2% to 3%) and type of functionalisation of graphene oxide (GO) on the mechanical properties of the epoxy system in which it was dispersed. To this aim, three-point bending tests were conducted on specimens containing different percentages of nanofiller to determine the stress, stiffness and fracture strain values for the nanofilled specimens, which were then compared to the respective properties of the pure resin. In addition, tests were performed to assess the effect of the nanofiller on the hardness of the material. Subsequently, to assess the dispersion of the nanofiller, the surfaces of the samples were analysed using scanning electron microscopy. Finally, the nanofiller was functionalised and dispersed in the epoxy system with the aim of defining the type of functionalisation that provided the best mechanical performance to the composite. The main results showed that the dispersion of a small amount of GO nanofiller (0.2%) allows to achieve higher values of maximum flexural strength. As far as stiffness is concerned, it has an increasing trend with increasing of the nanofiller content dispersed. These properties were further improved through a chemical functionalisation process. Since the mechanical properties of the composite with graphene oxide are comparable to those obtained by dispersing carbon nanotubes (CNTs), and the latter has significantly lower costs than GO, the following study focused on the investigation of the effect of carbon nanotube content on the mechanical properties of composite reinforced materials with long carbon fibres. In particular, multi-walled carbon nanotubes (MWCNTs) were dispersed in the epoxy resin in different amounts, from 0.5 to 4 per cent, in constant intervals of 0.5. The composites were realized by impregnating the fibres with the nanofilled resin using the infusion process followed by an autoclave polymerisation. The samples were tested to evaluate the void content and the tensile, bending and interlaminar shear behaviour. In addition, the samples were subjected to rheological, thermal (differential scanning calorimetry, DSC), dynamic light scattering (DLS) and dynamic mechanical analysis (DMA) analyses. SEM surface fracture analyses were also performed to study the effect of MWCNT content on fracture mechanisms and to evaluate their dispersion. The three-phase composite shows that the addition of up to 3% of MWCNT results in improved performance in terms of stress, stiffness and interlaminar shear strength compared to unfilled CFRP composites. In addition, environmental and economic impact assessments resulting from the addition of such nanocarriers into their respective materials were conducted through Life Cycle Assessment and Life Cycle Costing analyses. Following these analyses, carbon nanotubes have been found to be a sustainable solution both environmentally and economically for fiber-reinforced composites intended for structural applications. The final part of the research focused on the study of high-performance lattice structures obtained through fused filament fabrication (FFF) using a continuous carbon fiber filament binderized with epoxy resin and a nylon-based thermoplastic resin as the matrix. In particular, isogrid structures with different infill density percentages (from 10% to 80%) were manufactured and tested through buckling tests. The main results showed an increase in strength and strength-to-weight ratio with increasing infill density percentage used.
La presente tesi ha riguardato lo studio di soluzioni per migliorare le performance di manufatti in compositi. Il primo approccio si basa sul miglioramento delle performance attraverso la dispersione di nanocariche a base di grafene nella matrice polimerica. Il secondo approccio studiata strutture reticolari alto-performanti in materiale composito fibro-rinforzato realizzate con tecniche di fabbricazione additiva. Lo studio effettuato sui compositi nanocaricati ha riguardato dapprima l’analisi dell'effetto della tipologia, del contenuto e del tipo di funzionalizzazione dell’ossido di grafene sulle proprietà meccaniche del sistema epossidico in cui è stato disperso. A tal fine, sono stati effettuati dei test di flessione a tre punti, su provini con diverse percentuali di nanocarica. Da queste prove sono stati ricavati i valori di tensione, rigidezza e deformazione a frattura dei provini nanocaricati che sono stati successivamente confrontati con le rispettive proprietà della resina non nanocaricata. Inoltre, sono stati effettuati dei test di durezza e analisi al SEM per valutare l’effetto della nanocarica sulla durezza del materiale e la sua dispersione, rispettivamente. Infine, la nanocarica è stata funzionalizzata e dispersa nel sistema epossidico ed è stato valutato il tipo di funzionalizzazione in grado di apportare le migliori prestazioni meccaniche. I risultati mostrano che è sufficiente disperdere una ridotta quantità di nanocarica di GO per raggiungere i più alti valori di resistenza massima a flessione. Quanto alla rigidezza questa tende a crescere con il contenuto di nanocarica dispersa. Queste proprietà sono state ulteriormente incrementate con la funzionalizzazione chimica. Poichè le proprietà meccaniche del composito con GO risultano essere confrontabili con quelle ottenibili disperdendo al suo interno nanotubi di carbonio (CNT) e presentando questi ultimi costi significativamente inferiori, lo studio successivo si è concentrato sull’analisi dell'effetto del contenuto di CNT sulle proprietà meccaniche dei compositi rinforzati con fibre lunghe di carbonio. In particolare, sono stati dispersi all’interno di una resina epossidica CNT a parete multipla (MWCNT) in diversi quantitativi. I compositi sono stati realizzati impregnando con la resina nanocaricata le fibre utilizzando il processo di infusione seguita dalla cura in autoclave. I campioni sono stati testati per valutare il contenuto dei vuoti e il comportamento a trazione, flessione e a taglio interlaminare. Inoltre, tali provini sono stati sottoposti ad analisi reologiche, termiche (Differential Scanning Calorimetry, DSC), analisi Dynamic Light Scattering (DLS) e analisi Dynamic Mechanical Analysis (DMA). Anche in questo studio sono state analizzate le superfici di frattura mediante SEM per studiare l'effetto del contenuto di MWCNT sui meccanismi di rottura e per valutarne la dispersione. Il composito trifase mostra come l'aggiunta di MWCNT fino al 3% comporti, rispetto ai compositi CFRP non nanocaricati, un miglioramento delle prestazioni in termini di tensione, rigidezza e forza al taglio interlaminare. Inoltre, sono state effettuate delle valutazioni degli impatti ambientali ed economici dovuti all’aggiunta di tali nanocariche nei rispettivi materiali attraverso analisi di Life Cycle Assessment e Life Cycle Costing. A seguito di queste analisi si è riscontrato che i nanotubi al carbonio risultano una soluzione sostenibile sia a livello ambientale che economico per compositi fibrorinforzati finalizzati all’utilizzo in applicazioni strutturali. L’ultima parte della ricerca si è focalizzata sullo studio di strutture reticolari alto-prestazionali ottenute mediante fused filament fabrication (FFF) utilizzando un filamento continuo in fibra di carbonio e una resina a base di nylon come matrice termoplastica. In particolare, sono state realizzate strutture isogrid con diversi riempimenti mostrando un aumento della forza e della forza per unità di peso all’aumentare della percentuale di riempimento utilizzata
Miglioramento delle proprietà meccaniche dei compositi CFRP attraverso la dispersione di nanocariche all’interno della matrice e lo sviluppo di strutture alto-performanti / Gentili, Serena. - (2024 Jun 17).
Miglioramento delle proprietà meccaniche dei compositi CFRP attraverso la dispersione di nanocariche all’interno della matrice e lo sviluppo di strutture alto-performanti
GENTILI, SERENA
2024-06-17
Abstract
This dissertation work focused on the investigation of solutions to improve the mechanical performance of manufactured products in composite material. Several approaches were employed to achieve this goal. For what concerned the first approach, performance improvement was pursued through the dispersion of graphene-based nanofillers in the polymer matrix. In the second approach, high-performance lattice structures in fibre-reinforced composite materials wereinvestigated using additive manufacturing techniques. The study of nanofilled composites initially focused on analysing the effect of the type, content (0.2% to 3%) and type of functionalisation of graphene oxide (GO) on the mechanical properties of the epoxy system in which it was dispersed. To this aim, three-point bending tests were conducted on specimens containing different percentages of nanofiller to determine the stress, stiffness and fracture strain values for the nanofilled specimens, which were then compared to the respective properties of the pure resin. In addition, tests were performed to assess the effect of the nanofiller on the hardness of the material. Subsequently, to assess the dispersion of the nanofiller, the surfaces of the samples were analysed using scanning electron microscopy. Finally, the nanofiller was functionalised and dispersed in the epoxy system with the aim of defining the type of functionalisation that provided the best mechanical performance to the composite. The main results showed that the dispersion of a small amount of GO nanofiller (0.2%) allows to achieve higher values of maximum flexural strength. As far as stiffness is concerned, it has an increasing trend with increasing of the nanofiller content dispersed. These properties were further improved through a chemical functionalisation process. Since the mechanical properties of the composite with graphene oxide are comparable to those obtained by dispersing carbon nanotubes (CNTs), and the latter has significantly lower costs than GO, the following study focused on the investigation of the effect of carbon nanotube content on the mechanical properties of composite reinforced materials with long carbon fibres. In particular, multi-walled carbon nanotubes (MWCNTs) were dispersed in the epoxy resin in different amounts, from 0.5 to 4 per cent, in constant intervals of 0.5. The composites were realized by impregnating the fibres with the nanofilled resin using the infusion process followed by an autoclave polymerisation. The samples were tested to evaluate the void content and the tensile, bending and interlaminar shear behaviour. In addition, the samples were subjected to rheological, thermal (differential scanning calorimetry, DSC), dynamic light scattering (DLS) and dynamic mechanical analysis (DMA) analyses. SEM surface fracture analyses were also performed to study the effect of MWCNT content on fracture mechanisms and to evaluate their dispersion. The three-phase composite shows that the addition of up to 3% of MWCNT results in improved performance in terms of stress, stiffness and interlaminar shear strength compared to unfilled CFRP composites. In addition, environmental and economic impact assessments resulting from the addition of such nanocarriers into their respective materials were conducted through Life Cycle Assessment and Life Cycle Costing analyses. Following these analyses, carbon nanotubes have been found to be a sustainable solution both environmentally and economically for fiber-reinforced composites intended for structural applications. The final part of the research focused on the study of high-performance lattice structures obtained through fused filament fabrication (FFF) using a continuous carbon fiber filament binderized with epoxy resin and a nylon-based thermoplastic resin as the matrix. In particular, isogrid structures with different infill density percentages (from 10% to 80%) were manufactured and tested through buckling tests. The main results showed an increase in strength and strength-to-weight ratio with increasing infill density percentage used.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
