[en] The ambitious goal of zero emissions in the transport sector requires the development of new materials and technologies that can significantly contribute to weight reduction. Recent advances in Fused Filament Fabrication FFF extrusion 3D printing technology have made it possible to print continuous fibre-reinforced thermoplastics. This technology currently offers higher fibre bending capability than any other automated process. This makes it ideal for expanding the design and manufacturing spaces of steered-fibre composite materials for its application, for example, in components with structurally critical holes. This situation motivated the present thesis. The objective of the thesis is to characterise and model the mechanical behaviour of 3D printed continuous fibre composites for the design of structural components with non-conventional fibre orientations. In this thesis the composition, microstructure and mechanical properties of both the constituents and the printed composite were characterised. For this purpose, standard experimental methods for the physical and mechanical characterisation of conventional composite materials were applied. Defects such as a large number of voids, non-homogeneous distribution of fibres and poor bonding between beads and layers were identified. These defects are the result of insufficient thermo-mechanical consolidation of the material during the printing process. The mechanical behaviour in the longitudinal direction is satisfactory; however, the mechanical performance under transverse and interlaminar loads, which is matrix-dominated, is highly influenced by the manufacturing defects. It is concluded that this process needs further development to be considered viable for high-performance structural applications. In this respect, it was observed that hot-pressing post-treatment improves significantly the interlaminar behaviour of the printed composite. On the other hand, 3D printed Variable-Stiffness (VS) laminates were designed, manufactured and tested. A curvilinear function was used to describe the fibre trajectory, which enabled the parametrisation of a design-oriented meso-scale model based on the finite element method. Conventional stress-based models for the estimation of damage initiation and ultimate failure strengths were adapted to the characteristics of the 3D printed composite material. These models successfully reproduced the fibre-dominated behaviour of the printed laminate. Current commercial printers have severe limitations for fibre path planning, so the design had to be adapted to meet manufacturing requirements. The designed VS laminates improved significantly the open-hole tensile behaviour of the reference quasi-isotropic laminates, demonstrating that composite 3D printing is a suitable technology for the manufacture of lightweight components with small discontinuities.

[eu] Garraioaren sektorean zero emisioko erronka lortzeko, ibilgailuen pisua nabarmen murrizten lagundu dezaketen material eta teknologia berriak garatu behar dira. FFF Fused Filament Fabrication estrusio-teknologian berriki egindako aurrerapenei esker, zuntz jarraituz indartutako termoplastikoak inprimatu ahal dira. Teknologia honek, gaur egun zuntzak kurbatzeko beste edozein prozesu automatizatuk baino gaitasun handiagoa ematen du. Ezaugarri horri esker, ezin hobea da fibra-gidatudun material konposatuen diseinu- eta fabrikazio-espazioak handitzeko, adibidez, zulo estrukturalki kritikoak dituzten osagaietan aplikatzeko. Egoera horrek eragin zuen doktorego-tesi hau. Tesi honen helburua, 3D inprimaketaren bidez fabrikatutako zuntz jarraituko konpositeen portaera mekanikoa karakterizatzea eta modelizatzea da, zuntz orientazio ez-konbentzionalak dituzten osagai estrukturalak diseinatzeko. Tesi honetan osagaien eta konposite inprimatuaren konposizioa, mikroegitura eta propietate mekanikoak karakterizatu ziren. Horretarako, ohiko konpositeen karakterizazio fisiko eta mekanikorako araututako teknika esperimentalak aplikatu ziren. Inprimatutako laminatuan fabrikazio-akatsak identifikatu ziren: porositate handia, zuntzen banaketa ez-homogeneoa, eta kordoien eta laminen arteko atxikidura baxua. Akats horiek, inprimaketa-prozesuan ematen den materialaren kontsolidazio termomekaniko urriaren ondorio dira. Zuntzen norabidean materialaren portaera mekanikoa egokia da; hala ere, matrizea nagusi den zeharkako eta laminarteko kargapeko portaeran fabrikazio-akatsek eragin handia dute, eta propietateak eskasak dira. Ezaugarri altuko aplikazio estrukturaletan bideragarritzat jotzeko FFF inprimaketa prozesuak garapen handiagoa behar duela ondorioztatzen da. Ildo horretan, ikusi zen beroan prentsatu ondoren nabarmen hobetzen dela konposite inprimatuaren laminarteko portaera. Bestalde, zurruntasun aldakorreko VS (Variable-Stiffness) laminatuak diseinatu, fabrikatu eta probatu ziren. Funtzio kurboa erabili zen VS laminatuen zuntzaren ibilbidea deskribatzeko, eta, horrek, diseinura bideratutako meso eskalako elementu finituen eredua parametrizatzea ahalbidetu zuen. Materialaren hausturaren hasiera eta azken haustura aurreikusteko, tentsioegoeran oinarritutako eredu konbentzionalak erabili ziren, baina inprimatutako material konposatuaren ezaugarrietara egokituta. Eredu horiek, laminatu inprimatuaren zuntzak nagusi diren portaera zuzen aurreikusi zuten. Gaur egungo inprimagailu komertzialek muga handiak dituzte zuntzaren ibilbidea konfiguratzeko, eta, beraz, laminatuaren diseinua egokitu behar izan zen fabrikazio-baldintzak betetzeko. Diseinatutako VS laminatuek nabarmen hobetu zuten erreferentziazko laminatu kuasi-isotropoen trakziozko open-hole portaera. Honela, baieztatzen da 3D inprimaketa teknologia egokia dela etendura txikiak dituzten osagai arinak fabrikatzeko.