The student Mikel Iragi Sampedro obtained an OUTSTANDING CUM LAUDE qualification
The student Mikel Iragi Sampedro obtained an OUTSTANDING CUM LAUDE qualification
The student Mikel Iragi Sampedro obtained an OUTSTANDING CUM LAUDE qualification
Thesis title: Caracterización y Modelización del Comportamiento Mecánico de Materiales Compuestos de Fibra Continua con Orientaciones No-Convencionales fabricados mediante Impresión 3D
Court:
- Chairmanship: Carlos Daniel González Martínez (UPM)
- Vocal: Norbert Blanco Villaverde (Universitat de Girona)
- Vocal: Germán Castillo López (Universidad de Málaga)
- Vocal: Cristina Pascual González (Instituto de Ciencias de Materiales de Madrid-CSIC)
- Secretary: Aritz Esnaola Arruti (Mondragon Unibertsitatea)
Abstract:
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.