The student Itxaro Sukia Mendizabal an EXCELLENT CUM LAUDE with mention INTERNATIONAL DOCTORATE
The student Itxaro Sukia Mendizabal an EXCELLENT CUM LAUDE with mention INTERNATIONAL DOCTORATE
The student Itxaro Sukia Mendizabal an EXCELLENT CUM LAUDE with mention INTERNATIONAL DOCTORATE
- Thesis title: Development of bio-inspired sandwich structures manufactured by 3D printing of composites
Court:
- Presidency: Rubén Ansola Loyola (UPV/EHU)
- Vocal: Maria Lissner (University of Oxford)
- Vocal: Iban Lizarralde Madina (ESTIA)
- Vocal: Maider Iturrondobeitia Ellacuria (UPV/EHU)
- Secretary: Borja Erice Echavarri (Mondragon Unibertsitatea)
Abstract:
As climate targets become increasingly ambitious, reducing greenhouse gas emissions from transportation has become a critical priority. Road vehicles account for over 70% of EU transport emissions, driving the need for lightweight and sustainable structural solutions. Minimising vehicle weight is essential, especially for electric vehicles (EVs), where mass directly affects energy consumption and driving range. Sandwich panels offer a promising solution due to their excellent stiffness-to-weight ratio. However, conventional manufacturing methods—often involving multi-step assembly, adhesives, and dissimilar materials—can hinder production efficiency, recyclability, and reliability. Innovative fabrication approaches are needed to overcome these limitations while maintaining or improving mechanical performance.
This doctoral thesis investigates the design, optimisation, and multifunctional integration of sustainable sandwich structures fabricated via additive manufacturing (AM). The focus lies on structural performance, material efficiency, and environmental impact, with emphasis on functionally graded, bio-inspired cores and materials such as foamable PLA (LW PLA) and Onyx®. The development process combines mechanical characterisation, structural design, and life cycle analysis to produce lightweight, high-performance, and environmentally responsible panels.
The first research axis explores trabecular cores inspired by natural structures and manufactured through AM. Architectures based on beetle forewings outperform conventional hexagonal patterns, offering enhanced stiffness and energy absorption under crush loading. Further improvements were achieved using functionally graded (FG) and topology-optimised (TO) designs, where local variations in cell geometry tailor responses to complex loads. A structural grid was added at interfaces to improve load transfer and delay failure. Onyx® characterisation revealed strain-rate sensitivity and anisotropic behaviour, highlighting the role of print orientation, though geometry and architecture remained the dominant performance drivers.
The second axis examines sustainable cores made from foamed biopolymer filament. Testing and modelling revealed strong correlations between printing parameters, density, and mechanical properties. A tunable density range of 460–1115 kg/m³ enabled precise control over structural behaviour. The best samples achieved tensile moduli of 2.85 GPa and compressive strengths of 23.3 MPa. Life Cycle Assessment (LCA), normalised to mechanical function, showed that FG LW PLA cores consumed over 70% less energy per unit of absorbed impact energy than homogeneous designs. Compared to conventional foams, AM cores offered competitive or superior specific properties, tunability, integrated fabrication, and reduced waste.
The final axis addresses photovoltaic (PV) integration for energy harvesting without compromising strength. Multifunctional panels were developed by embedding flexible PV cells within sandwich structures composed of 3D-printed trabecular cores and resin-infused fibreglass face-sheets. Panels underwent impact, perforation, and torsional testing. Results showed the PV layer had a negligible effect on mechanical behaviour; slight reductions in specific strength were offset by increased energy dissipation and added functionality. The panels retained mechanical robustness and electrical operability, validating the concept of multifunctional, energy-autonomous sandwich components.