Abstract
The growing demand for advanced materials with superior mechanical properties and energy absorption capabilities has driven extensive research into foam-based sandwich composites. This thesis investigates the static and dynamic performance of 3D-printed lattice composite sandwich structures with open-cell foam cores, with a particular focus on carbon fiber-reinforced polyamide 6 (CF/PA6) composites. The research emphasizes novel modeling methods, material characterization, and performance optimization strategies. Advanced computational techniques—including the Centroidal and Capacity Constrained Power Diagram (CCCPD) algorithm and an ABAQUS-based user-defined material subroutine (VUMAT)—are employed to reconstruct foam microstructures and predict mechanical responses under various loading conditions.The CCCPD-based modelling approach was utilized to generate microstructures that closely resemble real foams, providing insights into the influence of foam architecture on deformation mechanisms. Experimental validation confirmed the accuracy of these models in predicting stress-strain behaviour, with parametric studies revealing the impact of geometric configurations on elastic modulus - where triangular cross-sections exhibited the highest stiffness, while regular hexagonal sections displayed the lowest.
A new constitutive model for viscoelastic composite foams was developed and implemented in ABAQUS using the VUMAT subroutine. The parametric analysis of Kelvin foam compression confirmed that both the Young's modulus and yield stress are highly dependent on loading rates and foam density, offering critical insights for optimizing energy absorption in dynamic loading conditions.
The study further investigates the low-velocity impact behaviour of composite sandwich structures with regular and irregular lattice cores. Results showed that Kelvin cell configurations outperformed traditional honeycomb cores in energy absorption, while CCCPD irregular lattices exhibited enhanced performance under low-energy impacts. Multi-scale optimization techniques, including face sheet thickness modulation, significantly improved impact resistance. A comprehensive finite element framework, integrating custom material models, successfully predicted complex failure modes, facilitating effective parametric optimization for impact protection.
A detailed analysis of the bending and vibration performance of 3D-printed lattice composite sandwich structures was conducted. Findings highlighted the pivotal role of lattice geometry in bending efficiency, with CC lattice structures demonstrating superior energy absorption. Comparative material studies revealed substantial improvements in energy absorption and flexural modulus for fiber-reinforced composites. Moreover, accurate prediction of natural frequencies was emphasized as crucial in preventing resonance-induced structural failure under dynamic loading conditions.
This research provides valuable insights into the design and optimization of lightweight, high-performance sandwich structures for applications in aerospace, civil engineering, and other industries requiring enhanced energy absorption, vibration resistance, and mechanical strength. The findings lay a robust foundation for future studies on dynamic loading, multi-scale optimization, and the development of advanced foam and lattice-based materials.
| Date of Award | 15 Oct 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Jian Yang (Supervisor), Jian Xu (Supervisor) & Nai Yeen Gavin Lai (Supervisor) |