Shaping Sustainable Self-sensing Structures

Abstract

The transition towards a sustainable aviation sector requires a fundamental rethinking of how structural materials are designed, manufactured, joined, and used. Lightweighting alone is insufficient if achieved through materials and processes that are energy-intensive, difficult to recycle, or incompatible with circular use. This thesis explores an alternative paradigm: sustainable structural systems that integrate bio-based materials, eco-efficient multi-material design, adhesive-free joining, and ultimately self-sensing functionality.

Firstly, the thesis develops sustainable joining strategies for wood-based structures. Ultrasonic welding is studied as an adhesive-free joining method that exploits the thermoplastic behaviour of native lignin by introducing three-dimensional printed, lignin-rich energy directors. This method has demonstrated improvements in joint strength and durability while maintaining compatibility with circular design principles and scalable manufacturing.

Secondly, the thesis advances computational and experimental methods for an eco-efficient multi-material design framework. The topology optimisation framework is extended to include environmental performance metrics alongside mechanical objectives, enabling explicit trade-offs between stiffness, mass, and environmental impact. These designs are realised using multi-material additive manufacturing, demonstrating how selective material placement can reduce waste, improve performance, and enable functional integration.

Thirdly, focusing on lignocellulosic material systems, particularly wood, lignin, and fungal mycelium, the work addresses the question of how traditionally passive bio-based materials can be transformed into functional, adaptive, and circular structures. Three complementary research directions are pursued. First, the thesis investigates fungal biology and signalling, examining how living mycelial networks embedded within composites exhibit bioelectrical activity that responds to environmental and mechanical stimuli. These findings point toward the possibility of structural materials that inherently sense and report on their own condition.

Finally, the results demonstrate that sustainable structures cannot be achieved solely through material substitution. Instead, performance, sustainability, sensing capability, and manufacturability must be addressed simultaneously. By combining living and self-sensing materials, optimised multi-material architectures, and sustainable joining and manufacturing techniques, this thesis lays the groundwork for a new class of structural systems that are lightweight, circular, and functionally active.