Development of a composite combat helmet using structural metamaterials

Abstract

The protection of military personnel from traumatic brain injuries (TBI) is a critical concern, as head injuries are the leading cause of battlefield fatalities. This thesis investigates the potential of using mechanical metamaterials in the design of composite combat helmets to enhance protection against ballistic impacts. The study explores the development, characterisation, and modelling of additively manufactured composite materials and structures tailored for impact resistance.

The research begins with the mechanical characterisation of 3D-printed nylon, with and without short carbon fibre reinforcement. The effects of print orientation, infill pattern, and strain rate on these materials' tensile and compressive properties are analysed. Findings show significant improvements in strength and modulus with the addition of carbon fibres and optimisation of print parameters. Numerical material models incorporating plasticity, damage and strain rate dependence are developed for each material. These models are validated using both low and high-velocity impact experiments.

A progressive damage model for woven composites is developed and validated, including for the ballistic impact of Kevlar. This is used, in conjunction with the aforementioned material models, to numerically investigate the ballistic response of mechanical metamaterials. These investigations showed that compared to equivalent non-auxetics, auxetic structures reduce transmitted force over 40% and prolong the duration of the force pulse, both key factors in reducing injury.

The final part of the thesis combines these findings and applies them to the design of a composite combat helmet. Numerical models are developed, incorporating additively manufactured cellular cores. The performance of these innovative designs is assessed using industry-standard injury metrics which demonstrate significant improvements in head protection when the cellular structure is auxetic.

This work contributes to the advancement of combat helmet design by leveraging the unique properties of structural metamaterials. The findings suggest that the integration of optimised 3D-printed composites can significantly enhance the protective capabilities of combat helmets, thereby reducing the risk of TBI for military personnel.

This thesis is embargoed for 1 year, until 31st July 2026

Date of Award	Jul 2025
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Engineering and Physical Sciences Research Council
Supervisor	Zafer Kazancı (Supervisor), Brian Falzon (Supervisor) & Humberto Almeida Jr (Supervisor)