Intergration of phononic metamaterials in aircraft structures

Abstract

The aviation industry is constantly pursuing enhancing passenger comfort and safety, with noise reduction within aircraft cabins being a critical area of focus. Traditional soundproofing methods, often involving the addition of heavy and voluminous materials, conflict with the industry's goal of maintaining lightweight aircraft and minimising fuel consumption. Previous research suggests that Helmholtz resonators offer a promising approach to noise control. Their simple structure, consisting of an enclosed volume connected to the external environment through an aperture, allows for customisable and scalable noise control applications.

The thesis presents exploratory research into integrating Helmholtz resonator-based metamaterials into lightweight composite acoustic sandwich panels for aircraft cabins. First, the stiffness of the resonator's enclosure is investigated, followed by determining the effects of placing the inlet within the resonance chamber. Next, the implications of creating resonators for single-layer acoustic sandwich panels are studied. Finally, three reinforcement fibres are investigated for acoustic suitability: fibreglass, carbon fibre and flax fibre. The study concludes with a weight comparison between the developed metamaterial sandwich panel and commercial designs.

The findings reveal that the lay-up of the face sheets significantly affects sound absorption. Introducing non-resonant volumes between the metamaterial's unit cells is the most effective method to prevent interference between the resonators. The resonator's inlet disrupts the stress flow in one of the face sheets, leading to locally increased stress values. The need for specific acoustic properties requires core cell sizes larger than those typically used in standard cabin panels, compromising the stability of the face sheets. Support columns are proposed as a solution, lessening the impact on stability. The thesis proves that lightweight composite single-layer acoustic panels are achievable by incorporating Helmtolhtz resonator-based phononic metamaterials.