Hybrid composite ply joints for integrating radiofrequency apertures in multifunctional aircraft structures
Creators: name: Ahamed, Jasim
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400102
subject: Aerospace structures
classificationCode: 401602
subject: Composite and hybrid materials

description: Optimal utilisation of dissimilar materials is fundamental to the development of high-performance multifunctional structures, especially in lightweight aerospace applications. For multifunctional load-bearing antenna structures, utilisation of composite materials with dissimilar electrical properties enable the integration of radiofrequency transparent apertures in load-bearing aircraft structural skins. Aircraft skins are typically fabricated from advanced carbon fibre polymer composite, while the aperture requires an electrically non-conductive composite material such as quartz or glass fibre polymer composite. One method of achieving efficient load transfer between the structural skin and the aperture is to employ ply joints. Ply joints are co-cured composite joints produced by forming butt-splices and/or overlaps between individual plies while intelligently tailoring the relative positions and spatial distribution of the ply terminations. In this thesis, novel structural concepts for hybrid ply joints enabling multifunctional load-bearing antennas are developed.<br><br>The load-carrying capacity of hybrid ply joints depends strongly on several design parameters such as the distance between ply terminations (step length), overlap length, the spatial distribution of ply terminations, joint thickness and the mechanical stiffness and coefficients of thermal expansion of the dissimilar composite materials. An experimental program was created to investigate the influence of these key design parameters on the load-carrying capacity of hybrid ply joints. Several ply-interleaved and ply-overlap joint configurations were evaluated under quasi-static uniaxial tensile and compression loading conditions. Fractographic analysis is also performed to determine the failure mechanism. The findings of the experimental program are used to guide the development of predictive capability for the structural performance of hybrid ply joints. Both analytical and high-fidelity computational models were developed; the analytical models are based on strength of materials and linear elastic fracture mechanics methods while computational models employ continuum damage mechanics and cohesive element method.<br><br>The study revealed that the principal damage mode in hybrid ply joints is delamination emanating from the vicinity of ply terminations. The loss of load-carrying capacity is caused by transverse matrix as they promote the coalesce of delaminations. Through judicious selection of the spatial distribution of ply terminations and step/overlap length, hybrid ply joints can be designed to reach the design ultimate strength of the load-bearing skin structure. The analytical and computational predictive capability developed for hybrid ply joints enable the design optimisation of structurally integrated radiofrequency transparent apertures for multifunctional load-bearing antenna structures.<br>