The progress in aircraft structures is influenced not only by the search for novel materials but also by the development and improvement of manufacturing techniques. Considerable focus has been placed on the revolutionary advantages of composite materials in improving the effectiveness and weight-bearing capabilities of aerospace structures. However, it is crucial to emphasise the changes in production techniques that accompany these innovative materials. These changes have also triggered a revolution in aerospace workshops. A valuable use of these composite materials is in the form of pre-impregnated sheets, which consist of fibres embedded in resin, each possessing distinctive compositions. This material, also referred to as ‘prepreg’, optimises the fibre/matrix ratio while speeding the layering procedure for laminates. This improvement results in greater mechanical performance and less waste compared to alternative solutions.

The process of manufacturing an aircraft component from prepreg entails several sequential steps: layering, heating, moulding, consolidation, curing, and demoulding. Every stage possesses its own distinct array of technologies. This thesis explores the thermoforming manufacturing method, which is widely adopted in the modern aerospace industry. Thermo- forming is a process that entails using heat to shape a pre-laminated, uncured prepreg onto a mould and then using pressure to consolidate it. This approach effectively covers the heating, moulding, and consolidation stages, resulting in structurally complex single components, minimising the requirement for mechanical joints. Yet, for all its adaptability, thermoforming with uncured prepregs has certain constraints. Imperfections such as wrinkles, folds, and uneven thickness might degrade the effectiveness of the component, presenting a difficulty in guaranteeing constant quality.

In this research, we provide a comprehensive mechanical analysis of the uncured AS4/8552 prepreg, an area not extensively documented in the scientific literature. Addressing the challenges encountered during mechanical testing of these laminates, we introduce novel modifications to standard experimental methods. These modifications involve incorporating new processing phases into the manufacture of test samples. The findings are substantial and provide a basis for an initial attempt to create a mathematical material model that can be used for computational simulations. A novel viscoelastic material model is introduced, implementing the equations that describe a generalised Maxwell element. The study concludes that the interaction between the laminate layers and the degree of movement freedom they possess while not cured is responsible for a sizable fraction of the imperfections in the laminate.