Tow steering for the structural dynamics of launch vehicles

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Typically, structural elements account for 60% of a launch vehicle's dry mass, and hence significant effort is being undertaken by both academia and industry to develop highly mass-efficient structures. Such structures will allow for larger payloads to be delivered to orbit by next-generation launch vehicles. Consequently, NASA has identified lightweight materials and structures amongst the highest priorities for next-generation space vehicles to enable future manned exploratory missions beyond Low Earth Orbit. Tow-steered composites, those in which the reinforcement fibres follow curvilinear reference paths, represent structures which can be tuned by the designer to satisfy desirable criteria. Tow-steered composites have shown proven benefits to the axial compression load case of cylindrical launch vehicle structures.During ascent, the loads experienced by launch vehicle structures are not solely static, significant dynamic loading arises from sources such as staging, engine noise and aerodynamic buffeting. Hence, the investigation of the benefits of tow-steered composites to the dynamic response of thin-walled cylinders is pertinent. However, very little research exists into the potential benefits of this concept to the dynamic loading regime. Hence, this project aims to address this scarcity. The typical means of manufacturing tow-steered composites within the literature is by Automated Fibre Placement (AFP), which is prone to process-induced defects. Instead, this project will investigate tow steering using the Continuous Tow Shearing (CTS) process. CTS mitigates the process-induced defects of AFP by shearing instead of bending material tows. The in-plane shearing of material tows gives rise to an orientation-thickness coupling which can be exploited as integrated stiffening features on a CTS cylinder. Aims & Objectives This project aims to both numerically and experimentally develop tow-steered composites to optimise the dynamic response of launch vehicle structures. Furthermore, a link between the two loading cases, both axial compression and vibration, shall be developed as to produce fibre paths which are beneficial for structures under combined loading. The project aims shall be fulfilled by following a staged work plan to meet the following objectives: 1. Explore the potential design space of tow-steered composites through development of numerical models. Numerical tools shall be developed to quantify and explore these novel performance benefits. 2. Conduct rigorous optimisation studies to identify tow-steered designs which exhibit both single and multiple load case performance benefits in addition to revealing the potential for significant mass efficiencies. 3. Manufacture the optimised structure utilising the CTS process and evaluate the quality of this structure. 4. Design and conduct experimental tests to validate the predicted dynamic performance benefits. Applications & Benefits The primary benefits to be found in this PhD are those afforded to launch vehicle structures. By improving the dynamic performance of thin-walled launch vehicle structures the opportunity to avoid instabilities will be revealed. Such instabilities may cause damage to sensitive payloads or the loss of the entire vehicle, and hence the opportunity to avoid these will prove to be invaluable when designing new structures. Research Novelty The novelty in this project is in the determination of potential dynamic performance benefits of thin-walled CTS cylinders. Additionally, the multi-loading case optimisation will propose a link between the two primary loading cases of launch vehicle structures and develop methodologies to satisfy requirements in both regimes.