Tow steering for the structural dynamics of launch vehicles

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.

There are seven principal groups of beneficiaries for our new EPSRC Centre for Doctoral Training in Composites Science, Engineering, and Manufacturing.

1. Collaborating companies and organisations, who will gain privileged access to the unique concentration of research training and skills available within the CDT, through active participation in doctoral research projects. In the Centre we will explore innovative ideas, in conjunction with industrial partners, international partners, and other associated groups (CLF, Catapults). Showcase events, such as our annual conference, will offer opportunities to a much broader spectrum of potentially collaborating companies and other organisations. The supporting companies will benefit from cross-sector learning opportunities and

- specific innovations within their sponsored project that make a significant impact on the company;
- increased collaboration with academia;
- the development of blue-skies and long-term research at a lowered risk.

2. Early-stage investors, who will gain access to commercial opportunities that have been validated through proof-of-concept, through our NCC-led technology pull-through programme.

3. Academics within Bristol, across a diverse range of disciplines, and at other universities associated with Bristol through the Manufacturing Hub, will benefit from collaborative research and exploitation opportunities in our CDT. International visits made possible by the Centre will undoubtedly lead to a wider spectrum of research training and exploitation collaborations.

4. Research students will establish their reputations as part of the CDT. Training and experiences within the Centre will increase their awareness of wider and contextually important issues, such as IP identification, commercialisation opportunities, and engagement with the public.

5. Students at the partner universities (SFI - Limerick) and other institutions, who will benefit from the collaborative training environment through the technologically relevant feedback from commercial stakeholder organisations.

6. The University of Bristol will enhance their international profile in composites. In addition to the immediate gains such as high quality academic publications and conference presentations during the course of the Centre, the University gains from the collaboration with industry that will continue long after the participants graduate. This is shown by the

a) Follow-on research activities in related areas.
b) Willingness of past graduates to:

i) Act as advocates for the CDT through our alumni association;
ii) Participate in the Advisory Board of our proposed CDT;
iii) Act as mentors to current doctoral students.

7. Citizens of the UK. We have identified key fields in composites science, engineering and manufacturing technology which are of current strategic importance to the country and will demonstrate the route by which these fields will impact our lives. Our current CDTs have shown considerable impact on industry (e.g. Rolls Royce). Our proposed centre will continue to give this benefit. We have built activities into the CDT programme to develop wider competences of the students in:

a) Communication - presentations, videos, journal paper, workshops;
b) Exploitation - business plans and exploitation routes for research;
c) Public Understanding - science ambassador, schools events, website.