Additively manufactured cellular materials for personal protective equipment
Lead Research Organisation:
University of Cambridge
Department Name: Engineering
Abstract
Improving head impact protection is an important objective for a wide range of industry sectors, including sports, transport (cycling, motorcycling), and Personal Protective Equipment (PPE) for the emergency services and others. The specific focus of this research is the reduction of traumatic brain injury (TBI) in contact sports, which is an issue of growing concern for both professional and amateur sport. The project is part of an ongoing research collaboration between Cambridge University, Cardiff University and equipment manufacturer Charles Owen Ltd, which has resulted in a recent successful entry in the National Football League (NFL) Head Health Challenge III.
The specific aim of this PhD project is to develop improved understanding of the use of additive manufacturing (AM) - or 3D printing - in the delivery of improved head impact protection solutions for contact sports. Preliminary results have shown the potential for 3D printed cellular materials manufactured from flexible thermoplastic elastomers (TPEs) to outperform traditional impact attenuating materials (such as polystyrene foam). However, this approach has significant potential for development. Recent advances in AM enable the manufacture of cellular structures without the geometrical restrictions arising from traditional manufacturing routes. This introduces unparalleled design freedom. The use of elastomeric TPE cellular materials offers much greater potential to design for repeated impacts, compared to traditional solutions. There is also scope to exploit the capabilities of AM to enhance ergonomics (thermal insulation, breathability, fit, weight) compared to traditional PPE materials. However, for this to progress, better understanding is required of:
1. the dynamic mechanical performance of additively manufactured TPE cellular materials,
2. the influence of the AM process (fused deposition modelling, FDM, or laser sintering, LS) on the properties of the constituent TPE and the resulting AM cellular material,
3. the relationship between the cellular architecture and head impact injury metrics,
4. the design tools necessary to optimise these materials for practical applications.
The PhD project will consist of the following tasks:
1. Characterisation and modelling of TPE cellular materials for PPE, produced using a FDM-based AM process. Material property data will be measured for a commercially available TPE material compatible with AM, using a range of mechanical testing techniques. This data will be used to fit appropriate material models. A combined experimental, numerical (Finite Element Analysis) and analytical investigation will then be carried out to develop understanding of the quasi-static and dynamic response of AM cellular materials under uniaxial compression. Two categories of cellular material will be assessed: honeycombs and lattices.
2. The influence of the AM process on the mechanical performance of flexible cellular materials for PPE. This will extend task 1, focussing on the same sub-set of cellular structures, but comparing the response of materials produced using alternative AM routes. Three material / process combinations will be considered: (i) low shore hardness TPE, FDM route, (ii) high shore hardness TPE, FDM route, (iii) high shore hardness TPE, LS route. Differences in stiffness, energy absorption and buckling modes will be considered. The mechanical testing will be extended to consider mechanical resilience, specifically fatigue and shear failure. A combination of experiments and FEA will again be used.
3. The mechanics of curved shells comprising flexible AM cellular materials. This will extend the knowledge developed in tasks 1 or 2, to consider the influence of conforming a cellular material to the head on its mechanical performance. Alternative conforming strategies will be assessed, including cell morphing and cell trimming. Numerical and analytical modelling will be used.
4. Material selection tool for a h
The specific aim of this PhD project is to develop improved understanding of the use of additive manufacturing (AM) - or 3D printing - in the delivery of improved head impact protection solutions for contact sports. Preliminary results have shown the potential for 3D printed cellular materials manufactured from flexible thermoplastic elastomers (TPEs) to outperform traditional impact attenuating materials (such as polystyrene foam). However, this approach has significant potential for development. Recent advances in AM enable the manufacture of cellular structures without the geometrical restrictions arising from traditional manufacturing routes. This introduces unparalleled design freedom. The use of elastomeric TPE cellular materials offers much greater potential to design for repeated impacts, compared to traditional solutions. There is also scope to exploit the capabilities of AM to enhance ergonomics (thermal insulation, breathability, fit, weight) compared to traditional PPE materials. However, for this to progress, better understanding is required of:
1. the dynamic mechanical performance of additively manufactured TPE cellular materials,
2. the influence of the AM process (fused deposition modelling, FDM, or laser sintering, LS) on the properties of the constituent TPE and the resulting AM cellular material,
3. the relationship between the cellular architecture and head impact injury metrics,
4. the design tools necessary to optimise these materials for practical applications.
The PhD project will consist of the following tasks:
1. Characterisation and modelling of TPE cellular materials for PPE, produced using a FDM-based AM process. Material property data will be measured for a commercially available TPE material compatible with AM, using a range of mechanical testing techniques. This data will be used to fit appropriate material models. A combined experimental, numerical (Finite Element Analysis) and analytical investigation will then be carried out to develop understanding of the quasi-static and dynamic response of AM cellular materials under uniaxial compression. Two categories of cellular material will be assessed: honeycombs and lattices.
2. The influence of the AM process on the mechanical performance of flexible cellular materials for PPE. This will extend task 1, focussing on the same sub-set of cellular structures, but comparing the response of materials produced using alternative AM routes. Three material / process combinations will be considered: (i) low shore hardness TPE, FDM route, (ii) high shore hardness TPE, FDM route, (iii) high shore hardness TPE, LS route. Differences in stiffness, energy absorption and buckling modes will be considered. The mechanical testing will be extended to consider mechanical resilience, specifically fatigue and shear failure. A combination of experiments and FEA will again be used.
3. The mechanics of curved shells comprising flexible AM cellular materials. This will extend the knowledge developed in tasks 1 or 2, to consider the influence of conforming a cellular material to the head on its mechanical performance. Alternative conforming strategies will be assessed, including cell morphing and cell trimming. Numerical and analytical modelling will be used.
4. Material selection tool for a h
Organisations
People |
ORCID iD |
| Graham McShane (Primary Supervisor) | |
| Ooyang Kim (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509620/1 | 01/10/2016 | 30/09/2022 | |||
| 1730213 | Studentship | EP/N509620/1 | 01/10/2016 | 30/09/2020 | Ooyang Kim |
| Description | I have been investigating the mechanics of elastomeric honeycombs in respect to their quasi-static and dynamic impact response in compression. It has been a detailed study where we have identified and characterised the full response of such structures to for design optimisation. The findings can be summarised as follows: 1) Materials characterisation of a 3D printed (FDM) thermoplastic polyurethane filament, which was used to base the experimental studies upon. 2) Modelling techniques for the 3D printed polyurethane material (Hyperelastic material model, viscoelastic model, modelling imperfections and other modelling tools) 3) The quasi-static characterisation of elastomeric honeycombs in compression in the out-of-plane direction. This includes the stress-strain response of honeycombs in respect to variables such as relative density, specimen geometry, young's modulus of solid material) 4) The dynamic impact mechanics of elastomeric honeycombs (triangular, square, hexagonal) in the out-of-plane direction. This includes comprehensive experimental data. Such honeycombs have bee characterised and can be used for design optimisation, the variables of interest include: impact energy, peak acceleration, energy absorption efficiency, coefficient of restitution, young's modulus, relative density) 5) The final study currently in progress is the study of honeycombs in shear and oblique impact. |
| Exploitation Route | The findings will allow design optimisation of elastomeric honeycombs for impact absorption in any context. For example if one wishes to apply the use of elastomeric honeycombs in a helmet design, they can refer to our findings and select the optimal geometrical properties (wall thickness, unit cell length, height, ect) and identify the required wall material properties (type/grade of polymer in terms of young's modulus) for their required range of impact energies. Others can also use our modelling tools to create computational models of their own applications to verify and study the behaviour. Similarly my experimental techniques can be used to verify with real data the behaviour of other specimens for impact absorption. |
| Sectors | Aerospace, Defence and Marine,Construction,Leisure Activities, including Sports, Recreation and Tourism,Manufacturing, including Industrial Biotechology,Pharmaceuticals and Medical Biotechnology |
| Description | Division C Conference - University of Cambridge |
| Form Of Engagement Activity | A talk or presentation |
| Part Of Official Scheme? | No |
| Geographic Reach | Local |
| Primary Audience | Postgraduate students |
| Results and Impact | I presented the key findings of my research at the annual Division C Conference, held in the Engineering Department of Cambridge, in both 2017 and 2018. This was an opportunity to present my research to other PhD students, Post-Doc Researchers and Academics, with the aim to share interesting findings and research approaches, as well as to gain feedback and discuss challenges. In both 2017 and 2018, I was awarded First Prize for the best presentation, which was covertly voted via ballot by all attendees, at the end of the conference. It was useful to gain experience in presenting research at an academic conference, and the discussions sparked ideas for future work. I have also presented multiple times to the undergraduate engineering students at Cambridge, where I was able to share my research concepts and findings. These talks often led to discussions with individuals with questions regarding the research as well as general questions concerning a PhD. |
| Year(s) Of Engagement Activity | 2017,2018 |