Structural Efficiency and Multi-Functionality of Well-Behaved Nonlinear Composite Structures

Lead Research Organisation: University of Bristol
Department Name: Aerospace Engineering


Composite materials and advanced structures are predicted to be major drivers for the growth and competitiveness of UK's value-added manufacturing economy. Maintaining and further enhancing the current national competitive advantage has been identified as a government strategic priority. This fellowship will contribute toward this goal by considering engineering structural design and composite materials in a different light.

When conceiving structures, it is common practice to rely on well-established design principles and robust analysis tools. This may be for several reasons, but the lack of experience with different approaches is probably the most important. Exploring the opportunities that are available outside the 'designer comfort zone' is a risky, expensive and time-consuming gamble that engineering companies can rarely afford to take.

History shows several examples of structural designs that, despite being at the forefront of current material technologies, missed out on remarkable engineering opportunities. The Iron Bridge, across the river Severn near Coalbrookdale, is probably the most famous case in point in Britain. Completed in 1779, the bridge was the world's first to be made of cast iron and is renowned for being substantially overdesigned, having been conceived following rules for wood rather than metal constructions. Composite materials are a modern example. One of their most remarkable features is the versatility that allows engineers to design not only a structure but also its constituent materials. However, partly due to their excellent specific stiffness, there is often the tendency to use them to replicate the well-known behaviour of isotropic materials, thus missing the opportunity to exploit many of the benefits that they could potentially provide. Owing to the colour of carbon fibre composites, this modus operandi is known as the 'black metal' approach. In a similar way, structural design is normally limited to linear regimes. In other words, structures are often designed to be stiff and exhibit small displacements, i.e. to respond linearly to the applied loads. Under these circumstances design methods are well established and based on decades of experience. This is indeed the engineer's comfort zone. Designers usually avoid large displacements because they may cause unwanted shape changes and trigger the transition to nonlinear regimes, potentially leading to catastrophic and often sudden, uncontrolled failure. However, if we could learn to control such behaviour, it could actually be exploited for a benefit.

The aim of this proposal is to explore the possibilities given by nonlinear responses in structural design. The principal objectives are the development of a new generation of adaptive/multifunctional structures working in elastically nonlinear regimes and the creation of novel paradigms for structural efficiency. The ambition is to harness the possibilities presented by composite materials and to deliver new design principles by removing the barriers imposed by the current practice of restricting structures to behave linearly. Imagine aircraft wings or wind turbine blades tailored to be lighter and still meet the requirements imposed at different operating conditions, thanks to nonlinear stiffness characteristics; buildings whose structural response is compliant only if subjected to extreme earthquake loads, so as to prevent catastrophic failure; or a bridge whose stiffness increases in case of strong winds preventing detrimental aeroelastic instabilities. This is my vision. This is what the elastic properties of composite materials can offer, if we move away from the 'black metal' approach.

Planned Impact

The UK government has identified Advanced Materials as one of Eight Great Technologies to be promoted for the implementation of its industrial strategy. Furthermore, composite materials and advanced structures are considered key factors for the competitiveness, development and success of the UK economy. My proposal seeks to reach into new and unexplored areas of structural and composites design. The goal is to govern structurally nonlinear behaviours and to exploit them for a benefit.

I anticipate that exploiting well-behaved nonlinear composite structures will contribute to driving the growth of UK's value-added manufacturing economy. As a result of this fellowship novel cutting edge technology might be produced. An impact on the UK economy will be made if manufacturers will be able to exploit it to maintain or gain a competitive market positions. The most direct pathways to impact will be sought with ongoing involvement in the research of the parties that have indicated their interest with the Statements of Support. The current ACCIS (Advanced Composites Centre for Innovation & Science) and Engineering Faculty's industrial partners provide additional links. In due course, the support of the National Composites Centre can act as a catapult to project innovations towards higher Technology Readiness Levels and right into the manufacturing sector. Where possible, any potentially exploitable concept will be dealt with the help of the Bristol's Research and Enterprise Development (RED) office and protected with patenting and licensing mechanisms.

I will develop the design principles and the methodologies arising from this fellowship into a novel set of skills to be transferred to engineers and technical people. This new expertise might play a key role for British companies in creating the much sought competitive advantage. The University of Bristol and its Engineering Faculty are particularly well-positioned to convey novel skills, via the ACCIS Centre for Doctoral Training, the Industrial Doctorate Centre and their numerous industrial links. I intend to make the most of this position by organising annual workshops to share the results of the proposed research and to transfer the methods that will be developed.

A direct impact on the people's quality of life will derive from the development of novel standards for structural efficiency. Using less mass more effectively will indeed result in greener structures and vehicles, with an obvious advantage to the environment.

Delivering all of the aforementioned impacts would produce wealth and growth and consequently have a positive influence on wider society.
Description This fellowship aim at exploring the possibility of using nonlinear structural mechanics, i.e. large deformations under applied loads, to create more efficient structures and/or to multifunctional structures. We have created innovative computational analysis tools, demonstrated that nonlinear structural deformations should not be seen as a failure mode, and delivered a series of structural concepts and design philosophies that meet the intend objectives.
Exploitation Route Through publications and engagement with industry we have made all of our findings, design methodologies and analysis tools publicly available.
Sectors Aerospace, Defence and Marine,Construction,Digital/Communication/Information Technologies (including Software),Education,Energy

Description It is early to say whether impact will materialise but we have been working with several companies, including Simulia, Airbus and Embraer, to transfer our novel computational methodologies and design philosophies into the organisations. Some joint patents are currently being drafted.
Sector Aerospace, Defence and Marine
Description Aerospace Technology Institute (ATI) Specialist Advisory Group (SAG) membership
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
Description EPSRC Institutional Sponsorship 2016
Amount £45,000 (GBP)
Organisation University of Bristol 
Sector Academic/University
Country United Kingdom
Start 07/2016 
End 03/2017
Description Royal Academy of Engineering Research Fellowship
Amount £451,202 (GBP)
Funding ID RF_201718_17178 
Organisation Royal Academy of Engineering 
Sector Charity/Non Profit
Country United Kingdom
Start 03/2018 
End 02/2023
Title Data for "Beyond the Fold: Experimentally Traversing Limit Points in Nonlinear Structures" 
Description Data underlying the publication "Beyond the Fold: Experimentally Traversing Limit Points in Nonlinear Structures" 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Title Data for "Multistable Morphing Mechanisms of Nonlinear Springs" 
Description Underlying data for paper "Multistable Morphing Mechanisms of Nonlinear Springs" 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Title Data for "Spatial chaos as a governing factor for imperfection sensitivity in shell buckling" 
Description Underlying data for paper "Spatial chaos as a governing factor for imperfection sensitivity in shell buckling" 
Type Of Material Database/Collection of data 
Year Produced 2019 
Provided To Others? Yes  
Title Data for publication: Nudging axially compressed cylindrical panels towards imperfection insensitivity 
Description This repository contains the data used to produce the figures in the publication: Nudging axially compressed cylindrical panels towards imperfection insensitivity 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? Yes  
Title Numerical Continuation Finite Element Program 
Description The program extends the capabilities of current commercial finite element programs. The finite element method is the state-of-the-art established technique for modelling engineering structures, predicting fluid flows or modelling multi-physics problems. However, there is currently no commercial software package that incorporates bifurcation theory, which means that the efficient thin-walled structures of today, that are prone to instabilities, are cumbersome to analyse. We have developed this new capability over the last 18 months and this has dramatically changed the type of structures we can now analyse. 
Type Of Material Computer model/algorithm 
Year Produced 2017 
Provided To Others? No  
Impact In our research group the code has allowed us to easily analyse optimised structures that rely on nonlinearities to derive structural benefits. We intend to more widely disseminate the software in the near future. 
Description Collaboration with Darren Hartl 
Organisation Texas A&M University-Central Texas
Country United States 
Sector Academic/University 
PI Contribution This is a partnership on developing noise reduction devices for civil aircraft. The aim of the project is to use shape-adaptive devices to design a noise reduction device that passively deploys and stows. We have contributed a nonlinear snap-morphing design that is currently the lightest of the solutions being considered.
Collaborator Contribution The partners originated with the project idea, and conducted significant prior research on concepts and potential solutions. The partners are also conducting detailed fluid dynamics simulations of our designs.
Impact A conference paper and a journal publication are currently being drafted.
Start Year 2017
Description Collaboration with Just Herder 
Organisation Delft University of Technology (TU Delft)
Country Netherlands 
Sector Academic/University 
PI Contribution Mark Schenk and Just Herder have previously co-authored papers on zero stiffness structures, and in recent conversations identified a mutual interest in collaborating further to bring together Bristol's expertise in modelling nonlinear composite structures and TU Delft's experience in experimental characterisation of zero-stiffness structures.
Collaborator Contribution Professor Just Herder (JH) holds a chair in Interactive Mechanisms at TU Delft (The Netherlands), and has extensive expertise in compliant zero-stiffness structures. Such systems rely on geometrically non-linear behaviour of structures, and counterbalance positive and negative stiffness to form structures that can effortlessly deform over large displacements. A key challenge is to accurately characterise the nonlinear stiffness of the structural components experimentally. JH has agreed to support the project with a student who will be hosted in Bristol for a period of 4 months as part of their MSc research project. In due time, JH will visit Bristol to discuss progress, analyse preliminary outcomes and to explore means to support the proposal that this feasibility study will feed into.
Impact N/A. Too early.
Start Year 2017
Description Efficient modelling of delaminations 
Organisation National Aeronautics and Space Administration (NASA)
Department NASA Langley Research Centre
Country United States 
Sector Public 
PI Contribution We programmed an efficient predictive model for delaminations in composites based on our shared expertise in the field. This work was then written up as a journal publication by our team.
Collaborator Contribution NASA Langley funded the work under the Advanced Composites Project, hosted RMJ Groh at NASA Langley for 3 weeks and one of the researchers at NASA, Dr Alex Tessler, was directly involved in the numerical work and writing of the publication.
Impact A peer-reviewed publication which is currently under review.
Start Year 2016
Description Material Science meets Human-Computer Interface 
Organisation University of Bristol
Department Department of Computer Science
Country United Kingdom 
Sector Academic/University 
PI Contribution My partners in the Computer Science and myself wrote a review paper of the intersection between material science and human-computer interface technologies. I provided the insight into the material science aspect of the collaboration such as shape changing materials, auxetics, meta-materials, etc.
Collaborator Contribution My partners provided the insight and expertise into human-computer interface side of the collaboration and the funds to publish at the ACM CHI Conference on Human Factors in Computing Systems in Montreal, Canada.
Impact This collaboration is multi-disciplinary and combines computer science and material science. Current outcomes are a review paper which received an honourable mention at the ACM CHI Conference on Human Factors in Computing Systems in Montreal, Canada.
Start Year 2017
Description Post-buckling of variable stiffness composites 
Organisation University of Calabria
Department Department of Computer, Modeling, Electronics and Systems Engineering
Country Italy 
Sector Academic/University 
PI Contribution We hosted a PhD student from Calabria for two months and provided mathematical guidance on modelling of variable stiffness composites. Our predictive models were used to validate theirs.
Collaborator Contribution The partner research group funded a two-month placement of a PhD student and also paid for the ECCOMAS conference that they presented our joint work at. Furthermore, they developed their models to include variable stiffness composites.
Impact Two peer-reviewed journal publications and one conference presentation.
Start Year 2015
Description Stresses in Corrugated Panels 
Organisation ETH Zurich
Department Department of Mathematics
Country Switzerland 
Sector Academic/University 
PI Contribution We provided the technical expertise and guidance in developing predictive models for the type of structure to be analysed. We also hosted a PhD student for three months in 2015.
Collaborator Contribution The partners funded a three-month visit of one of their PhD students to Bristol University.
Impact The research has resulted in one peer-reviewed journal article, one conference presentation and another peer-reviewed article currently under review.
Start Year 2015
Description Aerospace Engineering Podcast 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact The Aerospace Engineering Podcast features conversations with engineers and researchers in industry and academia to reveal their fascinating real-world stories of innovation, and provide a glimpse into the future of the industry by discussing cutting-edge research and promising new technologies. The podcast is produced on a monthly basis and intends to engage as many people as possible with the world of aerospace engineering. The podcast currently reaches an audience of around 1000 people per episode.
Year(s) Of Engagement Activity 2017,2018
Description Aerospace Engineering Website 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact The aim of the website is to provide insights into the history, technology and research in aerospace engineering. The website currently has 1000 active subscribers and 10000 monthly readers. I publish widely on a number of technical topics and as a result and actively engaged with students all over the world that contact me via the website.
Year(s) Of Engagement Activity 2012,2013,2014,2015,2016