Certification for Design - Reshaping the Testing Pyramid
Lead Research Organisation:
University of Bristol
Department Name: Aerospace Engineering
Abstract
The performance and strength of a composite aero-structure is established incrementally through a programme of analysis and a series of experimental tests conducted using specimens of varying size and complexity. The process utilises a so-called 'building block' or 'testing pyramid' approach with tests at each of the following levels: (i) Coupon, (ii) Structural detail, (iii) Component, and (iv) Sub-structure or full structure. The 'building block' approach provides a comprehensive and systematic methodology to demonstrate airworthiness and structural integrity, and as such represents the backbone of the certification processes for composite aero-structures. The vast majority of certification tests are conducted at the coupon level, whereas far fewer certification tests are conducted at the subsequent higher pyramid levels. The complexity, cost and time of each test escalates up through the testing pyramid. The underlying assumption is that the material properties derived from tests at the lower levels can be used to define the requirements and design allowables at higher length scales and component complexity. At the mid-pyramid level, the as-manufactured strength of parts is currently assessed by empirical 'manufacturing knockdown factors', and the uncertainties in this assessment, together with uncertain in-service damage, propagate up the pyramid to the full component and structure levels. At best, this leads to conservative, over-constrained design. At worst, there is risk that potentially unsafe scenarios can develop where combinations of weakening events cascade into premature failure. Thus, the very time consuming and expensive testing at the coupon level, produces conservative strain limits with questionable relevance to the strength of large parts or at the full structure level. Also, innovative material and technology developments, which facilitate lightweighting, safer and more damage tolerant composite design, are only relevant at the sub-structure and component levels, and therefore cannot be incorporated into applications because of the current validation practices. Accordingly there is increasing evidence that the building block approach has severe limitations, particularly the high cost of certification, time to market, and the general inability to characterise and predict limit states that may lead to failure at structural scales. There is increasing awareness that, in its current form, the 'building block' approach prevents the innovative use of composites, and consequently that the potential benefits of using advanced composites in terms of lightweighting and efficiency cannot be fully realised under current certification and regulatory procedures.
The vision and ambition of the PG are:
AMBITION: To enable lighter, more cost and fuel efficient composite aero-structures through developing the scientific foundations for a new approach for integrated high-fidelity structural testing and multi-scale modelling and 3D product quantification based on Bayesian learning and statistical Design of Experiments (DoE), incorporating understanding of design features at structural lengths scales.
VISION: To enable more structurally efficient and lightweight airframes that are essential for meeting future fuel and cost efficiency challenges and to maintain and enhance the UK's international position in the aerospace industry.
The PG provides a route for lessening regulatory constraints, moving towards a more cost/performance optimised philosophy, by reducing the multiple coupon level tests at the bottom of the test pyramid. Instead structural behaviour will be accounted for in a new culture of virtual design and certification focusing on the higher levels of the testing pyramid. This will promote a change towards virtual testing, enabling reduction of empiricism, significant mass savings, expansion of the design and performance envelopes, and reduction of design costs and associated development time.
The vision and ambition of the PG are:
AMBITION: To enable lighter, more cost and fuel efficient composite aero-structures through developing the scientific foundations for a new approach for integrated high-fidelity structural testing and multi-scale modelling and 3D product quantification based on Bayesian learning and statistical Design of Experiments (DoE), incorporating understanding of design features at structural lengths scales.
VISION: To enable more structurally efficient and lightweight airframes that are essential for meeting future fuel and cost efficiency challenges and to maintain and enhance the UK's international position in the aerospace industry.
The PG provides a route for lessening regulatory constraints, moving towards a more cost/performance optimised philosophy, by reducing the multiple coupon level tests at the bottom of the test pyramid. Instead structural behaviour will be accounted for in a new culture of virtual design and certification focusing on the higher levels of the testing pyramid. This will promote a change towards virtual testing, enabling reduction of empiricism, significant mass savings, expansion of the design and performance envelopes, and reduction of design costs and associated development time.
Planned Impact
The PG is essential to enable continued growth of UK aerospace industry and take economic benefits from the opportunities inherent in the move towards more sustainable aviation, as it fills a knowledge gap, where there is no equivalent capability in the UK or internationally. The ATI Technology Strategy and Roadmaps show a clear need for continuing improvement in aircraft efficiency, which will require step changes in performance to enable e.g. the move to hybrid-electric powertrains and ultimately all-electric aircraft. These transformative technologies will impact on every aspect of the aerospace industry, but will specifically set very challenging targets in terms of the mass of aero-structures and new aero-structural forms as the industry transitions to blended wing/body and other advanced concepts.
Driven by regulatory requirements, and the need for reduced CO2 emissions, sustainability and energy efficiency, similar opportunities exist in other sectors, and, whilst this PG is focussed on the developing needs of the aero-structures industry, it will also enable development and growth in other sectors through the delivery of improved structures development and certification methodologies. In particular, the scientific outputs of the PG are transferable across sectors that are also in need of innovative, cost effective and sustainable composite solutions, and which are also subject to regulatory constraints that inhibit the uptake of composites, including the automotive, renewables, rail, construction, marine and oil/gas sectors. Moreover, the radically new integrated approach to virtual and physical test and product validation, has a potentially strong crossover into emerging technologies such as Additive Manufacturing that currently lacks comprehensive routes to validation and certification.
The near-term impact of the PG is by providing the scientific basis and fundamental methodologies for unlocking the barriers for innovation and efficiency gains set by current certification procedures. The output of the PG will provide the UK with the capability to be the decisive 'first mover' and gain advantage in the global market place. The PG will enhance the UK position in the technical revolution that embraces new materials and processes, by addressing an urgent need in aerostructures design.
The long-term impact will be the development of new methods for verification (certification) that will provide the world-leading advantage required for winning UK design and manufacturing workshare. The research impacts directly on certification authorities, industry, as well as with the High Value Manufacturing Catapults including the NCC.
The impact and speed of uptake of the research outputs will be maximised by close engagement with an Industrial Steering Group, which will include representatives of industrial partners Airbus, GKN Aerospace, Rolls Royce, BAE systems and CFMS, and stakeholders NCC and the European Aviation Safety Agency EASA.
The impact into the industrial base will be further facilitated by secondments of Postdocs, researcher mobility and internships of the PhD students. Dissemination of research outputs will be through face-to-face meetings, industry seminars/workshops, scientific articles, articles/ communications directed towards industry, a PG sharepoint/website, conference presentations and learned society activities.
The PG will provide PhD/EngD graduates with unique and world-leading competence in testing, modelling and qualification/certification of advanced composite aerostructures, and will continue to have an impact well beyond the term of the PG, both as highly skilled engineers in industry and as a new generation of researchers and academics.
Driven by regulatory requirements, and the need for reduced CO2 emissions, sustainability and energy efficiency, similar opportunities exist in other sectors, and, whilst this PG is focussed on the developing needs of the aero-structures industry, it will also enable development and growth in other sectors through the delivery of improved structures development and certification methodologies. In particular, the scientific outputs of the PG are transferable across sectors that are also in need of innovative, cost effective and sustainable composite solutions, and which are also subject to regulatory constraints that inhibit the uptake of composites, including the automotive, renewables, rail, construction, marine and oil/gas sectors. Moreover, the radically new integrated approach to virtual and physical test and product validation, has a potentially strong crossover into emerging technologies such as Additive Manufacturing that currently lacks comprehensive routes to validation and certification.
The near-term impact of the PG is by providing the scientific basis and fundamental methodologies for unlocking the barriers for innovation and efficiency gains set by current certification procedures. The output of the PG will provide the UK with the capability to be the decisive 'first mover' and gain advantage in the global market place. The PG will enhance the UK position in the technical revolution that embraces new materials and processes, by addressing an urgent need in aerostructures design.
The long-term impact will be the development of new methods for verification (certification) that will provide the world-leading advantage required for winning UK design and manufacturing workshare. The research impacts directly on certification authorities, industry, as well as with the High Value Manufacturing Catapults including the NCC.
The impact and speed of uptake of the research outputs will be maximised by close engagement with an Industrial Steering Group, which will include representatives of industrial partners Airbus, GKN Aerospace, Rolls Royce, BAE systems and CFMS, and stakeholders NCC and the European Aviation Safety Agency EASA.
The impact into the industrial base will be further facilitated by secondments of Postdocs, researcher mobility and internships of the PhD students. Dissemination of research outputs will be through face-to-face meetings, industry seminars/workshops, scientific articles, articles/ communications directed towards industry, a PG sharepoint/website, conference presentations and learned society activities.
The PG will provide PhD/EngD graduates with unique and world-leading competence in testing, modelling and qualification/certification of advanced composite aerostructures, and will continue to have an impact well beyond the term of the PG, both as highly skilled engineers in industry and as a new generation of researchers and academics.
Organisations
- University of Bristol, United Kingdom (Lead Research Organisation)
- BAE Systems (Collaboration)
- National Composites Centre (NCC) (Collaboration)
- GKN (Collaboration)
- Centre Modelling and Simulation (CFMS) (Collaboration)
- Alan Turing Institute (Collaboration)
- Siemens Gamesa Renewable Energy (Collaboration)
- Airbus Group (Collaboration)
- Rolls Royce Group Plc (Collaboration)
- GKN Aerospace Services Ltd, United Kingdom (Project Partner)
- BAE Systems, United Kingdom (Project Partner)
- CFMS Ltd, United Kingdom (Project Partner)
- National Composites Centre, United Kingdom (Project Partner)
- EADS Airbus, United Kingdom (Project Partner)
- The Alan Turing Institute (Project Partner)
- Rolls-Royce plc, United Kingdom (Project Partner)
Publications

Bachmayr M
(2020)
Unified Analysis of Periodization-Based Sampling Methods for Matérn Covariances
in SIAM Journal on Numerical Analysis

Bastian P
(2022)
Multilevel Spectral Domain Decomposition
in SIAM Journal on Scientific Computing

Butler R
(2020)
High-performance dune modules for solving large-scale, strongly anisotropic elliptic problems with applications to aerospace composites
in Computer Physics Communications


Chuaqui T
(2021)
A data-driven Bayesian optimisation framework for the design and stacking sequence selection of increased notched strength laminates
in Composites Part B: Engineering

Detommaso G
(2019)
Continuous Level Monte Carlo and Sample-Adaptive Model Hierarchies
in SIAM/ASA Journal on Uncertainty Quantification

Dodwell T
(2019)
Multilevel Markov Chain Monte Carlo
in SIAM Review

Dodwell T
(2021)
Multilevel Monte Carlo simulations of composite structures with uncertain manufacturing defects
in Probabilistic Engineering Mechanics

Dodwell TJ
(2021)
A data-centric approach to generative modelling for 3D-printed steel.
in Proceedings. Mathematical, physical, and engineering sciences
Description | CerTest was affected by the COVID-19 pandemic in several ways. Most RA positions have now been filled, and despite delays of research also due to lab closures in 2020 and to a certain extent in 2021 and reduced access to labs after lab reopened, decisive progress has been made towards the CerTest objectives. This includes novel methodologies to multi-scale modelling of composite aerostructures, statistical modelling and also hybrid testing and fusion of model and data-rich experimental data. Rich interactions with the industrial partners on the specific technologies developed have been developed, with a focus on industrial transfer and uptake. |
Exploitation Route | The methodologies relating to multi-scale statistical modelling, non-destructive evaluation (NDE) and testing methods (NDT), experimental full field techniques and hybrid testing methodology for the testing on component and substructure scale, fusion and integration of computational modelling and data-rich experimental data, and finally Design of Experiments based on Bayesian techniques can be transferred into other sectors like eg automotive, renewable energy (most notably wind turbine and tidal blades), construction and other sectors. |
Sectors | Aerospace, Defence and Marine,Construction,Energy,Manufacturing, including Industrial Biotechology,Transport |
URL | http://www.composites-certest.com |
Description | 2019-2020: The CerTest projet is is now approaching its mid term state when the impact of covid is accounted for. As part of the impact strategy for the Programme Grant, Profs Thomsen (PI, Uni Bristol), Barton (co-I, Uni Bristol) and Butler (co-I, Uni Bath) organised a workshop on 'Modernising Composite Regulations: New Opportunities for Research and Development' during the 22nd International Conference on Composite Materials (ICCM22), that was held 11-16 August 2019 in Melbourne, Australia. The ICCM series of conferences are the largest and most important scientific conferences on composite materials in the world. The key talk that set the background and need was given by Profs Thomsen and Butler outlining the CerTest aims and objectives, and this was followed by a series of specially invited lectures given by leading academics and industrial representatives. The workshop ran over an entire afternoon on Tuesday 12 August 2019. About 150 attended the workshop, and with the lectures inspiring deep and profound discussions about the challenges at hand and the need to rethink composite regulatory frameworks across sectors, the workshop is assessed to have very successful. A similar workshop organised by the CerTest team will be organised at the next ICCM conference, ICCM23 to take place in Belfast in 2023 . 2020-2021: COVID pandemic has prevented the CerTest team to attend planned workshops and conferences. |
First Year Of Impact | 2019 |
Sector | Aerospace, Defence and Marine,Construction,Energy,Manufacturing, including Industrial Biotechology,Transport |
Impact Types | Economic |
Description | Pump priming funding from University of Bristol, Faculty of Engineering Research Committee |
Amount | £5,000 (GBP) |
Organisation | University of Bristol |
Sector | Academic/University |
Country | United Kingdom |
Start | 12/2021 |
End | 06/2022 |
Description | Airbus UK |
Organisation | Airbus Group |
Department | Airbus Operations |
Country | United Kingdom |
Sector | Private |
PI Contribution | Project partner. Definition of project demonstrators. Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Collaborator Contribution | Definition of project demonstrators. Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Impact | Too early. Project in start up phase. |
Start Year | 2020 |
Description | BAE Systems |
Organisation | BAE Systems |
Department | BAE Systems Military Air & Information |
Country | United Kingdom |
Sector | Private |
PI Contribution | Project partner. Definition and delivery of demonstrators. Secondment of postdocs, PhDs and academic staff. |
Collaborator Contribution | Definition and delivery of demonstrators. Secondment of postdocs, PhDs and academic staff. |
Impact | Too early. Project in startup phase. |
Start Year | 2020 |
Description | CFMS |
Organisation | Centre Modelling and Simulation (CFMS) |
Country | United Kingdom |
Sector | Charity/Non Profit |
PI Contribution | Project partner. Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Collaborator Contribution | Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Impact | Too early. Project in kickoff phase. |
Start Year | 2020 |
Description | GKN & Royal Academy of Engineering Research Chair |
Organisation | GKN |
Department | GKN Aerospace |
Country | United Kingdom |
Sector | Private |
PI Contribution | Bi-monthly research meetings; reports; papers; software support; data |
Collaborator Contribution | Bi-monthly research meetings; data; supply of material; industrial expertise |
Impact | Over 10 PhD studentships; 50 papers; over £5M third party funding |
Start Year | 2011 |
Description | GKN Aerospace |
Organisation | GKN |
Department | GKN Aerospace |
Country | United Kingdom |
Sector | Private |
PI Contribution | Definition of project demonstrators. Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Collaborator Contribution | Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Impact | Too early to say. Project still in start up phase. |
Start Year | 2020 |
Description | National Composites Centre NCC |
Organisation | National Composites Centre (NCC) |
Country | United Kingdom |
Sector | Private |
PI Contribution | Project partner. Definition and delivery of demonstrators. Secondment of postdocs, PhDs and academic staff. |
Collaborator Contribution | Definition and delivery of demonstrators. Secondment of postdocs, PhDs and academic staff. |
Impact | Too early. Project in startup phase. |
Start Year | 2020 |
Description | Rolls Royce |
Organisation | Rolls Royce Group Plc |
Country | United Kingdom |
Sector | Private |
PI Contribution | Project partner. Definition of project demonstrators. Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Collaborator Contribution | Definition of project demonstrators. Secondment of postdocs, PhDs and academic staff and of Airbus staff to partner universities |
Impact | Too early. Project in startup phase. |
Start Year | 2020 |
Description | Siemens Gamesa Renewable Energy |
Organisation | Siemens Gamesa Renewable Energy |
Country | Spain |
Sector | Private |
PI Contribution | Siemens Gamesa Renewable Energy sponsors the project via the CDT in sustainable infrastructure systems at the University of Southampton |
Collaborator Contribution | Sponsorship in addition to technical input and manufacturing of wind turbine blade substructures for testin |
Impact | A number of research outputs presented at workshops and international conferences. Journal papers presently under preparation. Novel techniques for high-fidelity structures testing and fusion of numerical and experimental data. |
Start Year | 2016 |
Description | The Alan Turing Institute |
Organisation | Alan Turing Institute |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | Project partner. Secondment of postdocs, PhDs and academic staff. Focus on data centric engineering. Organisation of workshops. |
Collaborator Contribution | Secondment of postdocs, PhDs and academic staff. Focus on data centric engineering. Organisation of workshops. |
Impact | Too early. Project in startup phase. |
Start Year | 2020 |
Description | Bristol Composites Institute Annual Conference |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Industry/Business |
Results and Impact | Presentation entitled "Developments in Imaging Approaches for Composite Structures" |
Year(s) Of Engagement Activity | 2019 |
Description | Presentation at Roedean Girls School Brighton |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Schools |
Results and Impact | A presentation to celebrate International Woman's day 2020 entitled "Engineering the future with images" |
Year(s) Of Engagement Activity | 2020 |
Description | Seminar at University of Surrey |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Postgraduate students |
Results and Impact | A presentation entitled "INFRARED THERMOGRAPHY APPROACHES FOR QUANTITATIVE FATIGUE AND FRACTURE STUDIES IN METALS AND COMPOSITES" |
Year(s) Of Engagement Activity | 2019 |
Description | Workshop for General Admission |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Postgraduate students |
Results and Impact | The event was organised by Prof Janice Barton, Co-I on the CerTest project. It was a a Workshop on "Advances in Digital Image Correlation" by an invited speaker from the University of Ghent - Dr Pascal Lava - who spoke to an audience comprising mainly of postgraduate students, Researchers and interested industry and government colleagues. It took place on 17 February 2022.in the Wills Memorial Building, It was followed by a networking event and was attended by approximately 35 people. |
Year(s) Of Engagement Activity | 2022 |
URL | https://www.eventbrite.co.uk/e/workshop-on-advances-in-digital-image-correlation-dr-pascal-lava-tick... |