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.

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.

Publications

10 25 50
 
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...