STO-Activities: (no title)

Activity title: Bonded Joint Design Validation and Inspection Methods to Achieve Certification
Activity Reference: AVT-412
Panel: AVT
Security Classification: NATO UNCLASSIFIED
Status: Active
Activity type: RWS
Start date: 2024-01-01T00:00:00Z
Actual End date: 2026-12-31T00:00:00Z
Keywords: Adhesive, Bonded Joint, Bonded Repair, Certification, Composites, Nondestructive Evaluation, Primary Structure
Background: Adhesively bonded joints and repairs for both composite, metallic, and hybrid structures offer many advantages over mechanically fastened joints in terms of mechanical, dynamic, hydrodynamic, signature, and aerodynamic performance, as well as weight. In particular, bonded joints are often the only method when parts are too thin for bolted repair, or when other requirements, such as external shape and stealth properties, are to be maintained or safety restricts grinding or welding (hot-work). In spite of positive experience of bonded repair on secondary and tertiary aircraft and ship structures, as well as its successful applications on some primary structures of military platforms, such as F/A 18 and MIG29, there are significant challenges in using bonded repairs to provide or restore and maintain structural integrity of primary structures – in particular with regard to certification. Bonding as an initial manufacturing joining method is widely recognized of carrying significant cost and weight benefits. These benefits can only materialize with a sound design and material driven approach. Still the same certification criteria for bonded repairs apply, which is limiting the use of bonded joints for structural applications.
 
There exist certification approaches to bonded joints on primary structures, but they are limited to specific parts and platforms and require test data validating repair performance. For aviation the bonding repair size limit is limiting the size of structural repairs as such the surrounding parent structure needs to have limit load capability patch off. Previous NATO STO activities have focused on composite and bonded structural applications. AVT-266 “Use of Bonded Joints in Military Applications” (Turin, Spring 2018) showcased the recent progress in adhesive bonding and certification methods, including bonded repair, among the participating NATO nations. Exploratory Team (ET) AVT-ET-201 (“Certification of Bonded Repair on Composite Aircraft Structures”), approved during the TCMSM of the AVT-43rd Panel Business Week (Slovakia, 20th -24th May 2019) transitioned to a successful Research Workshop (RWS), AVT-361 “Certification of Bonded Repairs of Composite Aircraft Primary Structures” (Amsterdam, NL October 2022).
 
AVT-361 RWS presentations and discussions highlighted the state of the art and industry’s current needs in regards to testing and application of bonded repair and bonded joint applications across both aerospace and maritime industries. Though a proposed roadmap for bonded repair certification exists and research is focused on individual aspects of the roadmap, application of bonded repairs and joints of primary structure is limited. The conclusions and recommendations of the RWS participants and technical evaluator are that more test data and research is required to validate numerically predicted service life of arbitrary bonded joint configurations and develop the capability to infer in-situ bond strength. Research, numerical prediction, and design should include integration of moisture, fatigue, and temperature degradation with further validation of damage tolerant joint configurations is required. In addition to prediction efforts, development of nondestructive inspection techniques and integration of those techniques with machine learning to help interpret the complex data with the purpose of inferring true bond strength of the repair or joint are required for certification. Current consensus is that certification can be achieved with the ability to design for damage tolerance. However, because bond strength is dependent on material selection and bond surface conditions both before and during service, the ability to measure strength at all stages of service life will facilitate certification of optimized bonding in primary structures.
 
*Due to character limitations, please see "Exploitation and impact" section for the last paragraph of the "Background" Section
Objectives: The primary objectives of the project are to discuss and share recent developments related to: (1) the state of the art (SoA) for validation of numerical prediction methods for bonded joints and repairs from structural performance to adhesive strength that incorporate production and service-life degradation, (2) demonstration of bonded joint strength and performance for the design service-life and environment, and (3) share latest developments of NDE techniques and SHM systems to measure or infer adhesive bond strength in-situ.
 
The RWS will cover:
1. Design and analysis methods that include novel design features or analysis methods that include adhesive performance degradation over the service-life of the bonded joint or bonded repair. (Design features, design methods, analysis methods)
2. Testing and validation methods being developed to demonstrate bonded joint and bonded repair performance over the design service-life of the structure. (ageing, test methods, data substantiation)
3. SoA of the technology and methods to both perform and predict nondestructive evaluation of bonded joints and repairs to quantify or infer the bond strength achieved or remaining. (Inspection methods, numerical prediction of inspection methods)
4. Development of structural concepts for bonding initial design
Topics: The major scientific RWS topics concentrate on technology to support the certification of adhesive bonded joints and repairs and more specific the application of design features in order to comply with one of the Means of Compliance (MoC). The specific design issues and analysis methods related are discussed together with methods to investigate the effect of ageing on the bondline strength.
 
Specific topics expected to be discussed include: (1) Design and analysis of novel configurations for durable bonded joints, (2) numerical prediction methods for crack initiation and propagation, (3) numerical prediction and quantification of in-situ bond strength using nondestructive methods, and (4) moisture diffusion and degradation of the adhesive, adherends, and adhesive to adherend.
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Created at 20/10/2023 15:00 by System Account
Last modified at 16/05/2024 08:00 by System Account
 
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