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Non-destructive testing of bonded assemblies

Sealed Without A Kiss (SWAK): Non-destructive testing of bonded assemblies


Adhesive joints are used to join structural elements in aircraft. Compared to the conventional structural joining techniques such as bolting, riveting and welding, adhesive joints minimize stress concentration and fatigue problems. Adhesive joints are susceptible to environmental degradation and manufacturing defects, hence it is imperative to use methods of inspection which provide information on these structural joints. In this project we focus mainly on a specific type of defect known as KISSING BOND defect.

A kissing bond is sometimes referred to as a zero-volume dis-bond between adhesive and adherend. In such defects, there is intimate solid-solid contact, and the dis-bond has no volume at the interface between adhesive and adherend. Furthermore, despite this intimate contact, there is no tensile strength across the interface. Together, these two factors make the dis-bond both very difficult to detect non-destructively, and very dangerous in that the joint strength is severely compromised. A zero-volume dis-bond can occur during joint manufacture due to poor preparation of the adherents. If adequate control of the adherend preparation is maintained, the occurrence of these types of dis-bond can be dramatically reduced. However, this type of kissing bond is difficult to produce intentionally. Hence a special method will be developed in this project out of extensive research.


The main objective of this project is to develop a manufacturing control procedure to generate Kissing Bond defects in bonded joints made out of composite materials and a non-destructive technique (NDT) to detect Kissing Bond defects in these samples. Different adherence models and NDT methods for different material bonded structures will be reviewed. Test samples are fabricated based on the review. Various NDT methods for bonded structures will be reviewed. An innovative NDT technique will be developed to detect Kissing Bonds defect.


  • SWAK developed solutions based on NDT of adhesively bonded structures will reduce the usage of rivets and bolts, promoting the application of adhesives in aircraft structures and components, thus, will contribute to the reduction of weight overall that will reduce fuel consumption and will cut emissions ultimately.
  • SWAK will have a direct impact on the safety of aircraft as it will enable zero defects NDT and mechanical testing techniques for bonded structures and geometries to be deployed in aircraft structures.
  • SWAK will reduce the labour cost of products made of composites by reducing the number of assemblies. In turn it improves the strength of assembly while reducing number of parts.

Brunel Innovation Centre's Role

BIC takes part in the development of NDT technologies to detect kissing bond defects.

Project Partners

  • GMI Aero
  • TWI Ltd
  • Brunel University London

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Project last modified 25/02/2021