1st Project-Half (M1-M18) Overall Progress

The ComBoNDT project has just completed its first 18 months, out of its planned 36-month duration. 

The overall objective of ComBoNDT is to develop a quality assurance concept for adhesive bonding of load-critical Carbon Fibre Reinforced Plastics (CFRP) primary aircraft structures, which is applicable within the whole life cycle of the aircraft to overcome the current limitations regarding certification of composites. Therefore, a detailed approach regarding in-line extended non-destructive testing (ENDT) for CFRP materials with increased technological readiness level (TRL), in-process and post-process, will be established.

The work performed and the positive results will lead to both industrial and societal benefits. For the aeronautics industry, it is important to develop reliable testing methods to ensure the bond quality during the entire life of an aircraft; and the certification of (structural) adhesive bonding marks a key step for full integration of CFRP, as adhesive bonding is the optimum CFRP joining technology. The surface assessment techniques which are being developed will allow reduction of time and cost, because they would permit identifying which contaminated areas need to be cleaned. The adhesive bonds assessment techniques which are being examined could lead to reduction of time and cost related to repairs caused by undetected weak bonds. Moreover, the downtime of the aircraft will be reduced leading to costs reduction.

In summary, the positive results provide promising expectations with regards to the potential of the developed technologies to enable time and cost efficiency, increased safety and reducing as well production and maintenance, repair and overhaul (MRO) costs. Time savings of up to 70 % and cost savings of up to 50 % in related production, MRO and retrofit processes are expected from the application of ENDT technologies resulting from ComBoNDT.

Summary of work realized

  • Definition of test scenarios, sample preparation and overview of sample measurements; The task realized a concise listing of all relevant contaminants identified by the ComBoNDT project partners and specifically those to be examined within the project. Additionally, it was the production and repair use-cases to be considered were defined, as well as the size of specimen, mechanical tests scenarios and codification system.
  • Sample preparation for the test scenarios, sample characterization by reference methods and mechanical testing; The contaminated CFRP samples were prepared, characterized by means of conventional laboratory surface analytical methods regarding their physico-chemical properties and by means of non-destructive testing methods regarding their structural integrity (conventional defect inspection). Mechanical performance of the samples was characterized by mechanical testing. Ultrasound inspection results led to the conclusion that true weak bonds were successfully produced in most of the cases, as defects were rarely revealed. Finally, the negative effect of the contamination on the bondline integrity was mainly revealed by the results of the fracture toughness tests. The study performed constitutes a stepping stone towards understanding and expanding the use of adhesive bonds in aerostructures.
  • Development and specific adaption of ENDT techniques for quality assurance of surfaces parts; The work performed included the improvement of sensitivities and reliability of detection for each technique. Singly as well as multiply contaminated coupon samples were subjected to surface analytical investigations. The techniques were then adapted and improved in order to meet the requirements of better quantification and reproducibility in both the repair as well as the production scenarios.
  • Development and specific adaption of ENDT techniques for quality assurance of adhesive bondline; Singly as well as multiply contaminated coupon samples were investigated. The first results for the laser adhesion tests are promising and show that the technology could be used to test and detect weak bonds.
  • Validation of ENDT techniques and technological assessment which is an important step towards the certification of the techniques; Within the first 9 month of the project duration the TRL criteria were defined and for each concerned technology the initial assessment took place. The status of each method is monitored and made measurable. The technologies have reached TRL 3 to 4 which was the expected range to start the innovations planned in ComBoNDT. Again, close to the end of the project the progress will be evaluated by TRL review.
  • Dissemination outreach; ComBoNDT activities have been disseminated in 16 scientific events, 1 trade fair and 2 open events which were addressed to the general public. Furthermore, a series of open-access publications are planned to be realized within 2017. Finally, ComBoNDT research and results are being incorporated within academic material and support the development of academic thesis, as several young scientists and engineers are getting involved in the project, through the participating institutions.

Main achievements and expected impact

  • Definition of concrete fields of application, sample geometries, surface states and relevant contamination types and levels by taking into account production and repair use-cases of high relevance and representative for aerospace industry
  • For many of the contaminants studied there has not been any previous mechanical characterization in the literature, or it has been only for Mode I fracture toughness tests and not for Mode II and centrifuge tests. A fully experimental characterization and explanation is now provided for the effect that various commonly encountered in aeronautics contaminations have on the integrity of the bondline of adhesive composite joints, thus moving a step forward to understanding and expanding the use of adhesive bonds in aerostructures
  • The surface assessment techniques which are being developed allow reduction of time and cost, once they would permit identifying which contaminated areas need to be cleaned. The data from the ENDT methods were successfully compared to the results from laboratory based reference characterisation methods and correlated to the degree of surface contaminations
  • Assessment of adhesive bond New signal processing algorithms are being developed in order to assess the bonds and correlate the response with bond quality. For some cases equipment is also modified and new devices are being developed to obtain efficient tools of bond assessment. If the techniques under development are proven to be effective it will allow to reduce time and cost related to repair caused by undetected weak bond. Moreover, the downtime of the aircraft will be reduced leading to costs reduction
  • The findings of the project may be interesting for other fields where adhesive bonding is being applied, i.e. wind energy. Furthermore, they may lead to new research topics for which funding may be sought in future calls on national and international level. The gained knowledge and experience can be included in the teaching and training activities conducted at the partner institutions. Moreover, the effective bond assessment tools can lead to wider acceptance (industrial and societal) of adhesive bonding for joining of the composite parts
  • Validation of ENDT techniques and technological assessment contributes to the awareness of how to evaluate the maturity of technologies within the academic and research world to brighten the views of which requirements need to be fulfilled for a successful development of a product to make it mature for the market

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 636494.

This project is endorsed by the European Aeronautics Science Network - EASN.

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