Skip to main content
European Commission logo

In-field CFRP surfaces Contamination Assessment by aRtificial Olfaction tool

European Union
Complete with results
Geo-spatial type
Total project cost
€237 037
EU Contribution
€177 778
Project Acronym
STRIA Roadmaps
Vehicle design and manufacturing (VDM)
Transport mode
Airborne icon
Transport policies
Societal/Economic issues,
Environmental/Emissions aspects,
Transport sectors
Passenger transport,
Freight transport


Call for proposal
Link to CORDIS

In CFRP bonded repair applications, it is mandatory to ensure surface cleanliness for achieving robustness and reliability of the bonds. Unfortunately, aircraft surfaces can be affected by several potential contamination sources that may hamper the bond strength; such contaminations have to be detected before a bonded repair takes place. Maintenance and repair operating conditions also require that any contamination detection technique should be operated on a portable basis and measurement results be readily available to the operator.

Artificial olfaction (AO) technologies could represent an optimal framework to develop such a detection tool (i.e. an electronic nose). They are based on the integration of gas sensing devices and pattern recognition (PR) algorithms. Their working principle mimics mammal’s olfaction systems: a gas sensor array, being exposed to a gas mixture, produces a distinct response pattern that can be interpreted by software components to produce qualitative and quantitative estimation on the mixture composition.

Our proposal addressed the investigation of AO technology suitability and the development of an e-nose prototype for surfaces contamination detection to be used in bonded repair of aircraft composite structures. The selection of an ad-hoc sensing array was carried out, investigating the use of several gas sensors based on different operating principles. Their capability to reliably react to volatiles emitted by potential aeronautics contaminants (e.g. skydrol, fuels, etc.) and to exhibit limited drift behaviour was firstly investigated in controlled environment. Once a response database was recorded, a PR component was designed and developed to provide qualitative and quantitative readings. Design and development efforts of a final prototype inspection tool was focused on portability in order to achieve operative capability.


Parent Programmes
Institution Type
Public institution
Institution Name
European Commission
Type of funding
Public (EU)
Specific funding programme
JTI-CS - Joint Technology Initiatives - Clean Sky
Other Programme
JTI-CS-2010-5-SFWA-01-007 In field surface inspection tool for contamination detection before bonded composite repair


Executive Summary:

Transport industry accounts for a significant percentage of CO2 emissions. Obtaining a lower fuel per mile ratio will not only help to reduce pollution and greenhouse gas emissions, it will also contribute to the competitiveness of aerospace industries and airlines. As such, Europe is significantly investing in research that pursues the achievement of the so called Green Aircraft industry with the CleanSky joint technical initiative targeting, among others technologies, increased reliance on laminar flows and improved usage of composite material for structural components in aircrafts.

CFRP components assembly is not achieved through riveting, it actually relies on adhesive bonding. A significant increase in the adoption of CFRP technology in primary structures will only be achieved if a reliable quality assurance technology will ensure the mechanical properties of the bonded panels. Up to now, no objective technology has been validated to ensure the quality of bonds and that is having a detrimental effect on the quest for the Green Aircraft. With the ICARO proposal (Infield CFRP surfaces Contamination Assessment by aRtificial Olfaction tool, JTI SP1-JTI-CS-2010-05, GA Number 286786) , ENEA was tackling the challenge primarily targeting pre-bond inspection and specifically the search for surface contaminants in maintenance and repair scenarios. Contamination in fact strongly affects the mechanical properties of adhesive joints assembly lowering the amount of force needed to cause joint failures. In fact, more than 20% (and up to 70%) reduction of interlaminar fracture toughness is expected to occur based on exposure to hydraulic fluids and release agents. A number of different fluids can act as surface contaminant both in the assembly and operative life of the aircraft: hydraulic fluids, moisture, release agents (assembly phase) and de-icing fluids being among the most dangerous.

During the ICARO project, benefitting from the CleanSky contribution, the ENEA electronic nose technology had been studied and adapted for the use as a highly portable, fast contaminant detection and quantification tool and eventually developed in the ICARO e-nose prototype. The combined use of different solid-state sensing technologies as well as pattern recognition methodologies have given birth to a tool that is able to detect surface cleanliness state and purposely quantify the amount of contamination especially in the maintenance scenario. After the scarfing process and before the patch adhesion and curing process, the ICARO e-nose can be used to detect contaminations ensuring the quality of the maintenance patch adhesive bond.

Thanks to the JTI efforts the ICARO prototype had been tested versus the capability to detect hydraulic fluids, moisture and anti-ice agents. Cooperation with SFWA partners and specifically with Fraunhofer IFAM institute (as a task responsible) had allowed developing the tool in a realistic framework thanks to appropriate sample preparation methodologies and focusing versus relevant contaminant and relevant contaminants concentrations in the maintenance scenario. During the project some limitations of artificial olfaction technology had been tackled and successfully solved while a long-term test period allowed to finally fuelling the validation of the use of e-nose technology as a CFRP fast pre-bond inspection tool.

After the execution of the test procedures, the ICARO prototype had shown the ability to obtain performance in excess of 96% correct classification when dealing with a test scenario including the detection of Skydrol 500-B hydraulic fluid and Kilfrost as surface contaminants in the range of 2 grams per m^2.


Lead Organisation
Agenzia Nazionale Per Le Nuove Tecnologie, L'energia E Lo Sviluppo Economico Sostenibile
Lungotevere Grande Ammiraglio Thaon Di Revel 76, 196 Roma, Italy
EU Contribution
€177 778
Partner Organisations
EU Contribution


Technology Theme
Non destructive testing
Extended NDT for CFRP structures and bonds
Development phase
Demonstration/prototyping/Pilot Production

Contribute! Submit your project

Do you wish to submit a project or a programme? Head over to the Contribute page, login and follow the process!