Inspecting aircraft coatings for degradation
Air transport is a major contributor to carbon dioxide emissions and those emissions are released directly into the atmosphere. The EU and its aerospace industry are committed to reducing the environmental impact of aircraft. Scientists have increasingly turned to a phenomenon inspired by nature. Sharks have been darting around in deep waters for millions of years, their speed and predatory prowess increased by their specialised skin layer containing dermal denticles. The engineered equivalent is called riblets, tiny grooves parallel to the direction of flow. Riblets are maturing rapidly and researchers set out to develop important inspection technology to speed the process with the EU-funded 'Quantification of the degradation of microstructured coatings' (MICROCOAT) project. The first step was to enable laboratory investigations of specimens coated with riblets in order to fully characterise the microstructure under different conditions. Researchers took impressions of real riblet structures of aeroplane surfaces and, using confocal microscopy and newly developed data extraction methods, determined important parameters necessary to assess wear and long-term durability. Riblets are typically applied in an automated spray-coating process. The entire surface covered can be on the order of a few thousand square metres, meaning that in-line quality control must be fast to be useful. The prototype system has a 2D camera, a specialised lens and sensor, and a laser scanning microscope. It inspects flat geometries relatively quickly and is capable of detecting defects thanks to novel image processing algorithms that enable the extraction of values, including the very tiny riblet radius, riblet width and riblet height. MICROCOAT's inspection system has many uses, including in-line quality control during riblet application, monitoring to determine ageing, and even inspection of micro-structured surfaces in other applications. It is thus poised for major uptake among the aircraft, materials and manufacturing sectors with important benefits for the competitiveness of the EU.
Keywords
Aircraft, coatings, degradation, riblets, microstructured coatings
