MICROCOAT

Quantification of the degradation of microstructured coatings

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 Obiettivo del progetto (Objective)

'For a successful geometrical characterization of the described microstructured coatings, the lateral resolution of the measurement device should be higher than 250 nm. Therefore, a confocal microscope or white light interferometer will be used for the laboratory measurements. To obtain reliable and accurate geometrical information, the optical measurement results will be verified by a secondary electron microscope (SEM). Its advantage is the higher lateral resolution and the ability to detect steep angles. Though a SEM only produces 2D images, it is possible to evaluate the 3D-geometry of local structures using the shape from shading method. For a degradation analysis, the 3D measurement results will be used for calculation of the task-relevant geometric parameters. For this purpose different mathematical instruments such as Fourier analysis and statistical estimation can be used. The parameters are presented as histograms and correspondent distributions. The solutions, which were developed for laboratory tests, cannot be directly used for quasi-real time measurements because the micro-coating production rates are usually distinctly higher. For this reason, the surface is examined using 2d cameras. Here not the real 3D topography, but secondary characteristics, such as the specific reflection of corners or the darker indications from tilted surfaces, are being controlled. The areal scanning will be achieved with the aid of highly precise linear axes. If a divergence from the desired course is found during the camera examination, this spot will be examined with confocal microscopes. These microscopes can be installed on positioning devices. The 3D measurement results are additionally tested for their precision and robustness. If necessary, improvements may be implemented which aim particularly at the elimination of oscillations in the system. In conclusion, time optimization is performed by distributing the control of the system on several synchronized workstations.'

Introduzione (Teaser)

One important way to reduce fuel consumption by aircraft is to reduce friction and drag. A novel system to inspect specialised coatings that do just that could speed their commercialisation with important cost and environmental benefits.

Descrizione progetto (Article)

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.