Thickness Measurement of Coatings on Composite Structures for Aerospace, Railway and Transportation Applications

Thickness Measurement of Coatings on Composite Structures for Aerospace, Railway and Transportation Applications

The use of composite materials for aerospace and transportation applications offers advantages such as significant reductions in weight (lightweighting), increases in strength, and ease of molding into shapes not practical for metals. These composite materials can include carbon fiber reinforced plastics (CFRP), fiber reinforced plastics (FRP) and glass reinforced plastics (GRP).
Approximately 50% of the Boeing 787 aircraft is comprised of composite materials such as CFRP and other composites. Only about 35% of the airframe are metals such as aluminum and titanium. The Airbus A350 also utilizes composite materials for approximately 50% of its structure. These materials enable both aircraft to have advantages such as lower fuel consumption and higher cabin pressurization for greater passenger comfort.

For railway applications ranging from short range light rail transit to high speed railcars, composite materials offer energy savings due to reductions in weight, reduced wear on wheels and railway track, and corrosion resistance. In addition, composite materials provide high strength and can readily be molded into complex shapes. Many high speed rail power cars have composite nose cones due to the difficulty in fabricating these complex shapes out of steel or aluminum.

A composite exterior component or panel on a high speed rail car will typically have at least two or three layers. There will be a primer surfacer layer to smooth surface imperfections. Dry film thickness may range from 100 to 150 microns. A basecoat or topcoat layer may range from 50 to 100 microns. An anti-graffiti layer may have a minimum dry film thickness specification of 150 microns and a maximum of 225 microns.

Importance of Coating Thickness Measurement

For coatings on aircraft composite surfaces, excessive paint thickness can lead to undesired additional weight and a reduction in the effectiveness of lightning strike protection systems. For transportation applications, insufficient topcoat can lead to reductions in weather, UV, and corrosion resistance, and a shortened service life of the protective coatings. For rail
transit vehicles, it is important to be able to be able to verify anti-graffiti coating thickness. With its multi-layer capability, PELT ultrasonic measurement gauges can verify that anti-graffiti coatings have been applied to the manufacturer’s specifications in new equipment while also enabling monitoring of the thickness of the coatings for in-service vehicles.
High speed rail applications include coatings on composite nose cones and front faces, roof panels, and other composite components that can not be measured with magnetic induction or eddy current methods.

Multi-Layer Ultrasonic Measurement

BYK-PELT ultrasonic technology will provide non-destructive individual layer thickness measurement capability for up to 5 layers for virtually any substrate encountered in aerospace and transportation applications. Substrates include composites such as fiberglass, carbon fiber, plastics, and titanium, steel, and aluminum. The PELT coating thickness gauges utilize high frequency transducer technology and ultrasonics that enables precise high resolution measurements.