Composite materials such as carbon fiber-reinforced plastic (CFRP), glass fiber-reinforced plastic (FRP), and glass-reinforced plastic (GRP) are increasingly being used in the aerospace and transportation sectors due to their lightweight, high strength, and excellent formability—offering dual benefits of enhanced performance and improved efficiency. Precise measurement of coating thickness in these composites is critical to ensure optimal protection, effective weight management, and full compliance with regulatory standards, particularly in multi-layer systems commonly found in applications like aircraft and high-speed railways. The BYK-PELT ultrasonic thickness gauge provides non-destructive, high-resolution measurements across a variety of substrates, capable of assessing up to five coating layers, helping industries achieve reliable quality control.

Aerospace, railway, and transportation sectors

Composite Material Surface Coating Thickness Measurement: Composite materials offer numerous advantages in the aerospace and transportation sectors, such as significantly reducing weight (lightweighting), enhancing strength, and enabling the easy formation of complex shapes that are difficult to achieve with metals. These composite materials include carbon fiber-reinforced plastic (CFRP), fiber-reinforced plastic (FRP), and glass fiber-reinforced plastic (GRP).

About 50% of the Boeing 787 aircraft's structure is made from composite materials such as carbon fiber-reinforced polymer (CFRP), while only around 35% of the fuselage uses metal materials like aluminum and titanium alloys. Similarly, composite materials account for approximately 50% of the Airbus A350's structure. These advanced materials enable both aircraft models to achieve benefits such as reduced fuel consumption and improved cabin pressurization levels, ultimately delivering a more comfortable flying experience for passengers.

Figure 1: Boeing 787

In the railway application field, from short-distance light rail to high-speed trains, composite materials have delivered remarkable energy-saving benefits thanks to their weight-reducing properties, ability to minimize wheel-to-track wear, and exceptional corrosion resistance. Moreover, these materials combine high strength with the flexibility to be easily molded into intricate shapes. Many high-speed train power cars feature composite material nose cones precisely because such complex structures are difficult to produce using steel or aluminum.

Composite exterior components or panels on high-speed train carriages typically feature at least a two- to three-layer structure. The primer layer is applied to smooth out surface imperfections, with a dry film thickness ranging from 100 to 150 micrometers. Both the primer and topcoat layers have dry film thicknesses between 50 and 100 micrometers. The graffiti-resistant layer, meanwhile, must have a minimum dry film thickness of 150 micrometers, while its maximum thickness does not exceed 225 micrometers.

The significance of coating thickness measurement: For coatings applied to aircraft composite surfaces, an excessively thick layer of paint can lead to added weight and reduce the effectiveness of the lightning protection system. In transportation applications, insufficient topcoat on railway locomotives weakens the coating's weather resistance, UV protection, and corrosion resistance, thereby shortening the service life of the protective coating.

For public transportation vehicles, verifying the thickness of anti-graffiti coatings is crucial. With its multi-layer measurement capability, the PELT ultrasonic gauge can both confirm whether the anti-graffiti coating on new equipment meets the manufacturer’s specifications and monitor the thickness of coatings on vehicles in service.

High-speed railway applications include coating inspections of composite material nose cones and front-end surfaces, roof panels, and other composite components—parts that cannot be measured using magnetic induction or eddy current testing methods.

Figure 2: High-Speed Railway

Multi-layer ultrasonic measurement: BYK-PELT ultrasonic technology offers non-destructive, layered thickness measurement capabilities for nearly all substrates encountered in the aerospace and transportation industries—capable of measuring up to five layers. Applicable substrates include composite materials such as glass fiber and carbon fiber, as well as metallic materials like plastics, titanium, steel, and aluminum. The PELT coating thickness gauge utilizes high-frequency transducer technology combined with ultrasonic principles to deliver highly accurate and high-resolution measurements.

Figure 3: Application Example of Composite Substrate Coating Systems in Railway Systems