In the aerospace industry, many structural components such as wing panels and radomes are made with fiberglass and advanced composites that need accurate thickness control. Composites are often stronger than conventional materials and weigh less. Advanced composites are typically made by combining graphite or carbon fibers with epoxy, polyamide, or polyimide resins.
Aerospace inspectors can use gauges to take instant, nondestructive thickness measurements on parts such as wings, fuselage, ducts, panels, and fan blades. Ultrasonic thickness gauging can be performed during fabrication or after installation to help ensure correct wall thickness.
Note: The inherent nature of composite materials can produce varying degrees of anisotropy and sound velocity variation. Carefully evaluate the composite material to check that the sound velocity is uniform enough to permit the required measurement accuracy.
Equipment
Aerospace inspectors can use ultrasonic thickness gauges or the Magna-Mike™ Hall-effect thickness gauge for composite thickness measurement.
In general, the thickness of most composite materials for aerospace applications in the range of 0.050–0.750 in. (1.25–20 mm) can be measured with the handheld 38DL PLUS™ or 45MG (with single element software) ultrasonic gauges and a transducer—commonly an M106 2.25 MHz contact transducer. Certain composites that are very scattering or thicker than approximately 0.750 in. (20 mm) may require gauges with the HP (high penetration) software option and a lower-frequency transducer. In challenging cases, waveform display monitoring is recommended to permit on-site operator adjustment of setup parameters. To measure the wall thickness on composite materials thinner than 0.125 in. (3 mm), delay line transducers such as the M202 may also be recommended.
The 72DL PLUS™ ultrasonic thickness gauge is another useful tool for composite thickness measurements. It offers a large touch screen, fast measurement, and many connectivity options. The 72DL PLUS High-Frequency model works with transducers up to 125 MHz and is ideal for measuring coatings on composites in the aerospace industry.
Inspectors can also use the Magna-Mike 8600 Hall-effect thickness gauge if there is access to both sides of the test piece for a probe and a target ball, as in a manufacturing environment. The Magna-Mike gauge offers the advantage of couplant-free measurements that are independent of sound velocity variations. With an appropriate probe and targets, it can measure up to 1.00 in. (25.4 mm).
