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.
Instant, nondestructive thickness measurements can be made on parts such as wings, fuselage, ducts, panels, and fan blades. Advanced composites are often made by combining graphite or carbon fibers with epoxy, polyamide, or polyimide resins. Ultrasonic thickness gauging can be done during fabrication or after installation to ensure correct wall thickness.

NOTE: The very nature of composite materials produces varying degrees of anisotropy and therefore, sound velocity variation. Care should be taken when evaluating any specific composite application that the sound velocity is sufficiently uniform to permit the required measurement accuracy.

Equipment: In general, most composite materials for aerospace applications in the range of 0.125 in. to 0.750 in. (3 to 20 mm) can be gauged with the hand-held Model 35DL-HP or Model 35 and an M106 contact transducer. Models 35DL and 35 can also be used in many situations. Advanced composites that are very scattering or that are thicker than 0.750 in. (20 mm) can often be gauged with the Model 35DL-HP and a M2008 transducer (providing that curvature of the test piece allows use of the 1 inch diameter M2008 transducer). In especially challenging cases, the Model 35HP with waveform display is recommended to permit on-site operator adjustment of setup parameters.

To measure the wall thickness on composite products thinner than 0.125 in. (3 mm) it may be necessary to use the standard version of the Model 35DL and a M109 or M112 contact transducer. Delay line transducers such as the M202 may also be recommended.