Detecting internal defects – material-friendly and precise
Ultrasonic testing uses the physical propagation of high-frequency sound waves in solid materials. Short ultrasonic pulses are coupled into the component via a suitable probe. To ensure reliable sound transmission, a coupling medium – for example a gel or a liquid – is applied between the probe and the component surface.
The coupled sound waves propagate directionally in the material. As long as the material is homogeneous, sound propagation is uniform. If, however, the sound pulse encounters an interface with different acoustic properties – for example between base material and air entrapment, at an internal crack or at a material discontinuity – part of the sound energy is reflected and returned to the probe as an echo.
The instrument records these echoes and displays them as a function of time and amplitude. From the measured transit time, the position of the reflecting structure within the component can be determined because the sound velocity in the respective material is known. Signal amplitude provides indications of defect size and character.
Depending on the inspection task, different test procedures are used. Pulse-echo testing is most common, in which a single probe both transmits and receives. For certain applications, through-transmission may be used, with transmitter and receiver arranged separately.
In this way, ultrasonic testing enables volumetric examination of the component. Unlike purely surface-oriented methods, irregularities located inside the material can thus be reliably detected and assessed without mechanically affecting the component.
