Materials Testing Using Ultrasound

Researchers at the Fraunhofer Institute for Non-Destructive Testing IZFP in Saarbrücken have adapted the conventional sonar procedure – a simple ultrasound method – and have succeeded in generating three-dimensional images with the aid of innovative software. At the same time, they have increased the testing rate a hundredfold.

Many areas of quality assurance or production for the construction industry call for reliable testing methods: be it pipelines, railway wheels, components for power plants, bridge piers or items mass-produced by the thousands, there is a need to ensure that deep down the items produced are free from tiny fissures or imperfections. For many years, ultrasound has proven a valuable tool in non-destructive materials testing. An ultrasonic transducer radiates sound waves into the workpiece, and the time the signals require to travel and be reflected back indicates where material defects are located. Scanning workpieces in this way is relatively time-consuming, since, an inspection tact can only register a single beam angle. Thus, many measurements must be performed to assemble the composite image suitable for evaluation of inspection results.

However, this approach is too slow if ultrasound testing is to be integrated in ongoing production or applied to large components. That is why Doctor Andrey Bulavinov and his team have developed a new method that works at up to 100 times the speed. "We no longer use the sonar method that emits a sound field in just one particular direction. Instead, we use the probe – which experts refer to as a "phased array" – to generate a defocused, non-directional wave that penetrates the material. What we get back are signals coming from all directions, and the computer uses these signals to reconstruct the composite image." In a manner similar to subterranean seismic testing, it analyzes physical changes the wave encounters in the material – diffraction and heterodyning – and uses this information to determine the conditions within the material itself. "We follow the sound field," Bulavinov notes, "and calculate the workpiece characteristics on the basis of that." Similar to computer tomography in medicine, in the end we receive three-dimensional images of the examined object where any imperfections are easy to identify. The startling thing about this approach is that with it, a fissure is now visible even if the ultrasound was not specifically directed at it.; Source: Fraunhofer