Engineers at Bristol University in the UK say they have developed a way to use ultrasonic nonlinear imaging techniques to find structural weakness and cracks in materials used in things like bridges and airplanes. Researchers say this development will help find weaknesses that previously could not have been found and will enable timely replacement and repair. The research team uses nonlinear ultrasonics to look inside materials like metal.

"You're essentially making an acoustic lens to give you much better resolution an a given place," says Bristol University Senior Lecturer in Mechanical Engineering Anthony Croxford. “The result of that means we can use a phased array to image what's going on inside a piece of metal and that gives us a very high resolution image of all points within the piece of metal by focusing energy at one location"

The arrays being used send hundreds of sound signals through materials. These are then "listened to" in order to determine where they come from and what they sound like. Engineers can get a picture of what's inside the metal and where otherwise undetectable damage and cracks could be.

“The way this works is that your energy essentially shakes the crack. Once shaken, it produces harmonics. By using this novel approach, engineers can now pick up a crack close to a hole. This is relevant to aerospace applications where engineers are worried about cracks growing from rivet holes, “he says.