New technique to spot 'invisible' cracks

The next generation of aircraft could be thinner and lighter as researchers have developed a new imaging technique that could detect damage previously invisible to acoustic imaging systems.

The non-linear acoustic technique developed by the researchers will also improve safety of engineering structures, the study noted.

The researchers pointed out that the technique has been achieved using standard inspection equipment, which will allow for the rapid implementation of the technique in numerous applications.

"Imaging acoustic non-linearity not only provides sensitivity to smaller defects than is currently possible but may have the potential to detect damage before macroscopic material changes occur," said lead researcher Jack Potter, a research assistant at University of Bristol in Britain.

"This would enable intervention before cracks have even begun to form, as well as predicting the remaining life of an engineering structure," Potter added.

It has long been understood that acoustic non-linearity is sensitive to many physical properties, including material microstructure and mechanical damage.

The lack of effective imaging has, however, held back the use of this important method.

Currently engineers are able to produce images of the interior of components using ultrasound, but can only detect large problems such as cracks.

Imaging of acoustic non-linearity is achieved by exploiting differences in the propagation of fields produced by the parallel and sequential transmission of elements in ultrasonic arrays.

The study appeared in the journal Physical Review Letters.