How do acoustic emissions reveal structural flaws while a material is being stressed?

Acoustic emission is a form of nondestructive testing that identifies structural flaws by detecting the sound waves generated when a material is subjected to stress.12

When a material undergoes stress, the release of elastic energy—often caused by the formation or growth of microcracks—produces stress waves. These high-frequency acoustic emissions serve as indicators of internal damage, allowing for the monitoring of structural integrity without damaging the material itself. This method is a distinct field within acoustics and is particularly valuable for detecting flaws that develop while a structure is under load.21