Acoustic resonance testing

Abstract

Acoustic Resonance Testing (ART) is a nondestructive test that uses the vibrational characteristics of an object to find defects. It is a whole-part test, so measurements taken in one place can indicate defects anywhere. It can be done quickly and requires minimal equipment. ART can be completely automated and make objective, quantitative judgments, eliminating human error. ART uses the fact that a part's physical structure causes it to have a distinct and unique set of characteristic frequencies. Every part with the same physical properties will have the same vibration properties, and any flaw will cause this vibration “fingerprint” to change. After a hammer impact, the characteristic frequencies of the part will be excited and every other frequency will quickly attenuate. By measuring the location and amplitude of several peaks of the part's dynamic response and comparing these values to a database of acceptable values, parts with defects can be quickly separated. ART can be used to find parts with out-of-tolerance dimensions, voids, and cracks, among other things. While the test will not determine the cause of rejection, with appropriate transducer sensitivity and software it can reliably find faults anywhere in a part. Currently Gassco is researching ways to use ART for in-line inspection of gas pipelines. ART is also being used on some automotive production lines to ensure 100% compliance with specifications. It is well-suited for quality assurance on drive train parts, piping sections, shielding and containment hardware, and other applications where fast and dependable flaw detection is critical.