TechSolutions 16: Selecting a Nondestructive Testing Method, Part VII: Acoustic Emission Testing

TechSolutions 16: Selecting a Nondestructive Testing Method, Part VII: Acoustic Emission Testing
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Acoustic emission testing (AET) is a nondestructive technique that monitors defect formation and failure within a material through the detection and analysis of acoustic emission (AE) signals – stress waves generated by the rapid release of strain energy.[1, 2] External stimuli, such as a temperature gradient or an in-service mechanical load, can cause changes to the internal structure of a material. Crack initiation and propagation (release of stored elastic energy), the opening and closing of cracks, twinning*, dislocation movement (i.e., slip), reorientation of grain boundaries, plastic deformation, and phase transformations (release of stored chemical and/or free energy) all lead to the release of AE signals.[1-6] AET is fundamentally different from other nondestructive testing (NDT) methods because it passively detects energy that is released from a material, whereas other methods require an energy input for the defect to be detected (i.e., x-rays, gamma rays, ultrasound, thermal energy, and microwaves).[2]

AET is effective for detecting fatigue and fracture behaviors in metals, composites, plastics, fiberglass, ceramics, concrete, and wood and is commonly used for the detection of faults and/or leaks in pressure vessels, piping systems, and tanks and to monitor welding and corrosion progress.[1, 2, 7] As welds solidify, acoustic emissions are released and detected as a result of internal structural changes; these emissions stop when the welded joint is completely hardened. Corrosion, on the other hand, is detectable since it is a chemical reaction that involves the release of energy. This energy can be detected by AE sensors and as a result, corrosion progress can be tracked.

Publication Date: 
September 1, 2010

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