Ultrasonic analysis is similar to Acoustic emmission but different in the sence that it monitors much higher frequencies than SPM. I will try to answer your question with an explanation if both Acoustic Emmission and SPM(Shock Pulse Measurement).
SPM (it is one of the wider known ultrasonic evaluations and therefore I am refering to it for purpose of this post) is very good in following sence:
Frequency range: 5,000 Hz - 50,000 Hz
- Surface roughening (lack of lubrication)
- Micro spalls / cracks (over stressing / fatigue)
- Surface indentations (hard contaminant micro pitting)
- SPM measures only ultrasonic data, a basic vibration spectrum can be obtained but it is time consuming.
Do not respond to/identify:
- Lower frequency vibration data (purposely filtered out in the design of SPM accelerometers)such as cracked raceways or mechanical defects: misalignment, unbalance .
(Neither spike energy or shock pulse energy detect below 5,000 Hz / 30,000 cpm)
Accoustic Emmission inspection technique detects elastic waves generated within a test specimen by such mechanisms as plastic deformation, fatigue and fracture. It differs from ultrasonic inspection, which actively probes the structure; acoustic emission listens for emissions from active defects and is very sensitive to defect activity when a structure is loaded beyond its service load in a proof test. This process can detect flaws and imperfections such as the initiation and growth of fatigue cracks in steel structural members; the failure of bonds, fibres and filaments in composite materials and the appearance of potentially hazardous flaws in metal or synthetic pressure vessels.
I did once use accoustic emmission on a prime loader to detect the "load zone" on the slew bearing (3,5m diameter) to allow maintenance to move the bearing "load zone" and extend the service life. This has been a great success but it is costly and was only attempted as an evaluation type of test.
Ultrasonic testers (SPM) is great for maintenance to use it and assist Condition Monitoring technicians in detecting bearings with lubrication related defects and then acting on it.
Hope it helped.