AE - ISO 22096 - The Alternative Approach

AE - Acoustic Emissions (ISO 22096) - monitoring the energy from impact and stress - monitor by transducer with direct interpretation

Acoustic Emissions are one facet of vibration at frequencies much higher than are monitored by traditional vibration techniques; frequencies well above the audio. You are looking for high frequency signals from cracks or impact rather than repetitive synchronous movement from vibration.  It is a purely passive technique unlike ultrasonic inspection in which ultrasound is transmitted and detected through objects.

Acoustic emissions are independent of transducer orientation, machinery speed or rolling element configuration. As a result of these properties, it is possible to diagnose incipient machinery damage prior to undertaking any sophisticated or lengthy diagnosis.

Much of what we now refer to as Acoustic Emissions (AE) was developed in the 1970-80's by the aircraft industry, specifically Boeing and Rolls Royce. In this application there was little time for sophisticated analysis and a high incentive to detect the very early onset of machinery fault conditions. In-flight engine failure is best avoided!

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Acoustic Emission - a side note:

Many materials make an audible noise when they fail (paper, wood, cloth etc); the word 'crack' is onomatopoeic ("sounds like") being based on a description of a sound that material makes as it fails. 60 years ago, Josef Kaiser showed that metals also make very low amplitude sound as they fail. These signals are best dectected at high frequencies.

AE technology was developed to address this requirement using low noise signal conditioning and novel signal processing techniques available from Holroyd.

AE is widely used in materials research programs, for CM of machinery and the assessment of structural integrity. It has a long history going back to the 1960's when research at Boeing identified that by detecting signals with sensors resonant at high frequency (up to 90kHz) it was possible to clearly see incipient aero engine failure.

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Increasingly the Acoustic Emission (AE) technique is being seen as offering a quicker and simpler first step in CM in comparison to VA. AE has application to a wide range of machine types and structural configurations.  AE retains a comparable the high sensitivity to faults detectable by VA but without its associated complexities of configuration and data processing.

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Note: technologies used by Holroyd were initially developed by Advanced Research Labs of Rolls Royce Derby before being spun off as an independent company in 1991.  Trevor Holroyd successfully developed the company, finally becoming part of the Kittiwake group ion 2011.

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