Abstract
Detection and location of the source of acoustic emission in a thin aluminum panel is demonstrated using a multichannel fiber laser sensor system. Acoustic emission generated by a crack in an aluminum panel used as a test coupon in an accelerated fatigue experiment is detected and the location of the crack identified. Acoustic emission is detected over a bandwidth of around 0.5 MHz from a serially multiplexed array of four laser sensors and compared with measurements taken from four piezo-electric sensors co-located with the fiber laser sensors. The location of the crack is determined by first estimating time difference of arrival of signals at each sensor using a novel algorithm based on the cumulative distribution transform method with hyperbolic positioning. The fiber laser sensor is shown to match the signal-to-noise ratio of the industry standard (Mistras S9225) piezo-electric acoustic emission sensor.
Highlights
Acoustic emission (AE) is a release of mechanical energy that occurs when a material undergoes an irreversible change in its internal structure
The location of the crack is determined by first estimating time difference of arrival of signals at each sensor using a novel algorithm based on the cumulative distribution transform method with hyperbolic positioning
The source location of the AE event is determined by first estimating the time difference of arrival (TDOA) via cumulative distribution transform (CDT) and using those estimates to perform source localization by the procedure described in Ref. 5
Summary
Acoustic emission (AE) is a release of mechanical energy that occurs when a material undergoes an irreversible change in its internal structure. Bragg grating-based fiber optic sensors provide a number of benefits over existing piezo-electric sensors These include extremely small sensor size (a single optical fiber), immunity to electromagnetic interference, resistance to sensor corrosion, wide area coverage with multi-point measurements, and the ability to be retrofitted onto the surface of existing structures using standard bonding techniques. A common technique involves tuning a probe laser to a steep band edge of a Bragg grating, external Fabry–Perot cavity, or resonant feature of an optical cavity such as a phase shifted Bragg grating.9 These implementations require a probe laser for each sensor, and the probe lasers must have extremely high frequency stability to achieve measurement resolutions comparable to the fiber laser sensors.. The cumulative distribution transform is presented and used to identify the crack location
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