LIGO Document T1600382-v2

Acoustic Emissions in Metals

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T - Technical notes
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Crackling noise occurs when a system responds to slowly changing external conditions with discrete energy events at higher frequencies. This effect may be significant in the maraging steel blades used in the suspension system of Advanced LIGO. Vertical displacement noise caused by crackling events could couple with horizontal displacement noise along the path of the interferometer, influencing Advanced LIGO’s sensitivity. The goal of this project is to continue a previous experiment aimed at directly detecting energy released from crackling events in the form of acoustic waves. This consists initially of calibrating the output of ultrasonic acoustic emission microphones in terms of energy released into the blades in a crackling event. The microphones are calibrated via a simple ball drop experiment to compare the known energy of a system to the energy in the microphones. Additionally, the microphones are used to search for crackling events in loaded maraging steel blades modulated with a drive of variable frequencies and amplitudes. The ultimate goal of the project is to find an upper limit on crackling noise, even if no crackling events are directly detected.
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