LIGO Document T1500427-v1

Experimental Study of Crackling Noise as Micro-mechanics of Flow

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T - Technical notes
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In crystalline materials, dislocation dynamics can generate strain noise upon being applied by rapidly-changing, oscillatory stress in the elastic regime. This so-called crackling noise may arise inside the maraging steel blades of the quadruple pendulum that serve as the suspension system of the Advanced LIGO. The study focuses on the nature and origin of crackling noise in metals. Monocrystalline copper nanopillars are used as model systems for this purpose. Sinusoidal load perturbation to quasi-static compressive loading were applied to copper nanopillars with different system sizes and the loss and storage moduli were measured as function of static stress. Amorphous fused silica nanopillars were also studied as to eliminate non-dislocation-dynamics effect. It was found that the loss moduli, which characterize the energy dissipation mechanism of the system, are not constant throughout the static, elastic stress range in copper; and it was also found that the size of the copper nanopillars also affects their dynamic mechanical behavior. This evidence should confirm the elastic dislocation mechanics and hence the deviation from the perfectly linear elastic picture.
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SURF 15 final report

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