Dislocation movement and hysteresis in Maraging blades

Abstract

All seismic isolation systems developed for gravitational-wave interferometric detectors, such as LIGO, Virgo and TAMA, make use of Maraging steel blades. The dissipation properties of these blades have been studied at low frequencies, by using a geometric anti-spring (GAS) filter, which allowed the exploration of resonant frequencies below 100 mHz. At this frequency an anomalous transfer function was observed in the GAS filter: this is one of several motivations for this work. The many unexpected effects observed and measured are explainable by the collective movement of dislocations inside the material described with the statistic of self-organised criticality. At low frequencies, below 200 mHz, the dissipation mechanism can subtract elasticity from the system even leading to sudden collapse. While Young's modulus is weaker, excess dissipation is observed. At higher frequencies the applied stress is probably too fast to allow the full growth of dislocation avalanches, and less losses are observed, thus explaining the higher Q-factor in this frequency range. The domino effect that leads to the release of entangled dislocations allows the understanding of the random walk of the Virgo and TAMA inverted pendula, the anomalous GAS filter transfer function as well as the loss of predictability of the ring-down decay in the LIGO seismic attenuation system inverted pendula.

Anomalous low frequency dissipation processes in metal springs

“…For lack of time only some of our experimental observations were illustrated in the conference presentation, and for lack of space even fewer of them are reported here, please refer to [29] and to the forthcoming longer paper [30] for more detail.…”

“…The Quality factor of GAS filters was observed to increase dramatically above a threshold of 0.2 Hz [29,30]. Below 0.2 Hz it behaves quadratically, as expected from time independent (completely developed avalanches) dissipation processes.…”

Improving the sensitivity of future GW observatories in the 1–10 Hz band: Newtonian and seismic noise

“…The evidence points towards a phase transition from dissipation dominated by movement of individual dislocations, resulting in viscous-like behavior, to collective dislocation activities, in a Self Organized Criticality state, resulting in avalanche dominated dissipation, spontaneous equilibrium point changes, and sudden temporary drops of the Young's modulus [25,26]. This anomalous behavior was observed to reduce the effectiveness of harmonic oscillators as vibration filters [27].…”