The role of Self-Organized Criticality in elasticity of metallic springs: Observations of a new dissipation regime

We present investigations of low-frequency stochastic deviations from elasticity of Maraging steel springs used in the seismic isolation of the Virgo, Advanced LIGO, and TAMA interferometers. Our studies reveal unexpected facets of elasticity and dissipation in metals, in which a spring is observed to abandon its linear behavior. Various forms of anomalous low-frequency oscillator behavior are characterized, quantified and discussed. These include fluctuations of the Young’s Modulus, hysteretic properties, random walk of equilibrium point and spontaneous de-stabilization events, which occasionally lead to collapse. We made a conjecture that rationalizes all of the anomalies, namely that the observed effects are due to collective interactions of entangling and disentangling dislocations. A phase transition involving switching from a linear to a chaotic regimes is observed —at time scales less than one second— and is shown to be consistent with Self-Organized Criticality (SOC). The threshold frequency to this regime is determined by the material characteristics, as well as by the physical shape and dimensions of flexures.