Experimental Characterization of Crackling Noise in Microplastic Regime of Bulk Metallic Materials

During plastic flow, metallic materials deform through collective dislocation activities, and exhibits mechanical fluctuation, i.e. crackling noise. Micro-plastic deformation, associated with smaller dislocation activities prior to nominal yielding, has been detected in sub-micron-scale single crystals. Such mechanical noises, arising in metallic materials subjected to nominal elastic stress excitations, can be a relevant problem for instrumentation that requires high strain sensitivity, e.g., gravitational wave detectors like Advanced LIGO. In this study, we endeavor to detect and characterize the mechanical up-converted crackling noise in macroscopic samples. An instrument has been custom-built based on a Michelson interferometer. It has achieved an ultra-high displacement noise resolution of 1e-14 m/sqrt(Hz) in the frequency range of 10~1000 Hz. We resolved a stress-modulated noise in a pair of cm-scale maraging steel spring cantilevers under nominal elastic loading. The characteristics of the noise resemble those of the micro-plastic noise predicted from micro-mechanical simulations developed based on the microscopic experiments.