The Influence of Crystal Anisotropy on Failure Stability: Evidence from Multiple-Cracking Noises

Abstract:

Failure of crystals under some external loads often exploit cleavage planes as planes of weakness. The nucleation and extension of “defects” in most cases results in emission of acoustic (phonon) excitations. While X-ray diffraction methods describe the structure of crystals well, the relationship between cleavage planes and unstable failure during cracking of crystals is less well established. In this study, we analyze the polarization patterns of multiple acoustic excitations using functional acoustic network theory. The experiment involves fracturing a small sample placed on a thick aluminum plate using a sharp tip. A load is slowly applied to the testing material until failure inducing the propagation of elastic waves through the aluminum plate. Once the defects’ disturbances have traveled to the opposite side of the plate, they are recorded by a symmetric array of 15 Panametrics V103 sensors. The V103 sensors were calibrated in-situ and showed a roughly flat displacement sensitivity of 73 mV/nm between 20 kHz and 1 MHz. We characterize the emitted noises from Graphite, Gypsum, and Halite and show that microscopic cracking noises carry a signature of plasticity (dislocation growth). We describe the analysis of defects’ slip-direction and growth, inferred from polarization patterns in the weakening phase, and we relate these patterns to individual cleavage plane(s). Further, using multiplex complex networks, we explore the angular tendency of micro-cracking, and estimate the anisotropic nature of micro-defects. Next, we use elasto-dynamic and linear-time-invariant (LTI) systems theory to deconvolve the instrument response and wave propagation functions from the recorded waveform leaving only the source term. Finally, we compare the results from both methods, drawing conclusions about the relationship between crackling noises and plasticity.