Effect of the loading condition on the statistics of crackling noise accompanying the failure of porous rocks

We test the hypothesis that loading conditions affect the statistical
features of crackling noise accompanying the failure of porous rocks by
performing discrete element simulations of the tensile failure of
numerical rock samples and comparing the results to those of compressive
simulations of the same specimens. Cylindrical samples are constructed by
sedimenting randomly sized spherical particles connected by beam elements
representing the cementation of granules. Under a slowly increasing
tensile load, the cohesive contacts between particles break in bursts
whose size fluctuates over a broad range. Close to failure breaking
avalanches are found to localize on a highly stressed region where the
catastrophic avalanche starts and the specimen falls apart into two pieces
along a spanning crack. The fracture plane has a random position and
orientation falling most likely close to the center of the specimen
perpendicular to the load direction. In spite of the strongly different
strengths and spatial structure of damage of tensile and compressive
failure of numerical rocks, our calculations revealed that the size,
energy, and duration of crackling avalanches, and the waiting time between
consecutive events all obey scale free statistics with power law exponents
which agree within the error bars in the two loading cases.