Precursor phenomena of creep failure in disordered materials


David Fernandez-Castellanos

Wednesday, 28.06.2017, 17:00
WW8, Raum 2.018, Dr.-Mack-Str. 77, Fürth

Sub-critical failure is produced when materials are loaded under creep conditions, i.e., over extended periods of time at a constant stress below their short-term strength. Acoustic emissions in form of avalanches of plastic events during the deformation process of disordered materials (wood, foams, porous rocks, metallic glasses etc.) have been experimentally identified as precursors of failure. A mesoscopic elasto-plastic model of plastic flow is presented which coarse-grains individual flow events in discrete yielding elements coupled via stress redistribution. The interplay between the statistics of avalanches, structure stability and strain localization as failure is approached is investigated. We find a thermal activation regime, characterized by the Omori's law of fore-shocks, followed by a mechanical activation regime which eventually leads to a mean-field fiber-bundle-like failure. We study the interplay and evolution of regimes, avalanche statistics, strain localization and structure stability, and establish connections between them which might help predict the approach to catastrophic failure.