ACCELERATION AND LOCALIZATION OF SUBCRITICAL CRACK GROWTH IN A NATURAL COMPOSITE MATERIAL S. Lennartz-Sassinek et al. Presented by Yingdi Luo for Ge277, 2016

EXPERIMENT SETTING  Cylindrical sandstone  L = 105mm D =50mm  Tri-axial loading  Pore pressure 10.5 MPa  Confining pressure 50.5 MPa  Constant strain rate 1.7e-6 /s  Acoustic Emissions (AE) signals recorded by 18+2 Piezoelectric Transducer (PZT), sampling rate 10 MHz  25,000 events  Hypocenter location uncertainty ± 1mm  Temporal wave velocity change corrected

STATISTICAL ANALYSIS OF THE AE RECORD SPATIAL LOCALIZATION (a) Histogram of events with respect to final failure plane (b) Hypocenter locations Redline: damage zone (±2.5mm from failure plane)

Inter-event times Brown: 50-events average Blue: exponential fit Differential stress EVOLUTION OF EXPERIMENTAL PARAMETERS all events in damage zone Average spatial separation

STATISTICAL PROPERTIES OF SCALED INTEREVENT TIME  Uncorrelated random process

STATISTICAL PROPERTIES OF SCALED INTEREVENT TIME

STATISTICS OF EVENT ACCUMULATION  Uncorrelated random process X Exponential decrease

STATISTICS OF AE AMPLITUDES G-R b ~ 0.7, No significant change of b all events in damage zone

STATISTICS OF EVENT ACCUMULATION Time derivative => reversed Omori-Law

DAMAGE ACCELERATION, SPATIAL CLUSTERING, AND CRACK GROWTH Plan view of the final failure plane. (a) Events 500–1 500 (b) Events 1 500–2 500 (c) Events 5 000–6 000 (d) Events 6 000–7 000 (e) Events 6 500– Circles: m/ ≤1.1 Squares: 1.1 ≤2.2 Triangles: m/ > 2.2. all events in damage zone

Conjugate planes complicate the study Events accumulation following reversed Omori-Law Amplitude-frequency following G-R relation with b ~ 0.7 TAKE HOME MESSAGES