The sound of damage in quartz: a cracking study

N. E. Timms1, Juan. M. Reyes1, D. Collins1, K. Mair2 and D. J. Prior1

1Department of Earth Sciences, University of Liverpool, Liverpool, L69 3GP, UK

2Lassonde Institute, University of Toronto, 170 College Street,

Toronto, M5S 3ES, Canada

n.e.timms@liverpool.ac.uk

In order to understand better the dynamic process of fracture propagation, this study uses acoustic emission techniques to monitor precisely microcracking and fracture development in single crystals of quartz during laboratory indentation experiments. Blunt (ball bearing) and sharp indenter tips were used to induce damage perpendicular to the c-axis in samples cut from natural single crystals of quartz in experiments at atmospheric pressures and temperature (Fig 1a). Acoustic emission (AE) is the ultrasonic elastic wave energy released when a microcrack occurs, and is analogous to a microscale earthquake. AE events were recorded during the experiments using radial arrays of twelve sensors (transducers) to monitor the evolution of damage within samples. As with global seismology, the source location, magnitude and mechanism of these events has been resolved and visualized in 3-D by processing AE waveforms collected at a number of sensors (Fig. 1b).

The fracture mechanics of indentation experiments are well understood, and sets of Mode I (opening) fractures are expected to form with a predictable median-radial geometry from the indenter tip. The preliminary AE results presented reveal the spatial and temporal evolution of damage in single crystal quartz during an experiment that resulted in the critical failure. Interpretations from AE are compared with the predicted mechanics and geometry of fracture development during indentation experiments, and current AE techniques are evaluated.

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Fig. 1 (a) Photos of the experiment setup. Two-tier radial arrays of pinducers positioned at the centre of each vertical face. A blunt indenter (ball bearing) mounted in steel cylinder used to create damage in the sample is shown. (b) Acoustic emission source locations from indenter experiment.