Acoustic emission detection of micro-cracks under high pressure and high temperature in a deformation large-volume apparatus at the endstation P61B, PETRA III.

Abstract

We successfully developed an in situ acoustic emission (AE) detection setup that allows recording of AE waveforms (triggered and streaming) and simultaneous x-ray diffraction and imaging on samples deformed at high pressure and high temperature (HPHT) conditions in the Aster-15 Large Volume Press at the synchrotron beamline station P61B. This high pressure AE detection system is a powerful tool to investigate AE phenomena from the HPHT chamber. Six commercial acoustic sensors, protected by a tungsten carbide support ring on each anvil of the same material, have excellent survivability throughout each successive experiment. By pulsing each sensor in succession, the average wave velocity through the anvils and cell assembly can be determined at any press load. The distance between the sensors is obtained by x-ray radiography and by logging the positions of each hydraulic ram. This provides a basis for accurately locating AE events in the sample. The feasibility of this AE detection setup was confirmed by compression and deformation test runs using several different self-designed AE sources in specialized assemblies. The present setup proves to be extremely efficient and accurate in measuring brittle processes in samples under HPHT. It is now available for applications for beam time and experiments without x rays at P61B. Combined with synchrotron x rays, in situ pressure, temperature, strain rate and stress, and phase changes can be monitored while recording AE activity. We provide a powerful tool to investigate the origin of earthquakes, for example, causing AE emissions due to brittle dehydration reactions or phase transformations in the Earth.