ABSTRACT:

Acoustic emission monitoring techniques are a powerful tool for analyzing deformation behavior and fracture characteristics of rock samples. Uniaxial compression tests have been carried out on three different types of sandstone for a better understanding of acoustic emission response with respect to rock deformation and damage development. All sandstone samples reveal congruent characteristic acoustic emission patterns which correlated directly with distinct stress-strain stages. However, the acoustic response and development within the individual stages prove to be entirely different due to variations in their microstructure.

1 INTRODUCTION

Acoustic emission testing is used as a type of nondestructive testing technology in the ultrasonic regime. In contrast to conventional ultrasonic procedures AE tools do not actively produce waves but passively detect emissions from acoustic sources in materials which occur with sufficient suddenness to generate acoustic pulses. Mechanical loading like uniaxial compression tests on rock samples can serve as an external stimulus to generate acoustic emissions which result from local rapid stress-releasing events. Acoustic emission techniques became an important tool in rock mechanics where the effect is often referred to as "microseismic activity" (Hardy 2003). The fracture behavior of a rock is known to be governed by the formation, growth and interaction of microcracks. In numerous earlier works that studied the fracture process in connection with acoustic emission the basis for correlations was predominantly the count of the acoustic events. With this paper an attempt is made to characterize the acoustic emission activity more fully by taking the amplitudes of the events into account which particularly mirror the intensity of the acoustic response. Uniaxial compression tests have been carried out on various sandstone samples and AE monitoring was used to define several stages of failure development and the corresponding change in stress-induced strain with respect to variations in the petrography of the rocks.

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