Abstract
The stress-induced microcrack evolution in rock specimens causes a series of physical changes and heterogeneous deformations. Some of these attributes (such as sound, electricity, heat, etc.) have been effectively used to identify the damage state and precursory information of the rock specimens. However, the strain-field heterogeneity has not been investigated previously. In this study, the relationship of the strain-field heterogeneity and damage evolution of three sandstone specimens under the uniaxial compressive load was analyzed statistically. The acoustic emission (AE) and two-dimensional digital image correlation were employed for real-time evaluation of the AE parameters and strain-field heterogeneity. The results showed that the strain-field heterogeneity was closely related to the rock damage that amplified with the applied stress, and exhibited two features; numerical difference and spatial concentration. Subsequently, these two features were characterized by the two proposed heterogeneous quantitative indicators (i.e., the degree and space heterogeneities). Further, their four transition processes were in agreement with the damage stages confirmed by AE parameters: a relatively constant trend; growth with a relatively constant rate; drastic increase trend; and increase with a high rate to maximum value. Moreover, a time sequence chain for damage precursor was built, where the heterogeneous quantitative indicators and AE parameters differed in sensitivity to microcrack development and can be used as a damage warning at the varying magnitude of the external load.
Highlights
Rock damage and catastrophic failure are the key issues in rock engineering, and often cause accidents, such as landslide, rock burst, roof collapse, and dynamic disaster in coal mines [1,2,3,4]
The stress, acoustic emission (AE) parameters, and speckle images of six specimens in time sequence were obtained experimentally, while the artificial speckle fell out at some point/zone of the Damage evaluation and precursor of sandstone under the uniaxial compression specimens during loading, and three specimens with complete surface speckle images were considered in this study, and marked as specimen No 1, No 2, and No 3 (Fig 1)
For all three specimens at the crack closure stage, due to the initial microcrack closure in rock specimens, there were few high-frequency elastic waves emitting from new microcrack, and the AE ring showed a very slight variation with increasing external stress, while the accumulated AE ring increased linearly, and the stress-time curve showed concave growth
Summary
Rock damage and catastrophic failure are the key issues in rock engineering, and often cause accidents, such as landslide, rock burst, roof collapse, and dynamic disaster in coal mines [1,2,3,4]. Rock damage mechanism and fracture process have been widely investigated [4,5,6]. Damage state assessment and precursory information identification remain difficult and have attracted significant attention of researchers. The rock damage process is characterized by the inner microcrack closure, initiation, penetration, and coalescence [7,8,9], accompanied by variations in physical features (such as sound, electricity, heat, etc.) that are associated with. Damage evaluation and precursor of sandstone under the uniaxial compression. The funders had no role in study design,data collection
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