Experimental investigation on the elastic-plastic failure evolution mechanism of high-temperature hot dry rocks using combined monitoring of acoustic emission and digital image correlation

Abstract

Hot dry rock (HDR) is a resource-rich, renewable, and clean energy source characterized by its great depth, high temperature, and high geostress. In underground environments, rocks are prone to significant elastoplastic deformation. However, research on the elastoplastic deformation, failure, and fracture mechanisms of HDR under high-temperature conditions remains limited. This study employs Acoustic Emission (AE) and Digital Image Correlation (DIC) as combined monitoring methods to conduct fracture toughness experiments on granite semicircular bend (SCB) specimens under high-temperature conditions. We obtained load-displacement curves, AE parameters, and strain fields near crack tips at various temperatures to reveal the mechanical mechanisms of elastic-plastic failure evolution in HDR. Experimental results indicate that both the peak load and fracture toughness of granite specimens decrease gradually with increasing temperature, with the peak load at 600 °C being 69.1 % lower than at 25 °C. DIC results show that the fracture process zone at the crack tip enlarges with rising temperature, while strain and crack width values decrease. Additionally, the attenuation of AE b-values at peak load relative to the initial loading phase increases, and the proportion of shear failure increases, with a maximum increase of up to 42.3 %. As temperature rises, the failure mechanism of artificial fractures transitions from brittle macroscopic fractures to plastic fine fractures. When the temperature exceeds 400 °C, plastic failure becomes more pronounced, with numerous microcracks forming and further coalescing into complex main cracks. This study provides important theoretical support for the efficient development of deep geothermal resources.