Tensile mechanical behavior and fracture characteristics of sandstone exposed to freeze-thaw treatment and dynamic loading

Abstract

Rock masses in high-elevation or cold areas are vulnerable to the joint results of freeze-thaw (F-T) action and dynamic loading, it is thus significant to evaluate the tensile mechanical behavior and fracture characteristics of F-T treated rocks under dynamic loading. In this study, based on the split-Hopkinson pressure bar (SHPB) device, the dynamic flattened Brazilian disc (FBD) tests are performed on sandstone to investigate the degradation mechanism of dynamic tensile response and fracture characteristics of rock induced by F-T treatment. Recur to high-speed photography and digital image correlation (DIC) technique, 3D scanning and scanning electron microscope (SEM), the macroscopic and microscopic fracture characteristics of F-T treated sandstone are comprehensively observed and discussed. Experimental results show that the dynamic tensile strength of sandstone constantly decreases with increasing F-T cycles at a specified loading rate. The failure mode of FBD specimen gradually transforms from slash mode to ‘Y’-shaped mode and then to ‘X’-shaped mode with increasing loading rates. 3D scanning results show that the roughness of the central fracture surface of FBD specimen decreases with increasing loading rate or freeze-thaw cycles. Furthermore, both microscopic tensile and shear fracture patterns are observed by SEM, and it is found that the trans-granular (TG) fracture become more prevalent under higher loading rate or higher freeze-thaw cycles. In addition, some hidden connection between microscopic fracture mechanism and macroscopic mechanical properties of F-T treated sandstone is analyzed and discussed.