Investigation on fracture behavior of sandstone with multiple grain sizes at different strain rates based on acoustic emission spatial localization

In order to reveal the fracture mechanism of rock due to the scale effect of grain size and strain rate, sandstone specimens with different grain size ranges were taken as the research object, and the fracture behavior at different strain rates ranging from 10^–5 s⁻¹ to 10^–2 s⁻¹ was analyzed from aspects such as strength, failure, crack and spatial damage. Experimental results and analysis show that for sandstone specimens with different grain sizes from fine to coarse, strength increased by 2.28 MPa, 2.38 MPa, 2.23 MPa and 3.58 MPa for every 10 times increase in strain rate, respectively, indicating that the larger the grain size of sandstone, the greater the effect of strain rate on its strength. As the strain rate and grain size increased, the failure mode transitioned from a single inclined shape into the complex cross distribution, more secondary cracks developed, and fragmentation increased. The larger the proportion of large-sized grains in sandstone, the more sensitive the cracking response was to strain rate. In terms of acoustic emission three-dimensional localization of internal damage in sandstone specimens, at lower strain rate of 10^–5 s⁻¹ and fine grain size, the fractal dimension of spatial damage was the highest, which is 3.444 at peak stress, while at higher strain rate of 10^–2 s⁻¹ and coarse grain size, the fractal dimension was only 2.33, which decreased by 32.3%, reflecting that with the increase of strain rate, the damage of coarse sandstone specimen tended to be more and more concentrated.