Abstract
In order to investigate the dynamic stress balance of different configurations of rock specimens, three-dimensional finite element models of SHPB were established. Five types of configuration disc specimens with a diameter of 75 mm and a thickness of 30 mm were impacted at a speed of 5 m/s using a special-shaped bullet. The propagation laws of stress wave on the contact surface of the specimen-bar and the inside of the specimen were analyzed, and the time history of the stress balance factors at different positions of the specimen was obtained. The results show that the amplitudes of the transmitted waves corresponding to the five types of disc specimens with different configurations have obvious differences, and the stress propagation in the specimen has three-dimensional characteristics. According to the ease of achieving stress balance, the five configuration specimens are ordered by notched semicircular bending disc, flattened Brazilian disc, cracked straight-through flattened Brazilian disc, Brazilian disc, and cracked straight-through Brazilian disc specimen. Among them, only the first three configurations of the specimen reached the stress balance. The dynamic stress balance is affected by the disc loading mode, end contact conditions, the presence of prefabricated cracks, and disc thickness. In addition, as the disc loading end is a processed platform, it is beneficial to achieve stress balance. Prefabricated cracks are not conducive to achieving stress balance. The loading method of the notched semicircular bending disc is more conducive to achieving stress balance. This research has a certain guiding significance for selecting suitable specimen configuration and research methods to carry out rock dynamic fracture experiments.
Highlights
With the gradual increase in coal mining depth, the stress level of coal and rock mass increases geological conditions such as gas and hydrology have become more complex [1,2,3], and dynamic disasters such as rock bursts, rock bursts, and mining disturbances have become more prominent [4,5,6]
Li et al [32] applied experimental and numerical simulation methods to show that the stress balance can be achieved inside the flattened Brazilian disc (FBD) with a diameter of 50 mm, but severe stress unevenness occurs at both ends of the specimen
In view of this, according to the improved Split Hopkinson Pressure Bar (SHPB) system proposed by ISRM [44], the model is used to generate a semisinusoidal stress wave by using a special-shaped bullet impact to eliminate the influence of the dispersion effect on the pressure bar
Summary
With the gradual increase in coal mining depth, the stress level of coal and rock mass increases geological conditions such as gas and hydrology have become more complex [1,2,3], and dynamic disasters such as rock bursts, rock bursts, and mining disturbances have become more prominent [4,5,6]. Ping et al [31] conducted a SHPB experiment with 50 mm diameter sandstone BD specimens and obtained a trapezoidal stress wave with a rising edge of about 50 μs, which was considered to be able to achieve stress balance before the specimen is destroyed. Li et al [32] applied experimental and numerical simulation methods to show that the stress balance can be achieved inside the FBD with a diameter of 50 mm, but severe stress unevenness occurs at both ends of the specimen. The contact area between the disc specimen and the pressure bar is small, and severe stress concentration occurs at the end of the specimen, and the two-dimensional effect produced is not negligible [40], this indirect method does not necessarily prove the true balance of the specimen. The research has certain guiding significance for SHPB testing of rock specimens with special structure
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
