Development and application of intermediate strain rate triaxial test system with the fully servo-controlled function

Conducting intermediate strain rate experiments is of significance to understand the rate effect of material mechanical characteristics in the full strain rate range. To overcome the drawbacks of current experimental apparatuses, a RMT401 intermediate strain rate triaxial test system with fully digitalized and servo-controlled functions was developed, which consists of three subsystems, i.e., axial loading subsystem with the high-frequency response function, confining pressure subsystem with the fully digitalized servo-controlled function and data acquisition subsystem. Furthermore, the measurement of force and deformation could obtain the dynamic mechanical characteristics of rocks under intermediate strain rate loadings(10-2-100s-1).To investigate the effects of the confining pressure and the strain rate on mechanical characteristics, a series of dynamic triaxial experiments on red sandstone samples under intermediate strain rate loadings were conducted in this study. The results show that the time to failure of thesamples changes from several microseconds to several seconds, and that increasing the strain rate leads to anexponential decrease of the timewhile the increase of the confining pressure induces an increasing trend of the time. The change of the peak strength as a function of the strain rate can be depicted by a power function formula. As for the effect of the confining pressure, the fitting effectsof the peak strength of red sandstone by both Mohr-Coulomb and Hoek-Brown failure criteria are both good, yielding the cohesion of 22.8MPa, the internal friction angle of 38° and the material constant mof12.1. The ultimate failure patterns mainly include two types including single failure plane pattern and double failure plane pattern. As increasing the strain rate and the confining pressure, the failure pattern gradually changes from the single failure plane pattern to the double failure plane pattern. The mean values of the failure angle for the double failure planes are 58.3°and-58.2°, respectively, which are consistent with the calculation values of β=±64°by the Mohr-Coulomb theory. © 2022, Science Press. All right reserved.