Dynamic Tension Tests of Pre-stressed Rocks

摘要

Over the past few years, significant progress has been made in the characterization of dynamic properties of rocks. Dynamic testing methods for dynamic compressive strength, dynamic tensile strength, and dynamic flexural strength have been developed and improved by the authors among other researchers. In these tests, rock samples are stressfree before being subjected to dynamic loading. However in rock engineering practices such as rock blasting, rocks are under various tectonic stresses. It is thus desirable to understand the effects of pre-stress on the dynamic properties of rocks. In this work, we propose a method to examine the effects of pre-load on the dynamic tension of rocks. We exert static tensile load to the rock samples before applying the dynamic load. The loading device is a modified split Hopkinson pressure bar (SHPB) system. The pre-stress is applied along the bar axis direction through a hydraulic press. For the tensile test, Brazilian disc (BD) method is utilized. A marble from Sichuan, China is studied using the new methods. The results show that the dynamic tensile strength and fracture toughness are clearly loading rate dependent for a given pre-load Furthermore, both rock dynamic mechanical properties exhibit a nonlinear dependence on the pre-load Empirical laws are proposed to relate the dynamic properties to the pre-load.