ABSTRACT:

Crack propagating at the rock-tool interface is of paramount importance while designing an excavation process. The present study aims to analyze the behavior of a crack propagating in brittle material like sandstone rock in comparison to ductile material like Aluminum alloy. A three-dimensional finite element model of split Hopkinson pressure bar setup was developed with a pre-cracked dog bone-shaped specimen to understand the behavior of crack using two non-linear strain rate dependent constitutive models, i.e., the Johnson-Cook model and Drucker Prager model. The numerical results were first validated with the experimental ones and then the effect of the crack parallel to the loading direction was studied under dynamic tensile loading conditions. The results show that the peak stress values are more at the center and tip of the crack for aluminum alloy than for the intact aluminum alloy specimens. However, it is completely opposite for sandstone rock.

INTRODUCTION

Construction of tunnels, caverns, development of galleries for extraction of minerals from a mine and various underground structures has always been a challenge due to complex geologic formations of varying hard and soft rock mass. Generally, from the design point of view in order to determine the stability of these subsurface infrastructures and create safer conditions, the overburden load of rock and soil mass is considered. These loads are assumed to be static in nature generating strain rate of 10−5 to 10−3 per second. But apart from that, there can also be external hazards in form of earthquake, drilling and blasting, terrorist attacks, missile attacks to name a few which are transient in nature. The strain rates caused by earthquakes may vary from 1/s to 100/s and those caused by blasts may vary from 102/s to 104/s. Figure 1 shows the approximate ranges of the expected strain rates achieved through various experimental techniques.

Such high rates of induced strain may have an impact on the rigidity and strength of rocks. Therefore, it is essential to characterize the host rock under both static and dynamic loading conditions for the resilient design of structures embedded in rock strata.

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