ABSTRACT
However, the above mentioned researches on the crack propagation of brittle solids containing single pore were all based on static or quasi-static loading. The dynamic strength and the corresponding crack propagation behavior for single pore rock specimen under impact loading have not been involved. The present study aims to observe the crack initiation, propagation and coalescence process and its failure modes for single pore rock specimen under impact loading by using high speed camera in Split Hopkinson Pressure Bar (SHPB) tests. The SHPB appartus have been used to obtain the complete stress-strain curves and to measure the dynamic properties for intact rock specimens (Zhou et al. 2010, Zhang & Zhao 2014). The dynamic strength and crack propagation velocity of single pore marble specimen were
1 INTRODUCTION
The crack behavior around single hole rock specimen has been extensively studied under static or quasi-static loading by both experimental and numerical methods. For example, Dyskin et al. (2003) studied the influence of shape and locations of initial 3-D cracks on their growth in uniaxial compression. Klein & Reuschle (2004) proposed a pore crack model to compare theoretical results with laboratory data obtained on four sandstones which were tested under conventional triaxial compression conditions with conning pressures between 0 and 35 MPa. The comparison showed that by using a small number of parameters (pore size, pore density, fracture toughness, and elastic moduli), the model was able to predict the rock behavior during the compressive tests and the stress level at rupture was consistent with the observations in a quite accurate way when the micro structural parameters were introduced. Tang et al. (2005) used MFPA2D (material failure process analysis) to numerically study the mechanisms of compression-induced axial splitting cracks for heterogeneous solids containing pre-existing single, triple and multi-pore-like aws. Various parameters, such as the hole diameter, the specimen width, and the geometrical arrangement of hole locations, were quantitatively used to characterize the crack growth process. Ma et al. (2006) investigated the failure process of a plate marble specimen containing a central hole by using specially designed deformation field inspection system (Geo-DSCM system), which showed that the deformation field was localized on the sections in tension at the early stage of loading. Wong et al. (2006) carried out a series of physical and numerical tests under uniaxial compression on samples containing a single hole
determined in the present study. Two types of pore shapes have been used, including round shape and oval shape in rectangular marble specimens. For round pore shape specimens, three different circle diameters were studied. For oval pore shape specimens, the ellipticity (ρ) and the angle (θ) between the loading direction and the long axes have been considered for the rock crack behavior. Moreover, a method to test the average dynamic crack propagation velocity was proposed. The strain rate of the present SHPB tests was about 40-50 s−1. This paper extended the rock crack behavior study from low strain rate (10−5-10−1 s−1) to high strain rate (101-102 s−1).
