Crack propagation processes of rock-like material containing a single pre-existing surface flaw under uniaxial compression are numerically investigated by the Realistic Failure Process Analysis(RFPA3D) code. Heterogeneity feature of rock sample is simulated by Weibull distribution. Numerical simulated results indicate that three types of cracks emerged from the surface flaw under uniaxial compression, namely wing cracks, anti-wing cracks and petal cracks. Anti-wing crack is the primary crack and developed by the growth of tensile cracks from the surface of the sample extending into the interior of the sample. The heterogeneity consideration in the RFPA3D code result in unsmooth crack path and unsymmetrical crack growth of the two antiwing cracks at the left and right lateral of pre-existing flaw, which are recognized to be realistic for heterogeneous materials. Numerical simulations in this studies show the failure process very clearly including the growth of wing cracks, anti-wing cracks, and petal cracks, especially the inside crack growth process which is difficult to observe in the conventional experiment. It provides a better understanding on crack development around a surface flaw.
Extensive research has been done on crack propagation in different brittle or quasi-brittle materials with a single pre-existing flaw under uniaxial compression loading. To investigate the growth mechanism of these cracks, plenty of studies are documented by laboratory tests[1–6]. And found that primary cracks which also named wing cracks appear first, and they are tensile cracks which start at the tips of the flaw and propagate in a curvilinear path as the loading is increased. Generally, wing cracks grow in a stable manner since an increase in load is necessary to lengthen the cracks and align with the direction of the most compressive load[1]. The secondary cracks appear later and propagate in coplanar of the flaw or with an inclination similar to the wing cracks but in the opposite direction. It can be seen from the previous studies about flaw movement that they much focused on the cracks initiation and propagation of simplified 2- D or internal 3-D pre-existing flaw, ignoring a type of flaw which penetrates into the sample a finite depth which named surface flaw(see Fig.2). Recent experiments of crack growth with a single pre-existing surface flaw under uniaxial compression showed that a new type of crack quite obviously occurred in the opposite direction of wing cracks, which named anti-wing cracks[[7–9]]. And it is found that the depth of the flaw significantly influence the crack pattern, i.e.
The heterogeneity of rock is regard as the source of nonlinear mechanical behavior of rock. And failures in heterogeneous material not only occurred at the high-stress site, but also start at the weaker locations due to the presence of micro-cracks and grain boundaries.
