The interactions between defects are important in the behavior of brittle materials. The micromechanical interactions between a circular hole and a crack under uniaxial compression are investigated in this paper. Experiments of specimens containing a hole and a crack are conducted. Subsequently, Particle Flow Code 2D (PFC2D) is adopted to simulate the fracture behavior. The crack initiation, propagation and coalescence with a hole are investigated. The propagating cracks contain first cracks and secondary cracks. Both first cracks and secondary cracks will disturb the stress field and displacement field. The DEM simulation explains the initiation position of secondary cracks observed in experiments, which is not necessarily located at the crack tips or on crack surfaces, but possibly in the intact part of the specimen at a distance away from the pre-existing crack. The hole will influence the crack initiation stress of the pre-existing crack and attract the propagating cracks. The present research paves the way for using the DEM to simulate the micromechanical interactions between a hole and a crack.
The interactions between a crack and a circular hole in rocks have been studied previously . However, the prior study focused on the fracture phenomena by experiments and did not analyze the inherent mechanism in-depth. Further, the interactions were interpreted by micromechanics ; however, the cracking behavior was ignored. The cracking process around a hole was examined in uniaxial compression tests in some papers and relative mechanism was interpreted [3,4]. Compared with the studies of specimens with a hole, there are much more research of specimens with pre-existing cracks in a brittle material. Wong and Einstein  observed and characterized the fracture behavior in gypsum and Carrara marble specimens containing a single crack under uniaxial compression and identified different crack types based on their geometry and propagation mechanism. Cracking behavior were investigated containing two parallel open flaws experimentally at macroscopic and microscopic level [6,7]. Specimens under the biaxial compression test were also investigated . Not only open flaws, but also closed flaws in a brittle material had been studied . Specimens with 3 and 16 cracks were made and tested in compression tests . However, these investigations did not consider the situation containing both a crack and a hole.