Development of fracture in bending experiments

Three point bending tests were conducted with acoustic emission (AE) monitoring on specimens with and without notches of two different sizes. To investigate mixed mode fracture, beam tests with off-center notches were studied as well. The experiments indicated that around peak stress, the AE localized to form an intrinsic process zone. The discrete element technique was used to mimic fracture in bending. The numerical model was made of rigid circular particles that interact through normal and shear springs. These particles were glued to each other using normal and shear bonds. A microcrack formed in tension or shear was simulated by breakage of the bond between two particles in contact. The simulated material was calibrated for elastic properties, unconfined compressive strength and bending tensile strength. In the model, slightly overlapped particles were used to obtain a more realistic ratio of compressive to tensile strength. The beam strength with and without notches and the fracture path were studied in the numerical experiments. Two models for normal bond failure were considered, namely an instantaneous normal bond breakage and normal breakage with softening models. The numerical results obtained were compared with those from laboratory experiments.