Analysing mixed mode (I-II) fracturing of concrete discs including chevron and straight-through notch cracks

Abstract

Pre-existing cracks in concrete material and discontinuities in concrete structures are seldom subjected to pure tensile loading (mode I); rather, they are subjected to compressive, shear (mode II) or mixed mode loading (mode I-II). Cracked Chevron Notched Brazilian Disc (CCNBD) and Semi-Circular Brazilian (SCB) specimens including chevron notch and straight-through cracks were used in this research to analyse mixed mode fracturing of concrete. Both the experimental and numerical results showed that the crack initiation angle (theta) was found dependent on the crack inclination angle (beta). Moreover, CCNBD specimens with chevron notch crack geometry was found more suitable than the SCB geometry with straight-through notch crack to analyse mixed mode fracturing behaviour of plain concrete. However, using CCNBD or SCB specimens straight-through notch cracks may be more useful for testing the fracturing properties of coarse-grained concrete as sharp chevron cracks reduce the possible Fracture Process Zone (FPZ) size in front of the notch crack tip. Further analyses showed that the critical crack length is found as 13 mm (dimensionless notch length (alpha) = 0.5). Thus, it is understood that the unstable crack propagation starts between the initial chevron notch crack and final chevron notch crack length and it shows all experiments were done accurately. This outcome would be useful for concrete researches to obtain the yield point by using the relative analysis for finding where the unstable crack propagation starts.