Fig. 3: Mechanisms of kinking during crack advancing in Sample 2.
From: Experimentally measuring weak fracture toughness anisotropy in graphene
a Mechanical energy release rate and fracture toughness plotted as functions of the orientation angle θ with KII/KI = 0 and 0.25. The star marks the direction of kinks to be activated. b Kink angles (the stars) determined by the local values of KII/KI = 0 and R. The direction changes between two armchair edges (±30∘) for R = 0.85, and between the armchair (±30∘) and zigzag edges (0∘) for R = 0.94. c The next-preferred edge cleavage plotted as a function of R and the value of KII/KI at the crack tip, which changes as the crack advances due to the finite size of clamped samples. The solid line is the result obtained with R = 0.94. The open or filled symbols indicate that the crack kinks or not in the next step of advancing. d The sequences of kinking during crack advancing (from left to right), the kink angles, and the changes induced in the ratio KII/KI.
