Effect of external loading conditions on crack propagation in anisotropic materials

Anisotropic materials are widely found in nature and engineering, and their crack paths often exhibit complex morphologies such as deflection, kinking, and zig-zag propagation. The formation of these patterns is governed not only by the anisotropic fracture toughness but also by the external loading, whose influence on the crack path is still not fully understood. In this work, we analysed crack propagation in a strongly anisotropic plate with an edge crack under three external loading modes: uniaxial tension (UT), a stationary K-field boundary (Stat-KB), and a surfing K-field boundary (Surf-KB) that moves with the nominal crack tip. A strongly anisotropic high-order phase-field model was used to simulate crack propagation, with the anisotropy degree controlled by a scalar χ. The results show that UT gives an almost straight crack, and Stat-KB leads to a single kinked but non-stationary path, whereas Surf-KB produces a quasi-steady zig-zag path whose kink angle and amplitude increase with χ.