A phase field fracture model for helical fiber-reinforced composites

Several biological and biomimetic materials are reinforced with diverse helical fibers, achieving tension–torsion coupling (TTC) and crack-bridging effects, which have significant influences on the fracture behaviors. To address the impact of helical fibers on crack propagation, we propose a novel unified phase-field framework that explicitly incorporates the TTC and anisotropy coefficients. Compared with classical fracture mechanics models based on the maximum energy release rate criterion and the micropolar cohesive zone model, the proposed framework yields predictions that are closer to experimental observations regarding critical failure loads and crack deflection paths. Theoretical analyses of a one-dimensional uniaxial tension bar reveal that the macroscopic stiffness and ultimate load of helical fiber-reinforced composites decrease monotonically as the TTC coefficient increases. Phase-field simulations demonstrate that the crack deflection angle is highly sensitive to the TTC effect under mixed-mode loading conditions. Furthermore, the anisotropy coefficient significantly influences the fracture toughness, critical energy release rate, and ultimate load of these composites. This work provides a robust predictive methodology for crack propagation in helical fiber-reinforced composites.