Fracture Behavior of Twin Boundaries in Pure Titanium Under Biaxial Loading

Six different twin boundary interface models were constructed by molecular dynamics simulations to investigate the effect of biaxial load ratio on the fracture behavior of titanium twin boundaries. Analysis of microstructural evolution indicates that twin boundaries exhibit a dual role during crack propagation. On one hand, they serve as preferential sites for void nucleation, promoting crack propagation along the twin boundary; on the other hand, they provide favorable sites for dislocation nucleation, inducing local plastic deformation at the crack tip, altering the crack path, and thereby hindering crack propagation. The crack propagation behavior in the (1¯011) and (1¯013) twin boundary models shows evident asymmetry: the crack on the left side mainly propagates through the void nucleation mechanism and exhibits a faster growth rate, while the right-side twin boundary inhibits crack propagation by favoring dislocation nucleation. In contrast, the crack propagation behavior in the (1¯012), (2¯111), (2¯112) and (2¯114) twin boundary models is largely symmetric on both sides, showing no significant difference in propagation rate. Stress field analysis further reveals that the differences in crack propagation behavior among the various twin boundary models mainly originate from the disparity in dislocation activity on both sides of the crack, resulting in different levels of stress concentration at the crack tip. When void nucleation occurs at the twin boundary interface, the stress concentration between the main crack and the void intensifies, promoting their coalescence and further propagation. Meanwhile, with an increase in biaxial load ratio, the stress concentration at the crack tip becomes more pronounced, further accelerating crack propagation.