Abstract：Crack initiation and propagation in structural components under complex mixed-mode loading conditions are highly sensitive to geometric irregularities. However, existing fracture studies predominantly focus on sharp-tip cracks, while the influence of non-tip geometric features on fracture response is often overlooked. Addressing this limitation is therefore essential for accurate damage tolerance evaluation and structural integrity assessment. This study investigates a lip-shaped crack configuration that incorporates both tip singularity and an outward convex non-tip geometry. Within a linear elastic fracture mechanics framework supplemented by conformal mapping, an I–II mixed-mode crack model is established, and theoretical predictions of the crack-tip energy release rate and fracture initiation angle are obtained based on the maximum energy release rate criterion. By varying the crack inclination angle to control the loading mode and characterizing the non-tip geometry through the width-to-length ratio, the effects of geometric parameters are systematically analyzed. Furthermore, crack-growth simulations, combined with elastoplastic finite element analyses of the evolving plastic zone and stress-field redistribution, are conducted to elucidate the mechanisms by which non-tip geometry influences crack failure behavior. Results indicate that the outward convex non-tip geometry reduces tip stress concentration, leading to a decrease in energy release rate and a deflection of the crack initiation angle. Changes in loading mode cause the stress concentration to shift from the crack tip to the non-tip region, giving rise to two distinct failure patterns—tip-dominated and non-tip-dominated—and a critical inclination angle governed solely by the width-to-length ratio is identified. This study highlights the essential role of non-tip geometry in mixed-mode fracture and provides theoretical guidance for structural failure prediction and damage-tolerant design. The findings offer practical value for safety-critical structures subjected to combined loading, particularly in aerospace, transportation, and advanced manufacturing applications.
2026, Vol. 47 
