A Peridynamic Fatigue Model for Thin‐Shell Structures Based on Microbeam Bonds

Thin‐shell structures subjected to cyclic loading exhibit strong coupling among in‐plane and out‐of‐plane deformation modes, which renders fatigue life assessment particularly challenging. Existing peridynamic (PD) fatigue formulations predominantly account for fatigue damage driven by axial bond deformation and are therefore not well suited for thin‐shell applications. To address this deficiency, this study introduces a microbeam bond‐based PD shell fatigue model. By employing the bond energy release rate range as a unified scalar fatigue‐driving parameter, the contributions of axial, bending, and torsional deformation modes are inherently incorporated without the need for empirical weighting factors. Building on this framework, phase‐dependent evolution equations are developed separately for the crack initiation and crack propagation stages. The capability of the proposed approach to predict crack trajectories and fatigue life is demonstrated through several numerical examples, with particular emphasis on a cylindrical shell benchmark containing circumferential and inclined cracks, in which local bending and torsional deformations at the crack tip are strongly coupled. Moreover, comparison with a conventional axial deformation‐driven PD fatigue model shows that neglecting bending and torsion leads to a substantial underestimation of the crack growth rate. These findings underscore the critical importance of accounting for coupled axial, bending, and torsional deformations and confirm the predictive capability and suitability of the proposed model for fatigue analysis of thin‐shell structures subjected to multiaxial loading.