Peridynamic Modeling of Fatigue Crack Initiation and Interaction in Modified Compact Tension Specimens

A state-based peridynamic (PD) fatigue framework is formulated for crack initiation, propagation, and interaction in Modified Compact Tension (MCT) specimens. By replacing local PDEs with a nonlocal integral model, discontinuities are handled without tip tracking or remeshing. Pin–fixture loading is represented via a nonlocal traction/contact mapping; fatigue damage evolves through a cyclic bond-degradation law consistent with S–N/Paris behavior. Driving forces are interpreted using a 3D PD J-integration and an energy-based bond-failure criterion, with quasi-static response advanced by adaptive dynamic relaxation. Calibration uses elastic/fracture properties referenced to baseline CT data, and validation combines finite-element benchmarks with targeted MCT tests recording load–displacement hysteresis, crack paths, and da/dN-∆K/∆J, trends across multiple ratios. The framework recovers nucleation sites without pre-seeded flaws, predicts mesh-insensitive growth rates and paths, and captures deflection, shielding/amplification, and coalescence. Quantitatively, path-angle discrepancies remain within a few percent, and life predictions fall within ~10% of experiments. Parametric studies on notch radius, ligament width, pin-hole diameter/offset, thickness/side grooves, stress ratio, and load amplitude establish how constraint and geometry govern initiation life, path stability, interaction distance, and failure mode. The result is a reproducible, mesh-independent route to fatigue-resistant MCT design and service-relevant assessment of metallic structures.