Experimental and numerical investigations of unified cohesive zone model incorporating monotonic and fatigue damage for low cycle fatigue

The understanding of the fatigue failure process is critical to the safety and reliability of engineering materials and structures. Crack propagation is a critical component of fatigue failure, and the study of the crack propagation behavior is of significant importance. The cyclic cohesive zone model (CCZM) is a useful method to simulate crack propagation behavior. However, existing CCZMs for low cycle fatigue often suffer from high model complexity and unclear damage mechanisms, posing significant challenges in life prediction. To address this limitation, a novel CCZM incorporating a unified traction-separation law is proposed, which considers the coupling influence of monotonic and cyclic fatigue damage on stiffness degradation. To validate the effectiveness of the model, crack propagation tests are conducted on CT specimens. The predicted results and computational accuracy of unified model, conventional models, and experiments are comparatively analyzed, validating the higher accuracy of the proposed model. Crack propagation behavior of the proposed model is also analyzed, providing a mechanism-based interpretation for enhanced performance of the unified model. The results indicate that the proposed model maintains accuracy throughout the entire prediction period. Although the proposed model experiences degradation in predictive fidelity across varying conditions, the prediction results remain within practically acceptable ranges and demonstrate good adaptability. The proposed model effectively captures the degradation of plastic mechanical properties and the interaction between monotonic damage and cyclic fatigue damage under heavy loading. This research provides a new and useful framework for low cycle fatigue crack propagation simulation.