Deep in-situ core-preserved coring: A novel full-cycle crack propagation model of the pressure storage chamber

The pressure storage chamber (PSC) for deep in-situ core-preserved coring (ICP-Coring) serves as the key component for in-situ coring and preserving of deep core samples. Subject to long-term in-situ high-temperature and high-pressure loads during service, the chamber surface is prone to fatigue crack initiation and progressive propagation, which may eventually lead to structural failure. To ensure its operational safety, gaining a deep insight into the full-cycle evolution process of surface crack propagation in the PSC is critical. Since existing formulations cannot adequately analyze multi-factor coupling effects, this study develops a full-cycle crack size propagation iterative model (FCS-PI model) for PSC surface cracks to address this limitation. This model incorporates a correction mechanism accounting for the coupled effects of stress states, material microstructures, and environmental factors, enabling the quantitative characterization of the full life cycle of crack propagation in PSC. The universality and accuracy of the proposed iterative model are validated by comparing crack propagation theory calculations with practical engineering cases. The FCS-PI model accurately predicts the fatigue crack growth rate (FCGR), yielding a sum of squared error (SSE) of 6.05 × 10^-6 and an average deviation of only 1 % in predicting the critical cycle number (N_c). Furthermore, it demonstrates the smallest crack size deviations—2.2 mm in depth and 6.9 mm in length—outperforming the NASGRO, Forman, and Walker models. The model developed in this study effectively characterizes the full-cycle crack propagation of PSC, providing a more accurate approach for the safety assessment of surface crack-induced failure under high-temperature and high-pressure loading.