Degradation-Based Reliability Analysis of Plunger-Pair Structure via Distribution Interference Theory

High-pressure plunger-cylinder pairs in axial piston pumps are prone to brittle failure due to local contact stress, time-dependent material degradation, and cyclic loading, which complicates long-term reliability assessment. To address this issue, an integrated reliability analysis framework is proposed for SiC ceramic plunger pairs, combining local stress identification, strength degradation, and fatigue damage modeling. A three-dimensional finite element model identifies the critical contact region, where the maximum equivalent stress reaches 1291.5 MPa. An exponential strength degradation model and a time-variant stress-strength interference approach based on lognormal stress and Weibull strength distributions are adopted, with 105 Monte Carlo simulations used to evaluate failure probability. The results indicate that although the initial static reliability is close to 1.0, it decreases nonlinearly with service time, reaching 0.9663 at 10,000 h under moderate degradation. In addition, fatigue reliability is assessed by integrating the S-N curve of SiC with a cumulative damage model, enabling reliability-cycle curve construction and fatigue life prediction. The proposed method provides a quantitative framework for static, degradation-driven, and fatigue reliability assessment of high-pressure ceramic tribological structures.