With the development of the industrial level, the service-oriented transformation of the manufacturing industry has become a new growth point for the interests of the manufacturing industry recognized by all countries, and in this transformation process, the health operation and maintenance (HOM) of equipment has become a crucial link, especially for complex equipment, and its health operation and maintenance level directly affects the overall efficiency of the manufacturing industry. However, with the improvement of intelligence and complexity, a more general and complete set of methods and theories is needed for the healthy operation and maintenance of complex devices with self-healing states. Based on an in-depth analysis of the key issues of complex equipment health operation and maintenance, this paper introduces digital twin technology as a breakthrough. Digital twins provide new ideas for the healthy operation and maintenance of complex equipment. By defining a digital twin-driven PHM (Prediction and Health Management) framework, this paper not only solves the problem of mobility (i.e., virtual and real connection) of the cross-platform health operation and maintenance model, but also focuses on improving the accuracy and evaluation indicators of the model (the consistency between the virtual model and the entity). Addressing issues of strategy development and effectiveness evaluation. Based on the digital twin technology, a general model was established, and the self-healing phenomenon and different maintenance strategies were introduced to explore its impact on reliability. Based on the game idea, the reliability model is used to evaluate different maintenance strategies. So as to develop the optimal operation and maintenance strategy. This not only improves the accuracy and efficiency of O&M, but also provides a solid theoretical foundation and technical support for the intelligent and autonomous health O&M of complex equipment.

As austempered ductile iron (ADI) is a key gear material for meeting the lightweight and cost-effective demands of new energy vehicles, its bending fatigue performance has a direct impact on vehicle transmission efficiency. In the present work, QTD 800 gears were subjected to bending fatigue testing using a combination of the conventional group method and the staircase method, with considerations given to fatigue life and fatigue limit at different reliability levels. Subsequently, the gears were characterized using optical microscopy and a microhardness tester to examine their metallographic structure and determine their hardness. The results indicate that the bending fatigue limits corresponding to gear reliability levels of 50%, 90%, and 99% are 390.00 MPa, 372.55 MPa, and 358.32 MPa, respectively. It was also observed that higher gear life stability corresponds to a lower sustainable fatigue limit stress. The analyses further reveal that under low loads, the main crack exhibits a relatively straight and smooth propagation trajectory, formed through the slow extension of an existing crack, whereas under high loads, the main crack displays a rough and serrated appearance, arising from the coalescence of microcracks initiated around graphite nodules.

The contact fatigue performance of carburized gear steels is critical for transmission durability, yet the mechanisms linking alloy-specific microstructure to failure modes remain complex. This study systematically compares the contact fatigue behaviors of 20MnCr5 and 20CrMoH gears using step-loading tests and multi-scale characterization. The results demonstrate a significantly higher contact fatigue limit for 20MnCr5 of 1709 ± 12 MPa compared to 1652 ± 40 MPa for 20CrMoH, despite the latter exhibiting higher initial surface hardness. This hardness–toughness paradox is mechanistically elucidated by the distinct roles of alloying elements: while Molybdenum in 20CrMoH refines the grain size for high static strength, it limits retained austenite stability, resulting in a brittle hard-shell and soft-core structure prone to interface decohesion at martensite lath boundaries. Conversely, Manganese in 20MnCr5 promotes a gentler hardness gradient via favorable diffusion kinetics and stabilizes abundant film-like retained austenite. This microstructure activates a Stress Compensation Mechanism, where strain-induced martensitic transformation generates compressive volume expansion to counteract cyclic stress relaxation. Consequently, 20MnCr5 exhibits mild plastic micropitting driven by transformation toughening, whereas 20CrMoH undergoes severe brittle spalling driven by the Eggshell Effect. These findings confirm that balancing matrix toughness with hardness is more critical than maximizing surface hardness alone for contact fatigue resistance.