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<p>High-speed train cooling fan shafts frequently undergo fatigue fracture under variable operating conditions, while conventional single-scale methods fail to clarify variable-load damage coupling and cross-scale failure mechanisms. This work establishes a micro–meso–macroscale (multi-scale) coupling framework to investigate the shaft fatigue fracture behavior. Multi-scale damage characteristics are identified through fracture observation, SEM characterization, and metallographic testing. A variable-condition shaft dynamic model is developed to reveal multi-scale coupling effects, and the key scale factors dominating fracture failure are quantified based on fatigue and damage accumulation theories. Results indicate that the shaft suffers torsion–bending composite fatigue failure, following a cross-scale progressive failure path: microstructural defects (network ferrite, insufficient hardenability) to mesoscopic stress concentration (machining marks, structural notches) to speed switching-induced macroscopic resonance load. The 17.33&#xa0;Hz resonance during speed transition elevates alternating bending stress by 53%, acting as the critical external incentive for accelerated fatigue damage. Microscopic network ferrite reduces local fatigue strength by over 40%, fundamentally inducing crack initiation. The proposed approach eliminates the limitations of single-scale analysis, clarifies the cross-scale fatigue fracture mechanism under variable conditions, and provides technical guidance for the anti-fatigue design and reliability improvement of high-speed train rotating components.</p>

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Fracture Behavior of Fan Shaft Under Multi-Scale Coupling Effects in Variable Operating Conditions

  • 期刊论文

  • 发表日期：

    2026年7月1日

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  • Xiaozhang Qu,
  • Jiarui Zhang

摘要

High-speed train cooling fan shafts frequently undergo fatigue fracture under variable operating conditions, while conventional single-scale methods fail to clarify variable-load damage coupling and cross-scale failure mechanisms. This work establishes a micro–meso–macroscale (multi-scale) coupling framework to investigate the shaft fatigue fracture behavior. Multi-scale damage characteristics are identified through fracture observation, SEM characterization, and metallographic testing. A variable-condition shaft dynamic model is developed to reveal multi-scale coupling effects, and the key scale factors dominating fracture failure are quantified based on fatigue and damage accumulation theories. Results indicate that the shaft suffers torsion–bending composite fatigue failure, following a cross-scale progressive failure path: microstructural defects (network ferrite, insufficient hardenability) to mesoscopic stress concentration (machining marks, structural notches) to speed switching-induced macroscopic resonance load. The 17.33 Hz resonance during speed transition elevates alternating bending stress by 53%, acting as the critical external incentive for accelerated fatigue damage. Microscopic network ferrite reduces local fatigue strength by over 40%, fundamentally inducing crack initiation. The proposed approach eliminates the limitations of single-scale analysis, clarifies the cross-scale fatigue fracture mechanism under variable conditions, and provides technical guidance for the anti-fatigue design and reliability improvement of high-speed train rotating components.