载荷形式对铁道车辆关键部件材料疲劳短裂纹行为的影响

Loading modes for railway vehicle in service are complex and changeable, which can lead to the variation of the fatigue properties of material, and in turn can affect the rationality of the assessment results of fatigue reliability and safety for structures or components. However, relevent research on the mechanism and the regularity of related phenomena is still immature and incomplete. In this project, based on the replica tests on short fatigue cracks of specimens for materials of railway vehicle key components, including axle, wheel and frame, with several single and composite loading modes, the influence of loading mode on the initiation and the propagation of short fatigue cracks are investigated. The essential reason of the phenomena that fatigue damage process changes with different loading modes is revealed from microcosmic viewpoint. Furthermore, by introducing a loading mode effect function, a new short fatigue crack growth model which can quantify the effect of loading mode is presented. The influence and its tendency of loading mode effect on the reliability of structure safety assessment is illustrated by utilizing the new model. Thereby, the principle and the method for choosing the crack growth rate curves reasonably while performing safety assessments of railway vehicle key components are investigated. The results can provide a theoretical foundation for the probabilistic safety assessment and management for related structures or components.

铁道车辆在实际服役过程中承受载荷的形式复杂多变，可能导致局部材料疲劳性能发生变化，进而对结构或零部件疲劳可靠性与安全性评价结果的合理性产生影响。现有针对相关现象的机理与规律性研究尚不完善。本项目通过完成包括车轴、车轮、构架在内的铁道车辆关键部件材料试样在多种单一和复合载荷形式作用下的疲劳短裂纹复型试验，对比研究载荷形式对材料短裂纹萌生与扩展行为的影响。从微观角度揭示载荷形式变化导致疲劳损伤过程发生改变的本质原因。进一步，引入“载荷形式效应函数”，建立一种可量化载荷形式影响的短裂纹扩展率新模型。基于该模型，阐明载荷形式效应对结构安全性评定结果可信度的影响及趋势；探索在进行铁道车辆关键部件安全性评价时，合理选择材料裂纹扩展率曲线的原则与方法，为相关结构和零部件的概率安全性评价与管理提供理论依据。

轨道交通车辆在实际服役过程中承受的载荷形式复杂多变，可能导致局部材料疲劳性能发生变化，进而对结构或零部件疲劳可靠性与安全性评价结果产生影响，现有针对相关现象的机理与规律性研究尚不完善。本项目针对铁道车辆关键部件材料（如LZ50钢、EA4T钢、CuNi2Si合金等），开展了轴向对称拉压、旋转弯曲、对称扭转等单一载荷形式和不同应力幅比、不同加载波形、不同相位差等拉扭复合载荷形式下的短裂纹复型对比试验、常载和过载条件下的短裂纹行为试验；通过显微观察和理论分析，开展了载荷形式与试验结果相互关系研究，揭示了载荷形式对车辆关键部件材料短裂纹行为影响的机理，并通过引入特定载荷形式修正函数，建立了包含载荷形式效应在内的扩展率模型；最后，开展了铁道车辆关键部件安全性评价中裂纹扩展率曲线选择原则与方法研究。结果表明，载荷形式的不同会对短裂纹萌生与扩展行为产生影响，这种影响在相同等效应力水平下，依参照的基础载荷形式与实际载荷形式的差异，或针对的复合载荷性质参数不同而显著性不一，需要在选取安全性评价裂纹扩展率曲线时予以必要考虑。