高速动车组合金车轴钢微粒子喷丸强化机理及超高周疲劳性能研究

The material applied to China's high-speed multiple units axle is still imported and the alloy steel is the selected material for the domestic research, while the surface strengthening method matching with the material is comparatively lagging. Meanwhile, the axle design standard, which is still based on the conventional fatigue limit, cannot guarantee its service safety. In this study, the strengthening mechanism of micro-shot peening on the alloy axle steel for high-speed multiple units is carried out; the relationship between micro-shot peeing parameters and surface properties is studied; the micro-shot peening process and residual stress distribution are simulated; the reliability of the residual stress is analyzed and the relaxation model based on the material properties and loading stress is established; meanwhile, the very high cycle fatigue tests are conducted to study the influence of micro-shot peening on fatigue properties; the effect of micro-shot peening on initiation mechanism for surface crack and internal crack as well as the propagation competing mechanism between them is clarified. Then the micro-shot peening parameters matching with the alloy axle steel to improve the very high cycle fatigue property is determined. Besides, the fatigue property under variable amplitude loading is analyzed and the fatigue cumulative damage model is proposed. The probability S-N curve model with different crack initiation mechanism is studied and the reliability evaluation method for very high cycle fatigue is established. The results of this study can supply information for surface strength treatment selecting, probability design and fatigue life prediction for localization alloy axle.

目前，我国高速动车组车轴材料仍然依赖进口，其国产化研究选择使用合金钢，而与之匹配的表面强化工艺研究相对滞后，同时，基于传统疲劳极限的车轴设计规范已无法保证其服役安全性。本研究针对高速动车组合金车轴钢开展新型微粒子喷丸强化机理研究，研究喷丸参数与表面性能的关系，仿真微粒子喷丸过程和残余应力分布，分析表层残余应力的稳定性，建立基于材料性能和载荷的残余应力松弛模型。同时，研究微粒子喷丸工艺对超高周疲劳性能的影响，阐明微粒子喷丸处理对合金车轴钢表面和内部裂纹萌生机制以及两种裂纹扩展竞争机制的影响，确定与其匹配的抗超高周疲劳的工艺参数。明确变载荷作用下的疲劳性能，建立变幅载荷作用下的累计疲劳损伤模型。研究不同裂纹萌生机制共存下的概率S-N曲线模型，建立超高周疲劳可靠性评估方法。本研究可以为国产化合金车轴表面强化处理工艺选择，可靠性设计和寿命预测提供指导。

我国高速动车组车轴尚未完全实现国产化，且国产合金车轴钢的超高周疲劳性能以及与之匹配的表面强化工艺研究相对滞后。研究中针对国产高速动车组合金车轴钢，开展了微粒子喷丸处理，研究了超高周疲劳性能和破坏行为；进行了微粒子喷丸过程及残余应力分布的有限元仿真分析；研究了表面缺陷对疲劳强度影响，并进行了变幅载荷作用下疲劳寿命预测和可靠性评估方法的研究。研究表明，微粒子喷丸显著提高合金车轴钢疲劳性能，基于表层性能和疲劳性能可以确定与合金车轴钢相匹配的微粒子喷丸工艺；在超高周区域，微粒子喷丸合金车轴钢没有发生自材料内部的疲劳破坏，仍然具有传统疲劳极限；疲劳加载使试样表面的残余应力发生静载松弛和快速松弛，松弛程度与材料性能和加载载荷有关；基于微粒子喷丸后试样表面的残余应力，表面组织硬化和表面粗糙度对疲劳强度的评估结果和试验结果符合较好；建立的随机多丸粒喷丸模型分析了弹丸直径、喷丸速度和喷射角度对表面残余应力分布和粗糙度的影响，且分析结果与试验结果一致；表面缺陷尺寸对合金车轴钢的疲劳强度有显著影响，随着缺陷尺寸的增加疲劳强度下降，使用修正的Haddad模型可以较好的评估缺陷尺寸对疲劳强度的影响，同时得到了不引起疲劳强度下降的临界缺陷尺寸；基于变载荷试验得到的试样表面残余应力和半高宽可以较好地进行疲劳寿命预测；采用不同的评估模型得到了微粒子喷丸车轴钢的概率S-N曲线，并分析了不同模型评估的特点和适用条件。相关研究成果，可以为提高合金车轴疲劳性能的表面处理工艺开发和抗超高周疲劳设计提供指导，也可为高速动车组合金车轴可靠性设计和寿命预测提供理论依据。