【作者】 宋川；

【导师】 朱旻昊；

【作者基本信息】 西南交通大学 ， 机械设计及理论， 2013， 博士

【摘要】 轴类构件过盈配合连接具有结构紧凑、对中性好以及冲击小等优点,被广泛用于传递动力和运动。但是,大量工业实践表明,过盈配合面间的微动损伤极大地降低了过盈配合构件的疲劳强度,造成了巨大的经济损失和人员伤亡。目前微动疲劳领域的研究大多集中在简化的切向微动疲劳模式,而工业中的轴类构件受旋转弯曲微动疲劳载荷,其损伤是弯曲微动疲劳和拉扭微动疲劳耦合作用的结果。关于旋转弯曲微动疲劳损伤的研究报道较少,开展轴类零件过盈配合结构的旋转弯曲微动疲劳研究,不仅对认识和深化复杂微动疲劳损伤机理有重要的理论意义,而且也能为实际工程的抗微动疲劳损伤设计提供的理论指导。为揭示轴类构件微动损伤的现象和本质,本研究以实际列车轮轴和电机轴／小齿轮轴的过盈配合部位为研究对象,利用光学显微镜、扫描电子显微镜、电子能谱、光电子能谱、里氏硬度仪和3D形貌仪等先进微观分析手段,进行了详细的失效分析,结果表明典型轴类部件过盈配合区的断裂失效是旋转弯曲微动疲劳的结果。本研究研制了一套模拟轮轴服役行为的旋转弯曲微动疲劳试验系统,实现了缩比结构的旋转弯曲微动疲劳试验模拟,很好地重现了轮轴的旋转弯曲微动疲劳损伤现象。本研究,针对LZ50车轴钢和30CrNiMo8钢,在不同参数(弯曲疲劳载荷、接触应力、旋转速度等)下系统地进行了轮轴缩比结构的旋转弯曲微动疲劳的试验研究,并结合有限元数值模拟,对旋转弯曲微动疲劳机理进行了深入研究。完成的主要研究内容及结论如下：(一)LZ50车轴钢旋转弯曲微动疲劳损伤机理研究轮轴缩比旋转弯曲微动疲劳的试验结果重现了实际服役轮座的损伤。在大量试验基础上,建立了LZ50车轴钢缩比试样的旋转弯曲微动疲劳S～N曲线,结果表明疲劳寿命随弯曲疲劳载荷的变化呈现强烈的非单调特征。微观分析发现,外侧损伤带(靠近弯曲载荷一侧)的损伤以微动磨损为主,而内侧损伤带的宽度较小,微动磨损较轻微,损伤主要表现为微动疲劳裂纹；有限元分析结果显示,外侧损伤带内的相对滑移幅值几乎是内侧的3倍,且依赖于外加疲劳载荷。缩比试样断口呈多源性和台阶状特征。研究发现旋转弯曲微动疲劳寿命随试验速度的增加而下降,但损伤机理未发生改变；研究发现改变接触应力(即过盈配合应力),试样的旋转弯曲微动疲劳寿命存在急剧减小的寿命凹区,即对应微动运行的混合区,说明工程应用中应避开该区域；有限元分析发现,Ruiz参数可以预测旋转弯曲微动疲劳寿命随接触应力变化的行为。(二)30CrNiMo8钢旋转弯曲微动疲劳损伤机理研究基于轮轴旋转弯曲微动疲劳缩比试验台,研究建立了30CrNiMo8钢的旋转弯曲微动疲劳S～N曲线,结果显示30CrNiMo8钢的旋转弯曲微动疲劳寿命急剧下降,其疲劳极限仅约90MPa。30CrNiMo8钢的旋转弯曲微动疲劳损伤现象类似于LZ50钢,但其寿命对微动疲劳损伤更敏感,几乎在所有外加疲劳载荷水平下,在试样损伤带内均发现了微动疲劳裂纹,表现出更强烈的对疲劳载荷的依赖性。(三)轴类构件旋转弯曲微动疲劳损伤机理的基本特征基于典型轴类部件过盈配合部位的失效分析和上述两种钢的旋转弯曲微动疲劳试验研究,总结归纳的旋转弯曲微动疲劳损伤机理的基本特征如下：(1)轴类构件的旋转弯曲微动疲劳的对数疲劳寿命分布特征并不符合传统的Basquin方程,表现出了较强的对疲劳载荷的依赖性。(2)微动损伤发生在过盈配区边缘,微动磨损最严重的位置发生在距接触区边缘一定距离的位置,微动磨损带的宽度主要取决于外加疲劳载荷的大小；试样表面微动磨损的机制主要为磨粒磨损、氧化磨损和剥层。(3)旋转弯曲微动疲劳的断口呈现多源性和台阶状特征；微动疲劳裂纹萌生于次表层,在裂纹萌生区可见孔洞等缺陷,微裂纹可能是孔洞联通的结果；裂纹扩展呈三阶段特征：a)接触应力控制阶段--裂纹与接触表面的法向呈小角度扩展(约20～40°),并与表面微动磨损倾斜裂纹沟通；b)接触应力和疲劳应力共同控制阶段--随着深度增加接触应力的影响下降,裂纹逐渐转向垂直于接触表面扩展；c)疲劳应力控制阶段--在裂纹垂直于接触表面扩展,其行为相同于常规疲劳,直至最后断裂。(4)在旋转弯曲微动疲劳损伤过程中存在局部磨损与疲劳的竞争机制：在接触区外侧区域,应力、应变和滑移幅值均较高,损伤较严重,主要表现为磨损,且磨损后,颗粒的脱落和第三体的形成有效降低了该区域的应力集中,裂纹形成受到抑制；而在内侧,磨损相对轻微,局部疲劳占优,裂纹易形成和扩展。(5)旋转弯曲微动疲劳损伤表现出了强烈的材料依赖性,即高强度材料的微动疲劳寿命下降因子高；同时,旋转弯曲微动疲劳损伤也体现出一定的运行速度和疲劳载荷依赖性。更多还原

【Abstract】 Axial components with interference fit are widely used to transfer power and motion due to the advantages of compact structure, better centering and lower impact. However, a great deal industrial application shows that the fatigue strength of shaft is decreased largely by the fretting damage between the interference fit interfaces, which induces a huge of economic losses and casualties. Presently, most of researches focus on tension-compression fretting fatigue in the field of fretting fatigue. However, the axial components are borne rotary bending fatigue loads whose fatigue damages are the results of the combination of bending fretting fatigue and tension-torsion fretting fatigue. The research reports on rotary bending fretting fatigue (RBFF) are very rare. Thus, the study on RBFF for the interference fit structure of shafts is not only a significant to understand the mechanisms of RBFF, but also can provide some efficient guidance on design of anti-fretting fatigue damage in actual engineering.In order to reveal the phenomenon and essence of fretting damage of axial components, the actual components of railway wheel-axle and electric motor axis/pinion shaft were used to do failure analysis in detail by using advanced micro analysis methods of optical microscope, scanning electrical microscope, electron energy dispersive spectrum, X-ray photo electron spectrum, Leeb hardness tester and3D profilometer. The results indicated that the fracture phenomena of interference fit positions of typical axial components are the result of RBFF.The main obtained research results are as follows:(I) Study on RBFF damage mechanisms of LZ50railway axle steelThe experimental results of railway wheel-axle in small scale reproduced the RBFF damage of the real wheel seat of axle in service.Based on a number of tests, the S-N curve of small scale samples of LZ50railway axle steel has been established, and the result shows the fatigue life presented a strong non-monotonic behavior with the change of bending fatigue load.The micro-analysis reveals that the outer damage band (close to the sideof bending load end) was dominated by fretting wear. However, in the inner damage band with a narrow width, fretting wear is slight, and the main damage exhibited cracking of fretting fatigue.The result of FEM simulation indicates that the relative slip amplitude in the outer damage band was about three times of the inner one and this value was dependent upon the imposed fatigue load.The fracture surface of small scale samples showed the profile of multi-source and step-like feature.The research found that the RBFF life decreased with the increase of test speed, however the damage mechanisms unchanged.lt has been found that with the change of contact stress (z.e.the interference fit stress), the RBFF life exhibited a concave zone in dramatically drop-down, and namely this contact stress region corresponded to the mixed regime of fretting running behavior. Thus, it indicated that the engineering application must avoid this zone/regime.The FEM analysis testified that the Ruiz parameter can be used to forecast the behavior of RBFF life varied with the contact stress.(Ⅱ) Study on RBFF damage mechanisms of30CrNiMo8steelBased on the small scale RBFF railway wheel-axle test rig, the S-N curve of RBFF of30CrNiMo8steel was established in this research. The result shows that the RBFF life of30CrNiMo8steel was sharply dropped to the RBFF fatigue limit of about90MPa. The fretting damage phenomena of30CrNiMo8steel were similar to the LZ50steel, however, its life was more sensitive to the fretting damage. Under almost all imposed fatigue load levels, the fretting cracks can be observed in all damage bands, which presented much stronger dependence of fatigue load.(Ⅲ) Basic characteristics of RBFF damage mechanisms of axial componentsBased on the results of failure analysis of typical axial components and the RBFF experimental research for the two steels mentioned above, the basic features of RBFF damage mechanisms were summarized as follows:(1) The distribution of RBFF logarithmic life of axial components does not obey the traditional Basquin function but shows an intensive dependence on fatigue loads.(2) Fretting damage occurred at the contact edge area of the interference fitted zone and the most serious wear location is located at a certain distance apart the contact edge. The width of fretting wear band is dependent upon the level of fatigue load. The main wear mechanisms of samples surface are abrasive wear, oxide wear and delamination. (3) The fracture surface shows the multi-source and step-like profile, which caused by the action of multi axial stress. The fretting fatigue cracks initiated at the sub-surface, some defects such as caves have been observed in the crack initiation area. The micro-cracks are probably induced by the conjunction of the caves. The propagation of fretting fatigue crack shows three stages:a) The stage control by contact stress--the crack propagates inclined to the normal of surface with an small angle (about20°～40°). And the inclined crack connects with the surface wear oblique cracks, b) The stage control by the combination of contact stress and fatigue stress--the effect of contact stress decreased with the increase of depth and the inclined crack gradually transforms to the normal of surface, c) The stage control by fatigue stress--, the crack propagates normal to the contact surface until to final fracture as same as the plain fatigue process.(4) The competition mechanism exists between the local wear and fatigue during the RBFF damage process. At the outer damage region, the stress, strain and slip amplitude are higher, and the damage is very serious mainly with local wear. And the stress concentration is effectively released by the particle detachment and the third-body formation after local wear. Thus, the fatigue crack initiation is restrained. However, in the inner side, the wear is slighter and the damage dominates by local fatigue, where the fatigue crack is easy to initiate and propagate.(5) The RBFF damage strongly depends upon the material properties, i.e. the higher strength of materials, the higher factor of life reduction. At meanwhile, the RBFF damage also shows dependence upon the running speed and fatigue load.更多还原