【作者】 丁俊；

【导师】 康国政；

【作者基本信息】 西南交通大学 ， 固体力学， 2013， 博士

【摘要】 微动疲劳是指结构件在外界疲劳载荷作用下,两个接触表面之间发生微米级的相对运动,从而导致结构件疲劳强度的降低或发生早期断裂的现象。微动疲劳广泛存在于航空、交通运输和海洋工程等领域的各种工程结构件中,比如：涡轮发动机、轮轴过盈配合、高空电力导线和螺栓等,它是这些结构件最主要的失效形式。要合理评估这些结构的安全性和可靠性,必须首先揭示微动疲劳的损伤特性和失效机理。根据外界交变疲劳载荷类型的不同,微动疲劳可分为拉压微动疲劳、弯曲微动疲劳和扭转微动疲劳。近几十年来,各国研究者对微动疲劳进行了许多研究,在实验研究、数值模拟和理论分析方面都取得了诸多的成果。然而目前已有的研究绝大多数都是关于拉压微动疲劳的,对弯曲微动疲劳和扭转微动疲劳的研究还很少,其研究还不够全面和系统。LZ50钢(循环稳定材料)、316L不锈钢(循环硬化材料)、调质42CrMo钢(循环软化材料)和6061-T6铝合金(循环软化材料)这四种材料由于各自良好的力学性能,常被用于制备列车轮轴等零部件,在其服役过程中会承受弯曲载荷而产生弯曲微动疲劳,因此,本文选用这四种材料进行弯曲微动疲劳的相关研究,继而揭示弯曲微动疲劳的失效特性,为弯曲微动疲劳的防护工程提供有力的依据和重要的参考价值。为了揭示这四种材料的弯曲微动疲劳的失效特性,本论文主要开展了以下研究工作：1.对调质42CrMo钢和6061-T6铝合金进行弯曲微动疲劳与常规弯曲疲劳实验,比较弯曲微动疲劳与常规弯曲疲劳之间的差异。通过系统的弯曲微动疲劳实验,研究疲劳寿命和循环弯曲载荷之间的关系；通过观察弯曲微动疲劳试样在不同弯曲载荷下的形貌和不同阶段的微动损伤情况,揭示弯曲微动过程的损伤演化特性。2.将能够合理描述循环硬化、循环稳定和循环软化等特性的循环弹塑性本构模型通过UMAT用户子程序移植到ABAQUS中用于弯曲微动过程的数值模拟。3.基于弯曲微动疲劳实验,通过三维有限元模型的等效载荷转换建立了简化的二维平面应变模型,并验证了其合理性。4.采用新发展并移植的棘轮循环本构模型对简化的二维有限元模型进行弯曲微动过程的数值模拟,分析接触区的应力和应变状态,并研究循环弯曲载荷、摩擦系数和法向载荷等因素对弯曲微动过程的影响,进一步揭示弯曲微动疲劳的失效过程。5.通过弯曲微动疲劳的实验研究和相应的数值分析,分析和总结四种材料弯曲微动疲劳的损伤演化特性和失效机理,为弯曲微动疲劳失效的防护提供充分的依据。进而采用SWT临界面法预测弯曲微动疲劳裂纹萌生的位置和寿命,并与实验结果进行比较。更多还原

【Abstract】 Fretting fatigue is the process of material damage due to micrometer-scaled movements at the interface between contact bodies caused by cyclic fatigue loads and fretting fatigue may finally result in lower fatigue strength and earlier failure than plain bending fatigue. Fretting fatigue occures widely in various structure components of aviation, transportaion and marine engineering, such as in turbine engine, railway axle, overhead electrical conductors, bolts, and so on. Fretting fatigue is the main failure mode of these structure components, so in order to assess the safety and reliability of these components, the damage characteristics and failure mechanism must be revealed. Fretting fatigue can be devided into three types:the tension and compression fretting fatigue, bending fretting fatigue and torsion fretting fatigue, accoding to different types of fatigue loads. In recent years, the fretting fatigue has been widely studied and some typical achievements have been obtained about the experimental techniques, numerical analysis and mechanism discussion. Howerer, most of the exsited studies focused on the tension and compression fretting fatigue, the bending and torsion fretting fatigue behaviors were rarely discussed. LZ50steel (cyclic stabilizing material),316L stainless steel (cyclic hardening material), tempered42CrMo steel (cyclic softening material) and6061-T6aluminium alloy (cyclic softening material) were widely used in the structure parts, such as train axle, where they would be subjected to bending fretting fatigue in the service. Therefore, the experimental study and finite element analysis were carried out to reveal the failure characteristics of bending fretting fatigue in this paper for these four kinds of metals. The obtained results can provide solid fundamentals for the preventation of bending fretting fatigue failure.In order to reveal the failure characteristics of bending fretting fatigue about the four kinds of materials, the following studies have been carried out in this thesis:1. The bending fretting fatigue and plain bending fatigue experiments of tempered42CrMo steel and6061-T6aluminium alloy were carried out to analysis the difference between the bending and plain bending fatigue behaviors. The relation of fatigue lives and cyclic bending loads was studied by systematic bending fretting fatigue experiments; the damage evolution characteristics during the bending fretting were revealed by observing the morphology of fracture surfaces under different bending loads and the fretting damage of specimens after different numbers of cycles.2. A cyclic elasto-plastic constitutive model which can describe the material characteristic (i.e. cyclic hardening, cyclic stabilizing, cyclic sofetening) reasonably was implemented into ABAQUS finite element software as a UMAT user subroutine.3. Based on the experiments of bending fretting fatigue, a simplified two dimensional plane strain finite element model with an equivalent normal force transformation from a three dimensional finite element model was established.4. The simplified two dimensional finite element model with the UMAT subroutine of cyclic constitutive model was used to simulate the bending fretting process, and then the stress-strain responses in the contact zone were analyzed. The effects of cyclic bending load, friction coefficient and normal force on the bending fretting were discussed.5. The damage evolution characteristics and failure mechanisms of bending fretting fatigue for four materials were analyzed by combining the experimental and numerical analyses, which is helpful to prevent the bending fretting fatigue failure. Finally, the crack iniation locations and lives of bending fretting fatigue were predicted by using a suitable critical plane model and volume average method. The predictions were in agreement with the experimental results.更多还原