| 摘要: |
| 20世纪90年代前，汽车上使用的各种圆柱螺旋弹簧（以下称弹簧）承受较低的扭转疲劳载荷，在交变正应力作用下，绝大多数发生的是宏观正断型疲劳断裂，其形貌呈45°斜断口。因为喷丸强化弹簧表层引入的残余应力与外施交变正应力间存在交互作用，所以都利用喷丸强化工艺中的“应力强化机制”提高其疲劳断裂抗力。但21世纪伊始，随着轿车结构的迅速发展，设计者迫切要求弹簧承受的扭转疲劳载荷水平与日俱增，由此导致喷丸强化的弹簧除正断型的疲劳断裂外，时而出现纵向或横向切断型的疲劳断裂，由此引发疲劳断裂抗力发生显著下降，以往很少出现这种难以理解的现象。目前从事喷丸强化工艺技术的弹簧制造行业很少有文献关注这类问题。文中通过逻辑思维对弹簧的受力分析得出的诠释发现：在切断模式下，喷丸引入的残余应力与外施交变切应力之间不存在交互作用，表明“应力强化机制”在改善切断型疲劳断裂抗力中的强化作用已经基本消失。根据作者提出的喷丸强化工艺原理，喷丸同步引入弹簧表层的是由残余应力与循环弹塑性变形改性的组织结构组成的一对“孪生”，通过分析作者发现，“孪生”中改性的显微组织结构形成的“组织结构强化机制”取代“应力强化机制”起到了改善切断型疲劳断裂抗力的作用。研究结果还表明，优化的喷丸强化工艺必须同时具备“组织结构强化机制”和“应力强化机制”，才能够起到改善正断型和切断型疲劳断裂抗力的作用。 |
| 关键词: 喷丸强化原理 疲劳断裂抗力 疲劳断裂强化机制 疲劳断裂模式分类法 |
| DOI：10.11933/j.issn.1007-9289.2016.04.001 |
| 分类号: |
| 基金项目: |
|
| Basic Principle of Shot Peening and Mechanisim Map of Adjusting and Controlling Normal Tensile/Shear Fatigue Fracture Resistance |
|
WANG Ren-zhi1, RU Ji-lai2
|
|
1.Metal Physics Laboratory, Beijing Institute of Aeronautical Materials, Beijing 100095;2.Metal & Chemistry Institute, China Academy of Railway Science, Beijing 100081
|
| Abstract: |
| Before 1990s, under the cyclic normal tensile stresses, the fatigue fracture mode for most of circular suspension springs in automobile subjected to torsion fatigue load was in normal tensile fracture mode (NTFM) and the fracture surface was under 45° diagonal. Because there exists the interaction between the residual stresses induced by shot peening and the applied cyclic normal tensile stresses in NTFM, which represents as "stress strengthening mechanism", shot peening technology could be used for improving the fatigue fracture resistance (FFR) of springs. However, with the rapid development in car's structure, the designed torsion fatigue load has been increased steadily since the beginning of 21 century. Therefore, the fatigue fractures occurred of peened springs from time to time are in longitudinal shear fracture mode (LSFM) or transverse shear fracture mode (TSFM) in addition to regular NTFM, which leads to a remarkable decrease of FFR. The phenomena hard to understand has been rarely happened before. At present there are few literatures concerning this problem among springs manufacture industry involving shot peening technology. By means of logical thinking and force analysis, it is found that there is no interaction between the residual stresses by shot peening and the applied cyclic shear stresses in the shear fracture mode. This means that the effect of "stress strengthening mechanism" for improving the FFR of the shear fracture mode is disappeared basically. According to the shot peening strengthening principle presented by the authors, both of residual stress and cyclic plastic deformed modified microstructure are induced synchronously like "twins" in the surface layer of a spring. It has been found by means of force analysis that, instead of "stress strengthening mechanism", "structure strengthening mechanism" produced by the modified microstructure in the "twins" can improve the FFR of the shear fracture mode. It is also shown that the optimum technology of shot peening strengthening must have both "stress strengthening mechanism" and "structure strengthening mechanism" simultaneously so that the FFR of both NTFM and the shear fracture mode can be improved more effectively by shot peening. |
| Key words: shot peening strengthening principle fatigue fracture resistance strengthening mechanisms of fatigue fracture classification on fatigue fracture mode |
