引言S—N 曲线在疲劳试验研究中占有很重要的位置。它不仅为疲劳寿命估算提供基本数据,而且也是疲劳设计的重要基础。因此,要全面地反映零部件在交变应力下对疲劳的抗力,必须测定 S—N 曲线及其等寿命曲线。如果给出了某种材料的 S—N 曲线,那么,根据最大应力 Smax 和应力比 R 或应力幅值 Sa 和平均应力 Sm,在 S—N 曲线上就可以直接查出零部件的寿命 N。但是,在实际中,零部件所 INTRODUCTION The S-N curve plays a very important role in fatigue test research. It not only provides basic data for fatigue life estimation, but also an important basis for fatigue design. Therefore, to fully reflect the fatigue resistance of parts under alternating stress, the S-N curve and its life-span curve must be determined. Given the S-N curve for a given material, the lifetime of the part N can be found directly on the S-N curve based on the maximum stress Smax and the stress ratio R or the stress amplitude Sa and the average stress Sm. However, in practice, parts and components