高温下机械零件受持久交变应力时的疲劳研究

The Study of Fatigue Strength of Machine Parts Under Persistent Alternate Stress at High Temperature

通过对实验结果的分析,发现了零件在低温时,疲劳曲线会出现转折点,以此点为界曲线分为左右意义不同的两支;在中等温度时,并不出现这种转折,随着循环次数的累加,允许承受的应力幅值迅速降低;高温时这种转折点反而明显的现象;分析了高温时出现这种转折的原因;利用对极限应力曲面和极限应力曲线的分析,给出了高温下机械零件承受持久交变应力时的安全系数的确定公式;指出了相当静应力σeτ和相当应力σ'eτ的计算方法;得出了高温时,零件在叠加于静应力上的交变应力作用下,蠕变是决定疲劳极限的重要因素和蠕变速度的提高应视作是疲劳损伤出现的结论。

Through the analysis of experimental results, we found the transition point of the fatigue curve at low temperature which divided the curve into two parts. At medium temperature, the curve does not appear such a transition point and the allowable stress amplitude rapidly reduced with the cumulative cycle increasingly. The transition point returns at high temperature. This paper analyzes the reason for such a transition at high temperature. Using the analysis of ultimate stress surface and ultimate stress curve, the formula of safety factor for mechanical parts under persistent alternate stress at high temperature and the calculation method for σeT, σeT are achieved. The conclusion of this study shows that the creep is an important factor to determine the fatigue limit and increasing the creep rate should be regarded as the occurrence of fatigue damage when the parts are under the static stress on persistent alternate stress at high temperature.