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应用基于压电超声疲劳试验技术开发的20kHz轴向振动疲劳试验系统,完成了室温下TC4钛合金超高周疲劳试验,获得了TC4合金在107~109周次范围内的轴向振动疲劳寿命曲线(S-N曲线);运用C.Paris推导公式预测了TC4合金材料的寿命,得到各应力水平下破坏率为50%、95%、99%的安全寿命。结果表明:在疲劳循环大于107周次时,试件仍会发生疲劳断裂,疲劳强度随循环次数的增加而下降,并不存在明显的疲劳极限。TC4合金的S-N曲线在107~109周次的范围内呈连续下降型。在轴向振动超高周疲劳试验中,试件的裂纹扩展寿命只占其在50%破坏率下疲劳安全寿命的一小部分,其疲劳寿命主要由试件的裂纹萌生寿命决定。
The ultrahigh-cycle fatigue test of TC4 titanium alloy at room temperature was completed by using 20kHz axial vibration fatigue test system based on piezoelectric ultrasonic fatigue test technology. The axial vibration fatigue life curve of TC4 alloy was obtained in the range of 107 ~ 109 cycles (SN curve). The life expectancy of TC4 alloy was predicted by C.Paris derivation formula, and the safety lifetimes of 50%, 95% and 99% were obtained under various stress levels. The results show that when the fatigue cycle is more than 107 weeks, the fatigue fracture of the specimen still occurs, and the fatigue strength decreases with the increase of the number of cycles. There is no obvious fatigue limit. The S-N curve of TC4 alloy showed a continuous descending pattern in the range of 107-109 cycles. In the test of axial vibration ultrahigh-cycle fatigue test, the crack propagation life of the specimen only accounts for a small part of the fatigue life under the 50% failure rate, and its fatigue life is mainly determined by the crack initiation life of the specimen.