超声疲劳试验方法在铸铝疲劳试验中的应用

应用20kHz频率下的超声疲劳设备完成亿周次疲劳试验，获得铸铝AS5U3G-Y35超高周疲劳特性。通过20kHz频率下的超声疲劳试验和35Hz频率下的常规试验，完成10^4～10^10周的S-N曲线。试验结果表明，在10^7周以上试件仍会发生疲劳断裂。在10^7～10^10周之间，当应力比R=-1时，疲劳强度随循环数的增加而下降；当应力比r=0．1时，在循环数超过10^8周时，疲劳强度不再下降，S-N曲线出现平台。比较20kHz和35Hz两种频率下的试验结果，在10^4～10^7周之间没有明显差别，即铸铝AS5U3G-Y35在超声疲劳试验中不存在频率效应。扫描电镜观察试件疲劳断裂面发现材料中分布许多小的缩孔，而且大多数试件的疲劳破坏都发生在试件表面或接近表面的缩孔处。

ULTRASONIC FATIGUE TEST METHOD FOR TESTING OF CAST ALUMINUM

Experiments were conducted to determine the gigacycle fatigue behavior of cast Aluminum AS5U3G-Y35 by ultrasonic fatigue test system. Specimens were tested at 20?kHz and 35?Hz with stress ratios of R=-1 and R=0.1. The S-N curves between 10 4 and 10 10 cycles were obtained. The experimental results show that fatigue failure can occur over 10 7 cycles, and the fatigue endurance stress continues to decrease with increasing number of cycles to failure between 10 7 and 10 10 cycles with R=-1, the fatigue endurance stress did not decrease after 10 8 cycles with R=0.1. The experimental results tested at frequencies of 20?kHz and 35?Hz respectively show that there is no apparent difference below 10 7 cycles. That is, there is no frequency effect on the fatigue properties of cast Aluminum AS5U3G-Y35. Scanning electron microscopy is used to examine the fatigue crack surface. The small voids are distributed in the material, and most fatigue crack emanate from the voids.