对20号钢进行了超声振动单向拉伸试验,对其内部应力进行了有限元分析,得出了工件在直径最小处两端的应力最大,中间次之,这和断口断裂的位置是一致的.研究了工件中心点处塑性应变及应力随时间变化的曲线,证明了在超声振动单向拉伸下工件内部受到的是一个交变的应力载荷.通过对超声与常态拉伸断口的比较,发现了所有断口都是杯锥型断口,而超声拉伸的断口杯状边缘更明显,断口内部更平整,断口更明亮；还发现了随着频率的降低,断口变得粗糙且不均匀,功率越大,典型疲劳条纹也越明显.%In this paper,the ultrasonic vibration uniaxial tensile test of the #20 steel was conducted and the internal stress was analyzed by finite element method.It is concluded that the stress of workpiece on both ends of the minimum diameter place is the biggest and that of the middle is bigger,which is consistent with the position of the fracture.Since the plastic strain and stress curve are changed with time,it is proved that the intemal workpiece is subject to an altemative stress load under ultrasonic vibration uniaxial tensile.Based on the comparison between the tensile fracture of the ultrasonic and that of the common condition,it is found that all the fracture is a cup of cone fracture type and the fracture has more apparent cup edges,more smooth and bright at ultrasound stretch.Furthermore,it is found that the fracture becomes coarse and uneven with the decrease of frequency.Therefore,the greater the power is,the more obvious the typical fatigue stripe is.
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