中文摘要：

为利用基于二次谐波的非线性超声方法检测镁合金材料的早期疲劳损伤，建立超声非线性系数β的测试试验系统，设计制作预设应力集中区的厚板镁合金疲劳试件，并通过有限元法仿真应力集中区的有效性。对三个不同疲劳加载模式的镁合金试件进行非线性超声检测试验研究。结果表明，在疲劳寿命的早期，三个试件的超声非线性系数均随疲劳周数明显增加。同时，测量其中一个试件在非应力集中区的超声非线性系数，与应力集中区相比，超声非线性系数变化幅度只有应力集中区的27％，进一步表明超声非线性系数的变化来源于镁合金材料疲劳引起的微缺陷变化，也证实试验的可靠性。另外，波速和弹性常数的试验结果表明，这两个线性参数对于镁合金材料的早期疲劳损伤不如超声非线性系数敏感。

英文摘要：

In order to monitor the early fatigue damage ofAZ31 magnesium alloy by nonlinear ultrasonic basing on second harmonic, the measurement system of ultrasonic nonlinearity parameters is established. Thick plate fatigue specimens of magnesium alloy are designed, these specimens are pre-stress concentration area, and the effectiveness of stress concentration area is simulated by the finite element method. Ultrasonic nonlinearity parameters fl of three magnesium specimens with different loading stress are measured, the experimental results show that there is a significant increase in β linked to fatigue degree in the early stages of fatigue life. Meanwhile, β of non-stress concentration area are measured to one specimen, the ultrasonic nonlinearity parameters magnitude is the 27% of stress concentration zone, and further show that the changes inβ derive from the changes of micro-defect by magnesium alloy material fatigue, and also confirm the reliability of the experiment. In addition, the experimental results of the wave velocity and elastic constants show that the two linear parameters are not sensitive to early fatigue damage of the magnesium alloy material.