非线性超声检测镁合金疲劳的仿真和试验

Simulation and Experiment of Fatigue Damage Measurement in Magnesium Alloy Using Nonlinear Ultrasonic

为了利用非线性超声检测AZ31镁合金的早期疲劳损伤,通过现有的本构关系建立了非线性超声检测有限元模型,计算了材料疲劳引起的内部微缺陷长度、数量和宽度变化对非线性超声系数的影响。计算结果表明,材料疲劳产生的微缺陷是产生二次谐波的原因,有限元方法可以有效模拟镁合金材料的超声非线性效应。进行了两个镁合金疲劳试件的非线性超声在线检测试验,研究发现,在镁合金疲劳早期,超声非线性系数随疲劳加载周数单调增加,但在疲劳后期出现了超声非线性系数减小的现象。试验结果表明,超声非线性系数对疲劳早期损伤非常敏感,可以用来表征材料的早期疲劳损伤程度,有限元计算结果与试验结果相吻合。

In order to monitor the early fatigue damage of AZ31 magnesium alloy by nonlinear ultrasonic,a nonlinear FEM model is established by a special element which accounts for a nonlinear stress-strain relation.The influence of the micro-defect with different length,quantity and width to ultrasonic nonlinearity parameters is calculated.The simulation results show that micro-defects in material fatigue is the cause of the second harmonic generation,finite element method can effectively simulate ultrasonic nonlinear effects in magnesium alloy material.Meanwhile,ultrasonic nonlinearity parameters of two magnesium samples are online measured.There is a significant increase inlinked to fatigue cycles in early stages of fatigue life,but at the late stage of fatigue,an experimental phenomenon of the decrease in fatigue cycles is obtained.The experimental results show that ultrasonic nonlinearity parameters can characterize the early fatigue damage of magnesium.The results of simulation verify experimental results.