非线性电磁超声对铝合金拉伸变形评价研究

Evaluation of the tensile deformation of aluminum alloy using EMAT for nonlinear ultrasonic detection

非线性系数是描述材料中微纳尺度损伤的特征参量,非线性系数常通过接触式压电超声进行检测,但耦合剂引起的非线性一般是未知的,针对这一问题,提出了一种非接触式电磁超声非线性纵波检测方法。该方法基于洛伦兹力机理在试件表面产生的振动弹性波,利用不同拉伸载荷下所制备的损伤试件,分别利用压电超声、电磁超声进行非线性超声系数测量。实验结果表明:利用两种非线性超声检测的相对非线性系数与铝合金的拉伸形变呈单调关系,同时也论证了电磁超声纵波基于非线性理论对塑性变形评估的可行性。

The nonlinearity acoustic parameter, which describes the micro-nano scale damage with a single scalar coefficient, is often measured by contact piezoelectric ultrasonic technique. However, the nonlinear feature from the couplant is unknown. Aiming at the problem of measurement process, a non-contact electromagnetic ultrasonic technique using longitudinal wave was proposed. The ultrasonic is stimulated in the specimen surface based oil Lorentz mechanism. The specimens were loaded by different levels of stretching stress and the relative acoustic nonlinearity parameter （ANP） were measured by piezoelectric ultrasonic and electromagnetic ultrasonic method respectively. The experimental results show that the relative ANP increases monotonically with the tensile strain of the aluminium alloy. This research also demonstrates that the nonlinear electromagnetic ultrasonic technique using longitudinal wave can be used to evaluate the plastic deformation.