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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。
Nonlinear coefficient is the characteristic parameter to describe the micro-scale damage in the material. The nonlinear coefficient is often detected by contact piezoelectric ultrasonic, but the nonlinearity caused by the coupling agent is generally unknown. To solve this problem, a non-linear coefficient Contact electromagnetic ultrasonic nonlinear longitudinal wave detection method. The method is based on the Lorentz forces generated on the surface of the specimen vibrational elastic waves, the use of different tensile load under the prepared specimen damage, respectively, the use of piezoelectric ultrasound, electromagnetic ultrasonic non-linear ultrasonic coefficient measurements. The experimental results show that the relative non-linear coefficients detected by the two kinds of nonlinear ultrasonic tests show a monotonic relationship with the tensile deformation of the aluminum alloy, and the feasibility of the plastic deformation assessment based on the nonlinear theory is also demonstrated.