脉冲反转技术在金属疲劳损伤非线性超声检测中的应用

材料性能退化总是伴随着某种形式的材料非线性力学行为,从而引起超声波传播的非线性,即高频谐波的产生。研究了利用脉冲反转技术测量金属材料超声学非线性系数的实验方法和信号处理算法,发展了一套可靠的测试实验系统,在相同条件下测量了同一试样在不同输入电压下的二次谐波和基波幅度,二次谐波幅度和基波幅度的平方近似成线性关系,表明实验系统是可靠的。利用该系统进行了一组LY12铝合金疲劳试样非线性超声检测实验。实验结果表明,超声非线性系数可以表征镁合金的疲劳早期退化,脉冲反转技术能够有效提取二次谐波时域信号,增强二次谐波的幅度,抑制主要由实验系统所产生的奇次谐波分量,为材料和结构早期力学性能退化的无损检测和评价提供一种有效的方法。

Applied research on pulse-inversion technique in acoustic nonlinear parameter measurement of fatigued metals

Material degradation is usually preceded by some kind of nonlinear mechanical behavior.When a single sinusoidal ultrasonic wave is launched to a nonlinear medium,the wave will be distorted as it propagates,so higher harmonics will be generated.The paper studies the measurement method of nonlinear parameters and signal processing algorithms with pulse-inversion technique,and develops a robust experimental system.There is linear relationship between amplitudes of the second-harmonic waves and the squared fundamental waves as a function of increasing input voltage amplitude,the experimental system is reliable.Using this method,ultrasonic nonlinear parameters of a group of LY12 aluminum samples fatigued are measured.The experimental results show that the acoustic nonlinear parameter can characterize the fatigue degree of LY12 aluminum,the pulse-inversion technique is very efficient in extracting the second-harmonic amplitude by canceling out the odd harmonics which are mainly due to the instrumentation.This technique can provide a practical way in the nondestructive characterization of material and structure degradation in early fatigue life.