中文摘要：

振动声调制（Vibro-acoustic modulation,VAM）是一种非线性无损检测方法,利用低频振动信号与高频超声波在结构损伤处产生调制现象来检测损伤。目前振动信号与超声波之间的耦合机理、损伤程度与调制强度的关联关系还不明确。以一块航空铝板为对象开展试验研究,通过对不同裂纹长度下的VAM信号进行AM-FM解调,从时频域分析振动信号与超声波是如何相互耦合的;研究激励参数和裂纹长度对VAM信号调制强度的影响。结果表明,当铝板中存在损伤时,振动信号与超声波之间既存在频率调制也存在幅值调制,调制波为振动信号的基波及各次谐波;VAM信号的调制强度受激励电压、铝板振动模态等因素的影响,与裂纹长度的关联关系并不是单调的,因此无法用于损伤程度的评估。根据非线性弹簧模型和影响VAM信号调幅特征的因素定义可用于损伤评估的相对指标,并进行验证。

英文摘要：

Vibro-acoustic modulation（VAM） is a nonlinear non-destructive testing technique,which detects damages by utilizing the modulation effects between high-frequency ultrasonic wave and low-frequency vibration.However,the coupling mechanism between the two excitations,and the relationship between damage severity and modulation intensity are still not well understood.VAM experiments are performed on an aeronautic aluminum plate under various crack lengths.The corresponding signals are AM-FM demodulated in time-frequency domain,aiming to investigate how the vibration and ultrasonic wave interact.The dependences of modulation intensity on excitation parameters and crack lengths are analyzed.The results show that,both amplitude and frequency modulations are present in the VAM signals when there is damage in the aluminum plate,and the modulation signal is the fundamental and higher-order harmonics of the vibration.The modulation intensity does not increase monotonically with increasing crack length due to the influences of excitation voltages and vibration modes of the plate.Thus it is not reliable to estimate the damage severity.According to the nonlinear spring model and the factors that affect the amplitude modulation of VAM signal,a damage index to estimate the relative damage severity is derived and verified.