中文摘要：

在基频与二倍频兰姆波相速度匹配但群速度失配的条件下，通过选择适当的兰姆波二次谐波时域信号的测量起止时间，可完全扣除换能器对二次谐波积分振幅测量所带来的影响。本文提出采用兰姆波二次谐波的积分振幅作为评价参量，以实现对板材表面性质的准确评价。当板材表面性质发生改变时，原本在理想表面条件下成立的基频与二倍频兰姆波相速度匹配的条件不再严格满足，这将显著地影响到兰姆波的二次谐波发生效率，相应的二次谐波积分振幅随表面性质的改变也将发生非常敏感的单调变化。实验结果表明，利用扣除换能器影响之后所测得的兰姆波二次谐波的积分振幅，可对板材表面性质的变化情况进行准确评价。

英文摘要：

Under the condition where there is a phase velocity matching but group velocity mismatching between the fundamental and double frequency Lamb waves, the influence of the transmitting and receiving transducers on the measurement of the integration amplitude of the second-harmonic signal can be completely eliminated by selecting the appropriate measurement start and end time of the second-harmonic signal of Lamb wave. It is proposed that the integration amplitude of the second-harmonic signal can be used as an effective indicator for accurately evaluating the properties of plate surface. When the properties of plate surface change relative to the case of perfect surface, the phase velocity matching between the fundamental and double frequency Lamb waves, which originally comes into existence, is no longer satisfied. This obviously influences the efficiency of generation of second harmonic by Lamb wave propagation, and thus the corresponding integration amplitude of the second-harmonic signal varies monotonically and sensitively with change in the properties of plate surface. The experimental results show that after the influence of the transducers on the measurement of second-harmonic signal is eliminated, the change in the surface properties of plate material can be well and truly evaluated with the integration amplitude measured of second harmonic of Lamb wave propagation.