一种定征复合板材粘接层性质的非线性超声兰姆波方法

借助于兰姆波频散曲线及导波激发的模式展开分析方法,对基频兰姆波时域信号及二次谐波时域信号的发生过程进行了直观的论述。结合Ritec-SNAP系统的测量功能,详细分析了二次谐波时域脉冲包络积分表达式的物理意义;该积分表达式可表征基频兰姆波时域脉冲传播过程中的二次谐波发生效率,以及基频与二倍频兰姆波模式之间的频散程度。在基频与二倍频兰姆波相速度相等(或近似相等)的频率附近,实验观察到显著的且无模式混叠的二次谐波信号,显示出在兰姆波的传播过程中的确可存在强烈的非线性效应。对于三种不同粘接情形的复合板材,实验结果表明,采用本文引入的非线性兰姆波应力波因子,结合二次谐波幅频曲线峰值所对应的频率值,可有效地对板材粘接层性质进行表征。

Characterization of adhesive joints of composite solid layers using a nonlinear Lamb wave approach

On the basis of the dispersion curves of the Lamb waves propagating in the composite solid layers and the approach of modal expansion analysis for guided wave excitation, the physical process of generation of the primary Lamb wave time-domain pulse and the corresponding second-harmonic time-domain pulse has been discussed. Considering the measurement function of the Ritec-SNAP system, the physical meaning of integral of the envelope of second-harmonic time-domain pulse has been detailedly analyzed. This integral can describe the efficiency of second-harmonic generation accompanying the primary Lamb wave time-domain pulse, as well as the dispersion degree between the primary and the double frequency Lamb waves. Within the specific frequency range where the phase velocities of the primary Lamb waves exactly or approximately equal that of the double frequency Lamb waves, the second-harmonic signals without overlapping of multi-modes of the double frequency Lamb waves have been clearly observed. This phenomenon shows that the strong nonlinearity does occur in the primary Lamb wave propagation process. For the three different adhesive joints, the experiment results show that both the stress wave factors of the nonlinear Lamb waves firstly introduced in the present paper, and the frequency values corresponding to the peaks of the amplitude-frequency curves of the second-harmonic signals can effectively characterize the properties of the adhesive joints.