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用有限元方法数值模拟了脉冲线源激光作用于厚铝管时产生的温升以及由此温升而产生的表面声波的情况,得到了逆时针向探测点和波源之间角度从=5°到=180°范围内一系列表面法向位移的时域波形,并对相同厚度不同外径的铝管的表面波进行对比。数值结果表明表面声波中显著的波为掠面纵波、头波和瑞利波,第一个瑞利波脉冲的极性在传播过程中发生了倒转现象,逆时针向看探测点离波源的角度,当较小时瑞利波脉冲是单极性的(负的),随着角度的增大,瑞利波脉冲逐渐变为双极性的,且双极性中正向极性逐渐增大,到=90°时变为完全双极性(正向和负向对称)。随着角度的进一步增加,双极性中负向极性逐渐减小,到=180°时瑞利波脉冲又变为单极性(正的)。不考虑衍射效应时,圆管中第一个瑞利波脉冲的极性和试样的尺寸无关,仅和探测点离波源的角度相关。
The finite element method was used to numerically simulate the temperature rise caused by the pulsed laser source laser and the surface acoustic wave generated by the temperature rise. The angle between the probe point and the wave source was obtained from = 5 ° to = 180 °, a series of time-domain waveforms of surface normal displacement were compared and the surface wave of aluminum tubes of different outer diameters of the same thickness were compared. The numerical results show that the significant waves in the surface acoustic wave are the longitudinal, the first and the Rayleigh waves, and the polarity of the first Rayleigh pulse reverses during the propagation. The angle of the detection point from the wave source When the 瑞 is small, the Rayleigh pulses are unipolar (negative). As the angle increases, the Rayleigh pulses gradually become bipolar, and the positive polarity in the bipolar phase increases gradually Becomes completely bipolar (positive and negative symmetric) up to = 90 °. With the further increase of angle, the negative polarity in bipolar gradually decreases, and the Rayleigh pulse becomes unipolar (positive) at = 180 °. Irrespective of the diffraction effect, the polarity of the first Rayleigh pulse in the tube is independent of the size of the sample, and only correlates with the angle of the probe from the wave source.