用于储罐底板缺陷检测的超声兰姆波模式研究

从超声兰姆波的声场方程出发,得到板材表面离面位移(法向位移)为零的条件,即当超声兰姆波的相速度等于板材介质的纵波声速时,在板材表面的离面位移为零。在给定适当频厚积的条件下,分别数值模拟了仅有切向位移而无离面位移的A1、S1、A2和S2兰姆波模式在有液体负载的单层钢板中的传播情形。结果表明:离面位移为零的S2模式频散较小且对板中缺陷更为敏感。

Examination of ultrasonic Lamb waves for detection of flaws in the bottom plate of oil tank

Based on the acoustic field equation of ultrasonic Lamb waves,the condition has been obtained for the zero out-of-surface displacement component at the plate surface.When the phase velocity of a Lamb wave is equal to the longitudinal velocity of the plate material,it can readily be shown that the out-of-surface displacement component at the plate surface is zero.For appropriate frequency-thickness products,some numerical simulations have been respectively carried out for the specific A1,S1,A2 and S2 Lamb waves propagating in a single steel plate with liquid loading,where these specific Lamb wave modes only have the horizontal displacement component at the plate surface.The present results show that the specific S2 Lamb wave mode has a slight dispersion,and is sensitive to the flaws in the steel plate.