固固界面剪切分层的超声波耦合共振机理

Ultrasonic Coupling Resonance Mechanism of Solid-Solid Interface Shear Layering

针对结构表面吸积层去除问题,提出了两种分层模型,研究了超声波激励下固固界面的剪切分层问题,揭示了固固界面剪切分层的超声波耦合共振机理。利用傅里叶积分变换方法,通过严格推导,获得了超声波激励下吸积层结构中的位移场与应力场,进一步获得了固固界面剪切应力场。通过数值积分方法,计算了铝与石膏界面的剪切应力幅值,研究了激励频率与吸积层厚度对界面剪切应力幅值的影响。在固固界面剪切分层条件的基础上,提出了超声波分层频率的选择方法。依据两种分层模型,分别建立了超声波分层实验系统,完成了铝和石膏的分层实验。通过理论分析可知,激励幅值与界面剪切应力幅值存在线性正相关性,界面剪切应力幅值存在共振特性。对于水平剪切(SH)波分层模型,界面剪切应力幅值在第2模态的截止频率处发生了耦合共振。3.5 mm厚的石膏层粘附于3 mm厚的铝板的耦合共振频率是86 kHz。对于Love波分层模型,界面剪切应力幅值在第1模态群速度最小的频率处发生了耦合共振。3.5 mm厚的石膏层粘附于半无限大铝基体的耦合共振频率是88 kHz。吸积层厚度增大,界面剪切应力幅值的耦合共振频率向低频移动。相同激励下,在耦合共振厚度范围内,吸积层厚度越大,界面剪切应力幅值越大。在耦合共振频率附近产生超声波分层频带。通过改变超声波换能器的输出功率调节激励幅值,实验验证了越厚的石膏层分层所需的输出功率越小的结论。随着超声波换能器输出功率的增大,粘附于铝板上的4 mm厚的石膏层首先掉落,接着2.5 mm厚的石膏层掉落,但是1 mm厚的石膏层未掉落;粘附于铝块上的4 mm厚石膏层首先掉落,接着1.5 mm厚的石膏层掉落。研究结果对超声波分层技术在航空航天、风电及空调等领域的推广具有重要价值。

Aiming at the problem of removing accretion layers on the structure surface,two layering models are proposed.Combining theory with experiment,the shear layering of the solid-solid interface under ultrasonic excitation is investigated,and the ultrasonic coupling resonance mechanism of solid-solid interface shear delamination is revealed.The displacement and stress fields in the accretion layer structure under ultrasonic excitation are obtained with Fourier integral transform method,and the solid-solid interface shear stress field is further evaluated.Via numerical integration,the shear stress amplitude at the interface between aluminum and gypsum is calculated,and the influence of excitation frequency and accretion layer thickness on the shear stress amplitude at the interface is achieved.Under the shear layering conditions at the solid-solid interface,a method for selecting ultrasonic layering frequencies is presented.According to the two layering models,the ultrasonic layering experiment systems are established,and the layering experiments of aluminum and gypsum are completed.The theoretical analysis shows that there is a linear positive correlation between the excitation amplitude and the interface shear stress amplitude,and the interface shear stress amplitude has a resonance trend.For the shear horizontal(SH)wave layered model,a coupled resonance of interface shear stress amplitude occurs at the cut-off frequency of the second mode.The coupling resonance frequency of a 3.5 mm thick gypsum layer adhered to a 3 mm thick aluminum plate is 86 kHz.For the Love wave layered model,the coupling resonance of shear stress amplitude occurs at the frequency at which the group velocity of the first mode gets the smallest.The coupling resonance frequency of a 3.5 mm thick gypsum layer adhered to a semi-infinite aluminum substrate is 88 kHz.As the thickness of the accretion layer increases,the coupling resonance frequency of the interface shear stress amplitude shifts to low frequencies.Under the same excitation and within the range of the coupling resonance thickness,the larger the thickness of the accretion layer,the larger the interface shear stress amplitude.The ultrasonic stratified frequency band is generated near the coupled resonance frequency.By changing the output power of the ultrasonic transducer to adjust the excitation amplitude,it is verified experimentally that the thicker gypsum layer requires less output power when layered.With the increasing output power of the ultrasonic transducer,the 4 mm thick gypsum layer adhered to the aluminum plate firstly drops,then the 2.5 mm thick gypsum layer drops,but the 1 mm thick gypsum layer does not fall.The 4 mm thick gypsum layer on the aluminum block drops firstly,then the 1.5 mm thick gypsum layer follows.This approach has both theoretical value and application prospects for promoting ultrasonic layering technology in the fields of aerospace,wind power and air conditioning.