单向载荷下铝板电磁超声兰姆波的波速响应特性

Wave Velocity Response Characteristics of Electromagnetic Ultrasonic Lamb Wave of Aluminum Plate under Unidirectional Load

鉴于兰姆波(Lamb波)在传播过程中衰减较慢,利用超声Lamb波对金属薄板的应力检测已成为国内外研究的热点。为了更深入了解Lamb波的传播特性与金属薄板应力之间的关系,该文根据Lamb波在各向同性板的频散计算公式,给出单向载荷不同应力下铝板的频散曲线,并数值分析了Lamb波基本模态和一阶模态与应力场在同方向上的传播变化。根据频散方程的计算结果,Lamb波A1模态在速度变化方面比使用其他模态要敏感;且越接近截止频率的一阶模态速度变化越明显。为了验证仿真结果,实验施加单向应力载荷作用于1mm厚的6061铝板,考虑到压电探头激发多模态特性,该文利用电磁超声换能器激发单模态Lamb波,对比基本模态与一阶模态相速度变化率,A1模态的波速变化明显,实验结果与仿真数据相符。因此,该文提出的单向应力加载下超声Lamb波传播特性的研究可为后续金属薄板应力检测提供重要依据。

In view of the fact that Lamb waves decay slowly during propagation,the use of ultrasonic Lamb waves for stress detection of thin metal plates has become a hot research method at home and abroad.In order to understand the relationship between the propagation characteristics of Lamb waves and the stress of thin metal plates,this paper gives the dispersion curve of aluminum plate under different stresses of unidirectional load according to the calculation formula of Lamb wave dispersion in isotropic plate.The propagation of the basic mode and first-order mode of Lamb wave and stress field in the same direction are analyzed.According to the calculation results of the dispersion equation,the Lamb wave A1 mode is more sensitive to speed changes than other modes,and the first-order modal speed closer to the cutoff frequency changes more obviously.The experiment of unidirectional stress load applying to a 6061-aluminum plate with a thickness of 1mm is carried out.Considering the multi-modal characteristics of piezoelectric probe excitation,the electromagnetic ultrasonic transducer is used to excite single-mode Lamb wave.Compared with the phase velocity change rates of the basic mode and the first-order mode,the wave velocity of the A1 mode changes obviously,and the experimental results are consistent with the simulation data,which can provide an important basis for the subsequent stress detection of thin metal plates.