【作者】 刘明明；

【导师】 杨理践；

【作者基本信息】 沈阳工业大学 ， 测试计量技术及仪器， 2012， 硕士

【摘要】 电磁超声(EMAT)因其无需耦合剂,耐高温,易操作等诸多优势,而被广泛研究。目前电磁超声波可以在火车车轮、钢板、铝板、钢管等缺陷检测中应用。在国内外已经成为主流的无损检测方法之一。基于电磁超声原理,进行了电磁表面波的研究。由于表面波具有单模式,能量集中,在试样的表层传播,因此其适合用于金属板材表面的大范围健康状况检测。课题研究了电磁超声表面波的产生原理以及传播特性,并以此为基础,采用ANSYS软件进行有限元仿真。利用折线形线圈和单磁铁的组合建立电磁超声换能器的3-D有限元模型。为简化有限元求解,将EMAT产生的电磁超声表面波分为电磁场、涡流、洛伦兹力、波动四个部分进行分析,之后对铝板进行了表面波的产生与传播的仿真。以有限元仿真为基础,搭建了由激励、接收和换能器组成的电磁超声表面波金属板探伤检测装置。该检测装置利用FPGA产生正负两路以及频率和周波数可调的脉冲串,并采用多级放大解决电磁超声回波的接收信号比较微弱的问题。利用产生的表面波对金属板中的缺陷进行检测,并进行了声场指向性试验。ANSYS仿真中,电磁超声换能器的3-D的有限元模型在厚度30mm的铝板中,产生的洛伦兹力使铝板发生质点位移变化,形成表面波。在实际试验中,在长600mm,宽300mm,厚30mm的铝板和钢板上进行试验,经试验验证,电磁超声表面波探伤检测装置可在铝板与钢板中产生表面波,产生的表面波能够对板中的缺陷进行检测。声场指向性试验证明表面波传播具有指向性。回波信号经小波降噪处理后,达到了预期效果,信号得以清晰展示。更多还原

【Abstract】 Many advantages of electromagnetic acoustic(EMAT), such as no couplant, high temperature resistant and easy operation, make it be widely studied. At present, electromagnetic acoustic has been used in the detection of train wheels, plate, aluminum and steel. Based on the principle of electromagnetic acoustic, electromagnetic surface wave was studied on in this paper. The electromagnetic surface wave is suitable for a wide range of health status detection on the surface of sheet metal because of its single pattern, energy concentration and propagating on the surface of the sample.This paper studied on the production principle of electromagnetic acoustic surface wave and propagation characteristics, based on which ANSYS software was used to conduct finite element simulations. The polygonal-shape coil and single magnet were combination to establish the 3D finite element model of the electromagnetic acoustic transducer. The electromagnetic acoustic surface wave produced by EMAT was divided into four parts, which were the electromagnetic field, eddy current, the Lorentz force and fluctuations, to make a analysis. And then the simulations of the aluminum plate were conducted to the production and propagation of the electromagnetic acoustic surface wave. The metal plate inspection detection device of the electromagnetic acoustic surface wave, which was consisted of the incentive, receiving and transducer, was put up based on the finite element simulation. The problem, which was the weak receiving single of the electromagnetic acoustic echo, was solved with the multi-stage amplification and the positive and negative two roads, the adjustable frequency and cycle of the pulse train generated by FPGA. The electromagnetic acoustic surface wave was used to detect the defects of the metal plate and the test of the sound field directivity was also conducted.The Lorentz force generated by 3D finite element model of the electromagnetic acoustic transducer made a displacement change of particle in the 30mm aluminum plate during the ANSYS simulation. The test was conducted on the aluminum plate and steel plate with 600mm long, 300mm width and 300mm thick. The test verified that the metal plate inspection detection device of the electromagnetic acoustic surface wave could generate a surface wave on the aluminum plate and steel plate, which could detect the defects in the plate. The test of the sound field directivity proved that the propagation of the surface wave had directivity. The echo single could reach the expected effect and the single could be displayed clearly by wavelet de-noising processing.更多还原