Study On The Effect Of Couplant On Ultrasonic Propagation Characteristics

Ultrasonic nondestructive testing technology is used to determine the defects in materials or workpieces by the detection of ultrasonic propagation characteristics in the media,which is widely used in the field of industry.In the process of ultrasonic nondestructive testing,in order to improve the transmission efficiency of sound energy between the ultrasonic transducer and the workpiece,it is usually necessary to apply a layer of couplant between the transducer and the workpiece.The couplant effect has a great influence in the detection results.If the type of couplant is not suitablely or improperly used,it may cause large error or incapable reception for received signal,which directly affects the validity and accuracy of the detection result.For the practical problems in this paper,the influence of propagation characteristics of ultrasonic wave for different types of couplant and thickness is studied by the method of pulse penetration to determine the coupling effect,and the coupling agent is used in the study mainly for Vaseline,oil and different ratio of epoxy resin.Firstly,the three-dimensional simulation model was established,the propagation characteristics of ultrasonic wave in double-layer media are analyzed and the influence of different types of couplant and thickness on the peak value of the received signal was studied by using COMSOL software of finite element simulation.Secondly,the signal launch board for the ultrasonic transducer to provide effective excitation signal is designed,and experimental platform is built on this basis.Finally,the effects of different types of couplant and thickness on peak,the maximum of amplitude spectrum and total energy of the received signal are studied by experiments.The simulation and experimentation show that the larger the acoustic impedance of the couplant for different types of couplant is,the better the sound impedance matching between couplant and the workpiece is,the better the coupling's effect.The order of the coupling effect is in turn the epoxy resin and curing agent ratio of 1: 1,the epoxy resin and curing agent ratio of 2:1,the epoxy resin and curing agent ratio of 1:2,the epoxy resin and curing agent ratio of 3:1,the epoxy resin and curing agent ratio of 1: 3,Vaseline and oil.Under the premise of constant couplant,the greater the thickness of couplant is,the greater the attenuation of the ultrasonic wave in the propagation process is,the worse the coupling effect is.