Study On The Effect Of Coupling Agent And Sample Surface Roughness On Ultrasonic Propagation In Vermicular Graphite Iron

Ultrasonic detection uses ultrasonic propagation,refraction,reflection and other phenomena to analyze the composition,tissue defects,structural form,etc.of ultrasonic mass in the workpiece,with good propagation,high sensitivity,strong penetration and other advantages.Ultrasonic non-destructive testing is increasingly used to detect the creep rate of creep-ink cast iron.Therefore,it is particularly important to study the influence factors of ultrasonic propagation to improve the efficiency of ultrasonic transmission and ensure the accuracy of detection.This paper mainly studies the effect of surface roughness of coupling agents and specimens on ultrasonic propagation.Because most of the coupling agents commonly used in the experiment are solid liquid and the thickness is not easy to control in the experiment,so the COMSOL simulation software is used for analysis and research.First,the COMSOL simulation model is set up to set the relevant parameters,the four coupling agents of epoxy resin,Vaseline,water and soft rubber are simulated,the influence law of coupling agent type,acoustic impedance and ultrasonic propagation is analyzed,and the influence of the thickness of the coupling agent on ultrasonic propagation is guaranteed under the condition that the type of coupling agent and other excitation signals are unchanged.Select the optimal thickness of the coupling agent in the experiment.Secondly,through the computer to produce a random rough surface in line with Gaussian distribution and simulate the rough surface of the isotropic and anisotropic functions of the same,and finally,using simulation software to study and analyze the different surface roughness entities,to obtain the relationship between roughness and sound propagation.Through simulation experiments,it is possible to obtain: the type of coupling agent has a greater impact on ultrasonic propagation,the closer the acoustic impedance of the coupling agent is to the sound impedance of the test-like,the higher the peak of acoustic pressure,the smaller the attenuation of the sound pressure,the higher the propagation efficiency,the better the coupling effect,among which the coupling and effect of epoxy resin is the best,the best coupling effect of soft rubber;When the thickness of the coupling agent is greater than 0.1mm,the sonic pressure peak and sound velocity of the ultrasonic increase decrease with the increase of the thickness of the coupling agent,and when the thickness of the coupling agent is less than 0.1mm,the ultrasonic pressure peak and sound velocity of the coupling agent increase with the increase of the thickness of the coupling agent.The simulation results show that the surface roughness affects ultrasonic acoustic propagation,and with the increase of surface roughness,the peak of acoustic pressure decreases.When the surface roughness is less than 4um,the peak of sound pressure basically does not change,when the surface roughness is greater than 4um,with the increase of roughness,the peak of sound pressure decreases significantly.With creep-and-ink cast iron as the object under test,the sound velocity of ultrasonic waves under different coupled agents,different coupler thickness and different surface roughness is measured.The experimental results show that the thickness of the coupling agent and the surface roughness of the specimen affect the sound velocity,the speed of the coupling agent decreases first when the speed of sound is reduced and then increases,the thickness of the coupling agent is greater than 0.1mm,the sound velocity decreases with the thickness,and when the surface roughness is less than 4um,the change of surface roughness does not affect the size of the sound velocity.When the surface roughness is greater than 4um,the speed of sound decreases with the increase of surface roughness.