Research On Correction Of Contact Ultrasonic Attenuation Coefficient Considering Surface Roughness

As one of the basic acoustic parameters of the material,the ultrasonic attenuation coefficient correlates with other information such as grain size,segregation and dislocations inside the material,which is of great significance in ultrasonic nondestructive testing.And the ultrasonic attenuation evaluation technique has already been widely applied in the non-destructive characterization of materials for its effectiveness and convenience.However,in an actual test,the surface roughness of the specimens will cause ultrasonic scattering and additional sound wave attenuation,which will induce extra measurement error of the ultrasonic attenuation coefficient,thereby reducing the credibility of ultrasonic attenuation evaluation.This paper researches the influence of surface roughness on ultrasonic attenuation coefficient using contact ultrasonic testing technology and corrects the acoustic attenuation caused by surface roughness in order to obtain more accurate ultrasonic attenuation coefficient,and then improve the accuracy of nondestructive evaluation of ultrasonic attenuation.Firstly,a theoretical calculation formula of ultrasonic attenuation coefficient considering the surface roughness based on the theory of scattering of elastic waves on rough interfaces in a contact measurement is derived,which is capable of correcting the energy loss in this situation.In view of the unstable and unreproducible coupling status of the contact-type ultrasonic transducer,the method of measuring the reflection and attenuation coefficient simultaneously is introduced to ensure the measurement accuracy.Secondly,the integral of each term in the frequency domain in the calculation formula of ultrasonic attenuation coefficient considering surface roughness is obtained based on the ultrasonic attenuation coefficient considering spectrum energy.Then,the calculation formula of ultrasonic attenuation coefficient considering the spectrum energy and surface roughness is proposed,which alleviates the impact of the distortion of the original signal on the evaluation results.Thirdly,an ultrasonic testing experimental platform was built,which consists of hardware and software.The former mainly includes the manufacture of test pieces,the selection of hardware equipment and the design of clamping devices,and the latter mainly includes the acquisition and analysis of data.Using this experimental platform,the test specimens with different roughness were tested and the test results were analyzed.Finally,the measured data is substituted into the calculation formula of the ultrasonic attenuation coefficient considering the surface roughness.The results show that at the same frequency,the corrected ultrasonic attenuation coefficient is independent of surface roughness and is approximately distribute on a horizontal line,which shows that the proposed ultrasonic attenuation coefficient calculation formula can surely regulate the attenuation loss caused by surface roughness.At the same time,the ultrasonic attenuation coefficients based on spectrum energy considering surface roughness are also distribute near a horizontal line with less fluctuations,which indicates that the proposed method takes advantage in anti-interference ability and accuracy.The results of experiment prove the effectiveness and reliability of the proposed method,which lays the foundation for the widespread use of ultrasonic attenuation nondestructive evaluation.