Study On Unianxial Stress Measurement Of Structural Steel Members Based On Ultrasonic Echo Phase Spectrum

Non-destructive testing of structural steel members is one of the important means to evaluate the performance and security of in-service structural steel members.Among the existing non-destructive testing methods,the ultrasonic method has the advantages of directional emission,strong penetrating power,and convenient carrying of measuring instruments compared with other methods,attracting the attention of scholars at home and abroad.At present,the research on uniaxial stress measurement of steel members is mainly focused on ultrasonic acoustic time method,while the ultrasonic acoustic time method is difficult to ensure the accuracy of stress measurement due to the complexity of time domain signal components and the lack of available information.The introduction of spectral analysis technology in ultrasonic testing can make full use of the information in the signal,which is beneficial to the improvement of the accuracy of stress measurement.In addition,the influence of the orthogonal direction of materials is often not considered in the stress measurement of the general steel members subjected to uniaxial stress.However,for a steel member with a certain deflection angle,this effect is not negligible.Based on the above,this paper proposes an uniaxial stress measurement method for steel members based on ultrasonic echo phase spectrum.The main contents of research are as follows:The establishment of a simplified theoretical formula for uniaxial stress measurement based on ultrasonic echo phase spectrum.Firstly,the relationship between the wave velocities of the two wave components and the stress when the steel member is in a uniaxial stress state is clarified by the principle of acoustoelasticity.Secondly,based on the transverse wave birefringence effect,the phase difference and its rate of change,which can express stress information,are given by establishing the mathematical model of the ultrasonic echo.Furthermore,by analyzing the relationship between the maximum value of the rate of change of the phase difference extracted from the rate of change of the phase difference and the wave velocities of the two wave components,the simplified theoretical formula of uniaxial stress measurement based on ultrasonic echo phase spectrum is derived.The establishment of a theoretical formula for uniaxial stress measurement considering the orthogonal direction of materials.The relationship between the wave velocities of the two wave components and the stress in the new coordinate system is determined by embodying the influence of the orthogonal direction of materials of steel members in the new coordinate system.On this basis,a new model of the ultrasonic echo is established to extract the first characteristic frequency from the rate of change of the phase difference and establish a relationship with the the wave velocities of the two wave components,and then derive a theoretical formula for uniaxial stress measurement considering the orthogonal direction of materials.The effect of the orthogonal direction of materials is verified by comparing the phase differences of the steel members with different deflection angles at different incident angles.Uniaxial stress measurement and verification based on ultrasonic echo phase spectrum.Based on the constructed system and the established simplified formula for uniaxial stress measurement,the accuracy of the measurement formula is explained by the preliminary experiment,and the corresponding implementation method of stress measurement is proposed.Based on this,the calibration test and the measurement test are carried out.The error analysis is performed on the test results to verify the accuracy of the measurement formula.At the same time,For the uniaxial stress measurement formula considering the orthogonal direction of materials,the corresponding stress measurement implementation method is proposed,and the stress measurement test is carried out to illustrate the effectiveness of the method.