Research On Separation Method Of Plane Stress For Steel Members Based On Ultrasonic Spectrum

In recent years,steel structures have been widely used in mid-to-high-rise and super-high-rise buildings in cities,and the internal stress state of steel components is an indicator of structural safety performance.The existing ultrasonic non-destructive testing method is usually the method of stress-sonic when identifying the stress of steel components.This method requires high equipment and the less sensitivity of ultrasonic velocity to stress,so its research of application is mostly limited to the identification of unidirectional stress of steel components.However,in actual civil engineering,steel components mostly exist in the form of plates,plane stress is more common for steel components.For the testing of plane stress,the method used in most research adopted a combination of multiple unidirectional stresses components to indirectly describe the plane stress field,and a few studies involving the separation methods of plane stress.At present,there is no method that can directly measure the three plane stress components inside steel components.Therefore,based on the principle of acoustoelasticity and spectrum analysis technology,this paper theoretically obtains the analytical relationship between the various components of the plane stress and the ultrasonic velocity,and combines the experiments to propose a method for separating the plane stress of the steel components.The main research content as follows:Derivation of the separation theoretical formula for plane stress of steel components.Two plane stress separation methods are proposed: the plane stress separation method based on the shear wave of steel components and the method of combining shear wave and longitudinal wave.These methods are based on the principle of acoustoelasticity,and the processed steel plate components are regarded as acoustic orthotropic materials.The paper use the plane stress separation method based on the shear wave of steel components and the method of combining shear wave and longitudinal wave to deduce their respective stress-wave velocity theory.Derivation of the theoretical formula of ultrasonic phase spectrum.The ultrasonic phase spectrum is used to capture the ultrasonic characteristic quantity.The longitudinal wave equation is processed mathematically,and the characteristic quantity of longitudinal wave velocity can be calculated from the phase difference of two adjacent longitudinal wave echoes.The mathematical model is established through birefringence of shear wave.From the phase spectrum of the corresponding shear wave echo,the shear wave phase difference can be obtained.The polarization shear wave velocity difference characteristic quantity and the shear wave polarization angle characteristic quantity can be calculated.Substituting the obtained characteristic quantity into the analytical expression of stress-wave velocity theory,and the theoretical analytical expression of stress-characteristic quantity can be obtained.Calibration test of plane stress acoustoelastic coefficient of steel components.There are many acoustoelastic constants in the theoretical analytical expressions of stress-characteristic quantities,which need to be determined by calibration experiments.The experimental samples were loaded with a one-way stepwise loading method,the ultrasonic experiment was carried out and the data was collected by the combination of shear wave and longitudinal waves and pure shear waves at each stress gradient.Analyze and process the data to obtain the ultrasonic characteristic quantity under the more stress gradient,and substitute it into the theoretical formula for fitting to determine the acoustoelastic constant.At the same time,the influencing factors such as ultrasonic frequency and steel plate thickness are explored in the paper.Validation experiment of plane stress separation method for steel components based on ultrasonic spectrum.An uneven plane stress field is established,four test points are determined on the sample,and the strain gauge method is used as a comparison to verify the correctness of the two separation methods.The results show that the separation method of combining shear wave with longitudinal waves has higher accuracy on thin plates,while the separation method of pure shear waves has higher accuracy on thick plates.Both of the two plane stress separation methods proposed in this paper can realize the direct measurement of plane stress and have high reliability and engineering application potential.