Research On The Weld Feature Guided Wave Characteristic And Scattering Mechanism At Weld Defects Based On Periynamics Theory

Welding is the main process of marine equipment construction,the quality of welding directly affects the overall quality,so it is necessary to carry out non-destructive testing(NDT).In order to improve the efficiency of welding NDT,this paper uses SH mode feature guided wave to test the weld,so it is necessary to study the propagation characteristics of SH mode feature guided wave in the weld and the scattering law at the defect.The finite element method is usually used in this research,but the mesh of the finite element method will deform near the defect and the partial derivative is no exist,resulting in the increase of the calculation amount and even distort the result.In order to overcome this problem,the peridynamics method is used to study the propagation characteristics of SH mode feature guided waves and the scattering of the defect.The peridynamic wave equation is a nonlocal integral equation.It is a meshless model and does not need derivative.Therefore,it is more suitable for the simulation and analysis of the model with defects.The main contents of this paper include:the integral equation and dispersion characteristics of peridynamics wave,the propagation characteristics of SH mode feature guided wave,the scattering law of SH mode feature guided wave at typical defects and the weld inspection experiment used by SH mode feature guided wave.1)Study on the wave equation and dispersion characteristics of peridynamics waves.By studying the basic theory of peridynamics,the stress wave equation of linear peridynamics is given.By analyzed the integral equation of linear peridynamic wave,the the dispersion,group velocity,phase velocity and other parameters of S-wave and P-wave in an infinite medium are given respectively by the numerical method.The influence of the weight function,the horizon and the mesh size on the dispersion is discussed.It is found that the dispersion is relatively small,when the weight function isexp(-(?)~2σ~2)and the horizon is three times of the mesh size.2)The propagation characteristics of SH mode feature guided waves.Based on the continuity of the force and displacement at the material point of refraction point,the refraction and reflection characteristics of SH wave in the peridynamics theory are obtained,which are similar to those of the classical theory.The correctness of the peridynamic refraction and reflection characteristics of SH wave is verified by simulating the propagation characteristics of SH mode feature guided wave in the weld structure.Compared with the propagation of SH mode guided wave in steel plate,it is found that the main reason for the formation of SH mode feature guided wave in weld is the reflection of SH wave with upper and lower surfaces.The difference of material parameters between weld seam and steel plate will aggravate the formation.The dispersion equation of SH mode feature guided waves in the weld is obtained by analyzing the stress on the virtual boundary layer near the weld surface.This dispersion equation is consistent with the classical theory,however,as the SH wave in an infinite medium has its own dispersion characteristics in peridynamics theory,it is concluded that the group velocity is slightly slower than that of the traditional theory,and this conclusion is verified by finite element simulation.The influence of different weld residual height and weld type on the formation of SH mode feature guided waves in the weld was studied by peridynamics simulation.It is noted that weld residual height is conducive to the formation of SH mode feature guided waves in the weld.With the increase of welding residual height,more energy is trapped in the weld and cause the signal confusion,making the echo signal not obvious,which does not conducive to detect the defects in the weld.Therefore,it can be possible concluded that the weld model of type II with the residual height about 5%of the weld width is more conducive to the guided wave NDT.3)Scattering of SH mode feature guided waves at typical defects of weld.According to the reflection characteristics of SH wave in peridynamics,the scattering of SH wave at the defect such as cracks and holes is a reflection problem.Through numerical simulation,the scattering nephogram of SH mode feature guided wave at this typical defects is given and analyzed.By analyzed the shear stress wave on the sensor E,the group velocity of SH mode feature guided wave in the weld is obtained,and the location of the defect is given with the error less than 1.3%.It is noted that the SH mode feature guided wave can accurately locate the weld defects.4)The experimental platform of SH mode feature guided wave detection in weld was constructed.Propagation characteristics of SH mode feature guided waves in the weld models at previous chapters are verified by experiments.It is found that the propagation characteristics of SH mode feature guided waves in the weld and steel plate are similar to those of the peridynamics simulation and it verified by finite element method.As the defects in the weld,the group velocity of SH mode feature guided waves is greatly reduced due to the dispersion in the experiment.However,the experimental signal can still locate the defects in the weld with the error less than 1.4%.