Echo Signal Prediction For Flaw Detection Based On Nonparaxial Multi-gaussian Model

Ultrasonic phased array inspection technology has an important position in the field of industrial nondestructive evaluation,Although certain beam propagation law can be concluded through lots of testing experiments,it's difficult to reveal the complex path of acoustic beam in the medium.The establishing of the ultrasonic measurement model for echo signal can help to further understand the defect detection process,and realize the quantitative research of the defects.Sound field simulation is an important part in defect detection,and existing models have low computational efficiency and is inaccurate in the off-axis area.Most of the models of echo signal are focused on single interface condition,and less for double interface case.According to the above problems,the paper made the following work:Firstly,based on the Rayleigh integral model in double media and the nonparaxial multi-Gaussian beam model in single medium,a nonparaxial multi-Gaussian beam model for an double interface condition for shear wave detection is proposed.Then this paper provided a systematic way to calculate radiated sound field produced in the interrogated solid medium by phased array transducers mounted on a solid wedge.And comparative analysis between the proposed model and paraxial multi-Gaussian beam model is performed for simulating beam field of shear wear detection.Secondly,the nonparaxial multi-Gaussian beam model is employed to compute the sound field,and this model is combined with the Kirchhoff approximation or the method of separation of variables which is used to calculate the far field scattering amplitude of the side-drilled hole and the system efficiency factor to establish a single medium side-drilled hole detection ultrasonic measurement model of linear phased array to calculate the echo signals.The simulation results of the proposed ultrasonic measurement model are compared with the simulation results of the ultrasonic measurement model based on the paraxial multi-Gaussian model and the experimental results,and the comparative analysis of two conditions including the different focal depths and steering angles are conducted in this paper.Then,the nonparaxial multi-Gaussian beam model is employed to compute the sound field of linear phased array transducer,and the non-paraxial multi-Gaussian beam model is combined with the Kirchhoff approximation and the system efficiency factor to establish a spherical hole detection ultrasonic measurement model of linear phased array transducer.The comparative analysis of three conditions including the different focal depths and steering angles and different diameters are conducted in this paper,and the simulation results of the proposed ultrasonic measurement model are compared with the simulation results of the ultrasonic measurement model based on the paraxial multi-Gaussian model.In addition,the paper studied the echo voltage change of the spherical hole defect by changing the focus depths,steering angles and diameters,which is compared with the side-drilled hole.Finally,we expanded defect detection ultrasonic measurement model in single medium to the double layer media,establishing ultrasonic measurement model under the acrylic resin-water-steel interface circumstance.The nonparaxial multi-Gaussian beam model for shear wave detection is employed to compute the sound field of ultrasonic measurement model for the calculation of echo signals in the far field of two conditions including the different focal depths and steering angles,and the paper also studied the echo voltage change of the above two kinds of defects by changing the steering angles and diameters.