Research On Key Technologies Of Flexible Ultrasonic Phased Array Testing For Complex Curved Components Defects

In recent years,with the rapid development of nuclear power,aerospace,and other fields,the shape of functional components has become increasingly complex,and the requirements for nondestructive testing technology are constantly increasing.Ultrasonic phased array technology has great advantages in the detection of complex curved surface components.It can flexibly control the ultrasonic beam steering and focusing through the time delay laws,so it has the advantages of wide detection range,high precision,and fast scanning speed.However,the traditional rigid ultrasonic phased array probe cannot be directly matched with the surface of the specimen,so the sound wave propagation needs to be carried out through water coupling or wedge coupling.Due to the difference in acoustic impedance between the coupling agent and the specimen,the sound field energy will attenuate when the wave passes through the interface,which in turn affects the probe sensitivity and leads to inaccurate defect positioning.To further improve the defect characterization performance of the ultrasonic phased array technology and avoid the influence of the coupling agent,the flexible ultrasonic phased array technology is developed.The flexible ultrasonic phased array probe can perfectly fit the surface of the irregular specimens,but due to the influence of the curved interface,the propagation of ultrasonic waves in the material is complicated.It is difficult to estimate the propagation characteristics and sound field in the specimen without accurate time delay laws,which may fail to receive flaw echoes,thereby reducing defect detection and characterization performance.In order to overcome the problem of defect detection of complex curved surface components and break the existing limitations of flexible phased array technology applications,this paper derives the time delay laws of the flexible phased array for complex curved surface components,and builds the flexible ultrasonic phased array sound field distribution analytical model,and the numerical simulation model of steering and focused acoustic wave propagation and defect scattering.Based on the theories and simulation,the practical application of the flexible phased array probe is studied.Firstly,the one-dimensional flexible array of single-layer concave,convex,concave/convex and the two-dimensional flexible array time delay laws for single-layer concave and convex components detection are established.Furthermore,based on Snell’s law and Fermat’s principle,the geometric model of sound propagation in the two-layer concave and convex components was established,and the accurate time delay law was derived.Secondly,based on Huygens’ principle,the normalized sound pressure amplitude expression of a single array element is derived,combined with the time delay law of each array element,the sound field distribution model of the entire flexible array for detecting single-layer and double-layer complex curved surface components is obtained.To verify the correctness of the analytical model,the distribution of the sound field with and without time delays of the concave,convex,and concave/convex specimens was simulated.The axial sound pressure plot of the sound field distribution diagram is extracted to qualitatively analyze the influence of the radius of the surface,the steering angle and the focusing length on the focusing characteristics of the sound beam.To optimize the design of flexible array probes and detection schemes,the effects of the array aperture,element pitch,array element width,probe frequency and steering angle on sound beam quality were investigated.Thirdly,based on the time delay focusing laws,the time-domain simulation model of sound field propagation and defect detection in complex curved surface specimens is established.The synthesized sound wave can propagate in a predetermined direction and focus on a specified position.Using the time delay laws to make the echo signals of each array element have the same phase,and then superimpose the echo signals.The sound pressure amplitude of the echo signal is greatly enhanced,and the superimposed signal can be used for defect location and quantitative analysis.Moreover,the simulation data of defect detection revealed the influence of array aperture,focal length,and beam steering angle on the detection results.Finally,a flexible phased array inspection platform was built to detect multiple hole defects in concave,convex,and concave/convex components.The B-scan view of defect detection is consistent with the actual position of the defects.The consistency between the A-scan signal of the defect testing and the finite element simulation echo data verifies the correctness and feasibility of the finite element simulation model of defect detection.In addition,different types and sizes of defect inspection for turbine blades were carried out.The results showed that the flexible phased array probe can accurately evaluate and characterize small defects in complex curved surface components using the derived time delay laws and sound field models.