| 主权项 |
1. A method for testing a defect based on an ultrasonic Lamb wave tomography, comprising following acts performed by a computer:
S1, selecting an imaging area on a material to be tested, and partitioning the imaging area into N1×N2 grids, wherein M electromagnetic acoustic transducers for emitting are set on a first side of the imaging area, M electromagnetic acoustic transducers for receiving are set respectively opposite to the M electromagnetic acoustic transducers for emitting on a second side of the imaging area, and N1, N2, M are positive integers; S2, exciting the M electromagnetic acoustic transducers for emitting to emit Lamb waves with a A0 mode in all directions and the M electromagnetic acoustic transducers for receiving to receive the Lamb waves successively, such that M×M testing waves corresponding to M×M Lamb waves are obtained; S3, performing a time-frequency analysis and a mode recognition on the M×M testing waves, so as to obtain time-of-flights of the M×M Lamb waves; S4, recording the time-of-flights of the M×M Lamb waves; S5, determining a first slowness of each grid according to the time-of-flights and a size of each grid to obtain a first defect area; S6, establishing a three-dimensional Cartesian coordinate system in the imaging area, and defining an original emission angle; S7, for a path of a Lamb wave through the defect, obtaining a phase velocity cp at a point P(x,y) on a forward direction of the Lamb wave through the defect and calculating ∂cp/∂x and ∂cp/∂y according to the phase velocity cp, where x is a coordinate value of the point P(x,y) in a x-direction, y is a coordinate value of the point P(x,y) in a y-direction; S8, calculating an extrapolation point of the Lamb wave through the defect by introducing cp, ∂cp/∂x and ∂cp/∂y into an extrapolation formula; S9, judging whether a coordinate value of the extrapolation point reaches or exceeds boundary coordinates of a corresponding grid, if no, using the extrapolation point of the Lamb wave through the defect as a new point on the forward direction of the Lamb wave through the defect and executing steps S6-S9, if yes, recording the coordinate value of the extrapolation point as a coordinate value of the end point of the Lamb wave through the defect; S10, judging whether the coordinate value of the end point of the Lamb wave through the defect reaches or is close to the electromagnetic acoustic transducers for receiving, if yes, obtaining a path with a shortest time-of-flight of the Lamb wave through the defect, if no, changing the original emission angle and executing steps S6-S10 until the path with the shortest time-of-flight of the Lamb wave through the first defect area is found; S11, obtaining a second slowness of each grid according to the time-frequency analysis result and the shortest time-of-flight and a change of a slowness curve in the defect to obtain a second defect area and to determine a size and a distribution of the second defect area. |
