Research On The Localization And Orientation Method Of Crack Based On Lamb Wave

The crane welded by several steel plates usually works in the bad environment such as the large temperature differences, cyclic loading and corrosion. The over allowable stress level usually causes the crack defect in the steel plate and buries safety issues. So the effectively, accurately and quickly detection for the crack is of great importance. Using the lamb wave as a carrier, a method of the detection and location of early crack in steel plate is researched by combing the method of finite element simulation and experiment.Firstly, based on the elastic dynamics theory and Lamb-Rayleigh equation, the property of the lamb wave is studied. The methods for the generation of the lamb wave, as well as the results by using different window function, different center frequency and different wave number are established in ABAQUS and they works as a basis for the determining of the generate signal. The generation of the single mode lamb wave is realized according to the dual incentive theory. The different mode of lamb wave is separated with the help of the wave structure characters.Secondly, a three-dimensional modal is established by using the explicit integral algorithm. The boundary reflected wave is removed by adding the material based on the absorbing boundary which has the increasing damping coefficient. The numbers of the boundary floor is determined by comparing different results of the numbers. Then the two interaction properties are studied in the ABAQUS. One interaction property is the lamb wave of different incident angle with the crack while the other is the lamb wave with the cracks of different length. The scattering matrix is established by using the method of symmetry transform and interpolation.Finally, the number and the layout of sensors are determined by using the method of comparing results of different numbers and layout which is based on the elliptical localization algorithm. A method to detect the crack’s location and orientation is then proposed by adding scattering matrix as a correction factor into the Delay-and-Sum imaging method. The feasibility of this method is validated by experiment based on the lamb wave. The error of the location is less than 5mm as well as the error of the orientation is within plus or minus 5degree.