| In the production and service process,plate structure easily generate cracks,holes,corrosion and other defects in the surface and internal.One of them,Crack defects are the most common and great harm to structure.In the event of alternating stress,temperature and other external factors,the crack will show a tendency to accelerate the expansion,so that the structure of the residual strength is rapidly reduced,thereby leading to a sudden breakage of the structure.At the same time,the crack has obvious direction,and the damage degree of the crack in different directions is different.When the cracks section is perpendicular to the bearing direction of the structure,the crack is the most harmful and the structure is suddenly broken.If not timely detection and take appropriate measures,it is likely to cause serious consequences.Therefore,on the basis of the existing research,this paper mainly carries out the improvement of the plate structure Lamb wave transducer array detection technology and imaging method.The research work mainly includes:(1)Improvement of Lamb wave array imaging algorithm for plate defects.On the basis of vector full focus imaging,considering the phase information of the detection signal,development of an improved Lamb wave array imaging algorithm for quantitative recognition of plate defects--phase-based vector full focal imaging algorithm.Based on the simulation and experimental data,this method is applied to the quantitative detection of crack in plate structure.Compared with conventional vector full focus imaging,phase-based vector full focus imaging is more accurate for measuring the direction and length of the crack.(2)Guided wave mode separation technology researching based on dispersive matched filtering.The use of Lamb wave propagation characteristics,the development of a dispersive matched filtering signal processing technology for multi-modes Lamb wave mode separation;The effect of sliding window width,sliding step and threshold on the accurate extraction of single mode signal is studied,and the dispersive matching filter parameters suitable for Lamb wave multi-modes separation are selected.The guided wave mode separation technique based on dispersive matched filtering is applied to the Lamb wave array imaging to study the imaging influence of different mode.The results show that the Lamb wave array imaging effect is improved and the detection rate of defect is improved after dispersive matched filtering.In order to evaluate the imaging effect comprehensively,a multi-modes Lamb wave composite imaging method based on the amplitude distribution of received signals is proposed.It is found that the effect of Lamb wave composite imaging is better than that of single mode imaging.(3)Design of Lamb wave array transducer.A single ring/linear array of multimode Lamb wave superimposed ultrasound field calculation model is established,and the influence of the amplitude and phase of the element on the control of the Lamb wave mode is studied.Based on the amplitude and phase control techniques,an excitation method for the excitation of ring/linear array transducer for generating single mode Lamb wave is developed.The results show that the method can realize the mode control of the ring/linear array transducer. |
