Numerical Simulation Of Laser Ultrasonic Detection Of Surface And Internal Defects In Aluminum Cylinder

In industrial production,metal cylinder is easy to cause corrosion and fatigue damage,which leads to serious accidents because it works in bad environment for a long time.At present,most of the damage state assessment techniques are relatively backward,and the geometric characteristics of the cylinder itself make the defect detection more difficult,so it becomes a difficult problem in the field of nondestructive testing.In this paper,the nondestructive,surface defect and internal defect models of aluminum cylinder are established by finite element method.Firstly,the propagation process of surface acoustic waves and the interaction between surface acoustic waves and surface defects were simulated.Then,the surface defect models with different depths were simulated.Finally,the simulation results were verified by experiments.The results show that: 1.The phase of surface wave will be reversed after propagating around the circle,and the reflected surface wave generated by the defect has the same phenomenon of phase shift;2.The receiving time of P-wave peak is delayed due to the change of defect depth.The propagation path of P-wave peak is speculated and the corresponding formula is proposed to prove,the calculated results are in good agreement with the simulation results.3.The A-scan data obtained from the experiment were linearly fitted,and the error percentages of the calculated results were controlled within 6.4%;The frequency spectrum analysis shows that the experimental results and the simulation results show a similar downward trend.For internal defects,the propagation characteristics of S-wave in aluminum cylinder are analyzed by finite element method.Numerical models of circular hole defect with different radius,rectangular defect with different position and rectangular defect with different length were established,and the effects of circular hole defect radius,rectangular defect offset distance and rectangular defect length on S-wave propagation were investigated.The results show that: 1.The main energy of S-wave changes from 15°-36° to 20°-35° at different times,and the peak energy is located near 28°.According to the results,an approximate equilateral triangle propagation path is proposed and verified by the formula.2.When the rectangular defect enters the main energy range of S-wave,S-wave is more sensitive to the change of defect position,and the fitting formula is used to quantitatively estimate the defect offset distance,and the error percentage of the results is controlled within 3.5%.3.With the increase of the length of the rectangular defect,the transmitted wave ST energy and shock weaken,and the receiving Angle decreases,presenting an approximate linear energy distribution.The corresponding propagation path and length calculation formula are proposed,and the error percentage of the calculated results is controlled within 6.5%.