Lamb Wave Testing And Simulation Of Stainless Steel Sheet Welded Joint Of Laser Welding

Plate-like structu， civil and medical industry， as its small deformation， lightweight and enough strength to meet the requirements. But in the laser welding process，laser welding joints always have a number of defects， such as pores， lack ofpenetration which seriously threat the safety of structure. For this kind of structure，traditional detection technique such as transverse and longitude wave testing cann’tsatisfy the requirements of detection because of its dead zone. Lamb wave techniqueshave large coverage area，long propagation length，high detection efficiency which makeit suitable for the detection of plate like structure.This article starts from the basic theories of Lamb wave， and preliminarilydetermines the test mode by the comprehensive analysis of frequency dispersion curve，Lamb wave structure and mode oneness.The propagation of different Lamb waves in thin model specimens and the actualwelding specimens was simulated through the finite element method. The differentvibration mode and different frequency wave acoustic field distribution and their effectson defects were analyzed. The relation of the flaw echoes reflection coefficient anddefects of the size was analyzed. The results show that， for thin simulative specimens，S0(2.5MHz) mode was the best for defect recognition， and A0(2.5MHz) and A1(2.5MHz) mode were obvious to determine the size of large defect. For the actual weldingspecimens，A0(2.5MHz) mode wave was the best，A good agreement with the result offinite element method.Using different pattern Lamb wave for testing， the transmission characteristics ofthe Lamb waves in plate and the actual welding specimens was studied. The results showthat， for artificial defects in thin plate， the effect of defects recognition of S2(2.5MHz) mode Lamb wave was the best.， A0(2.5MHz) mode Lamb wave was best fordetermine the size of effect which is in good agreement with the result of finite element.For the actual welding specimen， A0(2.5MHz) mode a wave testing was the best.Use the method of HHT to do time-frequency analysis for Lamb wave signal in thesheet defects specimens and demonstrate that the method is effective and superior in thepattern recognition of the Lamb wave.and It is also proved that using instantaneousamplitude peak value of the IMF1component as the defect size preferences has goodfeasibility， accuracy. At the same time the Lamb wave mode of thin-walled welded specimen has been effectively recognized by using this method and the defect size hasbeen characterized by using IMF1component instantaneous amplitude peak value.