| Ultrasonictestingisveryimportantinthenondestructiveexaminationofthick-plate austenitic stainless steel welds. But in pratics, the signal-to-noiseratio(SNR) is low, which is caused by the structure noise of weld histology,therefore mathematical treatment is needed to increase the SNR of theultrasonic back wave. In this research, 60 mm thick austenitic stainlesssteel(SUS304) plates were multilayer butt-welded with single and doubleU-groove, and then horizontal through holes with diameter 2mm weremachined along the middle lines and fusion lines. The horizontal throughholes in weld joints were detected by the shear and longitudinal wave anglebeam probes with differentcrystal plate sizes and K values. The results showthat it gets the better effect when the narrow pulse longitudinal wave anglebeam probes wereusedandtheSNRreaches 12 dB,whileSNR islowerthan8dB when the narrow pulse shear wave angle beam probes were used Thewelds were sampled in different area. Associating the stainless steelmetallurgy theory, the metallograph of welds samples were analyzed. It isfound the thick-plate austenitic weld joint is made up of parallel columncrystal austenite andδferrite distributed along the column crystals, and ischaracterized by transverse isotropy with 5 independent elastic constants.Basedonthefeatureofultrasonicscattered fieldincoarse-grainedmaterial,apoint source synthesis model of scattered fields was built. The CTS-3000 digital ultrasonic flaw detector and computer were used to collect theultrasonic back wave digital signal of through holes. The signal data wasimputed into MATLAB software and was denoised automatically by using1-Dwavelettransform.Comparedwiththesignalbeforedenoising,thesignalSNR underusingvariousprobeincreases4～6dB.
|
PDF Full Text Request