| Radii part of T-shaped aluminum alloy is easily influenced by the corrosion environmentand external loads,which will lead to the production and extension of Stress Corrosion Cracks.Such cracks have various orientations,large variations in length,and complex morphology.Affected by the actual testing conditions,it can only be detected from the outside of the T-shaped beam.The conventional non-destructive testing method has low detection rate and quantitative accuracy.And the orientation is difficult to be quantified.In order to solve the appealed problem,this paper studies the quantification,orientation and morphology characterization of cracks in the Radii part of T-shaped aluminum alloy beam based on the phased array ultrasonic testing technology.The quantitative and orientation ability of conventional phased array ultrasonic detection is studied for different orientation and different height of through wall cracks,and the oblique-incidence multi mode full focus method is introduced to study the crack morphology characterization ability of direct mode,half skip mode and full skip mode,and the influence of probe aperture on the imaging effect is also studied.The main research content is as follows:(1)According to the statistical results of actual stress corrosion crack orientation,the artificial flaw test blocks with the crack orientation angles of 20°,55°,-55°,and-33° were designed to research the quantitative ability of phased array ultrasonic testing.Using CIVA simulation software to simulate the sound field of the probe,the results show that when the deflection angle is greater than 40°,the effective focusing range of the acoustic beam is reduced with the increase of the deflection angle,so the low deflection angle focused beam is selected as possible to make ensure the effective focus of the target area when the detection is performed.With the increase of actualt depth of focus,the coverage of the focused sound field will expand,but if the focus depth is set too large,the focus column at the focus will become wider,the resolution will be reduced.Finally,10 mm of focus depth is determined experimentally(2)Conventional phased-array ultrasonic detection of artificial defect test blocks is performed,and the causes of quantitative errors is analyzed.The results show that,for cracks of different orientation angles,the height of through wall more than 0.5 mm can be detected and more than 1.0 mm can be quantified,and the quantitative error is within ±0.5 mm;the quantitative error of the crack orientation of the positive direction(20°,55°)is small,and the maximum error is-6.4°.the quantitative error of the crack orientation of the negativedirection(-33°,-55°)is larger,and the maximum error can reach-30.6°,which is mainly caused by the R angle structure and the orientation of the crack.The actual stress corrosion cracking defects in Radii Part of T-shaped Aluminum Alloy were detected and quantified.The quantitative error of through wall height was less than 1.0 mm.(3)Based on the simulated echo signals of cracks with different orientation angles,the morpholoy characterization effects of the oblique-incident total focus method with different modes were compared.And the effect of the probe aperture size on the imaging results was also studied.The results showed that the TT direct mode(Transverse wave,T),TTT half-skip mode and TTTT full-skip mode can be respectively used to fully characterize the cracks with an orientation angle around 35°,0°and-35°.Increasing the probe's aperture can improve the ability of the probe to receive defect echoes,broaden the range of orientation angle to completely characterize crack morphology.And the experimental imaging results verify that the morphological characterization capability of different modes imaging is consistent with the simulation conclusion. |
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