Detection of crack defects in L-shaped R-zone components based on multi-mode total focusing method (MTFM)

Abstract

Traditional full matrix capture (FMC) based total focusing method (TFM) exhibits advantages in detecting pore-like and slag inclusion-like non-oriented defects. However, this method demonstrates major limitations in crack defect detection within curved components. Due to the complex geometry of the R-zone and the variable orientation characteristics of crack defects, a multi-mode total focusing method (MTFM) imaging based on defect orientation features is proposed. The optimal acoustic paths and time-of-flight (TOF) data for the MTFM were determined through the development of a multi-parameter path selection model based on Snell’s law and Fermat’s principle. This approach effectively mitigated scattering interference from the curved surface and maintained a favorable angle of incidence with respect to the defects. For L-shaped components with 20 mm thickness, 10 mm inner diameter, and 30 mm outer diameter containing R-zone cracks at −30°, 0°, and 30° orientations, both MTFM imaging simulations and experimental results demonstrate significant variations in the algorithm’s sensitivity to defects at different angles. The detection of 2 mm by 8 mm crack defects with three different orientation angles was achieved, with a defect localization error of ≤ ±5 mm. The defect signal-to-noise ratio (DSNR) consistently exceeded the 6 dB requirement of core aviation standards.