Embedded Flaw Quantification and Imaging in Curved Components Using Phased-Array Ultrasound SAFT

The detection and quantification of embedded flaws are important for high reliability-demanding parts. To improve the spatial resolution and sizing accuracy of phased-array ultrasonic inspection on curved surfaces, a direct time-domain synthetic aperture focusing technique (SAFT) method is proposed. The overall method is composed of grid construction, data mapping, in-phase summation based on time-of-flight (TOF), and flaw quantification. To accommodate curved inspection surfaces, a polar coordinate grid construction scheme is developed to optimize the grid parameters by minimizing the coefficient of variation of number of the sampling points in the individual grid elements. With proper signal processing procedures, the extent and shape of the flaws can be identified. The quantitative calculation of unknown defects using the distance-gain-size (DGS) method can access their size. Laboratory experiments are performed using 10 MHz ultrasonic transducers to collect data from a disk part having closely spaced artificial flaws. The accuracy of flaw size quantification can be improved by utilizing the improved method. The results show that six closely spaced side-drilled holes ranging from 0.4 mm to 2 mm in diameter can be reliably identified. The quantification results are close to the actual sizes of the artificial flaws. The results of flaw quantification are compared for different coordinate systems. The mean relative error of the quantitative results of flaws is minimized by using the improved scheme.