This method provides 10¥ greater ability to resolve flaws in cylindrical CT data.
Ultra-thin-wall metallic cylinders are extremely difficult to analyze for flaws from top-view X-ray computed tomography (CT) slices and volume renderings. A protocol has been developed using software to unwrap and re-slice the ultra-thinwall cylinder CT data into 2D sheets from the exterior to the interior of the cylinder. This method is based on interior and exterior surface edge detection, and under proper conditions, is fully automated and requires no input from the user except proper voxel dimension from the CT experiment and wall thickness of the part. By performing this transformation to a series of 2D sheets, and utilizing a local contrast expansion method in which each sheet is automatically contrast expanded between its minimum and maximum gray values, the flaws “pop out” at the inspector. This software has allowed NASA to extend the in-house world-class micro-computed tomography method for 10x better flaw resolution for cylindrical structures.
Advantages of this software over other similar software that might be found commercially include first, ease of use; second, the ability to work with essentially unlimited size data sets; third, the inclusion of on-line slice histogram matching and sub-voxel precision alignment routines that are automatically performed prior to unwrapping and re-slicing; and fourth, visual cues that show the inspector where the re-slice is located within the volume. Fifth, and perhaps most significantly, the inspector can use analysis tools in the software to point and click on these flaws on the unwrapped re-slices. This results in the automated recall of the proper top view slice, and draws a line from the center of the top view slice to the exact angular/polar location of the flaw on the slice. This protocol not only results in the ability to find flaws that would not be found using the top-view slices and volume renderings alone, but it also makes the process of locating and characterizing flaws, at minimum, an order of magnitude easier and faster.
This software, entitled CT-CURS, is used in the Advanced Stirling Radioisotope Generator, Advanced Manufacturing, and Vehicle Systems Safety Technologies programs to assist inspectors in detecting and sizing flaws in metallic and composite materials. The executable software can be downloaded from https://sr.grc.nasa.gov/public/project/86/.
This work was done by Don J. Roth of Glenn Research Center.
Inquiries concerning rights for the commercial use of this invention should be addressed to NASA Glenn Research Center, Innovative Partnerships Office, Attn: Steven Fedor, Mail Stop 4–8, 21000 Brookpark Road, Cleveland, Ohio 44135. Refer to LEW-19030-1/1-1.