Volume 5, Issue 5 (September 1977)
Nondestructive/Destructive Test Correlations and Fracture Mechanics Analysis
In view of the recent developments in finite element stress analysis and materials processing and testing, the reliability of fracture mechanics analysis on service life prediction is critically dependent on the estimation of the flaws by nondestructive test (NDT) methods. This paper discusses the correlation between NDT indications and actual sizes of natural flaws determined by destructively examining flaws and shows the importance of this uncertainty on component life predictions. A section of a low-alloy steel forging was ultrasonically inspected, saw-cut into cubes containing flaws, and examined by C-scan and X-ray. Successive metallographic polishing was performed to reconstruct the shape, size, and location of the flaws. The flaws were identified by using electron microprobe energy spectrum analysis. The flaw sizes predicted by ultrasonic inspection were underestimated by up to 6.6 times the actual flaw area. It was demonstrated that underestimation of the sizes of natural flaws by NDT should be properly corrected to make realistic cyclic life predictions.