Study on ultrasonic detection and characterization of partially closed fatigue cracks.

摘要

This study consists of an ultrasonic characterization of two different fatigue cracks in 2024-T351 Aluminum. The first crack was grown with a 5 cycle overload, and the second was grown with a decreasing stress intensity. The first part of the study used through transmitted longitudinal ultrasonic waves to find a distinct change in the transmission coefficient as fatigue cycles were added following the overload and as the crack was statically loaded during the ultrasonic scanning. The second part of the study compared the differences in the through transmitted signals and the shear diffracted signals of the decreasing (Delta)K crack to a crack in the constant (Delta)K condition. In both parts of the study, estimates of the size of the closure region and the magnitude of the residual compressive stress intensity at the crack tip were made through the use of the distributed spring model. This model mathematically characterizes the reaction of an ultrasonic wave to a fatigue crack in a solid. 15 refs., 18 figs., 2 tabs. (ERA citation 15:035061)