Integrated peak spectral intensity for in situ crack detection

This paper presents an integrated peak spectral intensity method for in situ detection of a fatigue crack in a metallic material. The method employs a laser beam to illuminate the notch root of a central slot machined on test specimens. The diffracted images are digitized, recorded and processed on a personal computer. Subsequent image processing and analysis yield information from which fatigue crack initiation on the specimen is determined. The technique is applied to aluminium alloy specimens subjected to a cyclic tensile load with a constant stress amplitude. Unlike previous techniques, the present technique enables recording of speckle images and the subsequent detection of fatigue crack initiation without the necessity of unloading the test specimen from the testing machine.