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Striation spacing in weld toe cracks due to constant amplitude stress cycling was found to correlate with Bates' empirical equation. Adding closely spaced periodic overloads to the constant amplitude load history increases the striation spacing. Evidence of a decrease of striation spacing for widely spaced overloads, due to crack growth delay, could not be uncovered. About ten percent of the fatigue crack surface was striated, the remaining area being occupied by quasistriations and featureless regions. The lowest spacing detected in the direct surface scanning mode of electron microscopy was 3.3 x 10−8 m/cycle at a maximum magnification of X70 000. At that growth rate, about 80 percent of the crack propagation life had already expired. The microscopic striation spacings observed in this study, employing welded specimens fabricated from A588 structural steel, did not provide reliable indications of the average crack growth rate.
fatigue tests, weldments, striations, fatigue (materials), scanning, electron microscopy, overloads, structural steels.
Associate professor of Civil Engineering, University of Maryland, College Park, Md