AN EXPERIMENTAL INVESTIGATION OF THE GROWTH OF SMALL CORNER FATIGUE CRACKS IN ALUMINIUM6061-T651

Results of an experimental investigation of the fatigue growth of smal l corner cracks emanating from small flaws are presented. Growth-arres t behaviour was observed, and increases in crack length during growth periods were of the order of the transverse grain size. For the test m aterial, the corner crack front intersects, on average, only three-six grains in the small crack regime monitored, so only a small number of constrained, interior grains is encountered. It is suggested that the presence of partially constrained surface grains may contribute to th e 'anomalous' growth behaviour which has been observed by a number of investigators. The crack growth histories of the test data presented e xhibit considerable scatter. It is shown that a Student's t-test can b e used to estimate confidence intervals in order to provide a measure of the observed scatter. The variation in confidence intervals in the transition from small to long fatigue crack growth is discussed.