Abstract
The present work is a continuation of that published as Parts I (BCJ, 1976, 11, 143) and II (BCJ, 1979, 14, 216). The authors report two types of evidence confirming their new theory of active path formation (formulated in I and II), using (a) colorimetric indicators, and (b) Laser interferometry.
(a) The known indicatots for Al and Fe were applied to reveal the anodic regi. It was found that the tips of the electrolytically prepared notches (e.p.n.) in the Al alloy were more anodic (intensely redcoloured) than those of the mechanically prepared (m.p.n.) ones, as opposed to steel specimens, where no difference between the two types of specimen was found. Similar results were obtained using e.n.and m.n. Al and steel specimens after ‘denotching’.
(b) With Laser interferometry under conditions such as to produce ‘caustics’ (back reflections) it was found that, in both stressed and unstressed specimens, the tips of the e.p. notches of the Al alloy showed a higher stress concentration than, did those of the m.p. notches. On the contrary, no appreciable difference was found between the tips of e.p.n. and m.p.n. in steel. Similar results were obtained for both Al and steel using e.n. and m.n. specimens after ‘denotching’. These sets of data are a direct confirmation of the theory that sensitisation in the electrolytically prepared notched specimens in Al alloys leads to active path formation.
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