Accession Number:

AD0603522

Title:

RESEARCH ON THE MECHANISMS OF FATIGUE IN ULTRA SMALL SPECIMENS.

Descriptive Note:

Quarterly progress rept. no. 2, 1 Dec 63-31 Mar 64,

Corporate Author:

MIDWEST RESEARCH INST KANSAS CITY MO

Personal Author(s):

Report Date:

1964-03-31

Pagination or Media Count:

25.0

Abstract:

Two phases of the current work are described. The first phase, now completed, is concerned with possible dislocation rearrangement in fatigue-hardened aluminum during preparation of samples for transmission electron microscopy. The second phase deals with a theory of fatigue crack propagation. A method of thinning is described in which a thin 600 A anodic layer is kept intact on the surface of an Al foil during thinning. Such an arrangement suppresses both the escape of dislocations from the surface and their rearrangement within the foil. When rearrangement does occur, slip traces left at the foil-oxide interface record the manner in which this occurs. It was found that rearrangement in fatiguehardened polycrystalline aluminum, which contains a well developed cell structure, is confined to about 15 per cent of the cells and consists of dislocation motion from one boundary to another across the cell. No measurements were possible to determine actual dislocation loss during thinning, but it is suggested that a previous measurement by Ham may be in error due to pinning of dislocations in the interior of cells during rearrangement. Author

Subject Categories:

Distribution Statement:

APPROVED FOR PUBLIC RELEASE