Accession Number : AD0287962

Title :   THE EFFECT OF SIZE AND STRESS HISTORY ON FATIGUE CRACK INITIATION AND PROPAGATION

Corporate Author : WEIBULL (WALODDI) LAUSANNE (SWITZERLAND)

Personal Author(s) : WEIBULL,WALODDI

Report Date : AUG 1962

Pagination or Media Count : 1

Abstract : Geometrically similar sheet specimens of 2 different Al alloys were subjected to various load cycles. It was found that each size had its individual S-N sub i curve, considerably differing from those of other sizes. A reduction to one and the same size by means of the Neuber stress concentration factor K sub N was only partia ly successful. A static preload was found to increase the value of N sub i from 11 kc to 205 kc. Equations relating crack length to number of cycles are derived for two alternatives: constant stress cycle and constant load cycle applied to a sheet specimen. It was found that the rate of crack growth is constant after a transition period had been passed. The duration of this period is dependent on the duration of the preceding initiation period. For small values of N sub i it does not even exist. Also, a convenient method for interpreting the results was obtained by plotting crack length vs. number of cycles. It was fo nd that the propagation period starts with a transition period, followed by 1, 2, or even 3 stable propagation periods, the number depending on the magnitude of the applied load. An examination of the broken specimens showed that these periods correspond to different fatigue mechanisms. It is concluded that total fatigue life cannot be predicted without considering separately the parts of which it is composed. (Author)

Descriptors :   *ALUMINUM ALLOYS, *FRACTURE (MECHANICS), PROPAGATION, SHEETS, STRESSES, THEORY

Distribution Statement : APPROVED FOR PUBLIC RELEASE