Abstract
In order to investigate the influence of surface layer on the corrosion fatigue properties of metal prestrained by pulling, high cycle fatigue tests were performed on aluminum alloy (2017) sheet specimens under completely reversed plane bending stresses in laboratory air and in salt water (3.0% NaCl). The distributions of crack length at various stages of fatigue lives were examined, and these distributions for the specimen with surface layer (Non-polished) were compared with those for the specimen without surface layer (Polished). The conclusions obtained are summarized as follows.
(1) The crack length was found to be arranged by a single Weibull distribution in air and in the early stage of corrosion fatigue. In the latter half of corrosion fatigue, the distribution of crack length was made up of two types of crack groups. One is the crack which propagates individually, and the other is the crack which is accompanied with crack connection.
(2) The distributions of crack length at a certain stress cycles was able to be explained by a statistical calculation, which takes into account both the variation of number of cracks during stress cycling and the scatter of crack propagation rate.
(3) The influences of surface layer on the both crack initiation and propagation behaviors in corrosion fatigue were explained on the basis of Weibull distribution of crack length and the statistical calculation as mentioned above.
