抄録
The previous fatigue tests on annealed and electropolished 0.23%C steel specimens under two stress levels have shown that Miner's rule holds good for both crack initiation and crack propagation processes.
In this study, rotating bending fatigue tests were carried out on age-hardened aluminum alloy specimens under constant loading or under two-step loading. The behavior of fatigue cracks was observed successively by the replication method and the differenc between an age-hardened aluminum alloy and a carbon steel was examined.
The main results obtained are as follows:
(1) The crack propagation curves show that Miner's rule does not hold when analyzed based on the total fatigue life. Moreover, these curves explain the phenomenon that the value of the cumulative cycle ratio, n1/Nf1+n2/Nf2, is larger than unity when σ1<σ2, but becomes smaller than unity whenσ1>σ2.
(2) Miner's rule holds good for the crack propagation process where the crack propagetes from 0.5mm to final fracture.
(3) Miner's rule does not hold for the initiation process of small cracks (e.g. length of 0.1mm to 0.5mm). This is different from the case of a carbon steel. This may be explained based on the characteristics of fatigue behavior of an age-hardened aluminum alloy.
