Abstract
Reversed plane bending fatigue tests were conducted on two kinds of structural steels, JIS S35C and SCM435. The behavior of small surface cracks were continuously sampled by replica technique, and their probabilistic properties were investigated. The distributions of fatigue crack initiation life and fracture life were found to be represented by log-normal distributions. The fatigue crack growth rate of S35C in the range of crack length from 0.1mm to 3mm could be expressed by the equation of da/dn=C·σa7.7·a1.3, where σa and a are the stress amplitude and a half of surface crack length, respectively. It was found that the distribution of coefficient C also obeyed a log-normal distribution and its variance was nearly constant irrespective of magnitude of stress amplitude and crack length. Some trials to estimate the distribution of fatigue crack growth life were made based upon the above mentioned experimental results of growth rate.
