Technological effects in the fatigue of steel

Abstract

The manufacturing process of machine components changes the fatigue properties of the part. The influence of these factors is called technological effects. The ones discussed in this paper are material defects, microstructure, material thickness and surface finish. The analysis emphasizes that the fatigue testing should be performed with test specimens having the same fatigue characteristics as the target component. Design rules are given for the cases when this is not possible.

The main attention is paid on the effect of the surface roughness. It is shown that surface finish can be taken into account in more accurate manner using statistical methods. The only fatigue design method that supports this approach is the one developed by the author since it is based on the distribution of initiated cracks. The depth of the surface roughness can be combined to that statistically. The obtained estimate of total crack depth can be used to calculate the fatigue strength using fracture mechanics.