Section 5.2.0. Variable-Amplitude Loading
Baseline fatigue data are derived under constant-amplitude
loading conditions, but aircraft components are subjected to variable amplitude
loading. If there were not interaction
effects of high and low loads in the sequence, it would be relatively easy to
establish a crack-growth curve by means of a cycle-by-cycle integration. However, interaction effects of high and low
loads largely complicate crack-growth under variable-amplitude cycling.
In the following sections these interaction effects will be
briefly discussed. Crack
growth-prediction procedures that take interaction effects into account will be
presented in Section 5.2.3.