Nonlinear modal models for sonic fatigue response prediction: a comparison of methods

Accurate prediction of sonic fatigue response is important in designing aircraft structures for long life. Early prediction methods were based on single-mode, linear models which were not accurate for complex structures or large-amplitude response levels. Direct time integration of full, nonlinear, finite element models can provide accurate results, but at a prohibitive computational expense. Recent methods reduce the finite element model to a low-order system of nonlinear modal equations. The modal equations can then be integrated in the time domain. The computational burden is greatly reduced and an accurate response prediction can be accomplished. In this paper, several methods used to construct the nonlinear modal models are compared using a clamped-clamped beam as an example problem.