Safety factor maximization for trusses subjected to fatigue stresses

Abstract

This article presents a mathematical model for sizing optimization of undamped trusses subjected to dynamic loading leading to fatigue. The combined effect of static and dynamic loading, at steady state, is considered. An optimization model, whose objective is the maximization of the safety factor of these trusses, is developed. A new quantity (equivalent fatigue strain energy) combining the effects of static and dynamic stresses is presented. This quantity is used as a global measure of the proximity of fatigue failure. Therefore, the equivalent fatigue strain energy is minimized, and this seems to give a good value for the maximal equivalent static stress. This assumption is verified through two simple examples. The method of moving asymptotes is used in the optimization of trusses. The applicability of the proposed approach is demonstrated through two numerical examples; a 10-bar truss with different loading cases and a helicopter tail subjected to dynamic loading.