A New Method of d'Alembert's Principle Finite Element Based Fatigue Calculation with Input of Loads and Accelerations

The common practice in finite element based fatigue calculation with multiple channels of road load is to perform a set of unit load static stress analysis and conduct stress time history construction later during fatigue calculation. The main advantage of this so-called quasi-static finite element based fatigue calculation is to avoid time-consuming dynamic stress analysis and also reduce static stress analysis from millions of real load cases to a few dozens unit-load cases. The main disadvantage of this quasi-static finite element based fatigue calculation is the absence of vibration-induced stresses in stress time history construction and fatigue analysis. A decade ago, a modal transient finite element based fatigue calculation was proposed to introduce vibration-induced stresses into finite element based fatigue calculation. The idea is to add vibration-induced modal stresses to load-induced instant stresses in stress time history construction and fatigue calculation. But a time consuming modal transient dynamic analysis has to be conducted in generating modal coefficient time histories. This paper will introduce a new approach to include vibration stress in fatigue calculation without requiring any dynamic analysis. The concept is to have some critical acceleration data, acquired with load data during road load data acquisition, and convert the acquired acceleration data into additional operating loads for stress time history construction and fatigue calculation. This paper will present two steering linkage system prototype vibration fatigue case studies and demonstrate fatigue life calculation accuracy from this new d'Alembert's principle finite element based fatigue calculation.