Computer Aided Design of Vibrating Structures Accounting for Material Fatigue and Reliability

The numerical method for prediction of fatigue life of structure is presented. The finite element modeling and damage parameter calculation are based on algoritm described originally in [1]. As an example the optimization of double – disk rotor shaft system, presented if Figure 1, based on sensitivity analysis followed by the fatigue life estimation of optimized shaft is considered. The objective of optimization is to avoid resonance, which can cause excessive stresses leading to prematural fatigue cracks. Sensitivities of eigenvalues with respect to design variables are calculated by the Direct Differentiation Method (DDM) [2,3]. The optimization is performed with the objective to move natural frequencies as far as possible from resonance frequency. Next the shaft system is dynamically loaded. Fluctuation of stress established from FEM analysis by numerical code FEAP [4] are stored, cycles are counted by rainflow method and next fatigue life estimation is performed. Design parameters are diameters of selected shaft parts.