Fatigue lifetime estimation in structures using ambient vibration measurements

A methodology is proposed for estimating damage accumulation due to fatigue in the entire body of a metallic structure using output-only vibration measurements from a sensor network installed at a limited number of structural locations. Available frequency domain stochastic fatigue methods based on Miner’s damage rule, S-N fatigue cycle curves and Dirlik’s probability distribution of the stress range are used to predict the expected fatigue accumulation of the structure in terms of the power spectral density of the stress processes. In predicting the damage and fatigue lifetime, it is assumed that the unmeasured excitations can be modeled by stationary stochastic processes. The power spectral densities of stresses at unmeasured locations are estimated from the response time history measurements available at the limited measured locations using Kalman filter and a model of the structure. The proposed formulation is demonstrated using a MDOF spring-mass chain model arising from structures that consist of members with uniaxial stress states.