Fatigue Dynamics Under Statistically and Spectrally Similar Deterministic and Stochastic Excitations

Fatigue Life Estimation of Structures under Statistically and Spectrally Similar Variable Amplitude Loading

“…This numerical simulation environment uses an existing crack closure retardation model, an FCP method with only one predetermined material parameter. Despite its simplicity, it captured the dynamics of crack propagation and is comparable to the experimental observation in the previous studies [37,38]. Apart from time savings, this environment allows investigation the fatigue life under more sophisticated loading, which is not easily realizable in our experimental setup [47].…”

“…We consider two groups of loading. The first group is the experimental cycles-to-failure from the previous study, where the input to the mechanical system is the velocity solution of Duffing's oscillator and its random surrogate [37,38]. The second group is the simulated cycles-to-failure based on the crack closure model using four chaotic cases and Reference CDR Fig.…”

“…As a result, CDR cannot yield accurate fatigue life estimates if the statistical and probabilistic descriptions are nearly identical. Nguyen and Chelidze [37,38] conducted experiments to explore the fatigue lives under statistically and spectrally similar deterministic and stochastic loads. The resulting averaged time to failures (TTF) under chaotic excitation was twice as long as the one under the corresponding random surrogate.…”

“…Therefore, methods using only the linear statistics from the univariate distribution of stress history and power spectrum led to erroneous predictions. Instead, these differences were characterized by the local divergence rate (similar to the largest Lyapunov exponent, an invariant measure of nonlinear dynamical systems [39]) that reflects the divergence of two initially closely spaced trajectories in the phase space [37]. However, the estimation of such nonlinear factors is conceptually challenging and computationally expensive for real-time monitoring [40].…”

“…The rest of the paper discusses the proposed framework's details and its application to the two groups of cyclesto-failure data. Section 2 provides the details of the generation of load time histories used in this study and the justification for the simulations that qualitatively capture the fatigue crack propagation dynamics from a prior experimental work [37,38]. Section 3 focuses on the formulation of the proposed framework for fatigue life prediction under generic irregular loading.…”