Frequency‐based analysis of random fatigue loads: Models, hypotheses, reality

Abstract

Spectral methods use analytical expressions to estimate the fatigue damage in vibrating structures subjected to uniaxial or multiaxial random stresses. They exploit the random vibration theory which idealizes the random stress as a random process characterized by a power spectral density (PSD) in the frequency‐domain. The random process is hypothesized to be stationary or non‐stationary, Gaussian or non‐Gaussian, and with narrow‐band or wide‐band power spectral density. The accuracy of analytical spectral solutions depends on whether such hypotheses are fulfilled by actual random time‐histories encountered in practice. Knowing the range of applicability of each spectral method is then of utmost importance to avoid estimation errors. After a short account on the frequency‐domain description of random processes, this paper presents a brief survey on selected spectral methods for uniaxial and multiaxial random loading. It then analyzes when the hypotheses behind each spectral method are not verified in reality, with the purpose to provide recommendations for a safe use of frequency‐based methods.

A time-domain procedure for non-Gaussian stationary environmental testing using zero-memory nonlinear transformation

“…Figure 12 shows the kurtoses of the distorted signals y¯rdis, and we can see that the distortion only reshapes the power spectral densities of the signals. Known as “dynamic range loss,” the phenomenon is an intrinsic shortcoming of ZMNL transformations regardless of the type of ZMNL functions (Benasciutti and Tovo, 2018).…”

“…After, Smallwood (2005) supplemented technical details for selection of ZMNL functions for non-Gaussian tests with different skewness and kurtoses. ZMNL functions can rapidly generate time histories with different kurtosis and skewness, but they amplify the magnitude of the auto-power spectral density (ASD) and can twist its shape (Benasciutti and Tovo, 2018; Braccesi et al, 2009; Steinwolf, 2008). Zheng et al (2017) proposed a sequential phase modification method in 2017 and used the hyperbolic sine and inverse hyperbolic sine as ZMNL functions to increase and decrease kurtoses, respectively.…”

Fatigue Life Estimation with Mean Stress Effect Compensation for Lightweight Structures—The Case of GLARE 2 Composite

“…However, up to now, it was usually considered for isotropic materials, and rarely was discussed in terms of durability up to the crack initiation stage. There is a noticeable increase in interest in the frequency domain fatigue life estimation methods, as can be noticed by the number of publications related to this area published in the recent years by the research groups of Benasciutti et al [3,4], Cianetti et al [5,6], and Slavic et al [7,8].…”

Fatigue strength of S355JC steel under harmonic and random bending-torsion loading by a tri-axis shaker: Preliminary experimental results

“…In structural durability of mechanical structures, one of the most challenging goals is durability assessment under random multiaxial loading. Within this complex research field, several numerical and theoretical contributions are present in the literature and, specifically, the research group at the University of Ferrara carried out several activities [1][2][3][4][5] particularly in the frequency domain approach to fatigue damage assessment.…”