Advanced procedures for accelerated vibration-based durability tests

Among vibration qualification tests, durability testing is aimed at verifying components’ endurance against the fatigue damage induced by environmental vibrations. For the sake of practical feasibility, it is often required to accelerate the test duration with respect to the expected lifetime of the component still preserving the entire fatigue damage experienced by the latter during its operational life. The spectral function named Fatigue Damage Spectrum (FDS), which is assumed to estimate the fatigue damage potential of (measured) environmental excitations, is commonly used to synthesize vibratory signals that will then be used as input profiles in the accelerated tests. However, the standard practice presents some limitations: in fact, the synthesized signals are in the form of a Power Spectral Density, thus characterized by a Gaussian signal distribution. This could be a strong limitation given the recurring non-Gaussianity of signals measured in real applications. The statistical parameter known as kurtosis is usually employed to account for the deviation from Gaussianity and a number of kurtosis-control algorithms are proposed in the literature as a solution to make accelerated tests more realistic. Yet, some possible problems associated with these techniques should be highlighted: in particular, the kurtosis is only a global metric that roughly estimates the non-Gaussianity of the input signal neglecting the response of the system, on which – conversely – the calculation of the FDS is based. This presentation proposes new methodologies that are based on original algorithms able to synthesize test signals by controlling simultaneously the FDS in conjunction with other target parameters. Each algorithm can control different features of the signal to be synthesized and its selection depends on user demands. The common outcome of these algorithms is the synthesis of non-Gaussian signals, which aim to extend the standard procedures in order to make the accelerated tests more realistic and reliable.