On the defect tolerance by fatigue spectral methods based on full-field dynamic testing

Abstract

In real life production of dynamically loaded components, we might accept the risk of defects only if we can assess their position by NDT techniques, their effect by proper cumulative damage theory, the dynamic signature of the excitation and the structural dynamics of our structures in service. This work addresses the latter topic by means of experimental full-field optical techniques, which can provide accurate surface displacement distribution in a broad frequency band directly from real components, while recording the excitation, thus, with advanced numerical derivations, coming to an experiment-based full-field strain FRF characterisation, here applied on an aluminium plate. The knowledge of the material constitutive parameters is used to obtain the Von Mises equivalent stress FRFs. The signature of the excitation permits the evaluation of the Von Mises stress PSDs, which can be used in a spectral fatigue method (here the one from Dirlik), coming to a frequency-to-failure distribution. The same distribution can be scaled to a risk index and compared to the defect locations from NDT, in order to build a defect tolerance map and discriminate the product acceptance for dynamically loaded components. The smart exploitation of full-field optical techniques play a relevant role in measuring, with high spatial resolution, the manufactured components in their effective broad structural dynamics and give defect tolerance experiment-based maps, without the need of a highly tuned FE model.