Full Field ESPI Vibration Measurements to Predict Fatigue Behavior

Abstract

Durability of mechanical components is usually evaluated by means of virtual modelling, supported by accurate tests for validation. Besides, many structural parts easily exhibit high modal density with complex displacement patterns and strain fields, that might be difficult to estimate through tests on real samples. Electronic Speckle Pattern Interferometry (ESPI) gives nowadays the opportunity to measure 3D displacements with high spatial accuracy in a wide frequency range by means of optical techniques. Here is proposed an experiment-based procedure to exploit the full-field vibration ESPI measurements in the fatigue behaviour assessment of mechanical components. Starting from a brief description of dynamic ESPI technology, attention is here paid to the complex-valued nature of the fields that can be extracted from ESPI, as displacements and receptance FRF data. By means of a robust numerical differentiation approach and a constitutive model, complex-valued strain & stress fields are evaluated to assess fatigue life, accordingly with the durability model adopted. The whole experiment-based approach is applied on an aluminium isotropic rectangular plate and reported in detail.