ESPI measurements in structural dynamics: fatigue life assessment

Fatigue life assessment, independently of the modelling approach adopted, requires ever increasing precise measurements. Any estimation procedure has to choose the sensor location, a non-trivial task in presence of dynamic events, which may excite complex superposition of dynamic behaviours, not determinable without dedicated tests. Dynamic ESPI technology releases extended capabilities in structural dynamics, like increasing the detail in the description of the dynamic signature of the components, especially where complex-shaped displacement patterns are expected. An ESPI-based procedure for fatigue behaviour assessment of mechanical components is recalled in this paper, exploiting ESPI to enhance the description of the flexible behaviour of components in a wide frequency range. Dynamic ESPI technology is described in brief; the complex-valued nature of the fields that can be extracted from ESPI as displacements and receptance FRF data is commented. Bymeans 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 to a brake disk and to an aluminium isotropic rectangular plate, and reported in detail.