Residual elastic response in damaged woven laminates through local Impulse Excitation Technique

In this work, the assessment of the residual elastic response in damaged woven laminates is addressed through an innovative nondestructive technique. Based on the Impulse Excitation Technique (IET), the goal is to determine the local variation of the elastic properties through local vibrational tests. In particular, by non-destructively clamping its extremities, the vibrational response of the region of interest can be isolated and a vibrational mode can be excited, which depends only on the material properties of the inspected region. In presence of damage, the local degradation of the elastic response can be then correlated to the decrement of the first resonant frequency. The technique is applied to glass-fibre/epoxy laminates damaged by impact and its sensitivity to the size of the inspected region is investigated through three clamping devices of different dimensions. For validation, tensile tests are performed on specimens cut from the impacted plates, where the axial deformation is punctually measured through optic fibre glued along the specimen axis. Results show that the residual elastic properties assessed with the proposed technique are in very good agreement with those measured through the optic fibre, thus proving the effectiveness of the methodology.