Nondestructive determination of local material properties of laminated composites with the impulse excitation technique

An innovative experimental methodology for the nondestructive assessment of local elastic properties of composite materials is proposed in this paper. A local region of rectangular shape is isolated on the investigated laminate with a proper clamping system. The first resonant frequency of the retained region with clamped boundaries is determined through the Impulse Excitation Technique. In order to take into account the anisotropy of the composite laminate, values of the resonant frequency are measured after rotating the clamping system with respect to the composite plate. The material constants are finally obtained from the measured frequencies through an inverse optimization algorithm based on Finite Element analysis. The proposed methodology is validated on a unidirectional composite plate with known elastic properties. Boundaries of the investigated region are clamped by pressing two rectangular frames to the plate through a testing machine, thus localizing the measure of the resonant frequencies. The first resonant frequency is measured at different angles (0°, 30°, 60° and 90°) between fibers direction and main axis of the rectangular region. Dynamic elastic properties are finally assessed through the proposed inverse optimization algorithm. The small differences between the nominal and the estimated mechanical properties prove the effectiveness of the proposed methodology.