Identification of stiffness and damping material properties from forced vibrating plates

The paper presents a novel procedure to derive both stiffness and damping parameters from forced vibrating isotropic plates. The theory assumes that displacement and curvature fields are measured at different times on the whole surface of the plate using a suitable optical technique. These data are processed with the Virtual Fields Method (VFM). This procedure is applied to the measured fields with chosen virtual fields. To be kinematically admissible these latter must be complex with real and imaginary parts. In the case of an elastic isotropic material with viscous damping, the method leads to a linear system of equations valid for any excitation frequency. So the identification is possible out of resonance. Using finite element calculations of the harmonic response of the plate, the method is validated and its stability with respect to measurement noise is checked. A particular experimental set up is used for excitation and measurement of the kinematic fields. Measurement of the slope fields are taken at two times: in phase and at pi/2 lag, using a phase shifting treatment of images of the plate taken with a CCD camera triggered by the excitation. First results of measurements and identifications are presented.