This paper presents an alternative to modal analysis to extract stiffness and damping parameters from thin vibrating plates. Full-field slope measurements are performed through a deflectometry technique on a plate vibrating at a given frequency. Images are recorded in phase and at π/2 lag from the excitation. From this information, deflection fields are computed by integration and curvature fields are obtained by differentiation. This information is then input into the principle of virtual work to extract both stiffness and damping parameters. This procedure, known as the Virtual Fields Method, is detailed in the paper and the notion of special optimized virtual fields is extended to the present problem. Validation on simulated data is performed before moving to experimental data. One of the main advantages of this technique is that it is completely insensitive to the damping coming from the boundary conditions. This is illustrated experimentally on two tests where a viscoelastic layer and rubber washers are added in the experimental set up.
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