Estimation of Viscous Damping Parameters of Fibre Reinforced Plastic Plates using Finite Element Model Updating

A combined numerical-experimental technique has been implemented using the finite element model updating technique to estimate a set of proportional viscous damping parameters for determining the global responses of fibre reinforced plastic (FRP) plates over a chosen frequency range of interest. The experimentally determined frequencies and mode shapes are used to update the homogenised anisotropic in-plane material constants, before estimating the damping parameters from the directly observed frequency response functions (FRFs). Gradient based inverse sensitivity method has been implemented for the parameter estimation. Existing FRP structures may degrade considerably due to environmental effects over the long period of existence—changing the material and damping properties significantly compared to their initial values after fabrication—thus requiring updating. The estimated viscous damping parameters using the current technique reproduces higher values of modal damping factors for FRP plates. For nonviscous damping, estimation of a set of relaxation factors produces a more realistic estimate of modal damping factors. Increased value of the relaxation factors make the model coincide with the viscous one. A numerically simulated plate problem has been presented along with the experimental validation.