On the viscoelastic response of composite laminates

The present work deals with the determination of the viscoelastic propertie s of composite laminates based on the viscoelastic behaviour of the single lamina. A viscoelastic lamination theory is developed assuming that the lam ina stiffness matrix is fully complex and frequency dependent. For the measurement of the complete set of frequency dependent viscoelastic properties of the single lamina (i.e. complex moduli and Poisson's ratio) a new methodology has been introduced, based on the free and forced vibrati on of unidirectional and [45/-45](ns) composite laminates. All measurements have been performed both in air and in vacuum. Since the v ibration amplitude was very small, in order to fulfil linearity requirement s, the results do not show any significant difference due to air damping. The effects of experimental errors on the evaluation of the viscoelastic pr operties of the single lamina have also been discussed.