Experimental identification of the fractional viscoelastic model of isotropic materials

A mixed experimental-numerical technique for the identification of the fractional viscoelastic Standard Linear Solid model of isotropic materials is presented. Experimental forced vibrational and time relaxation measurements made on uniform, homogeneous specimens made of the same material but with a different geometry are used as input data. Input-output Frequency Response Function estimates are then obtained from forced harmonic excitation measurements in the mid to high frequency range, and from relaxation measurements in the low frequency range. An algebraic iterative identification procedure is introduced to obtain a consistent material model, taking into account the thermodynamical constraint relations between the material tensile and shear parameters. The proposed identification procedure is first validated with respect to numerically simulated virtual measurements obtained from known theoretical material models, taking into account some added numerically generated noise. Two real experimental test applications, related to the identification of the viscoelastic material model of a high-density polyethylene and of a custom composite material made of a dual component epoxy resin matrix and recycled carbon fibers, are detailed and the results are critically discussed.