Problems of identification of mechanical characteristics of viscoelastic composites

The problem of modelling and identification of viscoelastic properties of composites as asphalt concrete, based on experimental investigations is the subject of this paper. Only viscoelastic properties of such materials are taken into consideration and usefulness of linear constitutive relations in differential form is examined. The identification problem is formulated in terms of sensitivity analysis and optimization theory. An approach to select the "best" from the considered class of material models is proposed and the values of associated material parameters are determined by minimization of objective function representing a measure of a difference between theoretically calculated and experimentally obtained response of a sample to sinusoidal loading. Obtained this way, results are compared with those calculated using the method based on the approach proposed by Bland and Lee [1] for calculation material parameters of Burgers model. It has been shown that differential constitutive relations with constant coefficients have very restricted application in the considered case because they are in force in narrow domains of excitation frequency. The application of models with frequency-dependent coefficients is one of the possible solutions of this problem [2]. Another approach can also be proposed based on the application of fractional calculus in viscoelasticity, see Bagley and Torvik [3].