Creep and/or Relaxation tests on viscoelastic materials show a power-law trend. Based upon Boltzmannsuperposition principle the constitutive law with a power-law kernel is ruled by the Caputo’s fractionalderivative. Fractional constitutive law posses a long memory and then the parameters obtained by bestfitting procedures on experimental data are strongly influenced by the prestress on the specimen. As in factduring the relaxation test the imposed history of deformation is not instantaneously applied, since a unit stepfunction may not be realized by the test machine.Aim of this paper, it is shown that, the experimental procedure, and in particular the initial ramp to reach the constant stress (or strain) strongly influences the best fitting procedure and the coefficients of thepower-law.
|Number of pages||10|
|Publication status||Published - 2013|