Methodology for Parameter Identification in Nonlinear Viscoelastic Material Model
Two methodologies for identification of material functions in Schapery's nonlinear viscoelastic material model are compared in context to their ability to deal with deviations from Heaviside stepwise load application and unloading in real test conditions where the time intervals for load increase to plateau value and to unloading to zero are finite. In the first method the description of the whole loading, creep, unloading and recovery process is given by one-step load application and one-step unloading whereas in the second method the load increase and decrease intervals are approximated by two-step load application with 0.5 of the load applied in the increase region. Vinyl ester with known viscoelastic properties and incremental form of Schapery's constitutive equation is used to simulate “experimental data” for several length of load application and unloading. The two data reduction methodologies are applied to these “data” and the accuracy of identified material functions is compared with the true values (input data).
Keywordscreep strain recovery ramp loading incremental Vinyl ester nonlinear viscoelasticity
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