Creep and recovery of linear and non-linear rheological bodies

This research explored the possibility of using fractional creep functions for various rheological bodies to investigate the fractional time-derivatives for strain. It is shown that, by means of these creep functions, the time-dependent deformation behavior of bituminous material in terms of the retarded creep during loading and the relaxation behavior during unloading may be described more realistically than by using time derivatives of integer order. The fractional creep functions allow for the development of non-linear viscous strain during the creep process and to better match the observed behaviour of asphalt mixtures, compared to the use of conventional linear models. This study specifically investigated the retardation and relaxation times in creep and recovery and examined how these can be influenced by the choice of the fractional derivatives. The constitutive relationships were implemented in a non-linear computational model based on the finite element method. Modelling of the above-mentioned phenomena was presented and discussed with the help of numerical simulations and determination of model parameters with the help of actual test data.