Nonlinear viscoelastic response of asphalt binders: An experimental study of the relaxation of torque and normal force in torsion

A thermodynamically compatible model for describing the response of asphalt binders

“…In the case of the class of experiments that were considered for correlation, it transpired that a simplified model with only three parameters gave as a good correlation as the full six parameter model. However, neither of these models is capable of fully explaining the data obtained in the experiments of Narayan et al (2012) wherein one clearly observes two distinct relaxation times associated with the normal forces and the shear forces that are developed in a torsion experiment. In order to describe the distinct relaxation times, it seems necessary to construct a model that allows for two 'natural configurations' to be associated with the body.…”

“…Málek et al 298 hence from a philosophical and mathematical point of view, the use of the linearised viscoelastic model to describe such response would be incorrect. The experiments of Narayan et al (2012) and Krishnan and Narayan (2007) concern large deformations and hence the linear viscoelastic fluid model is inappropriate for describing the response of asphalt in these experiments. There are no two ways about it; the linearised model cannot be used despite such models being used to incorrectly describe large deformations by the community trying to describe the thermomechanical response of asphalt.…”

“…In order to describe the distinct relaxation times, it seems necessary to construct a model that allows for two 'natural configurations' to be associated with the body. In this paper, we develop such a model from a thermodynamic standpoint [see also Karra and Rajagopal (2009) for the derivation of a model with two natural configurations in a different context] and use it to corroborate against the experiments of Krishnan and Narayan (2007) and Narayan et al (2012), on asphalt binders. The model describes both sets of experiments very well.…”

“…The torsion experiment carried by Narayan et al (2012) shows that the relaxation time for the normal forces and the torque are very different, in fact an order of magnitude apart, and the models that are available in the literature are unable to describe this phenomenon adequately. Modelling this difference in the relaxation times is a challenge and we find that the recently developed notion of a body having more than one natural configuration associated with it is an ideal vehicle for describing such response.…”

“…One cannot use the linearised viscoelastic model to describe the experiments of Narayan et al (2012) and Krishnan and Narayan (2007) as the deformations are large and nonlinear, and this point cannot be overemphasised and we discuss it in detail at the beginning of Section 2 devoted to the development of our model.…”