Relaxation constitutive model of fly ash/polyurea composites

Relaxation constitutive model is widely employed for predicting the elastic properties of composite. However, the existing models are only valid for composites with low volume fraction inclusions and are unable to predicate the viscoelastic properties of composite. In this paper, a model to predict the relaxation moduli of ash/polyurea composites (FA/PU) was developed in Laplace domain using four-phase sphere method and afterwards modified using percolation theory. The meso-mechanical modeling of FA/PU along with the dependence of their viscoelastic properties on fly ash volume fraction are investigated. The computational results obtained using the current model and existing four-phase sphere model were compared to the experimental results of relaxation test. It was found that both the two models become less accurate as the volume fraction increases. However, the modified model shows better predictions with experimental results for the trends of master curves than that of the existing model.