Viscoelastic functionally graded finite element method with recursive time integration and applications to flexible pavements

The finite-element (FE) method is used for modeling geotechnical and pavement structures exhibiting significant non-homogeneity. Property gradients generated due to non-homogeneous distributions of moisture is one such example for geotechnical materials. Aging and temperature-induced property gradients are common sources of non-homogeneity for asphalt pavements. Investigation of time-dependent behavior combined with functionally graded property gradation can be accomplished by means of the non-homogeneous viscoelastic analysis procedure. This paper describes the development of a generalized isoparametric FE formulation to capture property gradients within elements, and a recursive formulation for solution of hereditary integral equations. The formulation is verified by comparison with analytical and numerical solutions. Two application examples are presented: the first describes stationary crack-tip fields for viscoelastic functionally graded materials, and the second example demonstrates the application of the proposed procedures for efficient and accurate simulations of interfaces between layers of flexible pavement.