Stress analysis of viscoelastic materials during drying: I - theory and finite element formulation

A theoretical basis for a nonlinear thermo-hydro viscoelastic boundary value problem was developed. An incremental finite element formulation was derived using the principle of virtual work. The effects of non-uniform temperature and moisture gradients and solution dependent material property functions are outlined. An appropriate computational procedure, which simulates the viscoelastic stresses due to the thermo-hydro and mechanical loads, is discussed. This approach can be used to model the viscoelastic and elastic behavior of materials with three-dimensional axisymmetric and two- dimensional geometries. The model was applied to simulate the stress states during the drying of grain kernels (soybean and corn) with heterogeneous properties. The finite element grid for the proposed models consisted of nine-noded lagrangian elements. The soybean kernel was approximated as an axisymmetric solid (in cylindrical coordinates) and the corn kernel was modeled in cartesian coordinates. This approach, in conjunction with a failure criteria, could be used to predict stress cracks in agricultural grains and food products during drying.