I want to model the evolution in time of stresses in a material that swells during water uptaking. until now I have done a transient mass diffusion analisys to calculate water concentration inside the material and I have imposed the nodal resoults as a field of teperature to calculate stresses due to water expansion. the problem is that the concentration of water in the material changes its mechanical properties, like Young modulus, coefficient of thermal expansion, coefficient of moisture expansion and so on...and when water concentration reach a certain value the material exibits viscoplasticity.. finally, if this is not enought, it has a diffusion dependence from the stresses ... I'm able to model this coupled behaviour in abaqus?with a UMAT subroutine for example??