FEM formulation for mass diffusion through UMATHT subroutine

This report summarized the development of a Finite Element framework for the description of bulk mass diffusion of a solute (hydrogen) in metallic materials (iron/steels). The implemented governing diffusion law accounts not only for the solute concentration gradients but also for the mechanical state (stress and strain) on the distribution of the solute. The different forms of the Finite Element formulations are described as well as the implementation in the Abaqus commercial code is made through the use of a user defined UMATHT subroutine. A final chapter is also dedicated to the conversion of the units for hydrogen concentration.