Supplementary transfer function of the transport of hydrogen in self-stressed metals

It is well established that the transport of hydrogen dissolved in metals is non-Fickian. This results from a non-zero partial volume of such hydrogen. Consequently, any gradient of hydrogen concentration in a metal causes its self-stress. Till now, the proposed transport equations taking stress into account have found analytical solutions only for quasi-equilibrium cases, and the transfer function (TF) spectroscopy is advocated as a unique technique for modelling the transport in question, and, in this way, estimating from experimental data the parameters that determine the kinetics of this process. In this paper, an additional TF – completing the set of previously proposed TFs – is presented and its applicability for estimating the values of the above parameters is numerically analysed with comparison to other analogous TFs. Although this TF is unique – being outwardly applicable also to the cases of foil and thin-layer specimens – it describes properly the transport in question solely in the case of membrane specimen.