This work is part of a multi scale computational and experimental approach in which first principle modelling, nanoscale experiments and continuum simulations are combined in order to represent hydrogen induced degradation and cracking. Nanomechanical testing in air and under electrochemical hydrogen charging conditions are carried out on µm sized single crystal cantilevers of Fe3%Si. Finite element simulations of the cantilever beam testing are performed to obtain the cohesive parameters best representing the yield point of the experimental load displacement curves. The cantilevers tested under hydrogen influence show brittle as well as increased plastic behavior as compared to testing in air. Best fit to the experimental results is obtained for traction separation laws that yielded cohesive energies of 10.1 J/m2 for air and 6.8 J/m2 for hydrogen charging conditions.