A new method for quasi- static analysis of fracture in imperfect crystals is presented. The proposed method combines the Inverse Broyden's Method suitable for finding the equilibrium state for a large system of atoms interacting through strongly non-linear potentials and the Recursive Inverse Matrix Algorithm (RIMA) capable of updating the inverse matrix when topological changes (broken or new bonds between the atoms) take place.

In this approach, the crystal structure is treated as a truss system while the forces between the atoms situated at the nodes are defined by the inter- atomic potentials. Since both the Broyden's and the RIMA algorithms deal with the inverse matrices of the structure their coupling makes the procedure computationally efficient. The developed code was verified by the comparison with an alternative numerical procedure based on energy minimization technique.

A code implementing the developed method was applied to study the phenomenon of hydrogen embrittlement of bcc iron and the hydrogen contribution to the near-neutral pH stress- corrosion cracking. A 3D crystal structure in which the interatomic forces between the hydrogen-iron and iron-iron atoms were defined, respectively, by the Morse and modified Morse potential functions was tested numerically.

The influence of hydrogen on the elastic, plastic and fracture behavior of bcc iron crystal has been simulated with nano -scale tensile tests and the stress—strain curves were obtained for the whole deformation process. The results of simulations are presented and discussed.