Abstract: Taking mode-Ⅰ interface crack of aluminum-steel composite material as the research object, the node displacement extrapolation method is used to solve the stress intensity factor ofmode-Ⅰ interface crack of the composite material. The obtained stress intensity factor was expressed by the node displacement. The finite element numerical simulation was carried out to study the relationship of stress ratio and stress intensity factor. The results show that under the same stress ratio condition, the stress intensity factor increases with the increase of crack size ratio. Under the same crack size ratio, the stress intensity factor increases with the increase of stress ratio.

Key words: aluminum-steel composite material, stress ratio, stress intensity factor, mode-Ⅰ crack, nodel displacement extrapolation