Two-scale model of low-cycle fatigue. Embrittlement of prefracture zone material

A model describing extension of the crack tip in low-cycle fatigue is proposed. This model is appropriate to the scheme by Laird and Smith and describes occurrence of striations in fatigue. The material is considered as composed of quasi-brittle fibers with thin layers. The initial mode I macrocrack is located perpendicular to the fibers. The necessary and sufficient criteria of non-local fracture at the generalized stress state are used. The detailed information on material strain in the prefracture zone is obtained: processes of formation of earing, healing of thin layer material, accumulation of damages in the fibers, extension of the crack tip in discrete steps, and failure of specimens are described.