Main crack propagation process in polycrystalline materials is very complex due to intercrystalline sliding mechanism effects. Multiple factors make it considerably difficult to analyze the state of stresses in the crack tip within the theoretical scope of linear fracture mechanics (LFM). As a basis for the suggested Bilby-Cottrell-Swinden model, we propose a method to determine the state of stresses in the tip of a propagating crack in microspecimens subjected to tension and measured inside a high voltage transmission electron microscope (HVTEM). Based on the electron microscopy observations of a main crack and the formation of microcracks in the plastic zone, the J-integral was determined. © 2014 Pedro Alejandro Tamayo-Meza et al.