Pedro Tamayo-Meza

The effect of crystal geometry on the formation and crack development in molybdenum single crystals

The systematic study of the defect structure evolution in single crystal specimens deformed in situ in the high voltage transmission electron microscope (HVTEM) was started around 1977 in the Baikov Metallurgy Institute of the USSR Academy of Sciences. All the experience gathered for the past 30 years has set up the basis for the determination of the way that metals adapt to the different physical factors inside the HVTEM column. In the present work the detailed phenomenology of the generation and propagation process of cracks in single crystals of Mo with different crystallographic orientations as well as the kinetics of opening of primary and secondary cracks and the tip evolution for cracks with different dislocation generation sources is presented.

A Method to Determine Energy and Power of a Fracture Process in Polycrystals by Means of HVTEM

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.