Modelling of the evolution of crack of nanoscale in iron

Metal owns the ability of self-healing to some extent, and the ability of the internal crack healing is most desirable for improving the reliability of metal. A molecular dynamics simulation has been further developed to investigate the evolution of a nanoscale crack in body centred cubic Fe crystal under the conditions of heating or compressive pressure. When system temperature drops, the evolution of the crack that was at elevated temperature has been studied for the first time. N-body potential according to the embedded atom method has been adopted. The original nanoscale crack is expressed by removing some atoms in the centre of the cell, and the minimum vertical distance between the atoms on the top and bottom crack surfaces has been defined as Dm for assessing the process of crack evolution. The results show that a crack healing process can be accelerated significantly with an increase of temperature. When the system temperature decreases, Dm of the crack that was in healing process does not change significantly but fluctuates in a narrow range. This means that the crack healing is the result of Fe atoms diffusing into the crack area but not the thermal stress incurred in the simulation cell at elevated temperature. The pre-compressive pressure under the condition of both biaxial and uniaxial loadings can help promote the crack healing significantly and results in more uniform distribution of defects after healing.