Microstructural and mechanical analysis on the shock-induced spalling with structural transformation in single crystal iron: Atomistic simulations

Recent research has demonstrated that the structural transition has an important influence on the fracture process. However, the microstructural evolution mechanism of the coupled development of structure transition and delamination damage has not been fully revealed. This work further discusses the connection between microstructure change and damage evolution of single crystal iron at the different shock intensities based on molecular dynamics simulations. Firstly, according to the microstructural characteristics in the tensile stage, four spall types are activated at different loading intensities. At the lower phase transformation degree, the zone of the twinning intersection and defect structure (stacking fault) as the void nucleation sites have the lower spall strength. At the higher phase transformation degree, we find that the BCC to HCP phase transition process is accompanied by Shockley dislocations, providing void nucleation sites. Meanwhile, the BCC to FCC phase transformation is helpful to transfer the loading and improves the tensile properties of iron, leading the FCC phase fraction at the spall plane to increase with the loading intensity. In addition, the initial temperature can change the microstructural characteristics to regulate spall types, which may cause an abnormal increase in spall strength with the increasing temperature. It is also found that randomly distributed disordered atoms exceeding a certain content are conducive to porous nucleation, which leads to different morphological characteristics of the spall surface. This paper mainly reveals the possible relationship between microstructures and damage evolution, which provides a physical reference for understanding the mechanism of structural transformation on spallation.