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Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies. [ABSTRACT FROM AUTHOR]

In our previous work, we have pointed out that the shock-induced phase transition in iron occurs with the help of interface energy which reduces the potential barrier between two phases. Here, through studying the nucleation and growth mechanisms of hcp domains in compressed iron, we find that the flatted-octahedral-structure (FOS) is the primary structural unit of the embryo nucleus and phase interface of hcp domains, and the interfacial energy is reduced via formation of FOSs. The phase transition process can be described by the following four stages: (i) Some atoms deviate from their equilibrium positions with the aid of thermal fluctuations to form FOSs with two different deformation directions in the local region; (ii) FOSs with different deformation directions aggregate to form a thin stratified structure like twin-crystal configuration; (iii) The thin stratified structure undergoes a relative slip to form the new hcp phase; (iv) The hcp phase domain grows up through the formation of new FOSs along the phase boundary. In addition, through comparing the time evolution curves of initial single phase domain, we find that the growth rate of single phase domain depends on the loading way and its occurrence time. [ABSTRACT FROM AUTHOR]

Emergence and time evolution of micro-structured new-phase domains play a crucial role in determining the macroscopic physical and mechanical behaviors of iron under shock compression. Here, we investigate, through molecular dynamics simulations and theoretical modelings, shock-induced phase transition process of iron from body-centered-cubic (bcc) to hexagonal-close-packed (hcp) structure. We present a central-moment method and a rolling-ball algorithm to calculate and analyze the morphology and growth speed of the hcp phase domains, and then propose a phase transition model to clarify our derived growth law of the phase domains. We also demonstrate that the new-phase evolution process undergoes three distinguished stages with different time scales of the hcp phase fraction in the system. [ABSTRACT FROM AUTHOR]