Molecular dynamics study on atomic elastic stiffness at mode I crack along bi-metal interface

Abstract

Propagation of mode I crack along bi-metal (001) interfaces of Fe/W, Fe/Ni, Fe/Co and Ti/Mg is simulated by molecular dynamics and discussed with the eigenvalue/vector of the atomic elastic stiffness, B i j a = Δ σ i a / Δ ε j , and surface energy. The crack does not propagate at the interface but in the adjacent phase of smaller surface energy, except in Fe/Ni. The 1st eigenvalue η a (1) , or the solution of B i j a Δ ε j = η a Δ ε i of each atom, clarifies the difference of ‘soft/hard’ of both phases at the onset of crack propagation. In the case of Fe/Ni, the η a (1) of Ni atoms remarkably decreases in the Fe/Ni bi-metal structure, even though Ni has higher η a (1) than Fe at no-load perfect lattices. Thus the rupture occurs in the Ni side even though the Ni has slightly higher (001) surface energy than Fe. Deformation modes at the crack propagation are also visualized by the eigenvector of η a (1) < 0 unstable atoms. This article is part of the theme issue ‘Fracture dynamics of solid materials: from particles to the globe’.

Fracture dynamics of solid materials: from particles to the globe

“…With the main keyword ‘fracture dynamics', this theme issue covers diverse subjects, extending from theoretical yet significantly important model analyses, such as J. D. Eshelby-based [14] collective treatment of damage evolution in brittle materials [3], to practical safety and environmental problems associated with mining or rock excavation engineering, including the fundamental study on the brand-new contactless rock drilling technique using thermal shock [4]. As stated earlier, the scale treated is also diverse, ranging from a fracture at the atomic or microscopic level [2] to largely macroscopic rock/strain bursts or sudden collapse of stopes in deep underground gold mines [9], field observation-based reliable physical estimation of earthquake source parameters [8] or even to megathrust rupture (fracture) near tectonic boundaries of the earth [11]. The theme issue also handles front-line topics like fracture asperity development during the change between stick-slip and stable sliding [5], fracture-induced gravitational perturbations that propagate at the speed of light [12] and seismic events induced by human activity like a fluid injection that can become concerns of the residents nearby [6].…”

“…More specifically, in the first part, Yashiro [2] describes the dynamic behaviour of cracks that develop along with bi-metal interfaces at an atomistic scale based on an ambitious molecular dynamics study. By taking into account his own concept of ‘atomic elastic stiffness' and surface energy, he shows that, depending on the combination of metals, the crack under consideration does not propagate along the bi-metal interface but moves rather in the adjacent phase of smaller surface energy.…”

“…The theme issue consists mainly of two parts where the above disciplines, methods and techniques are lined up in a balanced way. The former part [2–7] handles the fundamental mechanisms related to physical processes of dynamic fracture, basically at the laboratory scale. By knowing the essentials, the readers proceed to the latter part [8–12] where more practical and geophysical issues at larger scales are discussed.…”