Effect of segregated alloying element on the intrinsic fracture behavior of Mg

Abstract

The interaction between segregated alloying elements (Al, Li, Sn, Y, and Ca) and three crack systems is investigated in magnesium simple crystal under mode I loading condition. Using molecular statics in the framework of the (modified) embedded-atoms method, the effect of segregated alloying elements on both the fracture behavior and the intrinsic fracture toughness were identified, and analyzed quantitatively in the framework of the Rice's theory for dislocation emission at a crack tip (Rice, 1992. J. Mech. Phys. Solids 40 239-271). In addition, the variations of the critical stress intensity factor as a function of the misfit strain between the alloying element and magnesium are discussed. The results revealed the existence of a transition from cleavage to dislocation emission at a crack tip. Such transition from cleavage to dislocation emission at the crack tip depends on (i) the orientation of the crack system, and (ii) the nature of the alloying element segregated at the crack tip. Furthermore, when analyzed as a function of the misfit strain between the alloying element and magnesium, our data suggest a direct relation between the fracture toughness and the misfit strain, independently of crack orientation. While alloying element with compressive misfit strain enhances the intrinsic fracture toughness of magnesium single crystal, alloying element with tensile misfit strain worsens the intrinsic fracture toughness of magnesium single crystal.

On the thermodynamics of carbon nanotube single-file water loading: free energy, energy and entropy calculations

“…Thus the mean-square displacement (MSD) becomes quadratic in time indicating ballistic diffusion. This phenomenon has previously been reported for infinite (8,8) pores. 47 The ballistic diffusion was observed down to 30% loading; below these the concerted movement no longer happens, switching towards a Fickian regime.…”

“…dq N Á dq n Á e ÀbV ðN;n;NÞ (8) where V (N,n,N) = V N + V n , with V N and V n being the potential energies of the N and n systems respectively. b = 1/k B T, with k B the Boltzmann constant, T the temperature and C a constant.…”

“…5 For these reasons, the characterization of the flux of water (and other fluids) through CNTs is of vital importance, permitting a clearer understanding of the mechanics in more complex biological media. Molecular Dynamics (MD) has proven to be an ideal tool for the aforementioned studies, and since the first work published dealing with MD simulation of water within CNTs, 6 other studies have followed it, 1,[7][8][9][10][11] providing an improved picture of water dynamics within confined spaces.…”

“…One of the first studies demonstrated that water fills a (6,6) CNT spontaneously in a single-file fashion. 15,16 More recent studies employed different conditions such as pressure-driven water flux in hexagonal arrays of CNTs 8,17 or more realistic situations such as dipoles or charge distributions along the CNT, which are ubiquitous in biological systems. 9,18,19 Many authors have described the thermodynamics of the water-CNT interactions.…”

Molecular dynamics simulations of the lyotropic reverse hexagonal (HII) of Guerbet branched-chain β-d-glucoside

“…These interactions depend on the type of functional groups on the wall, 54,55 which could be stronger in the confined environment than in the bulk. 56,57 The famous examples of such conditions are water inside a carbon nanotube 58,59 and the aquaporin. [60][61][62] One of the direct consequences of the water-wall interaction is the flow properties of the confined water.…”