Effect of cooperative grain boundary sliding and migration on emission of dislocations from a crack tip in nanocrystalline materials

Abstract

Interaction of the cooperative grain boundary sliding and migration with a crack in deformed nanocrystalline materials is investigated using the complex variable method. Effects of the two disclination dipoles produced by the cooperative deformation on the emission of lattice dislocations from the crack tip are theoretically described. The complex form expressions of the stress field and the force field are divided. The critical stress intensity factors for the first dislocation emission are calculated. Influences of disclination strength, grain size, locations of the two disclination dipoles as well as crack length on the critical stress intensity factors are discussed in detail. Results show that, the cooperative deformation has great influence on dislocation emission from the crack tip. In general, the cooperative deformation can promote the lattice dislocation emission from the crack tip, thus improve the toughness of the nanocrystalline materials.

Stress-driven migration of deformation-distorted grain boundaries in nanomaterials

“…2d). The splitting processes do not have their analogs in the previously examined [3,5,7,10,11,[18][19][20][21][22][23] situations with conventional, non-distorted GBs and lead to formation of new nanoscale (sub)-grains in nanomaterials. With these theoretical results, one can conclude that, in parallel with previously examined grain refinement mechanisms such as (i) continuous dislocation ensemble evolution resulting in sequential formation of dislocation subboundaries, cells and high-angle GBs [43][44][45], (ii) formation and intersection of elongated laminate structures and microbands [46], and (iii) re-arrangements of GB disclination structures [47,48], the stress-driven splitting of deformation-distorted GBs (Fig.…”

“…This process is new for science of stress-driven migration of GBs in nanomaterials. The splitting process has no analogs in the previously examined [3,5,7,10,11,[18][19][20][21][22][23] situations with stress-driven migration of conventional, non-distorted GBs.…”

“…It has been revealed that stress-driven migration of GBs plays a significant role in grain growth, plastic deformation and fracture processes in nanomaterials and thereby essentially influences the outstanding mechanical properties of these materials having a huge potential for technological applications. The previous theoretical examinations and computer simulations [3,5,7,10,11,[18][19][20][21][22][23] of stress-driven migration were focused on conventional GBs having equilibrium structures. At the same time, real GB structures are intensively distorted by deformation processes in nanomaterials during their plastic deformation.…”

Dislocation Forces on an Edge Dislocation Near Crack Tip in Ferroelectric Materials

“…The brittle-ductile transition arising from the thermally activated dislocation slip can strongly influence the degradation mechanism such as fatigue, fracture and plastic deformation in high-temperature ferroelectric ceramics. Hence, the theoretical model of the process of the thermally activated dislocation slip should be first constructed by the dislocation forces (Hirth and Lothe, 1964;Feng et al, 2013).…”

Effect of special rotational deformation on dislocation emission from interface collinear crack tip in nanocrystalline bi-materials

“…For nc solids with cracks, the experimental studies and theoretical derivations have found that cracks can induce plastic shear by emission of lattice dislocations from crack tips as long as the stress intensity factor of crack tips is large enough, thus hindering cracks growth and improving the toughness of nc solids. So it is very meaningful to study the effects of special rotational deformation on the emission of lattice dislocations from various crack tips [29][30][31][32][33][34][35][36][37]. Our group has theoretically investigated the effect of special rotational deformation on the lattice dislocation emission from a line crack, a semi-elliptical blunt crack tip, and an elliptical hole in nc materials and has obtained a series of important conclusions.…”