Theory and Calculation of the J-Integral for Coupled Chemo-Mechanical Fracture Mechanics

In this paper,by introducing a chemical field,the J-integral formulation is presented for the chemo-mechanical coupled medium based on the laws of thermodynamics.A finite element implementation of the J-integral was performed to study the mode I chemo-mechanical coupled fracture problem.For derivation of the coupled J-integral,the equivalent domain integral(EDI)method was applied to obtain the mode I J-integral,with expression of the area integrals based on constitutive relationships of a linear elastic small deformation for chemo-mechanical coupling,instead of the finite deformation problem.A finite element procedure is developed to compute the mode I J-integral,and numerical simulation of the y-direction stress field is studied by a subroutine UEL(User defined element)developed in ABAQUS software.Accuracy of the numerical results obtained using the mode I J-integral was verified by comparing them to a well-established model based on linear elastic fracture mechanics(LEFM).Furthermore,a numerical example was presented to illustrate path-independence of the formulated J-integral for a chemo-mechanical coupled specimen under different boundary conditions,showing a high accuracy and reliability of the present method.The variation laws of J-integral and the y-direction stress field with external chemical,mechanical loading and time are revealed.The J-integral value increases with larger external concentration loading in the same integral domain.The extent of diffusion is much greater with larger concentration,which leads to a stronger coupling effect due to the chemical field.This work provides new insights into the fracture mechanics for the chemo-mechanical coupled medium.

Nanotwinned and hierarchical nanotwinned metals:a review of experimental,computational and theoretical efforts

The recent studies on nanotwinned(NT)and hierarchical nanotwinned(HNT)face-centered cubic(FCC)metals are presented in this review.The HNT structures have been supposed as a kind of novel structure to bring about higher strength/ductility than NT counterparts in crystalline materials.We primarily focus on the recent developments of the experimental,atomistic and theoretical studies on the NT and HNT structures in the metallic materials.Some advanced bottom-up and top-down techniques for the fabrication of NT and HNT structures are introduced.The deformation induced HNT structures are available by virtue of severe plastic deformation(SPD)based techniques while the synthesis of growth HNT structures is so far almost unavailable.In addition,some representative molecular dynamics(MD)studies on the NT and HNT FCC metals unveil that the nanoscale effects such as twin spacing,grain size and plastic anisotropy greatly alter the performance of NT and HNT metals.The HNT structures may initiate unique phenomena in comparison with the NT ones.Furthermore,based on the phenomena and mechanisms revealed by experimental and MD simulation observations,a series of theoretical models have been proposed.They are effective to describe the mechanical behaviors of NT and HNT metals within the applicable scope.So far the development of manufacturing technologies of HNT structures,as well as the studies on the effects of HNT structures on the properties of metals are still in its infancy.Further exploration is required to promote the design of advanced materials.

Hierarchical-vortex polarization domain pattern in nano polycrystalline ferroelectric

Domain pattern is the carrier of electromechanical property.A novel domain pattern will open a gate for ferroelectric nano device.A distinctive topological domain pattern termed as hierarchical vortex(Hvo)has been found in polycrystalline ferroelectric based on the first-principles-based atomistic method.The Hvo pattern displays a unique structure,which is a flux-closing vortex encircle an anti-vortex or a vortex and anti-vortex pair(VA).Each Hvo structure could be regarded as a single vortex to forming a vortex-anti-vortex pair with anti-vortex or forming a vortex-vortex array with the vortex.The mechanism of HVo obtained in polycrystalline ferroelectric has been found that the grain boundary(GB)equals the domain wall when the first-order vortex is in the vortex.The HVo will open a new view of the domain topology pattern and its evolution.

Super square carbon nanotube network: a new promising water desalination membrane

Super square(SS)carbon nanotube(CNT)networks,acting as a new kind of nanoporous membrane,manifest excellent water desalination performance.Nanopores in SS CNT network can efficiently filter NaCl from water.The water desalination ability of such nanoporous membranes critically depends on the pore diameter,permitting water molecule permeatration while salt ion obstruction.On the basis of the systematical analysis on the interaction among water permeability,salt concentration limit and pressure on the membranes,an empirical formula is developed to describe the relationship between pressure and concentration limit.In the meantime,the nonlinear relationship between pressure and water permeability is examined.Hence,by controlling pressure,optimal plan can be easily made to efficiently filter the saltwater.Moreover,steered molecular dynamics(MD)method uncovers bending and local buckling of SS CNT network that leads to salt ions passing through membranes.These important mechanical behaviours are neglected in most MD simulations,which may overestimate the filtration ability.Overall,water permeability of such material is several orders of magnitude higher than the conventional reverse osmosis membranes and several times higher than nanoporous graphene membranes.SS CNT networks may act as a new kind of membrane developed for water desalination with excellent filtration ability.