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Molecular Dynamics Simulation of Porous Layer-enhanced dislocation emission and Crack Propagation in Iron Crystal

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Journal of Materials Science & Technology 2011年第11期27卷 1025-1028页

作者： D. Li F.Y. Meng X.Q. Ma L.J. Qiao W.Y. Chu Department of Physics University of Science and Technology Beijing Beijing 100083 China Corrosion and Protection Center Key Lab of Environmental Fracture （Ministry of Education） University of Science and Technology Beijing Beijing 100083 China

The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e.9. when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking （SCC）. Molecular dynamics （MD） simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity KI, or stress. To respond to the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity KI, resulting in SCC.

关键词： Molecular dynamics simulation dislocation emission Crack propagation Porouslayer Stress intensity

Brittle-Ductile Transition of Ferroelectric Ceramics Induced by Thermally Activated dislocation emission

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Communications in Theoretical Physics 2013年第7期60卷 101-107页

作者： XIE Chao FANG Qi-Hong LIU You-Wen CHEN Jian-Kang MA Ting-Feng The Faculty of Mechanical Engineering and Mechanics Ningbo University Ningbo 315000 China College of Mechanical and Vehicle Engineering Hunan University Changsha 410082 China

Thermally activated dislocation emission in high-temperature ferroelectric ceramics is investigated through an assumption of thermal stability and a novel analytical method. The stress intensity factor (SIF) arising from domain switching is evaluated by using a Green's function method, and the critical applied electric field intensity factor (CAEFIF) for brittle fracture at room temperature is obtained. Besides, the lowest temperature for single dislocation emission before brittle fracture is also obtained by constructing an energy balance. The multi-scale analysis of facture toughness of the ferroelectric ceramics at high temperature is carried out. Through the analysis, the CAEFIF for crack extension is recalculated. The results show that the competition and interaction effects between dislocation emission and brittle fracture are very obvious. Besides, the higher critical activation temperature, the more columns of obstacles will be overcome. Additionally, the shielding effect arising from thermally activated dislocations is remarkable, thus, the brittle-ductile transition can promote the fracture toughness of high-temperature ferroelectric ceramics.

关键词： ferroelectric ceramics dislocation emission thermal activation shielding effect

Three-dimensional molecular dynamics simulation of hydrogen-enhanced dislocation emission and crack propagation

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Progress in Natural Science:Materials International 2002年第9期 79-82页

作者： LI Zhongji, CHU Wuyang, LI Jinxu, GAO Kewei and QIAO Lijie(Department of Materials Physics, University of Science and Technology Beijing, Beijing 100083, China)

A three-dimensional molecular dynamics simulation using the embedded atom method (EAM) potentials shows that for both pure Ni and Ni+ H, dislocations are firstly emitted during loading and the crack propagates after enough dislocations are emitted. In the case of hydrogen embrittlement, local plastic deformation is a precondition for crack propagation. For the crack along the (111) slip plane, one atom fraction in percent of hydrogen can decrease the critical stress intensity for dislocation emission KIe from 0. 42 to 0. 36 MPam1/2, and that for crack propagation KIp from 0. 80 to 0:76 MPam1/2. Therefore, hydrogen enhances dislocation emission and crack propagation.

关键词： molecular dynamics simulation hydrogen dislocation emission crack propagation nickel.

Edge dislocation emission from an Elliptically Blunted Crack Tip with Surface Effects

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Edge Dislocation Emission from an Elliptically Blunted Crack...

A dislocation-based Model for the Dynamics of Sliding Precursors

中国力学学会学术大会'2009

作者： Fang QH~*,Liu Y~*,Huang BY~*,Liu YW~+ * State Key Laboratory for Powder Metallurgy,Central South University,Changsha 410083,China, + College of Mechanics and Aerospace,Hunan University, Changsha 410082,China

The explicit expressions for critical stress intensity factors are derived for edge dislocation emission from an elliptically blunt crack with surface effects under modeⅠand modeⅡ*** influence of surface effects on ... 详细信息

关键词： edge dislocation blunt crack surface stress dislocation emission

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Acta Mechanica Solida Sinica 2021年第5期34卷 624-631页

作者： Yiran Li Ganyun Huang Department of Mechanics School of Mechanical EngineeringTianjin UniversityTianjin300350China

The onset of dynamic friction plays an important role in the study of sliding ***,the sliding precursors in the form of crack-like defects have been detected in experiments and their strain fields have been measured to be comparable to those of moving *** the present work,we considered the dynamics of sliding precursors by solving the elastic problem due to a moving dislocation in a half-plane and the transient emission of a dislocation at the *** has been found that both the strain field of a moving dislocation and the spatiotemporal evolution agree well with those of a sliding precursor detected in *** results may cast new light to the dynamics of sliding onset.

关键词： Sliding precursor Crack-like defects Moving dislocations dislocation emission

Influence of dislocation Pile-Up on Main Crack Propagation in Nanocrystals in the Hydrogen Environment

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Acta Mechanica Solida Sinica 2023年第6期36卷 851-859页

作者： Jiding Zhang Yue Sheng Hongda Yang Jinbo Wu Xiaoyu Jiang Applied Mechanics and Structure Safety Key Laboratory of Sichuan Province School of Mechanics and Aerospace EngineeringSouthwest Jiaotong UniversityChengdu 610031China

The influence of material micro-defects on the main crack growth under pure shear loading is studied *** mechanism behind the initiation of micro-cracks and crack propagation induced by dislocation accumulation near the grain boundary(GB)ismainly considered,and the influence of dislocation accumulation on the main crack propagation is *** research results reveal that the initiation of micro-cracks near the GB is prior to the propagation of the main *** a hydrogen environment,hydrogen can cause serious embrittlement of the crack tip and promote crack *** energy release rate in the main crack growth direction in the dislocation emission direction is the ***,the main crack will eventually merge with the micro-cracks at the GB along the direction of the slip band,resulting in fracture of the crystal *** research presented in this paper provides some new information for the first stage of crack propagation and contributes to the analysis of the mechanism of crystal metal fracture.

关键词： Crack propagation dislocation emission dislocation pile-up Grain boundary Energy release rate

A NEW N-BODY POTENTIAL AND ITS APPLICATION

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Acta Mechanica Sinica 1996年第4期12卷 358-367页

作者：汤奇恒王自强张永伟 Institute of Mechanics Chinese Academy of SciencesBeijing 100080China

Based on the embedded atom method (EAM) proposed by Daw and Baskes and Johnson's model, this paper constructs a new N-body potential for bcc crystal Mo. The procedure of constructing the new N-body potential can be applied to other metals. The dislocation emission from a crack tip has been simulated successfully using molecular dynamics method, the result is in good agreement with the elastic solution.

关键词： embedded atom method (EAM) N-body potential dislocation emission molecular dynamics

Microscopic study of mode I crack tip deformation

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Journal of University of Science and Technology Beijing 2005年第1期12卷 67-71页

作者： DeshunFan CaifuQian ZhongjunJiang CollegeofMechanicalandElectricalEngineering BeijingUniversityofChemicalTechnologyBeijing100029China

By simulating edge dislocation emissions from a mode I crack tip along multiple inclined slip planes, the plastic zone and dislocation-free zone around the crack tip are obtained. It is found that the shape of the mode I plastic zone consists of two leaning forward loops which is better agreement with experimental observations. Except at the crack tip there are also stress peaks in front of the crack tip. A formula of the maximum peak stress as a function of the applied stress intensity factor and the friction stress has been regressed.

关键词： dislocation emission mode I crack plastic zone stress intensity factor

TEM Study on Hydrogen-Induced Cracking of Fe_3Al Alloy

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Journal of University of Science and Technology Beijing 2001年第1期8卷 35-38页

作者： Biao Gu, Lijie Qiao, Wuyang Chu Material Science and Engineering School, University of Science and Technology Beijing, Beijing 100083, China Material Science/Engineering School Univ. of Science/Technology Beijing Beijing 100083 China

Hydrogen-induced cracking (HIC) of Fe3Al alloy was studied by in situ transmission electron microscope (TEM). Electron transparent specimens were mounted onto a constant displacement device. Stress was applied to the specimen by using a bolt through the device. The results showed that hydrogen enhanced the dislocation emission and motion in Fe3Al alloy. A dislocation free zone (DFZ) was formed following the dislocation emission. Microcrack initiated in the DFZ or at the main crack tip when the emission reached a critical extension. Hydrogen played an important role in the process of brittle fracture of Fe3Al alloy.

关键词： TEM Fe3Al intermetallics hydrogen induced cracking dislocation emission dislocation free zone