The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Wuyang Chu - One of the best experts on this subject based on the ideXlab platform.
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Molecular Dynamics Simulation of Porous Layer-enhanced Dislocation Emission and Crack Propagation in Iron Crystal
Journal of Materials Science & Technology, 2011Co-Authors: Fanyan Meng, L.j. Qiao, Wuyang ChuAbstract:The internal stress induced by a porous layer or passive layer can assist the applied stress to promote Dislocation Emission and crack propagation, e.g. 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.
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Molecular dynamics simulation of dealloyed layer-enhanced Dislocation Emission and crack propagation
Materials Letters, 2002Co-Authors: Yun Zhang, San-qiang Shi, Wuyang ChuAbstract:Abstract Three-dimensions molecular dynamics (MD) method by employing the embedded atom method (EAM) potential is used to simulate the effect of stress corrosion-induced dealloyed layer existed on the surface of a crack of Cu 2 Au alloy on Dislocation Emission and crack propagation. The simulations show that the existence of a dealloyed layer enhances Dislocation Emission and crack propagation, i.e., decreases the critical stress intensity for Dislocation Emission from K Ie =0.62 MPam 1/2 to K Ie *=0.556 MPam 1/2 and that for crack propagating after emitting large amounts of Dislocations from K IP =1.14 MPam 1/2 to K IP *=1.06 MPam 1/2 . This indicates that dealloyed layer-induced tensile stress can help the applied stress to enhance Dislocation Emission and crack extension.
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In-situ transmission electron microscopic observation of corrosion-enhanced Dislocation Emission and crack initiation of stress corrosion
CORROSION, 2000Co-Authors: Kewei Gao, Wuyang Chu, Tong Zhang, L.j. QiaoAbstract:Abstract A constant deflection device designed for use within a transmission electron microscope (TEM) was used to study the change in Dislocation configuration ahead of a crack tip during stress corrosion cracking (SCC) of brass in water, Ti-24% Al-11% Nb alloy in methanol (CH3OH), and the initiation of SCC. In-situ tensile tests in the TEM also were carried out to assess deformation without the influence of environment. Results showed that corrosion during SCC enhanced Dislocation Emission, multiplication, and motion as well as produced a Dislocation-free zone (DFZ). Nanocracks of SCC initiated in the DFZ or from the crack tip when the corrosion-enhanced Dislocation Emission and motion reached a certain condition. The action of the corrosion process prompted nanocrack propagation into a cleavage or intergranular microcrack rather than blunting into a void as seen during experiments in the TEM.
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In situ TEM research of Dislocation Emission and microcrack nucleation for Ti after adsorption by Hg
Corrosion Science, 1999Co-Authors: Yanbin Wang, Wuyang ChuAbstract:Abstract Using a special constant deflection device, the change in Dislocation configuration ahead of a loaded crack tip for a-Ti, before and after adsorption of Hg atoms, and the initiations of Hg-induced microcracks have been observed in TEM, as well as the in situ extension in TEM without Hg. The results showed that chemisorption of Hg atoms facilitates Dislocation Emission and motion. When the chemisorption-enhanced Dislocation Emission and motion develop into a critical situation, a microcrack in LME nucleates from the main crack tip and/or in the Dislocation free zone (DFZ), and propagates in cleavage mode. During in situ extension in TEM without liquid metal, when Dislocation Emission and motion induced by thermal activity and applied stress reach a certain critical condition, microcracks nucleate but do not blunt into a void.
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In situ observation of corrosion-enhanced Dislocation Emission and motion resulting in initiation of stress corrosion cracking
Corrosion, 1998Co-Authors: Wuyang Chu, K.w. Gao, Tong Zhang, Chimei HsiaoAbstract:A special constant deflection device for TEM was used to study the change in Dislocation configuration ahead of a crack tip during stress corrosion cracking (XC) of brass in water and of Ti-24Al-11Nb alloy in methanol as well as the initiation of SCC. In situ tensile test in TEM for brass was carried out to compare. The results show that corrosion process itself during SCC can enhance Dislocation Emission, multiplication and motion as well as a Dislocation free zone (DFZ) is formed. When the corrosion--enhanced Dislocation Emission and motion reaches certain a condition a nanocrack of SCC initiates in the DFZ or from the crack tip. Because of the action of the corrosion solution the nanocrack of SCC propagates into a cleavage or intergranular microcrack rather than blunts into a void like in situ tension in TEM.
Wei Yang - One of the best experts on this subject based on the ideXlab platform.
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Transient Dislocation Emission from a crack tip
Journal of The Mechanics and Physics of Solids, 2001Co-Authors: Wei Yang, Jia-cai Tang, Chien-ching MaAbstract:Abstract Transient nature of Dislocation Emission from a crack tip gives a new twist to the study of brittle-to-ductile transition. In a class of materials, only the Dislocations traveling at high speed may escape from the crack tip. The nucleation of a fast moving Dislocation, however, requires a higher level of activation energy, as supported by many experimental data. The present paper explores this scenario under the restriction that the Dislocation moves along the crack extension plane. Fundamental solutions of moving Dislocations are derived, and which provide the drag forces on the Dislocations and the shielding to the crack tip. Nucleation of a fast moving Dislocation is examined under the Peierls–Nabarro theory. Incremental Dislocation flux is created continuously from the crack tip, and moves away at a constant speed. At a judgmental time of Dislocation Emission, the displacement jump relates to the holding force along the crack extension plane by a periodic inter-planar potential, and the singular stress induced by the transient and rate-dependent displacement jump negates the original crack tip singularity. A dynamic overshoot calculation under quasi-steady assumption provides an escape velocity of Dislocations. To achieve it, extra activation energy is required for the transient Dislocation nucleation and that reduces the Dislocation nucleation rate along the crack front. When compared with the rate-insensitive process of cleavage, the transient Dislocation Emission process allows us to predict the rate dependency of the brittle versus ductile behavior of materials.
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A numeric study on chaotic Dislocation Emission
Communications in Nonlinear Science and Numerical Simulation, 1996Co-Authors: Honglai Tan, Wei YangAbstract:Abstract Crack tip atom-string model is devised to study non-linear features of Dislocation Emission processes under mode II loads. Dynamic analysis shows that the atom motion at the crack tip changes from periodic to chaotic as the stress intensity factor increases. Study on the Dislocation Emission band reveals the phenomenon of cloud-like drifting of the Dislocation core ahead of the crack tip.
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Nonlinear motion of crack tip atoms during Dislocation Emission processes
Journal of Applied Physics, 1995Co-Authors: Honglai Tan, Wei YangAbstract:Nonlinear features of Dislocation Emission processes under mode II loads are explored from an atomic scale. Crack tip atom string models coupling with the continuum mechanics analysis are devised. Dynamic analysis shows that the atom motion at the crack tip changes from periodic to chaotic, as the mode II stress intensity factor increases. The chaotic atom motion dictates the Dislocation nucleation process at the crack tip. Study on the Dislocation Emission band reveals the phenomenon of cloudlike drifting of the Dislocation core ahead of the crack tip.
Chien-ching Ma - One of the best experts on this subject based on the ideXlab platform.
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Transient Dislocation Emission from a crack tip
Journal of The Mechanics and Physics of Solids, 2001Co-Authors: Wei Yang, Jia-cai Tang, Chien-ching MaAbstract:Abstract Transient nature of Dislocation Emission from a crack tip gives a new twist to the study of brittle-to-ductile transition. In a class of materials, only the Dislocations traveling at high speed may escape from the crack tip. The nucleation of a fast moving Dislocation, however, requires a higher level of activation energy, as supported by many experimental data. The present paper explores this scenario under the restriction that the Dislocation moves along the crack extension plane. Fundamental solutions of moving Dislocations are derived, and which provide the drag forces on the Dislocations and the shielding to the crack tip. Nucleation of a fast moving Dislocation is examined under the Peierls–Nabarro theory. Incremental Dislocation flux is created continuously from the crack tip, and moves away at a constant speed. At a judgmental time of Dislocation Emission, the displacement jump relates to the holding force along the crack extension plane by a periodic inter-planar potential, and the singular stress induced by the transient and rate-dependent displacement jump negates the original crack tip singularity. A dynamic overshoot calculation under quasi-steady assumption provides an escape velocity of Dislocations. To achieve it, extra activation energy is required for the transient Dislocation nucleation and that reduces the Dislocation nucleation rate along the crack front. When compared with the rate-insensitive process of cleavage, the transient Dislocation Emission process allows us to predict the rate dependency of the brittle versus ductile behavior of materials.
Alexander H. King - One of the best experts on this subject based on the ideXlab platform.
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Effects of Grain Boundary Disorder on Dislocation Emission
Materials Letters, 2019Co-Authors: Valery Borovikov, Mikhail I. Mendelev, Alexander H. KingAbstract:Abstract It was recently reported that segregation of Zr to grain boundaries (GB) in nanocrystalline Cu can lead to the development of disorder in the intergranular structure (Khalajhedayati et al., 2016; Khalajhedayati and Rupert, 2015). In this study we employ atomistic computer simulations to investigate how this disorder affects Dislocation nucleation from the GBs under applied stress. It was found that a fully disordered grain boundary structure suppresses Dislocation Emission and significantly increases the yield stress. Depending on the solute concentration and heat-treatment, however, partial disorder may also occur and this aids Dislocation nucleation rather than suppressing it, reducing or eliminating the strengthening effect.
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Solute effects on interfacial Dislocation Emission in nanomaterials: Nucleation site competition and neutralization
Scripta Materialia, 2018Co-Authors: Valery Borovikov, Mikhail I. Mendelev, Alexander H. KingAbstract:Abstract Solutes added to stabilize nano-crystalline metals against grain growth, may segregate to grain boundaries and triple junctions where they can affect the process of the Dislocation Emission. We demonstrate that this effect can be very complex due to different rates of segregation at different interfaces. Moreover, at large concentrations, when the solutes form clusters, the interfaces between these clusters and the matrix can introduce new Dislocation Emission sources, which can be activated under lower applied stress. Thus, the strength maximum can occur at a certain solute concentration: adding solutes beyond this optimal concentration can reduce the strength of the material.
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Solute effects on interfacial Dislocation Emission in nanomaterials: nucleation site competition and neutralization
2017Co-Authors: Valery Borovikov, Mikhail I. Mendelev, Alexander H. KingAbstract:Interfacial nucleation is the dominant process of Dislocation generation during the plastic deformation of nano-crystalline materials. Solute additions intended to stabilize nano-crystalline metals against grain growth, may segregate to the grain boundaries and triple junctions where they can affect the process of the Dislocation Emission. In this Letter we demonstrate that the effect of solute addition in a nano-crystalline material containing competing solute segregation sites and Dislocation sources can be very complex due to different rates of segregation at different interfaces. Moreover, at large concentrations, when the solutes form clusters near the grain boundaries or triple junctions, the interfaces between these clusters and the matrix can introduce new Dislocation Emission sources, which can be activated under lower applied stress. Thus, the strength maximum can occur at a certain solute concentration: adding solutes beyond this optimal solute concentration can reduce the strength of the material.
Yanbin Wang - One of the best experts on this subject based on the ideXlab platform.
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In situ TEM research of Dislocation Emission and microcrack nucleation for Ti after adsorption by Hg
Corrosion Science, 1999Co-Authors: Yanbin Wang, Wuyang ChuAbstract:Abstract Using a special constant deflection device, the change in Dislocation configuration ahead of a loaded crack tip for a-Ti, before and after adsorption of Hg atoms, and the initiations of Hg-induced microcracks have been observed in TEM, as well as the in situ extension in TEM without Hg. The results showed that chemisorption of Hg atoms facilitates Dislocation Emission and motion. When the chemisorption-enhanced Dislocation Emission and motion develop into a critical situation, a microcrack in LME nucleates from the main crack tip and/or in the Dislocation free zone (DFZ), and propagates in cleavage mode. During in situ extension in TEM without liquid metal, when Dislocation Emission and motion induced by thermal activity and applied stress reach a certain critical condition, microcracks nucleate but do not blunt into a void.
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in situ tem observation of dissolution enhanced Dislocation Emission motion and the nucleation of scc for ti24al11nb alloy in methanol
Scripta Materialia, 1997Co-Authors: Yanbin Wang, Chimei HsiaoAbstract:Many experiments have showed that anodic polarization can facilitate ambient creep for various metals and alloys. Anodic polarization can decrease the yield strength, and enlarge the plastic zone on the surface ahead of a loaded crack tip. The density of Dislocations in a region very close to the fracture surface of SCC was much higher than that far away from the fracture surface. All of these experiments showed that anodic dissolution facilitated the localized plastic deformation. Up to now, however, direct proof of anodic dissolution or corrosion-enhanced Dislocation Emission, multiplication and motion is lacking. Using a special constant deflection device, the Dislocation configuration change ahead of a loaded crack tip before and after anodic dissolution together with the initiation of SCC for Ti-24Al-11Nb alloy in methanol can be in-situ observed in TEM. The results showed that the localized anodic dissolution could facilitate Dislocation Emission, multiplication and motion and SCC with size of nanometers would initiate in the Dislocation-free zone (DFZ) or at the original crack tip after the dissolution-enhanced Dislocation Emission and motion reached a critical condition.
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Chemisorption-facilitating Dislocation Emission, multiplication and motion
Scripta Materialia, 1997Co-Authors: Yanbin Wang, Wuyang ChuAbstract:The reduction in ductility and fracture stress of many metals tested in certain liquid metal environments is generally known as liquid metal embrittlement (LME). The evidence for plastic deformation on the fracture surfaces of LME failures has led Lynch to propose that the chemisorption of liquid metal can enhance localized plastic deformation. Up to now, however, direct proof of chemisorption facilitating Dislocation Emission, multiplication and motion is lacking. The purpose of this paper is to study now chemisorption facilitates Dislocation Emission, multiplication and motion. An in-situ tensile test in a TEM is the most direct and powerful method for studying the Dislocation Emission, multiplication and motion. Since there is no way to put the liquid metal into a TEM, a special constant deflection loading device has been designed. Using this device, the effect of chemisorption on Dislocation Emission and motion can be studied based on the Dislocation configuration change ahead of a loaded crack tip after chemisorption of liquid metal atoms but before the propagation of the original crack tip or initiation of a new microcrack.
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Chemisorption-facilitated Dislocation Emission and motion, and induced nucleation of brittle nanocrack
Science in China Series E: Technological Sciences, 1997Co-Authors: Yanbin Wang, Wuyang ChuAbstract:Using a special TEM constant deflection device, the change in Dislocation configuration ahead of a loaded crack tip before and after adsorption of Hg atoms and the initiation of liquid metal-induced nanocracks (LMIC) have been observed. The results show that chemisorption of Hg atoms can facilitate Dislocation Emission, multiplication and motion. Nanocracks will be initiated in the Dislocation-free zone (DFZ) or at the crack tip when chemisorption-facilitated Dislocation Emission, multiplication and motion reach a critical condition. On the basis of the available experimental evidence concerning liquid metal embrittlement (LME), a new mechanism for this phenomenon is considered. This involves the fact that the decrease in surface energy induced by chemisorption of Hg atoms results in a reduction in the critical stress intensity factors for Dislocation Emission and the resistance for Dislocation motion. On the other hand, the plastic work andK IC will decrease with the decrease in the surface energy.
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In situ TEM observation of magnetization-enhanced Dislocation Emission and motion for 60Fe40Ni alloy
Chinese Science Bulletin, 1997Co-Authors: Yanbin Wang, Qizhi Chen, Wuyang ChuAbstract:The magnetization for Fe40Ni alloy in the magnetic field can enhance Dislocation Emission, multiplication and motion.