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Snehanshu Pal - One of the best experts on this subject based on the ideXlab platform.
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intensification of shock damage through heterogeneous phase transition and Dislocation Loop formation due to presence of pre existing line defects in single crystal cu
Journal of Applied Physics, 2019Co-Authors: Vijay K Reddy, Chuang Deng, Snehanshu PalAbstract:In general, shock wave deformation studies of perfect single crystals may cause disagreement with the experimental findings as the complete elimination of all defects in the metallic system is not possible in reality. Here, we have studied the influence of edge and screw Dislocations on the intensification of damage produced during the propagation of shock at various velocities. Various analyses have been performed such as common neighbor analysis, atomic strain analysis, stress analysis, and kinetic energy mapping to investigate the underlying plastic deformation mechanisms. Results have revealed that the presence of edge Dislocations has caused intensified damage through localized amorphization and phase transition. In comparison with the perfect crystal, the presence of pre-existing edge Dislocations has incurred an additional damage of ∼17% to the specimen region. On the other hand, the presence of screw Dislocations in the specimen causes damage through shear bands and Dislocation Loop formation, which is found to constitute greater than 80% of the specimen region.In general, shock wave deformation studies of perfect single crystals may cause disagreement with the experimental findings as the complete elimination of all defects in the metallic system is not possible in reality. Here, we have studied the influence of edge and screw Dislocations on the intensification of damage produced during the propagation of shock at various velocities. Various analyses have been performed such as common neighbor analysis, atomic strain analysis, stress analysis, and kinetic energy mapping to investigate the underlying plastic deformation mechanisms. Results have revealed that the presence of edge Dislocations has caused intensified damage through localized amorphization and phase transition. In comparison with the perfect crystal, the presence of pre-existing edge Dislocations has incurred an additional damage of ∼17% to the specimen region. On the other hand, the presence of screw Dislocations in the specimen causes damage through shear bands and Dislocation Loop formation, whi...
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intensification of shock damage through heterogeneous phase transition and Dislocation Loop formation due to presence of pre existing line defects in single crystal cu
Journal of Applied Physics, 2019Co-Authors: Vijay K Reddy, Chuang Deng, Snehanshu PalAbstract:In general, shock wave deformation studies of perfect single crystals may cause disagreement with the experimental findings as the complete elimination of all defects in the metallic system is not possible in reality. Here, we have studied the influence of edge and screw Dislocations on the intensification of damage produced during the propagation of shock at various velocities. Various analyses have been performed such as common neighbor analysis, atomic strain analysis, stress analysis, and kinetic energy mapping to investigate the underlying plastic deformation mechanisms. Results have revealed that the presence of edge Dislocations has caused intensified damage through localized amorphization and phase transition. In comparison with the perfect crystal, the presence of pre-existing edge Dislocations has incurred an additional damage of ∼17% to the specimen region. On the other hand, the presence of screw Dislocations in the specimen causes damage through shear bands and Dislocation Loop formation, which is found to constitute greater than 80% of the specimen region.
E Pan - One of the best experts on this subject based on the ideXlab platform.
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elastic field by a Dislocation Loop in an anisotropic elastic half space with general boundary conditions and its application in nanoindentation of single crystals
International Journal of Mechanical Sciences, 2019Co-Authors: Y P Chen, Xiaoyu Zhang, E PanAbstract:Abstract The elastic displacement and stress fields induced by a Dislocation Loop of polygonal shape within an anisotropic homogeneous half-space with general boundary conditions on the flat surface z = 0 are obtained by employing the corresponding point-force Green's functions. We first study in detail the effects of the eight sets of boundary conditions on the elastic fields of Dislocation Loops. We then identify the elastic fields of Dislocation Loops corresponding to three of the eight sets of boundary conditions. These are the traction-free, completely, and partially sticking contact between the indenter and the indented single crystals, which are employed to establish the distribution Dislocation Loop model for simulating nanoindentation of single crystals. It is the first time that significant differences in the magnitude of sink-in and pile-up of the indented profile, and of the residual stress components, corresponding to different frictional boundary conditions, are observed, which could serve as benchmark in future nanoindentation study.
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interfacial elastic fields of a 3d Dislocation Loop in anisotropic bimaterials of finite thickness crystal films
Mechanics of Materials, 2017Co-Authors: Y P Chen, Ying Ying Cai, Jia Pei Guo, E PanAbstract:Abstract By combining the new superposition principle of linear elasticity used in discrete Dislocation plasticity and the recently available solutions of the elastic displacement and stress fields due to a polygonal Dislocation Loop within an anisotropic homogeneous full-space, the anisotropic elastic fields induced by a 3D polygonal prismatic or a glide Dislocation Loop (PP(G)DL) in a bimaterial of finite thickness crystal films are obtained. The location and orientation of the PP(G)DLs with respect to the fixed reference coordinate system are arbitrary. Factors influencing the interface elastic fields, such as the size of the PP(G)DLs, the distance between the PP(G)DLs and the interface, the thickness of the layer containing the PP(G)DLs and lastly the mismatch of crystallographic orientation of the adjacent layers are investigated in detail. The present model has two distinct features of easy extensibility to planar or nonplanar multilayered polycrystalline models and the ease of numerical implementation for parallel programming.
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line integral representations of the displacement and stress fields due to an arbitrary volterra Dislocation Loop in a transversely isotropic elastic full space
International Journal of Solids and Structures, 2013Co-Authors: Jianghong Yuan, E Pan, Weiqiu ChenAbstract:Transversely isotropic materials or hexagonal crystals are commonly utilized in various engineering fields; however, Dislocation solutions for such special materials have not been fully developed. In this paper, we present a comprehensive study on this important topic, where only Volterra Dislocations of the translational type are considered. Based on the potential theory of linear elasticity, we extend the well-known Burgers displacement equation for an arbitrarily shaped Dislocation Loop in an isotropic elastic full space to the transversely isotropic case. Both the induced displacements and stresses are expressed uniformly in terms of simple and explicit line integrals along the Dislocation Loop. We introduce three quasi solid angles to describe the displacement discontinuities over the Dislocation surface and extract a simple step function out of these angles to characterize the dependence of the displacements on the configuration of the Dislocation surface. We also give a new explicit formula for calculating accurately and efficiently the traditional solid angle of an arbitrary polygonal Dislocation Loop. From the present line-integral representations, exact closed-form solutions in terms of elementary functions are further obtained in a unified way for the displacement and stress fields due to a straight Dislocation segment of arbitrary orientation. The non-uniqueness of the elastic field solution due to an open Dislocation segment is rigorously discussed and demonstrated. For a circular Dislocation Loop parallel to the plane of isotropy, a new explicit expression of the induced elastic field is presented in terms of complete elliptic integrals. Several numerical examples are also provided as illustration and verification of the derived Dislocation solutions, which further show the importance of material anisotropy on the Dislocation-induced elastic field, and reveal the non-uniqueness feature of the elastic field due to a straight Dislocation segment.
Y P Chen - One of the best experts on this subject based on the ideXlab platform.
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elastic field by a Dislocation Loop in an anisotropic elastic half space with general boundary conditions and its application in nanoindentation of single crystals
International Journal of Mechanical Sciences, 2019Co-Authors: Y P Chen, Xiaoyu Zhang, E PanAbstract:Abstract The elastic displacement and stress fields induced by a Dislocation Loop of polygonal shape within an anisotropic homogeneous half-space with general boundary conditions on the flat surface z = 0 are obtained by employing the corresponding point-force Green's functions. We first study in detail the effects of the eight sets of boundary conditions on the elastic fields of Dislocation Loops. We then identify the elastic fields of Dislocation Loops corresponding to three of the eight sets of boundary conditions. These are the traction-free, completely, and partially sticking contact between the indenter and the indented single crystals, which are employed to establish the distribution Dislocation Loop model for simulating nanoindentation of single crystals. It is the first time that significant differences in the magnitude of sink-in and pile-up of the indented profile, and of the residual stress components, corresponding to different frictional boundary conditions, are observed, which could serve as benchmark in future nanoindentation study.
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interfacial elastic fields of a 3d Dislocation Loop in anisotropic bimaterials of finite thickness crystal films
Mechanics of Materials, 2017Co-Authors: Y P Chen, Ying Ying Cai, Jia Pei Guo, E PanAbstract:Abstract By combining the new superposition principle of linear elasticity used in discrete Dislocation plasticity and the recently available solutions of the elastic displacement and stress fields due to a polygonal Dislocation Loop within an anisotropic homogeneous full-space, the anisotropic elastic fields induced by a 3D polygonal prismatic or a glide Dislocation Loop (PP(G)DL) in a bimaterial of finite thickness crystal films are obtained. The location and orientation of the PP(G)DLs with respect to the fixed reference coordinate system are arbitrary. Factors influencing the interface elastic fields, such as the size of the PP(G)DLs, the distance between the PP(G)DLs and the interface, the thickness of the layer containing the PP(G)DLs and lastly the mismatch of crystallographic orientation of the adjacent layers are investigated in detail. The present model has two distinct features of easy extensibility to planar or nonplanar multilayered polycrystalline models and the ease of numerical implementation for parallel programming.
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interfacial elastic fields of a 3d polygonal prismatic Dislocation Loop in anisotropic bimaterials of spherical shells
International Journal of Mechanical Sciences, 2017Co-Authors: Ying Ying Cai, Y P Chen, Jia Pei GuoAbstract:Abstract By combining the new superposition principle of linear elasticity used in discrete Dislocation plasticity and the recently available solution of the elastic displacement and stress fields due to a polygonal Dislocation Loop within an anisotropic homogeneous full-space, the anisotropic elastic fields induced by a 3D polygonal prismatic Dislocation Loop (PPDL) in bimaterials of spherical shells are obtained. The location and orientation of the PPDLs with respect to the fixed reference coordinate system are arbitrary. Factors influencing the interfacial elastic fields, such as the size of the PPDLs, the thickness of the inner-layer and lastly the mismatch of crystallographic orientations of the adjacent layers are investigated in detail. The present model has two distinct features of easy extensibility to planar or nonplanar multilayered polycrystalline models and the ease of numerical implementation for parallel programming.
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an anisotropic distribution Dislocation Loop model for simulation of nanoindentation of single crystals
Mechanics of Materials, 2017Co-Authors: Y P Chen, Jia Pei Guo, Ying Ying CaiAbstract:Abstract An anisotropic distribution Dislocation Loop model is proposed for simulation of nanoindentation of single crystals based on the recently available solution of the elastic displacement and stress fields due to a polygonal Dislocation within an anisotropic homogeneous half-space ( Chu et al., 2012 ). The present investigation is a direct extension of the approach established by Mura et al. (1989) , and its recent application to triangular Dislocation Loop model ( Muraishi, 2013 ), which is only capable of describing the indentation processes of isotropic materials, thus ruling out the possibility of characterizing the nanoindentation of elastically anisotropic single crystals. By following the procedure of Mura et al. (1989) , we adopt square and triangular prismatic Dislocation Loops (PDLs) as building blocks with Burgers vectors normal to the free surface to simulate the Vickers and Berkovich indentation, respectively. However, we place all the prismatic Dislocation Loops within a semi-ellipsoidal volume rather than a semi-spherical region as adopted by Mura et al. (1989) after analyzing the existing simulation results based on Dislocation density formulation ( Huang et al., 2000 ). The nanoindentation is performed in [001] and [111] crystallographic directions employing Vickers and Berkovich indenters, respectively, and different magnitude of pile-up, sink-in and spring-back is observed in different directions, clearly demonstrating the effects of elastic anisotropy of the indented single crystals on nanoindentation, hence a further improvement of the original model of Mura et al. (1989) .
Vijay K Reddy - One of the best experts on this subject based on the ideXlab platform.
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intensification of shock damage through heterogeneous phase transition and Dislocation Loop formation due to presence of pre existing line defects in single crystal cu
Journal of Applied Physics, 2019Co-Authors: Vijay K Reddy, Chuang Deng, Snehanshu PalAbstract:In general, shock wave deformation studies of perfect single crystals may cause disagreement with the experimental findings as the complete elimination of all defects in the metallic system is not possible in reality. Here, we have studied the influence of edge and screw Dislocations on the intensification of damage produced during the propagation of shock at various velocities. Various analyses have been performed such as common neighbor analysis, atomic strain analysis, stress analysis, and kinetic energy mapping to investigate the underlying plastic deformation mechanisms. Results have revealed that the presence of edge Dislocations has caused intensified damage through localized amorphization and phase transition. In comparison with the perfect crystal, the presence of pre-existing edge Dislocations has incurred an additional damage of ∼17% to the specimen region. On the other hand, the presence of screw Dislocations in the specimen causes damage through shear bands and Dislocation Loop formation, which is found to constitute greater than 80% of the specimen region.In general, shock wave deformation studies of perfect single crystals may cause disagreement with the experimental findings as the complete elimination of all defects in the metallic system is not possible in reality. Here, we have studied the influence of edge and screw Dislocations on the intensification of damage produced during the propagation of shock at various velocities. Various analyses have been performed such as common neighbor analysis, atomic strain analysis, stress analysis, and kinetic energy mapping to investigate the underlying plastic deformation mechanisms. Results have revealed that the presence of edge Dislocations has caused intensified damage through localized amorphization and phase transition. In comparison with the perfect crystal, the presence of pre-existing edge Dislocations has incurred an additional damage of ∼17% to the specimen region. On the other hand, the presence of screw Dislocations in the specimen causes damage through shear bands and Dislocation Loop formation, whi...
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intensification of shock damage through heterogeneous phase transition and Dislocation Loop formation due to presence of pre existing line defects in single crystal cu
Journal of Applied Physics, 2019Co-Authors: Vijay K Reddy, Chuang Deng, Snehanshu PalAbstract:In general, shock wave deformation studies of perfect single crystals may cause disagreement with the experimental findings as the complete elimination of all defects in the metallic system is not possible in reality. Here, we have studied the influence of edge and screw Dislocations on the intensification of damage produced during the propagation of shock at various velocities. Various analyses have been performed such as common neighbor analysis, atomic strain analysis, stress analysis, and kinetic energy mapping to investigate the underlying plastic deformation mechanisms. Results have revealed that the presence of edge Dislocations has caused intensified damage through localized amorphization and phase transition. In comparison with the perfect crystal, the presence of pre-existing edge Dislocations has incurred an additional damage of ∼17% to the specimen region. On the other hand, the presence of screw Dislocations in the specimen causes damage through shear bands and Dislocation Loop formation, which is found to constitute greater than 80% of the specimen region.
Ning Gao - One of the best experts on this subject based on the ideXlab platform.
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in situ transmission electron microscopy study and molecular dynamics simulation of Dislocation Loop evolution in fecral alloys under fe irradiation
Materials Today Energy, 2021Co-Authors: Guang Ran, Ning Gao, Yang Chen, Qing Han, Hui Wang, Z H Zhou, J C HuangAbstract:Abstract FeCrAl alloys with excellent comprehensive properties are the most promising candidates to replace zirconium alloy fuel claddings. In our study, the Dislocation Loop evolution including initiation, migration, merging, growth, annihilation, and reaction in a FeCrAl alloy was investigated by using in situ transmission electron microscopy during 400 keV Fe + irradiation. The mechanism induced the growth of Dislocation Loops including the absorption of high-mobility point defects and defect clusters and the merging of two or more Dislocation Loops of different sizes. In the initial stage of irradiation, the Loop density was relatively stable and the Loop size increased rapidly with the increase in irradiation dose; however, owing to the formation of Dislocation networks, the Loop density decreased significantly in the later stage of irradiation. Both b = 1/2 and b = Dislocation Loops were formed in the FeCrAl alloy. The ratio of Loops was 49% after irradiation with 0.14 dpa at 723 K. Molecular dynamics simulations displayed the reaction of Dislocation Loops with different Burgers vectors and sizes. Although the presence of alloying elements (Cr and Al) would prohibit or delay the interaction process, Loop merging continued owing to the atomic rearrangement of Dislocation Loops.
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formation of 100 Dislocation Loop in bcc fe via the ternary Loop reaction
Scripta Materialia, 2019Co-Authors: Xiaoyang Wang, Ning Gao, Yinan Wang, Guogang Shu, Wei LiuAbstract:Abstract In nuclear power plants, body centered cubic (bcc) iron-based alloys are used widely and their mechanical properties are degraded significantly because of irradiation-induced defects. The prevalence of the ⟨100⟩ Dislocation Loops contradicts the rigorous condition for their formation. In this study, we report the process responsible for the formation of the ⟨100⟩ Dislocation Loop, which involves a 1/2⟨111⟩ Loop with a pre-existing sessile complex or simply three differently oriented 1/2⟨111⟩ Dislocation Loops. The formation of the ⟨100⟩ Loop via the tri-Loop mechanism has a very low energy barrier and is favored over the formation of the 1/2⟨111⟩ Dislocation Loop.
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atomistic simulation of interstitial Dislocation Loop evolution under applied stresses in bcc iron
Physica Status Solidi (a), 2018Co-Authors: Xue Hao Long, Ning Gao, Dong Wang, Wahyu Setyawan, Peng Liu, Richard J Kurtz, Zhiguang Wang, Xue Lin WangAbstract:Evolution of an interstitial 1/2〈111〉 Dislocation Loop under tensile, shear, and torsion stresses is studied with molecular statics method. Under a tensile stress, the dependence of ultimate tensile strength on size of Loop is calculated. The formation of small shear Loops around the initial prismatic Loop is confirmed as an intermediate state to form the final Dislocation network. Under a shear stress, the rotation of a Loop is observed not only by a change of the habit plane but also through a transformation between a shear and a prismatic Loop. Under torsion, a perfect BCC crystal may undergo a BCC to FCC or BCC to HCP transformation. The present work indicates that a 1/2〈111〉 Loop can delay these transformations, resulting in the formation of micro-crack on the surface.
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a new Loop punching mechanism for helium bubble growth in tungsten
Acta Materialia, 2017Co-Authors: Hongxian Xie, Ning Gao, Fuxing YinAbstract:Abstract Growth of helium (He) bubbles with different initial sizes in tungsten (W) has been investigated by performing molecular dynamics simulations. Based on the simulation results a new Loop punching mechanism for the large helium bubble growth is proposed. Different from the growth of small-size He bubbles by pushing out self-interstitial atoms and then rearranging into a prismatic Dislocation Loop, a large-size bubble grows by pushing out a Dislocation, subsequently cross-slipping of its screw components and finally evolving into a prismatic Dislocation Loop. Such Dislocations may react with each other to form a Dislocation net around the bubble rather than to convert to prismatic Dislocation Loops.