Dislocation Dynamics Simulation of Interaction between Prismatic Dislocation Loops and Voids in Irradiated Thin Films

2016 ◽  
Vol 725 ◽  
pp. 189-194
Author(s):  
Ying Ying Cai ◽  
Jia Pei Guo ◽  
Yi Ping Chen
Keyword(s):  
Thin Films ◽  
Radiation Damage ◽  
Image Force ◽  
Dislocation Dynamics ◽  
Dynamics Simulation ◽  
Dislocation Loops ◽  
Principle Of Superposition ◽  
Dislocation Glide ◽  
Calculation Results ◽  
Materials Used

At the microscopic scale fast neutron irradiation brings about a high density of small point defect clusters in the form of dislocation loops and voids. And such radiation damage is of primary importance for materials used in nuclear energy production. In the present investigation emphasis is placed on the understanding of the mechanisms involved in the evolution of prismatic dislocation loops by glide in the presence of external free surfaces and those of the voids and in the interaction between dislocation loops and voids within irradiated thin films, so as to simulate in situ Transmission Electron Microscopy (TEM) images of dislocations, which is an indispensable tool for extracting information on radiation damage. By employing 3D dislocation dynamics based on isotropic elacticity and principle of superposition, the calculation results show that the image force is determined by the distance of the dislocation loop from the external and void surfaces and scales with the film thickness; the dislocation glide force is determined by the image stress as well as the loop–loop interaction stress which is in turn governed by the loop spacing. It is also shown that the presence of voids in the thin films has a strong influence on the behaviours of prismatic dislocations.

A New Dislocation-Dynamics Model and Its Application in Thin Film-Substrate Systems

2005 ◽  
Vol 875 ◽  
Author(s):  
E.H. Tan ◽  
L.Z. Sun
Keyword(s):  
Thin Films ◽  
Mechanical Performance ◽  
Dislocation Motion ◽  
Dislocation Dynamics ◽  
Dislocation Segment ◽  
Dislocation Loops ◽  
Dynamics Model ◽  
Proposed Model ◽  
Simulation Results ◽  
Film Substrate

AbstractBased on the physical background, a new dislocation dynamics model fully incorporating the interaction among differential dislocation segments is developed to simulate 3D dislocation motion in crystals. As the numerical simulation results demonstrate, this new model completely solves the long-standing problem that simulation results are heavily dependent on dislocation-segment lengths in the classical dislocation dynamics theory. The proposed model is applied to simulate the effect of dislocations on the mechanical performance of thin films. The interactions among the dislocation loops, free surface and interfaces are rigorously computed by a decomposition method. This framework can be used to simulate how a surface loop evolves into two threading dislocations and to determine the critical thickness of thin films. Furthermore, the relationship between the film thickness and yield strength is established and compared with the conventional Hall-Petch relation.

Dislocations and Internal Stresses in Thin Films: A Discrete-Continuum Simulation

1999 ◽  
Vol 578 ◽  
Author(s):  
C. Lemarchand ◽  
B. Devincre ◽  
L.P. Kubin ◽  
J.L. Chaboche
Keyword(s):  
Thin Films ◽  
Critical Stress ◽  
Image Force ◽  
Dislocation Dynamics ◽  
Internal Stresses ◽  
Epitaxial Layers ◽  
Free Standing ◽  
Misfit Stress ◽  
Substrate Interface ◽  
Film Substrate

The plasticity of thin films and layers is of considerable technological interest. For instance, the relaxation of internal stresses in semiconducting epitaxial layers has been the object of many studies [1, 2]. This relaxation is usually treated via the concept of critical thickness, the latter being defined as the maximum layer thickness below which dislocations cannot spontaneously move and relax the internal stresses. The various internal stresses present in epitaxial layers (e.g. the misfit and elastic incompatibility stresses at the film/substrate interface and the image force in a free-standing film) can be computed within a continuum frame. However, the way they influence the motion of a dislocation has not yet been computed, even in a approximate manner. An useful approximation that allows treating the boundary condition at the surface of a free-standing film consists of making use of the concept of image dislocation. Then, the critical stress for moving a dislocation in a free-standing film is the same as that of a capped layer of thickness twice that of the film. To date, models and dislocation dynamics (DD) simulations are available that involve several levels of approximation for the treatment of the dislocation/interface and dislocation/surface interactions [3–7]. For reasons that are not clearly understood, however, these models predict critical thicknesses that are systematically larger than the expected ones. The comparison with experiment is, in addition, made difficult because stresses have to be artificially introduced to replace the internal stresses and approximations have to be done to treat the image stresses. In the present work it is shown that it is now possible to fully account for the contribution of the various sources of internal stresses to the critical stress for the motion of a threading dislocation. This is performed numerically with the help of a hybrid code that combines a DD code for the treatment of the dislocation dynamics and a Finite Element (FE) code for the treatment of the boundary conditions. In what follows, several applications of this discrete-continuum model (DCM) to the study of dislocation motion in epitaxial layers are presented. The motion of a dislocation in a thin film is considered, including the image force and successively adding a misfit stress and an elastic incompatibility stress at the film/substrate interface.

The Interaction of a Circular Dislocation Pile-up with a Short Rigid Fiber: a 3-D Dislocation Dynamics Simulation

2001 ◽  
Vol 683 ◽  
Author(s):  
Tariq A. Khraishi ◽  
Hussein M. Zbib
Keyword(s):  
Boundary Condition ◽  
Metal Matrix ◽  
Dislocation Dynamics ◽  
Dynamics Simulation ◽  
Dynamics Analysis ◽  
Matrix Composites ◽  
Dislocation Loops ◽  
Pile Up ◽  
Surface Loops ◽  
Distributed Dislocations

ABSTRACTThis paper presents a dislocation dynamics simulation of the interaction of a circular dislocation pile-up with a short rigid fiber, say as in metal-matrix composites. The pile-up is composed of glide dislocation loops surrounding the fiber. This problem is treated here as a boundary value problem within the context of dislocation dynamics. The proper boundary condition to be enforced is that of no or zero elastic displacements at the fiber's surface. Such a condition is satisfied by a distribution of rectangular dislocation loops, acting as sources of elastic displacements, meshing the fiber's surface. Such treatment is similar to crack modeling using distributed dislocations and falls under the category of “generalized image stress analysis.” The unknown in this problem is the Burgers vectors of the surface loops. Once those are found, the Peach-Koehler force acting on the circular dislocation loops, and emulating the fiber's presence, can be determined and the dynamical arrangement of the circular pile-up evolves naturally from traditional dislocation dynamics analysis.

Modelling of Irradiated Materials

2006 ◽  
Author(s):  
B. K. Dutta ◽  
P. V. Durgaprasad ◽  
A. K. Pawar ◽  
H. S. Kushwaha ◽  
S. Banerjee
Keyword(s):  
Radiation Damage ◽  
Energetic Particles ◽  
Dislocation Dynamics ◽  
Length Scale ◽  
Multi Scale ◽  
Discrete Dislocation Dynamics ◽  
Discrete Dislocation ◽  
Stacking Fault Tetrahedra ◽  
Wide Range ◽  
Materials Used

Irradiation of materials by energetic particles causes significant degradation of the mechanical properties, most notably an increased yield stress and decrease ductility, thus limiting lifetime of materials used in nuclear reactors. The microstructure of irradiated materials evolves over a wide range of length and time scales, making radiation damage and inherently multi-scale phenomenon. At atomic length scale, the principal sources of radiation damage are the primary knock-on atoms that recoil under collision from energetic particles such as neutrons or ions. These knock-on atoms in turn produce vacancies and self-interstitial atoms, and stacking fault tetrahedra. At higher length scale, these defect clusters form loops around existing dislocations, leading to their decoration and immobilization, which ultimately leads to radiation hardening in most of the materials. All these defects finally effect the macroscopic mechanical and other properties. An attempt is made to understand these phenomena using molecular dynamics studies and discrete dislocation dynamics modelling.

Anisotropic Elastic Field of 3D Prismatic Dislocation Loops in Bounded and Voided Single Crystal Films

2016 ◽  
Vol 725 ◽  
pp. 195-201
Author(s):  
Jia Pei Guo ◽  
Ying Ying Cai ◽  
Yi Ping Chen
Keyword(s):  
Thin Films ◽  
Elastic Field ◽  
Elastic Cylinder ◽  
Physical Parameters ◽  
Dislocation Loops ◽  
Principle Of Superposition ◽  
Elastic Fields ◽  
Crystal Films ◽  
Finite Medium ◽  
Anisotropic Elastic

Dislocations in a finite medium bring about image stresses. These image stresses play important roles in the dislocation behavior in finite sized systems such as thin films. Since the ratio of surface to volume is higher for thin films than for bulk materials, dislocation behaviors in thin films are greatly different from those in a corresponding infinite medium, which make it necessary to take into account the effects of free surfaces on the evolution of dislocations in thin films. In the investigations[4, 5], image stresses in an elastic cylinder and thin films are calculated by employing a Fourier transform (FFT) approach and isotropically elastic fields due to dislocations are adopted in their formulation. However, most crystals are anisotropic, and the anisotropic ratio changes with environment physical parameters, such as the temperature, moisture, electron field, magnetic field. A theorem based on anisotropic Stroh’s formula for calculating the image stress of infinite straight dislocations in anisotropic bicrystals has been developed by Barnett and Lothe[6]. Wu et al.[3] recently also make use of the FFT technique to investigate the general dislocation image stresses of cubic thin films, thus extending the formalism by Weinberger et al.[4,5] from isotropic to anisotropic thin films. It is clear that for the assumed in-plane elastic fields to be periodically defined within an unbounded region is an essential and indispensable prerequisite for the above FFT-based approach to be effectively implemented, thus ruling out the possibility of its being employed to analyse image stresses in bounded and/or voided thin cubic films. Our motivation here is then to make an further extension by first calculating the anisotropic elastic fields of dislocation loops in an unbounded thin film with cavities and then invoking FEM and the principle of superposition to seek the image stress solution.

Annealing Of Radiation Damage in Tungsten

1970 ◽  
Vol 28 ◽  
pp. 412-413
Author(s):  
Robert C. Rau ◽  
John Moteff
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Radiation Damage ◽  
Thermal Annealing ◽  
Neutron Fluence ◽  
Dislocation Loops ◽  
Defect Clusters ◽  
Polycrystalline Tungsten ◽  
Transmission Electron ◽  
Radiation Induced

Transmission electron microscopy has been used to study the thermal annealing of radiation induced defect clusters in polycrystalline tungsten. Specimens were taken from cylindrical tensile bars which had been irradiated to a fast (E > 1 MeV) neutron fluence of 4.2 × 1019 n/cm2 at 70°C, annealed for one hour at various temperatures in argon, and tensile tested at 240°C in helium. Foils from both the unstressed button heads and the reduced areas near the fracture were examined.Figure 1 shows typical microstructures in button head foils. In the unannealed condition, Fig. 1(a), a dispersion of fine dot clusters was present. Annealing at 435°C, Fig. 1(b), produced an apparent slight decrease in cluster concentration, but annealing at 740°C, Fig. 1(C), resulted in a noticeable densification of the clusters. Finally, annealing at 900°C and 1040°C, Figs. 1(d) and (e), caused a definite decrease in cluster concentration and led to the formation of resolvable dislocation loops.

Kinematics and Dynamics Simulation Research for Roller Coaster Multi-Body System

2011 ◽  
Vol 421 ◽  
pp. 276-280 ◽  
Author(s):  
Ge Ning Xu ◽  
Hu Jun Xin ◽  
Feng Yi Lu ◽  
Ming Liang Yang
Keyword(s):  
Structural Design ◽  
3D Model ◽  
Structure Design ◽  
Dynamics Simulation ◽  
Body System ◽  
Load Spectrum ◽  
Roller Coaster ◽  
Simulation Research ◽  
Calculation Results ◽  
Multi Body

To assess the roller coaster multi-body system security, it is need to extract the running process of kinematics, dynamics, load spectrum and other features, as basis dates of the roller coaster structural design. Based on Solidworks/motion software and in the 3D model, the calculation formula of the carrying car velocity and acceleration is derived, and the five risk points of the roller coaster track section are found by simulation in the running, and the simulation results of roller coaster axle mass center velocity are compared with theoretical calculation results, which error is less than 4.1%, indicating that the calculation and simulation have a good fit and providing the evidence for the roller coaster structure design analysis.

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