Microstructural Behavior and Failure of FCC Crystalline Aggregates

2006 ◽  
Vol 976 ◽  
Author(s):  
O. Rezvanian ◽  
M. A. Zikry ◽  
A. M. Rajendran
Keyword(s):  
Finite Element ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Inelastic Deformation ◽  
Crystalline Materials ◽  
Failure Initiation ◽  
Dislocation Densities ◽  
Modeling Techniques ◽  
Microstructural Behavior ◽  
Crystalline Aggregates

AbstractA unified dislocation density-based microstructural representation of f.c.c. crystalline materials, has been developed such that the microstructural behavior can be accurately predicted at different physical scales. This microstructural framework is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs), and grain boundary dislocations (GBDs). This interrelated dislocation-density formulation is then used with specialized finite-element modeling techniques to predict the evolving heterogeneous microstructure and the localized phenomena that can contribute to failure initiation as a function of inelastic deformation.

Statistically stored, geometrically necessary and grain boundary dislocation densities: microstructural representation and modelling

2007 ◽  
Vol 463 (2087) ◽  
pp. 2833-2853 ◽  
Author(s):  
O Rezvanian ◽  
M.A Zikry ◽  
A.M Rajendran
Keyword(s):  
Grain Boundary ◽  
Dislocation Cell ◽  
Misfit Dislocations ◽  
Triple Junctions ◽  
Crystalline Materials ◽  
Failure Initiation ◽  
Dislocation Densities ◽  
Physically Based ◽  
Crystalline Aggregates ◽  
Critical Regions

A unified physically based microstructural representation of f.c.c. crystalline materials has been developed and implemented to investigate the microstructural behaviour of f.c.c. crystalline aggregates under inelastic deformations. The proposed framework is based on coupling a multiple-slip crystal plasticity formulation to three distinct dislocation densities, which pertain to statistically stored dislocations (SSDs), geometrically necessary dislocations (GNDs) and grain boundary dislocations. This interrelated dislocation density formulation is then coupled to a specialized finite element framework to study the evolving heterogeneous microstructure and the localized phenomena that can contribute to failure initiation as a function of inelastic crystalline deformation. The GND densities are used to understand where crystallographic, non-crystallographic and cellular microstructures form and the nature of their dislocation composition. The SSD densities are formulated to represent dislocation cell microstructures to obtain predictions related to the inhomogeneous distribution of SSDs. The effects of the lattice misorientations at the grain boundaries (GBs) have been included by accounting for the densities of the misfit dislocations at the GBs that accommodate these misorientations. By directly accounting for the misfit dislocations, the strength of the boundary regions can be more accurately represented to account for phenomena associated with the effects of the GB strength on intergranular deformation heterogeneities, stress localization and the nucleation of failure surfaces at critical regions, such as triple junctions.

FINITE ELEMENT MODELING OF DAMPING CAPACITY IN NANO-CRYSTALLINE MATERIALS

2010 ◽  
Vol 01 (03) ◽  
pp. 421-433 ◽  
Author(s):  
M. YADOLLAHPOUR ◽  
S. ZIAEI-RAD ◽  
F. KARIMZADEH
Keyword(s):  
Finite Element ◽  
Energy Dissipation ◽  
Grain Boundary ◽  
Composite Model ◽  
Grain Structure ◽  
External Loading ◽  
Damping Capacity ◽  
Crystalline Materials ◽  
Nano Crystalline ◽  
Local Plastic Strain

Plastic deformation of materials is a major source of energy dissipation during external loading. In nano-crystalline (NC) materials, local plastic strain may arise even if the overall external load is below the yield stress of the material because of the grain structure. In this paper, the damping capacity of nano-crystalline materials is modeled by considering the grain structure. First, the grains are modeled by using a composite model. The composite model takes each oriented crystal and its immediate boundary to form a pair. Next, the finite element method in conjunction with the composite model is employed to evaluate the energy dissipation of nano-crystalline material under cyclic loading. The influence of the grain size and the external loading on the energy dissipation is investigated numerically. Energy dissipation in each of the two parts (i.e. grain and grain boundary) is also calculated as an attempt to understand the effect of grain boundary on energy dissipation.

Modeling of the Plastic Deformation of Polycrystalline Materials in Micro and Nano Level Using Finite Element Method

2013 ◽  
Vol 22 ◽  
pp. 41-60 ◽  
Author(s):  
Mohammad Jafari ◽  
Saeed Ziaei-Rad ◽  
Nima Nouri
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Finite Element ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Constitutive Equations ◽  
Nanocrystalline Materials ◽  
Boundary Phase ◽  
Polycrystalline Materials ◽  
Microcrystalline Materials

Recent experiments on polycrystalline materials show that nanocrystalline materials have a strong dependency to the strain rate and grain size in contrast to the microcrystalline materials. In this study, mechanical properties of polycrystalline materials in micro and nanolevel were studied and a unified notation for them was presented. To completely understand the rate-dependent stress-strain behavior and size-dependency of polycrystalline materials, a dislocation density based model was presented that can predict the experimentally observed stress-strain relations for these materials. In nanocrystalline materials, crystalline and grain-boundary were considered as two separate phases. The mechanical properties of the crystalline phase were modeled using viscoplastic constitutive equations, which take dislocation density evolution and diffusion creep into account, while an elasto-viscoplastic model based on diffusion mechanism was used for the grain boundary phase. For microcrystalline materials, the surface-to-volume ratio of the grain boundaries is low enough to ignore its contribution to the plastic deformation. Therefore, the grain boundary phase was not considered in microcrystalline materials and the mechanical properties of the crystalline phase were modeled using an appropriate dislocation density based constitutive equation. Finally, the constitutive equations for polycrystalline materials were implemented into a finite-element code and the results obtained from the proposed constitutive equations were compared with the experimental data for polycrystalline copper and good agreement was observed.

scholarly journals Investigation on the Effects of Grain Boundary on Deformation Behavior of Bicrystalline Pillar by Crystal Plasticity Finite Element Method

Crystals ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 923
Author(s):  
Hui Zhou ◽  
Pei Wang ◽  
Shanping Lu
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Misorientation Angle ◽  
Deformation Behavior ◽  
Boundary Misorientation ◽  
Crystal Orientations ◽  
Grain Boundary Misorientation ◽  
Element Method

A dislocation density–grain boundary interaction scheme coupled with the dislocation density-based crystalline plasticity finite element method has been established and used to investigate the deformation behavior of bicrystalline pillars with the same grain boundary misorientation angle but different crystal orientations. It is found that the angle between the activated slip systems, which is determined by the crystal orientations, rather than the grain boundary misorientation angle, influences the interactions between the plastic slip and the grain boundary, which further influence the heterogeneous deformation of bicrystalline specimens.

Prediction of Grain-Boundary Interfacial Mechanisms in Polycrystalline Materials

2001 ◽  
Vol 124 (1) ◽  
pp. 88-96 ◽  
Author(s):  
W. M. Ashmawi ◽  
M. A. Zikry
Keyword(s):  
Dislocation Density ◽  
Grain Boundary ◽  
Material Behavior ◽  
Polycrystalline Materials ◽  
Total Dislocation Density ◽  
Dislocation Densities ◽  
Multiple Regions ◽  
Polycrystalline Aggregates ◽  
And Control ◽  
Deformation Modes

A multiple slip dislocation-density based crystalline formulation has been coupled to a kinematically based scheme that accounts for grain-boundary (GB) interfacial interactions with dislocation densities. Specialized finite-element formulations have been used to gain detailed understanding of the initiation and evolution of large inelastic deformation modes due to mechanisms that can result from dislocation-density pile-ups at GB interfaces, partial and total dislocation-density transmission from one grain to neighboring grains, and dislocation density absorption within GBs. These formulations provide a methodology that can be used to understand how interactions at the GB interface scale affect overall macroscopic behavior at different inelastic stages of deformation for polycrystalline aggregates due to the interrelated effects of GB orientations, the evolution of mobile and immobile dislocation-densities, slip system orientation, strain hardening, geometrical softening, geometric slip compatibility, and localized plastic strains. Criteria have been developed to identify and monitor the initiation and evolution of multiple regions where dislocation pile-ups at GBs, or partial and total dislocation density transmission through the GB, or absorption within the GB can occur. It is shown that the accurate prediction of these mechanisms is essential to understanding how interactions at GB interfaces affect and control overall material behavior.

Microstructural Behavior of Energetic Crystalline Aggregates

2013 ◽  
Vol 1526 ◽  
Author(s):  
D. LABARBERA ◽  
M.A. ZIKRY
Keyword(s):  
Hot Spot ◽  
Extreme Temperature ◽  
Maximum Temperature ◽  
Crystalline Plasticity ◽  
Cyclotrimethylene Trinitramine ◽  
Dislocation Densities ◽  
Microstructural Behavior ◽  
Crystalline Aggregates ◽  
Hot Spot Formation ◽  
Spot Formation

ABSTRACTA dislocation-density based crystalline plasticity and specialized finite-element formulations were used to study the behavior of energetic crystalline aggregates. The energetic crystalline material studied was RDX (cyclotrimethylene trinitramine) with a polymer binder and different void porosities. The aggregate was subjected to different dynamic pressures, and the analyses indicate that maximum temperature increases, constrained dislocation densities, and plastic strain accumulations occurred around the void peripheries, which affected overall deformation behavior. These regions of extreme temperature rise and thermal decomposition can result in hot spot formation.

Dislocation density based crystal plasticity finite element simulation of Al bicrystal with grain boundary effects

2014 ◽  
Vol 1651 ◽  
Author(s):  
Zhe Leng ◽  
David P. Field ◽  
Alankar Alankar
Keyword(s):  
Finite Element ◽  
Dislocation Density ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Crystal Plasticity ◽  
Microstructure Evolution ◽  
Polycrystalline Materials ◽  
Boundary Character ◽  
Crystal Plasticity Finite Element ◽  
Grain Boundary Character

ABSTRACTCrystal plasticity finite element method is a useful tool to investigate the anisotropic mechanical behaviors as well as the microstructure evolution of metallic materials and it is widely used on single crystals and polycrystalline materials. However, grain boundary involved mechanisms are barely included in the polycrystalline models, and modeling the interaction between the dislocation and the grain boundaries in polycrystalline materials in a physically consisstent way is still a long-standing, unsolved problem. In our analysis, a dislocation density based crystal plasticity finite element model is proposed, and the interaction between the dislocation density and the grain boundaries is included in the model kinematically. The model is then applied to Al bicrystals under 10% compression to investigate the effects of grain boundary character, e.g. grain boundary misorientation and grain boundary normal, on the stress state and the microstructure evolution. The modeling results suggest a reasonable correspondence with the experimental result and the grain boundary character plays a crucial role in the stress concentration and dislocation patterning.

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