scholarly journals Three-dimensional cellular automata modelling of cleavage propagation across crystal boundaries in polycrystalline microstructures

2015 ◽  
Vol 471 (2177) ◽  
pp. 20150039 ◽  
Author(s):  
A. Shterenlikht ◽  
L. Margetts
Keyword(s):  
Cellular Automata ◽  
Grain Boundaries ◽  
Three Dimensional ◽  
Element Model ◽  
Length Scale ◽  
Orientation Tensor ◽  
Multi Scale ◽  
Ca Model ◽  
Orientation Distributions ◽  
Crystal Boundaries

A three-dimensional cellular automata (CA) with rectilinear layout is used in this work to create and cleave polycrystalline microstructures. Each crystal is defined by a unique randomly generated orientation tensor. Separate states for grains, grain boundaries, crack flanks and crack fronts are created. Algorithms for progressive cleavage propagation through crystals and across grain boundaries are detailed. The mesh independent cleavage criterion includes the critical cleavage stress and the length scale. Resolution of an arbitrary crystallographic plane within a 26-cell Moore neighbourhood is considered. The model is implemented in Fortran 2008 coarrays. The model gives realistic predictions of grain size and mis-orientation distributions, grain boundary topology and crack geometry. Finally, we show how the proposed CA model can be linked to a finite-element model to produce a multi-scale fracture framework.

Critical Manifolds in Polycrystalline Grain Structures

2004 ◽  
Vol 467-470 ◽  
pp. 1039-1044 ◽  
Author(s):  
Elizabeth A. Holm ◽  
J.H. Meinke ◽  
E.S. McGarrity ◽  
P.M. Duxbury
Keyword(s):  
Grain Boundaries ◽  
Optimization Algorithm ◽  
Network Optimization ◽  
Three Dimensional ◽  
Critical Length ◽  
Short Length ◽  
Length Scale ◽  
Length Scales ◽  
Critical Manifold ◽  
Grain Structures

With the development of new, fully three-dimensional metallographic techniques, there is considerable interest in characterizing three-dimensional microstructures in ways that go beyond twodimensional stereology. One characteristic of grain structures is the surface of lowest energy across the microstructure, termed the critical manifold (CM). When the grain boundaries are sufficiently weak, the CM lies entirely on grain boundaries, while when the grain boundaries are strong, cleavage occurs. A scaling theory for the cleavage to intergranular transition of CMs is developed. We find that a critical length scale exists, so that on short length scales cleavage is observed, while at long length scales the CM is rough. CMs for realistic polycrystalline grain structures, determined by a network optimization algorithm, are used to verify the analysis.

CNT Thin Film Network Failure due to Concentrated Current Loadings

2011 ◽  
Author(s):  
David A. Jack
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Electrical Response ◽  
Three Dimensional ◽  
Element Model ◽  
Scale Model ◽  
Lightning Strike ◽  
Similar System ◽  
Network Failure ◽  
Multi Scale

Polymer composite carbon nanotube (CNT) thin films have been hypothesized as a possible material for lightning strike protection for next generation aircraft structures. This study employs the author’s previously presented three-dimensional physics-based coupled thermal and electrical multi-scale model which constructs the non-deterministic nanostructure variations for a CNT thin film, and returns the bulk thermal and electrical response due to high electrical loadings. The key results of the present study are the presentation of a possible failure mechanism for CNT thin films under increasing electrical loadings. This paper discusses the nanoscale breakdown of the network conductivity using a quasi-static loading, and uses the nanoscale results in a macroscopic finite element model which couples resistive heating with thermal breakdown. The results are in reasonable agreement with those found in the literature for a similar system.

scholarly journals Examining oxidation in β-NiAl and β-NiAl+Hf alloys by stochastic cellular automata simulations

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Indranil Roy ◽  
Pratik K. Ray ◽  
Ganesh Balasubramanian
Keyword(s):  
Cellular Automata ◽  
Grain Boundaries ◽  
Oxide Scale ◽  
Oxidation Kinetics ◽  
Basic Principles ◽  
Stochastic Cellular Automata ◽  
Scale Thickness ◽  
Alloy Oxidation ◽  
Ca Model ◽  
Kinetics Of

AbstractWe present results from a stochastic cellular automata (CA) model developed and employed for examining the oxidation kinetics of NiAl and NiAl+Hf alloys. The rules of the CA model are grounded in diffusion probabilities and basic principles of alloy oxidation. Using this approach, we can model the oxide scale thickness and morphology, specific mass change and oxidation kinetics as well as an approximate estimate of the stress and strains in the oxide scale. Furthermore, we also incorporate Hf in the grain boundaries and observe the “reactive element effect”, where doping with Hf results in a drastic reduction in the oxidation kinetics concomitant with the formation of thin, planar oxide scales. Interestingly, although we find that grain boundaries result in rapid oxidation of the undoped NiAl, they result in a slower-growing oxide and a planar oxide/metal interface when doped with Hf.

A Cellular Automata Model for Nitriding of Nanocrystalline Iron

2015 ◽  
Author(s):  
Jingyi Zhao ◽  
G.-X. Wang ◽  
Yalin Dong ◽  
Chang Ye
Keyword(s):  
Experimental Data ◽  
Numerical Model ◽  
Cellular Automata ◽  
Grain Boundaries ◽  
Nitriding Process ◽  
Nitrogen Diffusion ◽  
Cellular Automata Model ◽  
Grain Sizes ◽  
Nanocrystalline Iron ◽  
Ca Model

In this study, a numerical model was developed to investigate the effects of grain refinement on the efficiency of nitrogen diffusion during the nitriding process. A cellular automata (CA) model without considering the effects of grain boundaries was built to simulate the nitriding process. The results from the numerical model were compared and validated by experimental data in the literature. Then, nanoscale grain boundaries were integrated into this CA model. The nitriding efficiency in materials with different grain sizes was investigated. The results demonstrate that nanocrystallization can significantly increase the nitrogen diffusion efficiency and thus make low temperature (300°C) nitriding possible.

Numerical analysis of punch shear failure and stress characteristics of three-dimensional braided composite with different braiding angles

2019 ◽  
Vol 28 (9) ◽  
pp. 1418-1437
Author(s):  
Yuanyuan Li ◽  
Zhijuan Pan ◽  
Bohong Gu ◽  
Baozhong Sun
Keyword(s):  
Shear Failure ◽  
Shear Bands ◽  
Three Dimensional ◽  
Element Model ◽  
Scale Model ◽  
Strain Rates ◽  
Braided Composites ◽  
Braided Composite ◽  
Multi Scale ◽  
Braided Structure

This paper presents a multi-scale finite element model to calculate the stress field and analyze the punch shear failure of three-dimensional braided composite at high strain rates. The multi-scale model was established based on real braided structure taking the surface and corner braiding yarns into consideration. Constitutive material modeling and failure criterions were introduced into the model. Three braiding angles of 25°, 35°, and 45° were applied to reveal the relations between failure states and braided structure. The results showed that the punch shear failure states and stress distribution were greatly dependent on the strain rates and braiding angles. Nonuniform stress propagation resulted in shear bands and different formation paths were observed on the composite with different braiding angles. The ultimate failure of braided composite was determined by comprehensive action of compressive and tensile stress. In addition, the progressive damage of typical braiding yarns in different conditions was obtained from the modeling simulation. The three-dimensional braided composites with different braiding angles showed unique failure morphology. It was closely determined by the complex braided structures.

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