Extending the Local Approach to Fracture: Methods for Direct Incorporation of Microstructural Effects Into Finite Element Models of Fracture

2002 ◽  
Author(s):  
J. H. Beynon ◽  
S. Das ◽  
I. C. Howard ◽  
A. Chterenlikht
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Cellular Automata ◽  
Finite Element Models ◽  
Low Alloy Steels ◽  
Structural Level ◽  
Local Approach ◽  
Gauss Point ◽  
Physical Scale ◽  
Macro Scale

The Local Approach to fracture phenomena has been very successful in helping to transfer information derived from testing one geometry on a material (laboratory specimens) to the prediction of the crack growth performance of another (the structure). At least in its most pervasive manifestations, it depends upon constructing finite element models with a ruling element size that is appropriate for the physical scale of the dominant failure mechanism. Since these are primarily of the order of the material microstructure, there is a consequential very strong mesh gradient towards the region of Local Approach interest. When applied to structures of engineering interest, which can be large, the resultant finite element models become very big, sufficiently so that they cannot be run on many computers, if at all. When there is more than one material scale involved, the situation becomes impossible to resolve with conventional finite elements, except through the use of compromise local finite element sizes that blend the requirements from each micro-scale into a smeared cell at the finite element level. Such models have shown considerable success in predicting the performance of a range of components and structures by a number of research groups. Even so, the method is constrained by the excessive computational costs associated with modeling realistic structures, and by other concerns derived from its smearing of possibly incompatible underlying physical effects. CAFE modeling, the coupling of Cellular Automata at the microstructural scale(s) with finite elements that are scaled only for the strain gradients expected at the macro-scale in the structure, offers a way out of these potential problems. The structural level field quantities, held at the element Gauss points, are modified according to information coming from the Cellular Automata with which each Gauss point is associated. Suitable code representing fracture initiation and propagation at the micro-level generates changes incrementally to the Gauss point field variables, which are then brought to equilibrium by the FE modeler (whenever it is an implicit FE system). The method allows a natural representation of the multiple scale interactions typical of the fracture of low alloy steels in the transition region.

Modelling Recrystallisation during Thermomechanical Processing Using CAFE

2004 ◽  
Vol 467-470 ◽  
pp. 623-628 ◽  
Author(s):  
S. Das ◽  
Eric J. Palmiere ◽  
I.C. Howard
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Cellular Automata ◽  
Thermomechanical Processing ◽  
Constitutive Models ◽  
Computational Time ◽  
Physical Sciences ◽  
Element Mesh ◽  
Dislocation Densities ◽  
Macro Scale

A common feature that stimulates modelling efforts across the various physical sciences is that complex microscopic behaviour underlies apparently simple macroscopic effects. Mathematical formulations attempt to capture the initial and evolving microstructural entities either implicitly or explicitly and link their effects to measurable macroscopic variables such as load or stress by averaging out any microscopic fluctuations. The implicit formulations that ignore the inherent spatial heterogeneity in the deforming domain form the basis of constitutive models for input to finite element (FE) systems. On the other hand, explicit formulations to capture and link microstructural entities rely on narrowing down the size of each finite element, thereby increasing the number of finite elements in the deforming domain, an effect accompanied by a rapid growth in computational time. The model described here, Cellular Automata based Finite Elements (CAFE), utilises the Cellular Automata technique to represent initial and evolving microstructural features (e.g., dislocation densities, grain sizes, etc.) in C-Mn steels at an appropriate length scale by linking the macro-scale process variables obtained using an overlying finite element mesh. Differences will be illustrated between single and two-pass hot rolling experiments.

Trabecular Surface Remodeling Simulation for Cancellous Bone Using Microstructural Voxel Finite Element Models

2001 ◽  
Vol 123 (5) ◽  
pp. 403-409 ◽  
Author(s):  
Taiji Adachi ◽  
Ken-ichi Tsubota ◽  
Yoshihiro Tomita ◽  
Scott J. Hollister
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Cancellous Bone ◽  
Applied Load ◽  
Morphological Changes ◽  
Finite Element Models ◽  
Structural Level ◽  
Loading Direction ◽  
Surface Remodeling ◽  
Trabecular Surface

A computational simulation method for three-dimensional trabecular surface remodeling was proposed, using voxel finite element models of cancellous bone, and was applied to the experimental data. In the simulation, the trabecular microstructure was modeled based on digital images, and its morphological changes due to surface movement at the trabecular level were directly expressed by removing/adding the voxel elements from/to the trabecular surface. A remodeling simulation at the single trabecular level under uniaxial compressive loading demonstrated smooth morphological changes even though the trabeculae were modeled with discrete voxel elements. Moreover, the trabecular axis rotated toward the loading direction with increasing stiffness, simulating functional adaptation to the applied load. In the remodeling simulation at the trabecular structural level, a cancellous bone cube was modeled using a digital image obtained by microcomputed tomography (μCT), and was uniaxially compressed. As a result, the apparent stiffness against the applied load increased by remodeling, in which the trabeculae reoriented to the loading direction. In addition, changes in the structural indices of the trabecular architecture coincided qualitatively with previously published experimental observations. Through these studies, it was demonstrated that the newly proposed voxel simulation technique enables us to simulate the trabecular surface remodeling and to compare the results obtained using this technique with the in vivo experimental data in the investigation of the adaptive bone remodeling phenomenon.

Modelling of Rotating Twisted Blades as 1D Continuum

2016 ◽  
Vol 821 ◽  
pp. 183-190
Author(s):  
Jan Brůha ◽  
Drahomír Rychecký
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Beam Theory ◽  
Parameter Tuning ◽  
Finite Element Models ◽  
Cross Sectional ◽  
One Dimensional ◽  
Rayleigh Beam ◽  
Twisted Blade ◽  
Sectional Parameters

Presented paper deals with modelling of a twisted blade with rhombic shroud as one-dimensional continuum by means of Rayleigh beam finite elements with varying cross-sectional parameters along the finite elements. The blade is clamped into a rotating rigid disk and the shroud is considered to be a rigid body. Since the finite element models based on the Rayleigh beam theory tend to slightly overestimate natural frequencies and underestimate deflections in comparison with finite element models including shear deformation effects, parameter tuning of the blade is performed.

scholarly journals REGULARITIES OF THE LINING STRESS-STRAIN STATE DURING OF THE PYLON METRO STATION CONSTRUCTION

2021 ◽  
pp. 19-27
Author(s):  
D. O. BANNIKOV ◽  
V. P. KUPRII ◽  
D. YU. VOTCHENKO
Keyword(s):  
Finite Element ◽  
Numerical Analysis ◽  
Finite Elements ◽  
Strain State ◽  
Finite Element Models ◽  
Bending Moments ◽  
Stress Strain ◽  
Normal Forces ◽  
Stress Strain State ◽  
Station Structure

Purpose. Perform numerical analysis of the station structure. Take into account in the process of mathematical modeling the process of construction of station tunnels of a three-vaulted station. Obtain the regularities of the stress-strain state of the linings, which is influenced by the processes of soil excavation and lining construction. Methodology. To achieve this goal, a series of numerical calculations of models of the deep contour interval metro pylon station was performed. Three finite-element models have been developed, which reflect the stages of construction of a three-vaulted pylon station. Numerical analysis was performed on the basis of the finite element method, implemented in the calculation complex Lira for Windows. Modeling of the stress-strain state of the station tunnel linings and the soil massif was performed using rectangular, universal quadrangular and triangular finite elements, which take into account the special properties of the soil massif. Station tunnel linings are modeled by means of rod finite elements. Findings. Isofields of the stress-strain state in finite-element models reflecting the stages of construction are obtained. The vertical displacements and horizontal stresses that are characteristic of a three-vaulted pylon station are analyzed. The analysis of horizontal stresses proved that at the stage of opening of the middle tunnel the scheme of pylon operation is rather disadvantageous. The analysis of bending moments and normal forces was also carried out and the asymmetry of their distribution was noted. Originality. Based on the obtained patterns of distribution of stress-strain state and force factors, it is proved that numerical analysis of the station structure during construction is necessary to take measures to prevent or reduce deformation of frames that are in unfavorable conditions. Practical value. In the course of research, the regularities of changes in stresses, displacements, bending moments and normal forces in the models of the pylon station, which reflect the sequence of its construction, were obtained.

scholarly journals Investigation of the effect of raster angle, build orientation, and infill density on the elastic response of 3D printed parts using finite element microstructural modeling and homogenization techniques

2021 ◽  
Author(s):  
Hassan Gonabadi ◽  
Yao Chen ◽  
Arti Yadav ◽  
Steve Bull
Keyword(s):  
Finite Element ◽  
Computational Models ◽  
Mechanical Response ◽  
Elastic Response ◽  
Scale Model ◽  
Finite Element Models ◽  
Fused Filament Fabrication ◽  
Homogenization Technique ◽  
Macro Scale ◽  
3D Printed

AbstractAlthough the literature is abundant with the experimental methods to characterize mechanical behavior of parts made by fused filament fabrication 3D printing, less attention has been paid in using computational models to predict the mechanical properties of these parts. In the present paper, a numerical homogenization technique is developed to predict the effect of printing process parameters on the elastic response of 3D printed parts with cellular lattice structures. The development of finite element computational models of printed parts is based on a multi scale approach. Initially, at the micro scale level, the analysis of micro-mechanical models of a representative volume element is used to calculate the effective orthotropic properties. The finite element models include different infill densities and building/raster orientation maintaining the bonded region between the adjacent fibers and layers. The elastic constants obtained by this method are then used as an input for the creation of macro scale finite element models enabling the simulation of the mechanical response of printed samples subjected to the bending, shear, and tensile loads. Finally, the results obtained by the homogenization technique are validated against more realistic finite element explicit microstructural models and experimental measurements. The results show that, providing an accurate characterization of the properties to be fed into the macro scale model, the use of the homogenization technique is a reliable tool to predict the elastic response of 3D printed parts. The outlined approach provides faster iterative design of 3D printed parts, contributing to reducing the number of experimental replicates and fabrication costs.

Evaluating the Effect of Nozzle Weld Stiffness When Using Shell Finite Element Models for ASME Code Evaluations

2012 ◽  
Author(s):  
Bryan Dunlap ◽  
Hassan Ziada ◽  
John Julyk
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Shell Element ◽  
Finite Element Models ◽  
Shell Elements ◽  
Asme Code ◽  
Section Viii ◽  
Shell Finite Element ◽  
Code Compliance ◽  
Division 2

Typically the use of SHELL finite elements to model nozzle/vessel interfaces will not include details of the weld at the interface. The omission of the weld details from SHELL element models is due to the difficulty in implementing such details and the assumption that additional interface stiffness due to the weld will have a negligible effect on results at locations of interest for Code evaluation. This study will demonstrate a proposed method for modeling weld details with SHELL elements and then evaluate the magnitude of the weld stiffness effect on results and Code compliance. The method of modeling the weld details with SHELL elements used in this study will follow the guidance provided by ASME BPVC Section VIII, Division 2, Annex 5.A [2] for such interfaces. Models of nozzle/vessel interfaces will be shown comparing results of SOLID element models with and without the weld detail, and then SHELL element models both with and without the weld detail. The results from these models will be evaluated and recommendations for future modeling and evaluation of nozzle/shell interfaces with SHELL elements will be offered.

scholarly journals Development of Practical Finite Element Models for Collapse of Reinforced Concrete Structures and Experimental Validation

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Mario Bermejo ◽  
Anastasio P. Santos ◽  
José M. Goicolea
Keyword(s):  
Finite Element ◽  
Reinforced Concrete ◽  
Finite Elements ◽  
Finite Element Model ◽  
Computational Cost ◽  
Concrete Structures ◽  
Element Model ◽  
Reinforced Concrete Structures ◽  
Finite Element Models ◽  
Explicit Finite Element

This paper describes two practical methodologies for modeling the collapse of reinforced concrete structures. They are validated with a real scale test of a two-floor structure which loses a bearing column. The objective is to achieve accurate simulations of collapse phenomena with moderate computational cost. Explicit finite element models are used with Lagrangian meshes, modeling concrete, and steel in a segregated manner. The first model uses 3D continuum finite elements for concrete and beams for steel bars, connected for displacement compatibility using a penalty method. The second model uses structural finite elements, shells for concrete, and beams for steel, connected in common nodes with an eccentricity formulation. Both are capable of simulating correctly the global behavior of the structural collapse. The continuum finite element model is more accurate for interpreting local failure but has an excessive computational cost for a complete building. The structural finite element model proposed has a moderate computational cost, yields sufficiently accurate results, and as a result is the recommended methodology.

scholarly journals MATHEMATICAL MODEL OF BASIC FINITE ELEMENTS IN THE FINITE-ELEMENTARY THEORY OF PORT LIFTING STRUCTURES

2018 ◽  
pp. 109-128
Author(s):  
Nikolay Nikitovich Panasenko ◽  
Alexey Vladimirovich Sinelshchikov
Keyword(s):  
Finite Element ◽  
Finite Elements ◽  
Power Plants ◽  
Computational Analysis ◽  
Elementary Theory ◽  
Seismic Stability ◽  
Finite Element Models ◽  
Nuclear Facilities ◽  
Engineering Structures ◽  
Operation Rules

The problem of computational analysis of the seismic safety of lifting cranes specified by the regulatory systems (FPP "Safety Rules for dangerous production facilities using Lifting mechanisms" for standard industrial application cranes; Regulation 31.1.02-2004 "Technical operation rules for carrying and lifting equipment in the sea merchant harbors" for harbor cranes; Code of Design-031-01 "Codes of Design of antiseismic atomic power stations" and Code of Design-043-11 "Rules of Design and safe operating hoisting cranes for objects of use of atomic energy" for cranes used at the nuclear facilities) is currently under discussion, despite the emphasis on the part of scientific community. All this has led to carrying out the research which presented a vision of the problems of designing cranes in earthquake-proof design as a finite element theory of structures, and on the basis of methods of the theory of seismic stability of structures - the linear spectral method, according to the Code 14.13330.2014 "Building in earthquake areas" and the method of dynamic analysis, according to Guidelines 1.5.2.05.999.0025-2011 "Calculation and design of earthquake resistant nuclear power plants". The article highlights the trend of recent years of the increasing complexity of calculated finite element models of structures, often combining both finite element models of buildings and supporting structures, and cranes. A computational analysis of such constructions leads to a combination in the design model of finite elements of different dimensions. The article points out that both the choice of the type of finite elements and the way they are connected together within the framework of one calculation model directly affect the reliability of the results obtained. Based on the practical experience of computational analysis of complex spatial engineering structures, the article proposes stiffness and mass matrices for one-, two- and three-dimensional basic finite elements for calculating port lifting structures.

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