scholarly journals Finite Element Modelling and Mechanical Characterization of Graphyne

2016 ◽  
Vol 2016 ◽  
pp. 1-15 ◽  
Author(s):  
Ricardo Couto ◽  
Nuno Silvestre
Keyword(s):  
Finite Element ◽  
Elastic Properties ◽  
Density Functional ◽  
Computational Models ◽  
Mechanical Characterization ◽  
Computational Simulation ◽  
Md Simulations ◽  
Small Strain ◽  
Fe Model ◽  
Linear Elastic

Graphyne is an allotrope of carbon with excellent mechanical, electrical, and optical properties. The scientific community has been increasingly interested in its characterization and computational simulation, using molecular dynamics (MD) simulations and density functional theory (DFT). The present work presents, for the first time (to the authors’ knowledge), a finite element (FE) model to evaluate the elastic properties of graphyne. After presenting a brief literature review on the latest developments of graphyne and its mechanical characterization through computational methods, the FE model of graphyne sheet is presented in detail and the calculation of its elastic properties described. The linear elastic properties (Young’s modulus, Poisson’s ratio, bulk modulus, and shear modulus) obtained from the proposed FE models are in general agreement with those previously obtained by other authors using more complex computational models (MD and DFT). The influence of van der Waals (vdW) interatomic forces on the linear elastic properties of planar graphyne is negligible and can be disregarded if small strain hypothesis is adopted. The FE models also show that graphyne exhibits marginal orthotropic behavior, that is, “quasi-isotropic” behavior, a fact that agrees with the conclusions reported by other researchers.

Age Dependent and Anisotropic Material Properties of Immature Porcine Sclera

2013 ◽  
Author(s):  
Jami M. Saffioti ◽  
Brittany Coats
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Anisotropic Material ◽  
Computational Models ◽  
Fe Model ◽  
Ocular Tissues ◽  
Load Bearing ◽  
Anisotropic Properties ◽  
Age Dependent ◽  
Testing Protocols

Current finite element (FE) models of the pediatric eye are based on adult material properties [2,3]. To date, there are no data characterizing the age dependent material properties of ocular tissues. The sclera is a major load bearing tissue and an essential component to most computational models of the eye. In preparation for the development of a pediatric FE model, age-dependent and anisotropic properties of sclera were evaluated in newborn (3–5 days) and toddler (4 weeks) pigs. Data from this study will guide future testing protocols for human pediatric specimens.

scholarly journals Nanoindentation simulations for large atomic systems : an analysis of molecular dynamics and bridged finite element - molecular dynamics methodologies

2021 ◽  
Author(s):  
Jonathan Vandersluis
Keyword(s):  
Molecular Dynamics ◽  
Finite Element ◽  
Md Simulation ◽  
Computational Simulation ◽  
Md Simulations ◽  
Single Step ◽  
Depth Interval ◽  
Simulation Tool ◽  
Custom Made ◽  
Computational Resources

This thesis develops a molecular dynamics (MD) custom made computational tool to perform nanoindentation simulations on copper nanomaterials, a Face Centred Cubic (FCC) metal. The Embedding Atom Method (EAM) is used to model the interatomic forces with the substrate. Further, a bridged finite element - molecular dynamics (FE-MD) simulation tool is also adapted to perform nanoindentation experimentation. Using this bridged FE-MD simulation tool, nanoindentations are performed much more effectively than the MD simulations while saving substantial computational simulation time. While the MD simulation experienced difficulties capturing the behaviour of the system during indentation especially at faster indentation speeds, the bridged FE-MD method is capable of reaching a state of equilibrium within a single step for each indentation depth interval analyzed throughout the nanoindentation. Although the hardness values for these simulations cannot be obtained without larger scale simulations using more powerful computational resources, the simulations provide insight into the behaviour of the copper nanomaterial during nanoindentation. As a result, it is clear that the bridged FE-MD nanoindentation tool is much more effective for executing nanoindentation simulations than the traditional MD methodologies.

scholarly journals Numerical Study of Stresses around Holes Drilled and Filled by Expansive Cement: Case of Isotropic Linear Elastic Block of Rock

2018 ◽  
Vol 2018 ◽  
pp. 1-14
Author(s):  
Mambou Ngueyep Luc Leroy ◽  
Gael Nkenwoum Chebou
Keyword(s):  
Finite Element ◽  
Elastic Properties ◽  
Numerical Study ◽  
Hole Diameter ◽  
Finite Element Code ◽  
Normal Stresses ◽  
Linear Elastic ◽  
Diameter Hole ◽  
Essential Problem ◽  
Expansive Cement

This work dealt with an essential problem of fragmentation of rocks with expansive cement. The redistribution and magnitude of stresses and displacement generated around holes were done by using Ansys Inc. Code which is based on finite element code. Blocks of rock with one hole, two holes, and nine holes drilled in square mesh and staggered mesh have been considered. Numerical results reveal that many factors can influence the mechanism of fragmentation of a rock by using expansive cement: hole diameter, hole spacing, panel mesh, expansive pressure applied, and the elastic properties of the massif. Stresses and displacements generated globally decrease when spacing holes increase. Normal stresses allow a better stress interaction between holes in the case of square mesh disposition. Staggered mesh disposition generates higher stresses than the square mesh disposition. But the square mesh disposition can be useful for controlled fragmentation in order to obtain block of rock with square geometry. For each expansive cement and rock, there exist suitable range of diameter and spacing hole which can generate high stresses for breaking the rock.

Geometrically Exact Analysis of Spatial Frames

1993 ◽  
Vol 46 (11S) ◽  
pp. S118-S128 ◽  
Author(s):  
Paulo M. Pimenta ◽  
Takashi Yojo
Keyword(s):  
Finite Element ◽  
Weak Form ◽  
Small Strain ◽  
Exact Expression ◽  
Galerkin Projection ◽  
Equilibrium Equations ◽  
Rodrigues Formula ◽  
Linear Elastic ◽  
3D Space ◽  
Shear Distortion

A fully nonlinear, geometrically exact, finite strain rod model is derived from basic kinematical assumptions. The model incorporates shear distortion in bending and can take account of torsion warping. Rotation in 3D space is handled with the aid of the Euler-Rodrigues formula. The accomplished parametrization is simple and does not require update algorithms based on quaternions parameters. Weak and strong forms of the equilibrium equations are derived in terms of cross section strains and stresses, which are objective and suitable for constitutive description. As an example, an invariant linear elastic constitutive equation based on the small strain theory is presented. The attained formulation is very convenient for numerical procedures employing Galerkin projection like the finite element method and can be readily implemented in a finite element code. A mixed formulation of Hu-Washizu type is also derived, allowing for independent interpolation of the displacement, strain and stress fields within a finite element. An exact expression for the Fre´chet derivative of the weak form of equilibrium is obtained in closed form, which is always symmetric for conservative loading, even far from an equilibrium state and is very helpful for numerical procedures like the Newton method as well as for stability and bifurcation analysis. Several numerical examples illustrate the usefulness of the formulation in the lateral stability analysis of spatial frames. These examples were computed with the code FENOMENA, which is under development at the Computational Mechanics Laboratory of the Escola Polite´cnica.

scholarly journals Nanoindentation simulations for large atomic systems : an analysis of molecular dynamics and bridged finite element - molecular dynamics methodologies

2021 ◽  
Author(s):  
Jonathan Vandersluis
Keyword(s):  
Molecular Dynamics ◽  
Finite Element ◽  
Md Simulation ◽  
Computational Simulation ◽  
Md Simulations ◽  
Single Step ◽  
Depth Interval ◽  
Simulation Tool ◽  
Custom Made ◽  
Computational Resources

This thesis develops a molecular dynamics (MD) custom made computational tool to perform nanoindentation simulations on copper nanomaterials, a Face Centred Cubic (FCC) metal. The Embedding Atom Method (EAM) is used to model the interatomic forces with the substrate. Further, a bridged finite element - molecular dynamics (FE-MD) simulation tool is also adapted to perform nanoindentation experimentation. Using this bridged FE-MD simulation tool, nanoindentations are performed much more effectively than the MD simulations while saving substantial computational simulation time. While the MD simulation experienced difficulties capturing the behaviour of the system during indentation especially at faster indentation speeds, the bridged FE-MD method is capable of reaching a state of equilibrium within a single step for each indentation depth interval analyzed throughout the nanoindentation. Although the hardness values for these simulations cannot be obtained without larger scale simulations using more powerful computational resources, the simulations provide insight into the behaviour of the copper nanomaterial during nanoindentation. As a result, it is clear that the bridged FE-MD nanoindentation tool is much more effective for executing nanoindentation simulations than the traditional MD methodologies.

A Finite Element Model of a Surgical Knot

2017 ◽  
Author(s):  
Arz Y. Qwam Alden ◽  
Andrew G. Geeslin ◽  
Jeffrey C. King ◽  
Peter A. Gustafson
Keyword(s):  
Finite Element ◽  
Soft Tissue ◽  
Computational Models ◽  
Mechanical Performance ◽  
Surgical Techniques ◽  
Element Model ◽  
Fe Model ◽  
Stress Concentrations ◽  
Suture Materials ◽  
Surgical Suture

Background Surgical knots are one of several structures which can fail during surgical repair. However, there is no universal agreement on the superiority (best/safest) of one particular surgical knot technique. Tensile testing of repaired soft tissue has been used to assess the efficacy of surgical knot tying techniques, however, few computational models exist. The purpose of this study was to create a validated biomechanical model to evaluate the effect of knot configuration on the mechanical performance of surgical sutures. Methods Two sutures were tested experimentally to find the mechanical properties and strength. Single throw knots were also tested for strength. Finite element models were constructed of each configuration and correlation was established. Results The finite element results are quantitatively and qualitatively consistent with experimental findings. The FE model stress concentrations are also consistent with published strength reductions. Model and experimental results are presented using as-manufactured No. 2 FiberWire as well as its core and jacket constituents separately. Clinical Relevance This paper describes a model which can evaluate the effect of knot topology on the mechanics of surgical suture. In the future, the model may be used to evaluate the mechanical differences between surgical techniques and suture materials. The findings may impact choices for suture and knot types selected for soft tissue repairs.

Finite element analysis of active Eustachian tube function

2004 ◽  
Vol 97 (2) ◽  
pp. 648-654 ◽  
Author(s):  
Samir N. Ghadiali ◽  
Julie Banks ◽  
J. Douglas Swarts
Keyword(s):  
Finite Element ◽  
Soft Tissue ◽  
Structural Properties ◽  
Elastic Properties ◽  
Eustachian Tube ◽  
Computational Models ◽  
Computational Technique ◽  
Fatty Tissue ◽  
Muscle Forces ◽  
Element Analysis

The inability to open the collapsible Eustachian tube (ET) has been related to the development of chronic otitis media. Although ET dysfunction may be due to anatomic and/or mechanical abnormalities, the precise mechanisms by which these structural properties alter ET opening phenomena have not been investigated. Previous investigations could only speculate on how these structural properties influence the tissue deformation processes responsible for ET opening. We have, therefore, developed a computational technique that can quantify these structure-function relationships. Cross-sectional histological images were obtained from eight normal adult human subjects, who had no history of middle ear disease. A midcartilaginous image from each subject was used to create two-dimensional finite element models of the soft tissue structures of the ET. ET opening phenomena were simulated by applying muscle forces on soft tissue surfaces in the appropriate direction and were quantified by calculating the resistance to flow (Rv) in the opened lumen. A sensitivity analysis was conducted to determine the relative importance of muscle forces and soft-tissue elastic properties. Muscle contraction resulted in a medial-superior rotation of the medial lamina, stretching deformation in the Ostmann's fatty tissue, and lumen dilation. Variability in baseline Rv values correlated with tissue size, whereas the functional relationship between Rv and a given mechanical parameter was consistent in all subjects. ET opening was found to be highly sensitive to the applied muscle forces and relatively insensitive to cartilage elastic properties. These computational models have, therefore, identified how different tissue elements alter ET opening phenomena, which elements should be targeted for treatment, and the optimal mechanical properties of these tissue constructs.

Modelling cement augmentation: A comparative experimental and finite element study at the continuum level

2009 ◽  
Vol 224 (7) ◽  
pp. 903-911 ◽  
Author(s):  
Y Zhao ◽  
Z M Jin ◽  
R K Wilcox
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Computational Models ◽  
Image Data ◽  
Fe Model ◽  
Micro Computed Tomography ◽  
Synthetic Bone ◽  
Pmma Bone Cement ◽  
Subject Specific ◽  
Cent Error

Subject-specific computational models of anatomical components can now be generated from image data and used in the assessment of orthopaedic interventions. However, little work has been undertaken to model cement-augmented bone using these methods. The purpose of this study was to investigate different methods of representing a trabecular-like material (open-cell polyurethane foam, Sawbone, Sweden) augmented with poly(methyl methacrylate) (PMMA) bone cement in a finite element (FE) model. Three sets of specimens (untreated, fully augmented with cement, partially augmented with cement) were imaged using micro computed tomography (μCT) and tested under axial compression. Subject-specific continuum level FE models were built based on the μCT images. Using the first two sets of models, the material conversion factors between image greyscale and mechanical properties for the pure synthetic bone and cement-augmented composite were determined iteratively by matching the FE predictions to the experimental measurements. By applying these greyscale related mechanical properties to the FE models of the partially augmented specimens, the predicted stiffness was found to be more accurate (∼ 5 per cent error) than using homogeneous properties for the augmented and synthetic bone regions (∼ 18 per cent error). It was also found that the predicted stiffness using the modulus of pure cement to define the augmented region was overestimated, and generally the apparent elastic modulus was dominated by the properties of the synthetic bone.

scholarly journals Main rotor blade modeling approaches comparison. Finite element and Craig-Bampton methods

2021 ◽  
Vol 2131 (3) ◽  
pp. 032096
Author(s):  
V Borisenko ◽  
J Leoro ◽  
A Didenko
Keyword(s):  
Finite Element ◽  
Rotor Blade ◽  
Element Model ◽  
Fe Model ◽  
Main Rotor ◽  
Linear Elastic ◽  
External Conditions ◽  
The One ◽  
Helicopter Main Rotor ◽  
Main Rotor Blade

Abstract The paper focuses on the helicopter main rotor blade FE model. And the main goal is to prove the feasibility of the helicopter main rotor MBD model in calculations of blade deformation as a result of applied aerodynamic forces. FE model is used as a basis for two different computational methods. A mathematical approach in the MBD based on the Craig-Bampton method on the one hand. And finite element model on the other hand. The results of high-frequency blade rotations are obtained. Calculations of these models are compared in order to determine the best method for modeling a linear-elastic blade. By the results, it is necessary to consider the preloaded state of the blade when using the Craig-Bampton method approach. The comparison of blade nodes displacements at various external conditions for both models are given. The influence of rotor MBS model damping parameters on the amplitude of blade oscillations under sinusoidal action is considered.

On the Effects of Residual Stress in Microindentation Tests of Soft Tissue Structures

2004 ◽  
Vol 126 (2) ◽  
pp. 276-283 ◽  
Author(s):  
Evan A. Zamir ◽  
Larry A. Taber
Keyword(s):  
Residual Stress ◽  
Soft Tissue ◽  
Elastic Foundation ◽  
Elastic Properties ◽  
Material Properties ◽  
Soft Tissues ◽  
Elastic Half Space ◽  
Fe Model ◽  
Linear Elastic ◽  
Tissue Structures

Microindentation methods are commonly used to determine material properties of soft tissues at the cell or even sub-cellular level. In determining properties from force-displacement (FD) data, it is often assumed that the tissue is initially a stress-free, homogeneous, linear elastic half-space. Residual stress, however, can strongly influence such results. In this paper, we present a new microindentation method for determining both elastic properties and residual stress in soft tissues that, to a first approximation, can be regarded as a pre-stressed layer embedded in or adhered to an underlying relatively soft, elastic foundation. The effects of residual stress are shown using two linear elastic models that approximate specific biological structures. The first model is an axially loaded beam on a relatively soft, elastic foundation (i.e., stress-fiber embedded in cytoplasm), while the second is a radially loaded plate on a foundation (e.g., cell membrane or epithelium). To illustrate our method, we use a nonlinear finite element (FE) model and experimental FD and surface contour data to find elastic properties and residual stress in the early embryonic chick heart, which, in the region near the indenter tip, is approximated as an isotropic circular plate under tension on a foundation. It is shown that the deformation of the surface in a microindentation test can be used along with FD data to estimate material properties, as well as residual stress, in soft tissue structures that can be regarded as a plate under tension on an elastic foundation. This method may not be as useful, however, for structures that behave as a beam on a foundation.

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