Simulating Atomic-Scale Defects with Atomic Methods and Extended Finite Elements

2012 ◽  
Vol 2012 (DPC) ◽  
pp. 001983-002005
Author(s):  
Jay Oswald
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Dislocation Core ◽  
Atomic Scale ◽  
Configurational Forces ◽  
Material Interfaces ◽  
Dislocation Glide ◽  
Discontinuous Enrichment ◽  
Specific Material ◽  
Micro Structures

A finite element method is developed for dislocations in arbitrary, three-dimensional bodies, including micro-/nano-devices, and layered materials, such as thin films. The method is also compatible with anisotropic materials, and can readily be applied to nonlinear media. In this method, dislocations are modeled by adding discontinuities to extend the conventional finite element basis. Two approaches for adding discontinuities to the conventional finite element basis are proposed. In the first, a simple discontinuous enrichment imposes a constant jump in displacement across dislocation glide planes. In the second approach, the enrichments more accurately approximate the dislocations by capture the singular asymptotic behavior near the dislocation core. A basis of singular enrichments is formed from analytical solutions of straight dislocation lines, which are shown to be applicable for more general, curved dislocation configurations. Methods for computing the configurational forces on dislocation lines within the XFEM framework have also been developed. For jump enrichments, an approach based on an energy release rate or J-integral is proposed. When singular enrichments are available, it is shown that the Peach-Koehler equation can be used to compute forces directly. This new approach differs from many existing methods for studying dislocations because it does not rely on superposition of solutions derived analytically or through Green's functions. This extended finite element approach is suitable to study dislocations in micro- and nano-devices, and in specific material micro-structures, where complicated boundaries and material interfaces are pervasive.

An adaptive p-FEM for three-dimensional concrete aggregate models

2020 ◽  
Vol 11 (01) ◽  
pp. 2050004
Author(s):  
Ruiqi Guo ◽  
Yingxiong Xiao
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Three Dimensional ◽  
Poor Quality ◽  
Numerical Results ◽  
Concrete Aggregate ◽  
Material Interfaces ◽  
Reinforced Composite ◽  
Text Version ◽  
Particle Reinforced Composite

Numerical simulation for concrete aggregate models (CAMs) with different shape aggregates usually requires high accuracy and convergence near the material interfaces. But high memory usage will be needed for those traditional finite element methods such as the method by using mesh refinement throughout the domain. Thus, an adaptive [Formula: see text]-version finite element method ([Formula: see text]-FEM) is proposed in this paper for the solution of 3D CAM problems, and meanwhile the resulting adaptive computational algorithm and post-processing program are presented. We firstly focused two typical 3D weak discontinuity problems on the influence of different convergence criterions for the computational results of each point on the interface in order to verify the efficiency and convergence of the resulting [Formula: see text]-FEM, and then this method is successfully applied to the numerical simulation of CAMs with different shape aggregates. In addition, an efficient hybrid realization method which combines ANSYS and Hypermesh software is also presented in order to quickly establish the geometric models of 3D CAMs. The numerical results have been shown that the proposed [Formula: see text]-FEM can efficiently solve the concrete-like particle-reinforced composite problems and more accurate numerical results can be obtained under the case of fewer elements used in simulation of CAMs, even there being some elements with poor quality.

Nonconformal mesh-based finite element strategy for 3D textile composites

2016 ◽  
Vol 51 (16) ◽  
pp. 2315-2330 ◽  
Author(s):  
B Wucher ◽  
S Hallström ◽  
D Dumas ◽  
T Pardoen ◽  
C Bailly ◽  
...  
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Material Properties ◽  
Three Dimensional ◽  
Textile Composites ◽  
Thermoelastic Properties ◽  
Material Interfaces ◽  
Local Correction ◽  
Finite Element Procedure ◽  
Woven Reinforcement

A finite element procedure is developed for the computation of the thermoelastic properties of textile composites with complex and compact two- and three-dimensional woven reinforcement architectures. The purpose of the method is to provide estimates of the properties of the composite with minimum geometrical modeling effort. The software TexGen is used to model simplified representations of complex textiles. This results in severe yarn penetrations, which prevent conventional meshing. A non-conformal meshing strategy is adopted, where the mesh is refined at material interfaces. Penetrations are mitigated by using an original local correction of the material properties of the yarns to account for the true fiber content. The method is compared to more sophisticated textile modeling approaches and successfully assessed towards experimental data selected from the literature.

Evaluation of High Strain Rate Characteristics of Metallic Sandwich Specimens

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Danish Iqbal ◽  
Vikrant Tiwari
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Volume Fraction ◽  
Split Hopkinson Pressure Bar ◽  
Three Dimensional ◽  
Wave Theory ◽  
Hopkinson Pressure Bar ◽  
Material Interfaces ◽  
Element Analysis ◽  
Pressure Bar

An attempt is made to investigate the dynamic compressive response of multilayered specimens in bilayered and trilayered configurations, using a split Hopkinson pressure bar (SHPB) and finite element analysis. Two constituent metals comprising the multilayered configurations were Al 6063-T6 and IS 1570. Multiple stack sequences of trilayered and bilayered configurations were evaluated at three different sets of strain rates, namely, 500, 800, and 1000 s−1. The experiments revealed that even with the same constituent volume fraction, a change in the stacking sequence alters the overall dynamic constitutive response. This change becomes more evident, especially in the plastic zone. The finite element analysis was performed using abaqus/explicit. A three-dimensional (3D) model of the SHPB apparatus used in the experiments was generated and meshed using the hexahedral brick elements. Dissimilar material interfaces were assigned different dynamic coefficients of friction. The fundamental elastic one-dimensional (1D) wave theory was then utilized to evaluate the stress–strain response from the nodal strain histories of the bars. Predictions from the finite element simulations along with the experimental results are also presented in this study. For most cases, finite element predictions match well with the experiments.

Finite Element Studies of Homogeneous and Heterogeneous Dislocation Nucleation based on the Rice-Peierls Framework

2011 ◽  
Vol 1363 ◽  
Author(s):  
T.L. Li ◽  
J.H. Lee ◽  
Y.F. Gao
Keyword(s):  
Finite Element ◽  
Finite Thickness ◽  
Three Dimensional ◽  
Crack Tip ◽  
Dislocation Core ◽  
Dislocation Nucleation ◽  
Small Scale ◽  
Direction Parallel ◽  
Element Simulation ◽  
Geometric Boundary

ABSTRACTThe study of dislocation nucleation has gained increasing attentions recently primarily due to the advancement of small scale mechanical testing methods. Based on the classic Rice model of dislocation nucleation from a crack tip in which the dislocation core is modeled by a continuous slip field, a nonlinear finite element method can be formulated with the interplanar potential as the input, and the development of interplanar slip field can be solved from the resulting boundary value problems. The effects of geometric boundary conditions, loading patterns, etc. can be conveniently determined, as opposed to the time consuming molecular simulations. To validate the method, we compare the simulations results of homogeneous dislocation nucleation and heterogeneous dislocation nucleation from a two-dimensional crack tip to the literature results. As proposed by Rice and Beltz (J. Mech. Phys. Solids, 1994), the activation energy for dislocation nucleation from a three-dimensional crack tip depends on the finite thickness in the direction parallel to the crack tip, which has been successfully reproduced in the finite element simulation results reported here.

A Three-Dimensional Atomic-Scale Finite Element Model for a Copper Nano Thin Film Subject to a Uniaxial Tension

2012 ◽  
Vol 579 ◽  
pp. 453-463
Author(s):  
Jinn Tong Chiu ◽  
Yeou Yih Lin ◽  
Ship Peng Lo
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Strain Rate ◽  
Three Dimensional ◽  
Strain Curve ◽  
Element Model ◽  
Tension Test ◽  
Atomic Scale ◽  
Stress Strain Curve ◽  
Stress Strain

A three-dimensional atomic-scale finite element model was developed in this paper for simulation of a nano-scale uniaxial tension. First, the Morse’s potential function was used to simulate the forces acting among particles. Furthermore, a non-linear spring and dashpot element with a lumped mass was used to establish an atomic model. The elongation of the spring at fracture was used to simulate the radius of fracture of the atomic link. This method was applied to investigate the proportional tension test of an idealized FCC single crystal copper film along the x direction. The study includes the stress-strain curve, the effect of five categories of atomic distances on the stress-strain curve; and the effect of strain-rate on the stress-strain curve. The results showed that (1)the simulated maximum stress for copper is very close to 30.0GPa, which is also the value of maximum equivalent stress obtained by Lin and Hwang [6], verifying the validity of the calculation of this paper. In the tension test of copper, necking develops gradually and eventually leads to fracture. The simulated deformed material element during each stage of deformation was similar to that simulated by Komanduri et al.[2](2)the influence of =6.2608 on the five categories of atomic distance considered was limited and it may be neglected to save computation time,(3)when the strain-rate was large, the resistance to deformation was also large, leading to an increase in the yield stress and fracture stress.

scholarly journals A Three-Dimensional Inverse Finite Element Analysis of the Heel Pad

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Snehal Chokhandre ◽  
Jason P. Halloran ◽  
Antonie J. van den Bogert ◽  
Ahmet Erdemir
Keyword(s):  
Experimental Data ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Material Properties ◽  
Three Dimensional ◽  
Element Analysis ◽  
Heel Pad ◽  
Tool Force ◽  
Specific Material ◽  
Inverse Finite Element Analysis

Quantification of plantar tissue behavior of the heel pad is essential in developing computational models for predictive analysis of preventive treatment options such as footwear for patients with diabetes. Simulation based studies in the past have generally adopted heel pad properties from the literature, in return using heel-specific geometry with material properties of a different heel. In exceptional cases, patient-specific material characterization was performed with simplified two-dimensional models, without further evaluation of a heel-specific response under different loading conditions. The aim of this study was to conduct an inverse finite element analysis of the heel in order to calculate heel-specific material properties in situ. Multidimensional experimental data available from a previous cadaver study by Erdemir et al. (“An Elaborate Data Set Characterizing the Mechanical Response of the Foot,” ASME J. Biomech. Eng., 131(9), pp. 094502) was used for model development, optimization, and evaluation of material properties. A specimen-specific three-dimensional finite element representation was developed. Heel pad material properties were determined using inverse finite element analysis by fitting the model behavior to the experimental data. Compression dominant loading, applied using a spherical indenter, was used for optimization of the material properties. The optimized material properties were evaluated through simulations representative of a combined loading scenario (compression and anterior-posterior shear) with a spherical indenter and also of a compression dominant loading applied using an elevated platform. Optimized heel pad material coefficients were 0.001084 MPa (μ), 9.780 (α) (with an effective Poisson’s ratio (ν) of 0.475), for a first-order nearly incompressible Ogden material model. The model predicted structural response of the heel pad was in good agreement for both the optimization (<1.05% maximum tool force, 0.9% maximum tool displacement) and validation cases (6.5% maximum tool force, 15% maximum tool displacement). The inverse analysis successfully predicted the material properties for the given specimen-specific heel pad using the experimental data for the specimen. The modeling framework and results can be used for accurate predictions of the three-dimensional interaction of the heel pad with its surroundings.

Linear and Nonlinear Numerical Investigations of Regular Open Cell Structures

Aerospace ◽  
2004 ◽  
Author(s):  
Mathias H. Luxner ◽  
Juergen Stampfl ◽  
Heinz E. Pettermann
Keyword(s):  
Finite Element ◽  
Cross Sections ◽  
Compressive Loading ◽  
Three Dimensional ◽  
Beam Element ◽  
Finite Samples ◽  
Cell Structures ◽  
Linear And Nonlinear ◽  
Regular Open ◽  
Micro Structures

Linear and nonlinear Finite Element simulations of various regular three-dimensional cellular solids (lattice structures) with relative densities ranging from 10% and 20% are presented. The structures consist of polymeric struts with circular cross sections. Two different Finite Element modeling techniques are employed. Beam element based models and continuum element based models are utilized and their applicability is assessed. Beam element based models compromise about the numerical model size and the detail resolution of the problem. Continuum element based models are used for highly detailed unit cell analyses. For simulations of the overall behavior the structures are treated as infinite media by a periodic microfield approach. The entire overall elasticity tensors are computed for the constitutive characterization of the effective mechanical behavior of the micro-structures. Overall stress-strain curves are predicted for uniaxial compressive loading, taking into account finite strains and elasto-plastic strut material. The predicted properties are evaluated with respect to direction dependence and density dependence. Finite samples of specimens are modeled for comparison to experimentally obtained results.

Effects of occlusal scheme on All-on-Four abutments, screws and prostheses: A three-dimensional finite element study

2020 ◽  
Author(s):  
Nurullah Türker ◽  
Hümeyra Tercanlı Alkış ◽  
Steven J Sadowsky ◽  
Ulviye Şebnem Büyükkaplan
Keyword(s):  
Finite Element ◽  
Three Dimensional ◽  
Good Prognosis ◽  
Von Mises Stress ◽  
Element Analysis ◽  
Group Function ◽  
Occlusal Contact ◽  
Maximum Deformation ◽  
Contact Points ◽  
Von Mises

An ideal occlusal scheme plays an important role in a good prognosis of All-on-Four applications, as it does for other implant therapies, due to the potential impact of occlusal loads on implant prosthetic components. The aim of the present three-dimensional (3D) finite element analysis (FEA) study was to investigate the stresses on abutments, screws and prostheses that are generated by occlusal loads via different occlusal schemes in the All-on-Four concept. Three-dimensional models of the maxilla, mandible, implants, implant substructures and prostheses were designed according to the All-on-Four concept. Forces were applied from the occlusal contact points formed in maximum intercuspation and eccentric movements in canine guidance occlusion (CGO), group function occlusion (GFO) and lingualized occlusion (LO). The von Mises stress values for abutment and screws and deformation values for prostheses were obtained and results were evaluated comparatively. It was observed that the stresses on screws and abutments were more evenly distributed in GFO. Maximum deformation values for prosthesis were observed in the CFO model for lateral movement both in the maxilla and mandible. Within the limits of the present study, GFO may be suggested to reduce stresses on screws, abutments and prostheses in the All-on-Four concept.

Comparison of Conventional and Pontic Fixed Partial Dentures Over Implants Using the Finite Element Method: Three-Dimensional Analysis of Cortical and Medullary Bone Stress

2020 ◽  
Vol 46 (3) ◽  
pp. 175-181
Author(s):  
Marcelo Bighetti Toniollo ◽  
Mikaelly dos Santos Sá ◽  
Fernanda Pereira Silva ◽  
Giselle Rodrigues Reis ◽  
Ana Paula Macedo ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Three Dimensional ◽  
The Finite Element Method ◽  
Medullary Bone ◽  
Principal Stresses ◽  
Bone Stress ◽  
Bone Damage ◽  
Rehabilitation System ◽  
Minimum Requirements

Rehabilitation with implant prostheses in posterior areas requires the maximum number of possible implants due to the greater masticatory load of the region. However, the necessary minimum requirements are not always present in full. This project analyzed the minimum principal stresses (TMiP, representative of the compressive stress) to the friable structures, specifically the vestibular face of the cortical bone and the vestibular and internal/lingual face of the medullary bone. The experimental groups were as follows: the regular splinted group (GR), with a conventional infrastructure on 3 regular-length Morse taper implants (4 × 11 mm); and the regular pontic group (GP), with a pontic infrastructure on 2 regular-length Morse taper implants (4 × 11 mm). The results showed that the TMiP of the cortical and medullary bones were greater for the GP in regions surrounding the implants (especially in the cervical and apical areas of the same region) but they did not reach bone damage levels, at least under the loads applied in this study. It was concluded that greater stress observed in the GP demonstrates greater fragility with this modality of rehabilitation; this should draw the professional's attention to possible biomechanical implications. Whenever possible, professionals should give preference to use of a greater number of implants in the rehabilitation system, with a focus on preserving the supporting tissue with the generation of less intense stresses.

Towards Predicting Relative Belt Edge Endurance With the Finite Element Method

1990 ◽  
Vol 18 (4) ◽  
pp. 216-235 ◽  
Author(s):  
J. De Eskinazi ◽  
K. Ishihara ◽  
H. Volk ◽  
T. C. Warholic
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Three Dimensional ◽  
The Finite Element Method ◽  
Shear Deformations ◽  
Element Analysis ◽  
Vertical Loading ◽  
Predicted Values ◽  
Element Method

Abstract The paper describes the intention of the authors to determine whether it is possible to predict relative belt edge endurance for radial passenger car tires using the finite element method. Three groups of tires with different belt edge configurations were tested on a fleet test in an attempt to validate predictions from the finite element results. A two-dimensional, axisymmetric finite element analysis was first used to determine if the results from such an analysis, with emphasis on the shear deformations between the belts, could be used to predict a relative ranking for belt edge endurance. It is shown that such an analysis can lead to erroneous conclusions. A three-dimensional analysis in which tires are modeled under free rotation and static vertical loading was performed next. This approach resulted in an improvement in the quality of the correlations. The differences in the predicted values of various stress analysis parameters for the three belt edge configurations are studied and their implication on predicting belt edge endurance is discussed.

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