scholarly journals Stress Distribution in Silicon Subjected to Atomic Scale Grinding with a Curved Tool Path

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1710 ◽  
Author(s):  
Xudong Fang ◽  
Qiang Kang ◽  
Jianjun Ding ◽  
Lin Sun ◽  
Ryutaro Maeda ◽  
...  
Keyword(s):  
Stress Distribution ◽  
Hydrostatic Stress ◽  
Three Dimensional ◽  
Md Simulations ◽  
Atomic Scale ◽  
Shear Stresses ◽  
Asymmetric Distribution ◽  
Tool Paths ◽  
Tool Trajectory ◽  
Fundamental Mechanism

Molecular dynamics (MD) simulations were applied to study the fundamental mechanism of nanoscale grinding with a modeled tool trajectory of straight lines. Nevertheless, these models ignore curvature changes of actual tool paths, which need optimization to facilitate understanding of the underlying science of the machining processes. In this work, a three-dimensional MD model considering the effect of tool paths was employed to investigate distributions of stresses including hydrostatic stress, von Mises stress, normal and shear stresses during atomic grinding. Simulation results showed that average values of the stresses are greatly influenced by the radius of the tool trajectory and the grinding depth. Besides the averaged stresses, plane stress distribution was also analyzed, which was obtained by intercepting stresses on the internal planes of the workpiece. For the case of a grinding depth of 25 Å and an arc radius 40 Å, snapshots of the stresses on the X–Y, X–Z and Y–Z planes showed internal stress concentration. The results show that phase transformation occurred from α- silicon to β- silicon in the region with hydrostatic stress over 8 GPa. Moreover, lateral snapshots of the three-dimensional stress distribution are comprehensively discussed. It can be deduced from MD simulations of stress distribution in monocrystalline silicon with the designed new model that a curved tool trajectory leads to asymmetric distribution and concentration of stress during atomic-scale grinding. The analysis of stress distribution with varying curve geometries and cutting depths can aid fundamental mechanism development in nanomanufacturing and provide theoretical support for ultraprecision grinding.

scholarly journals Porous Characteristics of Three-Dimensional Disordered Graphene Networks

Crystals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 127
Author(s):  
YongChao Wang ◽  
YinBo Zhu ◽  
HengAn Wu
Keyword(s):  
Pore Size ◽  
Low Temperatures ◽  
Gas Adsorption ◽  
Three Dimensional ◽  
Md Simulations ◽  
Structural Features ◽  
Atomic Scale ◽  
Critical Factors ◽  
Chlorination Process ◽  
Porous Morphology

The porous characteristics of disordered carbons are critical factors to their performance on hydrogen storage and electrochemical capacitors. Even though the porous information can be estimated indirectly by gas adsorption experiments, it is still hard to directly characterize the porous morphology considering the complex 3D connectivity. To this end, we construct full-atom disordered graphene networks (DGNs) by mimicking the chlorination process of carbide-derived carbons using annealing-MD simulations, which could model the structure of disordered carbons at the atomic scale. The porous characteristics, including pore volume, pore size distribution (PSD), and specific surface area (SSA), were then computed from the coordinates of carbon atoms. From the evolution of structural features, pores grow dramatically during the formation of polyaromatic fragments and sequent disordered framework. Then structure is further graphitized while the PSD shows little change. For the obtained DGNs, the porosity, pore size, and SSA increase with decreasing density. Furthermore, SSA tends to saturate in the low-density range. The DGNs annealed at low temperatures exhibit larger SSA than high-temperature DGNs because of the abundant free edges.

scholarly journals Stress distributions in maxillary central incisors restored with different high-stiffness post models: 3-D FEA

2018 ◽  
Vol 6 (1) ◽  
pp. 45
Author(s):  
Bassam Srayeddin ◽  
Ali Almuntashri
Keyword(s):  
Stress Distribution ◽  
Root Canal ◽  
Gold Alloy ◽  
Three Dimensional ◽  
Shear Stresses ◽  
Distribution Profile ◽  
Maxillary Central Incisor ◽  
Group I ◽  
Group Ii ◽  
Restoration Failure

Background: Dental root posts are recommended for endodontically treated weakened teeth.Objectives: The present computational FEA study aims to evaluate the effect of material and design of the post on the stress distribution under load in different root canal shapes of endodontically treated maxillary central incisor (MCI).Methods: Three-dimensional models of (MCI) were created by using CAD modeling software and divided into two groups. Group-I comprised five models of a weakened root restored using different post materials (stainless steel, titanium, gold-alloy, Ni-Cr, and zirconium). Group-II: involved four models of (MCI) with two different root canal shapes (small and wide) restored using cylindrical (C-Post) and two-stage tapered (T-Post) posts. Each tooth model was subjected to a 100 N oblique load at the palatal surface of the crown. Von Mises equivalent stresses on dentin and post, as well as shear stresses on the post cement, were evaluated.Results: In Group-I: Ni-Cr produced the lowest stress values on the dentin, where titanium and gold-alloy posts produced the lowest stresses in the post and post/root interfaces. In Group-II: Roots restored with a T-Post showed a lower concentration stress in the dentin and lower shear stresses in the cement layer compared with those restored with a C-Post.Conclusion: The geometry of the post and the corresponding material play an important role in the stress behavior of restored teeth. The use of titanium or gold-alloy T-Posts seems a good way to improve the stress distribution profile and reduce the risk of restoration failure.   

The heterodonty of Albertosaurus sarcophagus and Tyrannosaurus rex: biomechanical implications inferred through 3-D modelsThis article is one of a series of papers published in this Special Issue on the theme Albertosaurus.

2010 ◽  
Vol 47 (9) ◽  
pp. 1253-1261 ◽  
Author(s):  
Miriam Reichel
Keyword(s):  
Stress Distribution ◽  
Yield Criterion ◽  
Three Dimensional ◽  
Ct Scanning ◽  
Distribution Patterns ◽  
Shear Stresses ◽  
Form And Function ◽  
Southern Alberta ◽  
Tooth Form ◽  
And Function

The objective of this study is to analyze how different crown morphologies and different root lengths respond to stresses generated by the bite forces of Albertosaurus sarcophagus and Tyrannosaurus rex . Six well-preserved teeth of A. sarcophagus from the Albertosaurus bonebed in Dry Island Park (southern Alberta) were selected to study their biomechanics, and T. rex teeth were included for comparison. The three-dimensional (3-D) models were obtained through computerized tomography (CT) scanning and 3-D digitizing. Finite element analyses were performed in Strand7®. Bite forces for Albertosaurus and Tyrannosaurus were calculated based on cranial and jaw proportions. The results were viewed with the Tresca yield criterion. The ratios of shear stresses observed along the mesio-distal versus labio-lingual axes of all models allows the identification of similar stress distribution patterns in the upper and lower jaws of Albertosaurus and the upper jaws of Tyrannosaurus, with a higher amount of shear along the mesio-distal axis occurring in the mid-maxillary teeth. The dentary teeth of Tyrannosaurus, however, show a different stress distribution pattern, with a higher amount of shear occurring along the labio-lingual axis of the mid-dentary teeth. These differences in jaw mechanics suggest that the function of teeth in the lower jaw of Tyrannosaurus shifted a few positions to compensate different proportions in the dentary that cause the anterior dentary teeth to be aligned with the largest maxillary teeth in Tyrannosaurus. These results suggest that heterodonty in these groups is different and that tooth form and function are sensitive to jaw proportions.

Computational Nanomechanics of Graphene Membranes

2009 ◽  
Vol 1185 ◽  
Author(s):  
Romain Perriot ◽  
Xiang Gu ◽  
Ivan I. Oleynik
Keyword(s):  
Elastic Limit ◽  
Breaking Strength ◽  
Md Simulations ◽  
Atomic Scale ◽  
Graphene Monolayer ◽  
Shear Stresses ◽  
Linear Chains ◽  
Advanced Stages ◽  
Stable Linear ◽  
Graphene Membranes

AbstractMolecular Dynamics (MD) simulations of nanoindentation on graphene membranes were performed. The 2-d Young's modulus of the graphene monolayer was determined as 243 ± 18 N/m and the breaking strength as 41 ± 3 N/m. These values agree reasonably well with recent experimental results [1]. In addition, the simulations allowed us to examine the atomic-scale dynamics of membrane breaking during the nanoindentation, involving formation of an increasing number of lattice defects until membrane is completely broken. The onset of defect appearance allowed us to determine the true elastic limit of graphene and the corresponding yield strength 29 ± 1 N/m which was not accessible experimentally. The defects consist of vacancies and Stone-Wales type defects. Long stable linear chains of sp bonded carbon atoms (carbynes) were observed under the indenter at the advanced stages of indentation. The dynamics of fracture propagation is governed by the shear stresses developed in the sample.

Nanoindentation-Induced Collective Dislocation Behavior and Nanoplasticity

2007 ◽  
Vol 340-341 ◽  
pp. 39-48 ◽  
Author(s):  
Yoji Shibutani ◽  
Tomohito Tsuru
Keyword(s):  
Three Dimensional ◽  
Md Simulations ◽  
Dislocation Nucleation ◽  
Balance Model ◽  
Shear Stresses ◽  
Dislocation Loops ◽  
Nucleation Model ◽  
Dislocation Behavior ◽  
Discrete Dislocations ◽  
The Ideal

The present paper summarizes the crystallographic dependence of the displacement burst behavior observed in nanoindentation using two single crystalline aluminum (Al) materials and copper (Cu) with three kinds of surface indices, namely (001), (110) and (111). From the critical indent load at the first burst, the critical resolved shear stresses (CRSSs) of the collective dislocation nucleation were estimated in reference to molecular dynamics (MD) simulations. These are almost one-tenth of the shear modulus, which are close to the ideal values. We explain the nanoplastic mechanics by a comprehensive energy balance model to describe the linear relation between the indent load and the burst width of the first displacement burst and by the nucleation model consisting of three-dimensional discrete dislocations to evaluate the number of dislocations nucleating. The distance between the emitted dislocation loops of Al is found to be fairly large. Thus, Al is expected to exhibit a less tangled network of dislocations just below the indentation than Cu, which has a lower stacking fault energy.

scholarly journals Assessing Machine Learning versus a Mathematical Model to Estimate the Transverse Shear Stress Distribution in a Rectangular Channel

Mathematics ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 596
Author(s):  
Babak Lashkar-Ara ◽  
Niloofar Kalantari ◽  
Zohreh Sheikh Khozani ◽  
Amir Mosavi
Keyword(s):  
Shear Stress ◽  
Stress Distribution ◽  
Fuzzy Inference ◽  
Rectangular Channel ◽  
Tsallis Entropy ◽  
Shear Stress Distribution ◽  
Data Series ◽  
Shear Stresses ◽  
Inference System ◽  
Aspect Ratios

One of the most important subjects of hydraulic engineering is the reliable estimation of the transverse distribution in the rectangular channel of bed and wall shear stresses. This study makes use of the Tsallis entropy, genetic programming (GP) and adaptive neuro-fuzzy inference system (ANFIS) methods to assess the shear stress distribution (SSD) in the rectangular channel. To evaluate the results of the Tsallis entropy, GP and ANFIS models, laboratory observations were used in which shear stress was measured using an optimized Preston tube. This is then used to measure the SSD in various aspect ratios in the rectangular channel. To investigate the shear stress percentage, 10 data series with a total of 112 different data for were used. The results of the sensitivity analysis show that the most influential parameter for the SSD in smooth rectangular channel is the dimensionless parameter B/H, Where the transverse coordinate is B, and the flow depth is H. With the parameters (b/B), (B/H) for the bed and (z/H), (B/H) for the wall as inputs, the modeling of the GP was better than the other one. Based on the analysis, it can be concluded that the use of GP and ANFIS algorithms is more effective in estimating shear stress in smooth rectangular channels than the Tsallis entropy-based equations.

scholarly journals Three-Dimensional Finite Element Analysis of Stress Distribution in a Tooth Restored with Full Coverage Machined Polymer Crown

2021 ◽  
Vol 11 (3) ◽  
pp. 1220
Author(s):  
Azeem Ul Yaqin Syed ◽  
Dinesh Rokaya ◽  
Shirin Shahrbaf ◽  
Nicolas Martin
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Stress Distribution ◽  
Three Dimensional ◽  
Intraoral Scanner ◽  
Element Analysis ◽  
Dental Ceramic ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Ceramic Crown

The effect of a restored machined hybrid dental ceramic crown–tooth complex is not well understood. This study was conducted to determine the effect of the stress state of the machined hybrid dental ceramic crown using three-dimensional finite element analysis. Human premolars were prepared to receive full coverage crowns and restored with machined hybrid dental ceramic crowns using the resin cement. Then, the teeth were digitized using micro-computed tomography and the teeth were scanned with an optical intraoral scanner using an intraoral scanner. Three-dimensional digital models were generated using an interactive image processing software for the restored tooth complex. The generated models were imported into a finite element analysis software with all degrees of freedom concentrated on the outer surface of the root of the crown–tooth complex. To simulate average occlusal load subjected on a premolar a total load of 300 N was applied, 150 N at a buccal incline of the palatal cusp, and palatal incline of the buccal cusp. The von Mises stresses were calculated for the crown–tooth complex under simulated load application was determined. Three-dimensional finite element analysis showed that the stress distribution was more in the dentine and least in the cement. For the cement layer, the stresses were more concentrated on the buccal cusp tip. In dentine, stress was more on the cusp tips and coronal 1/3 of the root surface. The conventional crown preparation is a suitable option for machined polymer crowns with less stress distribution within the crown–tooth complex and can be a good aesthetic replacement in the posterior region. Enamic crowns are a good viable option in the posterior region.

Influence of the Welded Joint on the Mechanical Behavior of Steel Piles during Static and Dynamic Deformation

2007 ◽  
Vol 345-346 ◽  
pp. 1469-1472
Author(s):  
Gab Chul Jang ◽  
Kyong Ho Chang ◽  
Chin Hyung Lee
Keyword(s):  
Residual Stress ◽  
Stress Distribution ◽  
Mechanical Behavior ◽  
Welded Joint ◽  
Dynamic Deformation ◽  
Three Dimensional ◽  
Steel Structures ◽  
Residual Stress Distribution ◽  
Dynamic Mechanical Behavior ◽  
Steel Piles

During manufacturing the welded joint of steel structures, residual stress is produced and weld metal is used inevitably. And residual stress and weld metal influence on the static and dynamic mechanical behavior of steel structures. Therefore, to predict the mechanical behavior of steel pile with a welded joint during static and dynamic deformation, the research on the influence of the welded joints on the static and dynamic behavior of steel pile is clarified. In this paper, the residual stress distribution in a welded joint of steel piles was investigated by using three-dimensional welding analysis. The static and dynamic mechanical behavior of steel piles with a welded joint is investigated by three-dimensional elastic-plastic finite element analysis using a proposed dynamic hysteresis model. Numerical analyses of the steel pile with a welded joint were compared to that without a welded joint with respect to load carrying capacity and residual stress distribution. The influence of the welded joint on the mechanical behavior of steel piles during static and dynamic deformation was clarified by comparing analytical results

scholarly journals Patterns in Protein Flexibility: A Comparison of NMR “Ensembles”, MD Trajectories, and Crystallographic B-Factors

Molecules ◽  
2021 ◽  
Vol 26 (5) ◽  
pp. 1484
Author(s):  
Christopher Reinknecht ◽  
Anthony Riga ◽  
Jasmin Rivera ◽  
David A. Snyder
Keyword(s):  
Protein Flexibility ◽  
Molecular Machines ◽  
Md Simulations ◽  
Peptide Bond ◽  
Structure Calculation ◽  
Atomic Scale ◽  
Heavy Atoms ◽  
Structural Ensembles ◽  
Atomic Coordinates ◽  
Motional Behavior

Proteins are molecular machines requiring flexibility to function. Crystallographic B-factors and Molecular Dynamics (MD) simulations both provide insights into protein flexibility on an atomic scale. Nuclear Magnetic Resonance (NMR) lacks a universally accepted analog of the B-factor. However, a lack of convergence in atomic coordinates in an NMR-based structure calculation also suggests atomic mobility. This paper describes a pattern in the coordinate uncertainties of backbone heavy atoms in NMR-derived structural “ensembles” first noted in the development of FindCore2 (previously called Expanded FindCore: DA Snyder, J Grullon, YJ Huang, R Tejero, GT Montelione, Proteins: Structure, Function, and Bioinformatics 82 (S2), 219–230) and demonstrates that this pattern exists in coordinate variances across MD trajectories but not in crystallographic B-factors. This either suggests that MD trajectories and NMR “ensembles” capture motional behavior of peptide bond units not captured by B-factors or indicates a deficiency common to force fields used in both NMR and MD calculations.

Sign in / Sign up

Export Citation Format

Share Document