Micromechanical Model Research Papers - Academia.edu (original) (raw)

Micromechanical models used to predict mechanical and fracture properties of brittle metallic foams are validated experimentally for closed-cell aluminium foam (AlSi12Mg0.6) prepared by powder metallurgy route. Compression, tensile, tensile on notched specimens and fracture toughness tests were carried on, and the results are presented together with micromechanical models from literature. Moreover, the Digital Image Correlation technique was applied to identify the failure mechanisms of aluminium foams. Finally, the Theory of Critical Distances was employed to predict the fracture load of notched specimens. The novelty of the study is that the inherent stresses and critical distances were obtained by employing micromechanical analysis.

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- Digital Image Correlation, Aluminium Alloys, Micromechanical Model, Cellular Materials

The paper presents an assessment of the effect of fiber orientation on the strength properties of products made from wood-polymer composites by the injection molding process based on micromechanical analysis. For this purpose numerical analysis was carried out for the product model with geometry of the sample intended for the uniaxial tensile test. To determine the actual fiber orientation after the manufacturing process, the orientation tensor values were calculated using Auto-desk Moldflow Insight 2016 software. The micromechanical calculations were performed using Digimat FE commercial code. The results (stress-strain characteristics) of the numerical simulations taking into account the calculated fiber orientation ten-sor were compared to the experiment. To produce the wood-polymer composite, the polypropylene polymer matrix was Moplen HP 648T. As the filler Lignocel C120 wood fibers made by Rettenmeier & Sohns company were applied. A composite with a 10 vol.% content of wood fibers in the polymer was manufactured in the extrusion process by means of a Zamak EHP 25 extruder. For specimen manufacturing a Dr. Boy 55E injection molding machine equipped with a two cavity injection mold was used. Before the numerical simulations the uniaxial tensile test was performed using a Zwick Roell Z030 testing machine. The specimens were tested at the speed of 50 mm/min according to the PN-EN ISO 527 standard. The obtained stress-strain characteristics were used as a verification criterion for further numerical analysis. Moreover, the mechanical properties of the same composite products were predicted for hypothetical fiber orientation types. It was noted that the selection of fiber orientation has a significant impact on the quality of the obtained results compared to the experiment. PROGNOZOWANIE WPŁYWU ORIENTACJI WŁÓKIEN NA WYBRANE WŁAŚCIWOŚCI WYTRZYMAŁOŚCIOWE KOMPOZYTÓW TYPU DREWNO-POLIMER Przedstawiono ocenę wpływu orientacji włókien na właściwości wytrzymałościowe wyrobów kompozytowych na przyk-ładzie wyrobów z kompozytu typu drewno-polimer formowanych w technologii wtryskiwania. Przeprowadzono analizę numeryczną dla modelu wyrobu o geometrii próbki przeznaczonej do próby jednoosiowego rozciągania. W celu uzyskania danych o powtryskowej orientacji włókien w matrycy polimerowej przeprowadzono analizę numeryczną procesu wtryski-wania za pomocą oprogramowania Autodesk Moldflow Insigth 2016. Uzyskano w ten sposób wartości tensora orientacji włókien dla zadanych parametrów technologicznych procesu wytwarzania wyrobu. Obliczenia mikromechaniczne (analizy właściwości struktury kompozytu) przeprowadzono z wykorzystaniem oprogramowania Digimat FE. Wyniki analizy numerycznej dla obliczonej wartości tensora orientacji włókien porównano z eksperymentem. Ponadto, w celu ułatwienia definiowania w systemach CAE właściwości kompozytu wykonano prognozowanie jego właściwości mechanicznych dla hipo-tetycznych, uproszczonych przypadków orientacji włókien. Potwierdzono, iż dobór orientacji napełniacza (włókien) ma zna-czący wpływ na zgodność prognozowanych właściwości kompozytu z wynikami badań eksperymentalnych.

- by Grzegorz Janowski and +1
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- Composite Materials and Structures, Numerical Analysis, Composite Materials, Multiscale computational models

The paper presents the problems in selecting the fiber shape in numerical strength analysis for wood-polymer composites. For this purpose numerical analysis of the uniaxial tensile test for the wood-polymer composite sample was performed. Variable geometry of the fiber model was used. The fiber orientation data were obtained using Autodesk Moldflow Insight 2016 software. Micromechanical calculations based on homogenization methods were performed using Digimat FE commercial code. The results of the numerical simulations were compared with the experiment ones. To manufacture the WP composite , Moplen HP 648T polypropylene (PP) from Basell Orlen Polyolefins was used as the polymer matrix. As the filler 10 vol.% Lignocel C120 wood fiber manufactured by JRS-J. RETTENMAIER & Söhne Company was used. Adhesion promoter P613 by Dupont was used as well. A Dr Boy 55E injection molding machine was used to produce the test specimens. It was noted that the selection of the fiber shape has a significant impact on the consistency of the obtained results and consequently on compliance with the experiment ones. Fiber location calculations were performed for each geometry type available in the Digimat software. The most consistent results for numerical homogenization (Digimat FE) are associated with the choice of a curved cylinder shape of fiber. This may be due to the greatest convergence of the orientation tensor value received from the numerical simulation of the injection molding process during its transformations to the representative volume element model. In addition, this result may be due to the fact that the curved cylinder type of geometry is characterized by the most variable shape due to the degree of curvature. This reflects the real, non-standard problems to determine the shape of the wood fiber in the polymer matrix.

- by Grzegorz Janowski and +1
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- Numerical Analysis, Numerical Simulation, Injection Molding Process, Micromechanical Model

We use a physically-based crystal plasticity model to predict the yield strength of body-centered cubic (bcc) tungsten single crystals subjected to uniaxial loading. Our model captures the thermally-activated character of screw dislocation motion and full non-Schmid effects, both of which are known to play critical roles in bcc plasticity. The model uses atomistic calculations as the sole source of constitutive information, with no parameter fitting of any kind to experimental data. Our results are in excellent agreement with experimental measurements of the yield stress as a function of temperature for a number of loading orientations. The validated methodology is employed to calculate the temperature and strain-rate dependence of the yield strength for 231 crystallographic orientations within the standard stereographic triangle. We extract the strain-rate sensitivity of W crystals at different temperatures, and finish with the calculation of yield surfaces under biaxial loading conditions that can be used to define effective yield criteria for engineering design models.

Key Words: Prediction of Fracture Toughness for Open CellPolyurethane Foams By Finite-elementMicromechanical Analysis Emanoil Linul and Liviu Marsavina * Strength of Materials Department, Polytechnic University of Timisoara, Timisoara-300222, RomaniaReceived 9 April 2011; accepted 17 August 2011 T he fracture toughness was determined for cellular polymers by micromechanicalmodelling using finite element analysis. In this study, mode I and mode II of fracture toughness were evaluated with a 2D-solid model using fracture analysiscode FRANC2D/L. Simulation was performed for open cell polyurethane foams of different densities. Two cases were considered: constant cell length, l, and variable cellwall thickness; the former for constant cell wall thickness, t, and the latter for variablecell length. For estimation of fracture toughness the applied loads were progressivelyincreased to the point reaching the fracture strength of the solid material (130 MPa) inan un-cracked strut in front of ...

- by Levent Trabzon
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- Engineering, Mechanical Engineering, Physics, Materials Science

In this paper the numerical simulations of microcellular injection molding process for polymer composite with glass fiber for variable content of pores were carried out. In order to evaluate the strength of the three-phase composite structure (poly-propylene PP as a matrix, 20% wt. of glass fiber GF and 1-9 % vol. of the pores) a microstructural analysis was performed and strength calculations were conducted using the Mori-Tanaka homogenization model. The analyzed product (the base of industrial mop) was subjected to the loading in Ansys 14.5 commercial code, considering the impact of pores content on its mechanical properties. Furthermore, the paper presents the visualization of calculated composite microstructure for variable pores contents.

- by Grzegorz Janowski and +1
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- Deformation and strain, Porous Materials, Homogenization, Ansys

Rubble stone masonry walls are widely diffused in most of the cultural and architectural heritage of historical cities. The mechanical response of such material is rather complicated to predict due to its composite nature. Vertical compression tests, diagonal compression tests, and shear-compression tests are usually adopted to investigate experimentally the mechanical properties of stone masonries. However, further tests are needed for the safety assessment of these ancient structures. Since the relation between normal and shear stresses plays a major role in the shear behavior of masonry joints, governing the failure mode, a triplet test configuration is herein investigated. First, the experimental tests carried out at the laboratory of the University of L'Aquila on stone masonry specimens are presented. Then, the triplet test is simulated by using the total strain crack model, which reflects all the ultimate states of quasi-brittle material such as cracking, crushing, and shear failure. The goal of the numerical investigation is to evaluate the shear mechanical parameters of the masonry sample, including strength, dilatancy, normal, and shear deformations. Furthermore, the effect of (i) confinement pressure and (ii) bond behavior at the sample-plate interfaces are investigated, showing that they can strongly influence the mechanical response of the walls.

This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP) steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue tests were performed. In the numerical part, the representative volume element (RVE) was employed to study the effect of the DP steel microstructure of the low cycle fatigue behavior of DP steel. A dislocation-density based model was utilised to identify the tensile behavior of ferrite and martensite. Then, by establishing a correlation between the monotonic and cyclic behavior of ferrite and martensite phases, the cyclic deformation properties of single phases were estimated. Accordingly, Chaboche kinematic hardening parameters were identified from the predicted cyclic curve of individual phases in DP steel. Finally, the predicted hysteresis loop from low cycle fatigue modelling was in very good agreement with the experimental one. The stabilised hysteresis loop of DP steel can be successfully predicted using the developed approach.

- by Ali Ramazani
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- Fatigue, Micromechanical Model

- by Wiesław Frącz
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- Deformation and strain, Porous Materials, Homogenization, Ansys

We present a new approach to predict the evolution of anisotropic yield functions by coupling large scale forming simulations with crystal plasticity-spectral based virtual experiments, realizing a multi-scale model for metal forming. Employing a fast spectral method solver enables us to conduct on-the-fly full-field virtual experiments to evolve the yield surface at each integration point of the macroscopic finite element model. As illustrative example, two advanced anisotropic yield functions, namely Yld2000-2D and Yld2004-18p, are used in finite element simulations of deep drawing for a 2090-T3 aluminum alloy sheet. The simulated earing profiles are compared to the experimental ones as well as to simulations with non-evolving yield functions. It is found that the prediction of the earing is improved for the case of the evolving Yld2000-2D yield function. The evolution of the plastic anisotropy during cup drawing is systematically analyzed, showing that the evolution of anisotropy can have considerable effect on the prediction accuracy of the macroscopic simulations.

- by Dierk Raabe
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- Plasticity, Computational Materials Science, Sheet Metal Forming, Forming simulation

The cyclic plastic deformation of an archetypal microstructure dual phase steels has been examined via micromechanics modelling based on representative volume elements technique. The dual phase steel has soft ferrite – matrix with hard martensite – islands, which are distributed in a discrete manner. In the field of automobile industries, the suitable combination of strain hardening, strength and ductility, and their lean combination represent them as an economically desire option for huge multiple lightweight options. In this numerical approach, different microstructures for micromechanical modelling were constructed to detailed examination and analysis for the tensile and cyclic deformation response of dual phase steels. Due to the distinct difference in the stress–strain responses of ferrite and martensite phases, incompatibility of strain between matrix-softer ferrite and island-harder martensite phase arises during tensile straining. The effect of strain partitioning in cyclic plastic deformation response of dual phase steel has been studied in the present investigation. Apart from this, effect of martensite volume fraction on cyclic stress–strain response of dual phase steels, cyclic plastic deformation distribution in individual phases and cyclic deformation inhomogeneity at microstructural level have been systematically investigated.

- by Amit Kumar Rana and +1
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- Cyclic Plasticity, Micromechanical Model, Mechanical Properties of Dual Phase Steels, Deformation behavior of Materials

En el siguiente trabajo se dispone a calcular las propiedades efectivas de materiales compuestos elásticos isotrópico mediante el método Eshelby,Mori-Tanaka y Autoconsistente para el caso isotrópico.También se va a realizar una comparación entre los métodos expuestos para estudiar sus comportamientos para distintas fracciones volumétricas. 1 Introducción Determinar la respuesta de materiales heterogéneos ante la acción de una exci-tación externa a partir de relaciones constitutivas adecuadas, ha sido objeto de muchas investigaciones en el marco de la Mecánica de los Medios Continuos.Se trabaja con materiales homogéneos ideales a partir de una adecuada "homoge-neización" de los materiales heterogéneos. La idea básica de esta homogenei-zación consiste en reemplazar una pieza del sólido microheterogéneo por uno homogéneo cuyo comportamiento desde el punto de vista macroscópico sea el mismo. Los materiales compuestos presentan ventajas respecto a los materiales convencionales, ya que se construyen con el objetivo de mejorar las propiedades físicas que tienen sus constituyentes por separado. Estos consisten en la mez-cla manufacturada de dos o más constituyentes firmemente unidos. La mayoría de los materiales compuestos están constituidos por una fase continua llamada matriz que "envuelve" a otra fase dispersa, no continua, llamada refuerzo (usual-mente más fuerte). Nuestro objetivo es determinar las propiedades efectivas de un material compuesto en términos del tensor elástico de deformación, de las inhomogeneidades y de su respectiva fracción volumétrica. * aoharriz@estudiantes.fisica.uh.cu 1

- by Alejandro Oharriz Calderon
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- Micromechanics, Micromechanical Model

The spontaneous evolution of nanoporous sponges during dealloying is a fascinating process in nanotechnology. Originally
mostly studied as a (homogeneous) corrosion process, [ 1 ] dealloying has been early-on employed to produce Raney nickel. [ 2 ] Nanoporous gold (npAu) and other metals have been meanwhile proposed for applications from high-strength material, [ 3 ] catalysis, [ 4 ] and actuators [ 5 ] to energy storage [ 6 ] or biosensors. [ 7 ] Naturally, it is very important to understand the mechanical behavior and integrity of npAu and related nanometer-scaled functional materials. [ 8 ] Dealloying is often involved in localized corrosion and stress corrosion cracking, which is a major concern for the stability of metallic materials in general. [ 9 ] A localized dealloying mode can be triggered, for example, by a local breakdown of protective molecular-thin organic inhibitor fi lms. Due to the volume decrease in npAu, [ 10 ] the localized dealloying leads to stress that results in initiation and propagation of cracks. [ 11 ] Local changes in structure and morphology of the surface can thus decisively infl uence the fate of materials. However, a satisfying understanding of initial crack nucleation is still lacking. [ 12 ] Clarifi cation of the mechanisms of the incipient crack initiation and ensuing propagation implies unraveling the interplay and infl uence of both the substrate and the organic fi lm properties. Corrosion inhibition as well as functionalization
are often achieved by self-assembled monolayers (SAMs) employing molecules such as phosphonic acids, silanes, thiols, or selenols. [ 13 ] Apart from possibly preventing catastrophic cracking, a better understanding of the initial surface processes will also improve structural control during formation of (functional) nanoporosity. [ 14 ] Here, we offer a new approach to monitor crack initiation and propagation correlated to defined surface states. We control the localized dealloying on well-defi ned inhibitor fi lm–covered Cu 3 Au binary alloy surfaces by an applied electrochemical potential. The atomically smooth starting surfaces were prepared by sputter-annealing cycles in ultrahigh vacuum (UHV). We employed (1) defi ned surface orientations, which offer a variation of interatomic distances along the substrate surfaces, as well as (2) inhibition by different (molecularly ordered) SAMs based on cross-linking and noncross-linking thiol and selenol precursors. The observed density of initial defects and resulting cracks critically depends on the surface orientation. To our surprise we also fi nd a crystallographic nature of the cleavage planes within the opening microcracks. The detailed crack morphology also indicates a dependence on the chosen SAM precursor. We connect thus the understanding of well-ordered molecular interfaces on the atomic scale with a dangerous but fascinating macroscopic corrosion phenomenon.

- by Dierk Raabe
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- Corrosion Science, Nanotechnology, Mechanical Behavior Of Materials, Corrosion

A micromechanics-based constitutive model for compaction of composite powders at low relative density is implemented into the finite element framework. The micromechanical basis of the model is the mechanics of contact between individual particles, spherical but not necessarily of the same size or of the same material. The contact law is assumed to follow the similarity solution for viscoplastic particles. An appropriate averaging procedure leads to the continuum constitutive law, whereby the state of material at a point is described by the states of virtual contacts of an average particle, distributed over all directions. The outline of the finite element implementation is as follows.
For numerical purposes, the continuous distribution of contacts over a unit sphere is represented by a finite number of virtual contacts, distributed so that each contact represents the same solid angle. The mathematical structure of the model is similar to the crystal plasticity model, but with some important differences. The model is capable of describing development of anisotropy, tension-compression asymmetry and variation in elastic properties during the compaction. Some computational results are presented demonstrating the feasibility if the concepts.

- by Sinisa Mesarovic
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- Metal-Ceramic Powders, Micromechanical Model, Powder Compaction

1 Rzeszow University of Technology, Faculty of Mechanics and Technology, Department of Integrated Design and Tribology Systems al. Kwiatkowskiego 4, 37-450 Stalowa Wola, Poland 2 Rzeszow University of Technology, Faculty of Mechanical Engineering and Aeronautics, Department of Materials Forming and Processing al. Powstańców Warszawy 8, 35-959 Rzeszów, Poland *Corresponding author. E-mail: wf@prz.edu.pl

- by Ali Ramazani
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- Fatigue, Micromechanical Model, Metals

Granular matter is ubiquitous in our daily life yet far from completely understood. These granular materials have constituted a class of complex systems which exhibit global behaviors been reminiscent of solids, liquids, gases, or otherwise uniquely their own. The key to achieve good properties lies in the material structure from the molecules, via structures on nano and micro levels to the macroscopic material. This paper also reviewed selected approaches and models that have been developed for granular media prediction. However, development of new approaches at the micro and nano scales to sense the stress distribution characteristics of complex rock media, especially the grounds bearing petroleum resources of Nigeria has been of vital concern/importance to the area of petroleum drilling and exploration. By conducting such fundamental level research, development of highly efficient drilling processes with potentially much less energy inputs and minimizing the carbon blue prints is the best approach.

The purpose of hydraulic fracturing is improving well productivity propped with a propping agent. The success which is the product of the fracture width and the apparent permeability of the proppant within the fracture. After hydraulic fracturing treatment the fracture surface. As the fracture again closes, the resulting pressure deforms the proppants and embeds them in the surrounding rock, which significantly reduces fracture conductivity. pointed out proppant size, Young's modulus and P as factors which influence proppant embedment and fracture aperture. provide with a more precise result considering the random characteristic of th introduce the determination method of discrete element software Keywords-Proppant Hydraulic fracturing is a the treatment to enhance well productivity that results higher inflow and so production as well. This treatment is a multidisciplinary process [ treatment is initiated at the surface but indeed performed in the formation close to the bottom of the well. Hydraulic fluid, which contains water in 99 % and additives in 1 % to increase dy achieve the formation breakdown pressure that indicates fracture propagation (Fig. 1. shows the schematic hydraulic fractures in a well). After the fracture is created proppant is mixed into the hydraulic fluid t propping agent when pumping stops [ This is an open access article distributed under the terms of the Creative Commons Attribution License, Which Permits unrestricted use, distribution, and reproduction in any medium, provided the original and source are credited The purpose of hydraulic fracturing is improving well productivity propped with a propping agent. The success of this process depends highly which is the product of the fracture width and the apparent permeability of the proppant within the fracture. After treatment, well productivity is definitely affected by the interaction between the proppants and As the fracture again closes, the resulting pressure deforms the proppants and embeds them in the surrounding rock, which significantly reduces fracture conductivity. roppant size, Young's modulus and Poisson's ratio of proppant as well as formation, closu factors which influence proppant embedment and fracture aperture. provide with a more precise result considering the random characteristic of th the determination method of micromechanical properties of discrete element software and YADE DEM freeware software roppant; hydraulic fracturing; discrete element method I. INTRODUCTION Hydraulic fracturing is a stimulation treatment used in the upstream division of the petroleum industry. The goal of the treatment to enhance well productivity that results higher inflow and so production as well. This treatment is a disciplinary process [1] and is acclaimed as the most effective reservoir treatment is initiated at the surface but indeed performed in the formation close to the bottom of the well. Hydraulic fluid, which contains water in 99 % and additives in 1 % to increase dy achieve the formation breakdown pressure that indicates fracture propagation (Fig. 1. shows the schematic hydraulic fractures in a well). After the fracture is created proppant is mixed into the hydraulic fluid t propping agent when pumping stops [2].

- by Russell Crook
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- Optical Engineering, Optics, Remote Sensing, Systems Engineering

Mechanical response of nano-based composites is generally influenced by interaction of filler and matrix at interface. Increasing filler-loading within the composite may cause spatial limitation toward best dispersion of filler, and since synthesizing a totally agglomerated-free nanocomposite is difficult, filler and matrix interaction needs to be perfectly modeled. A micromechanical model is developed in this study based on the common Halpin–Tsai theory to predict the elastic stiffness of vinyl ester/exfoliated graphite platelet nanocomposites. The model considers near-rational ideal (uniformly dispersed) mixed with clustered filler-network to simulate filler-distribution conditions. A filler-dispersion level based on the filler concentration has been proposed mathematically in this study. Predictions of the proposed model considering filler morphology were compared with the predictions of the Halpin–Tsai model and the experimentally obtained results as well. The proposed model sho...

- by Carsten Könke
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- Fatigue, Micromechanical Model, Metals

This paper presents the effect of loading speed, material orientation and density on the properties of cellular materials, such as rigid polyurethane foams, subjected to compressive load. These parameters have a very important role because in many applications, foams are used as packing materials or dampers which require high energy impact absorption. The experimental tests were carried out on specimens in the form of cubes. The specimens were subjected to uniaxial compression with loading speed of 2 mm/min, except samples for determining the effect of loading speed where 1, 5, 10 and 20 mm/min loading speeds were used. One of the most significant effects of mechanical properties in compression of polyurethane foams is the density, but also the loading speed and material orientation influences the characteristics in compression.

- by Emanoil LINUL and +1
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- Micromechanical Model, Cellular Materials, Compression Tests, Experimental Tests

This paper deals with evaluating the elastic
response of several micromechanical structures used for simulating cellular materials under compression. For this
study polyurethane rigid foams were investigated, having
three relative densities: 0.085, 0.124 and 0.256. Their
microstructure was analysed using SEM images, determining
four types of cells that were consequently designed
using specialized CAD software: square cells with circular,
quadratic and/or hexagonal orifices and hexagonal
cells. An interdependent variation of the cells’ geometrical
parameters of the proposed structures was determined to
obtain geometrical variations at a required relative density.
Finite element analysis simulations were performed on
the designed microstructural models using a linear elastic
material model for the cell struts, resulting in the variation
of the elastic modulus of the structure with the variation in
cell geometry parameters. The final objective of this work
was to determine anisotropic bi-dimensional micromechanical
models for the studied cellular material that provides
accurate results in compression on both loading directions.
The anisotropic models for the proposed cell structures
were obtained by generating irregular geometries which
provided extra variables for the cell geometry parameters.
It was determined that some cell geometries are suitable
for simulating lower relative density materials while other cell geometries provide good accordance with experimental
data for higher relative density materials.

- by Emanoil LINUL and +1
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- Finite Element Analysis (Engineering), Anisotropy, Micromechanical Model, Cellular Materials
- by Mohammad Aljarrah
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- Micromechanical Model

The development of a simple particle redistribution model for estimating the effect on surface obscuration after particle shed from a neighboring surface during random vibration is discussed. The model uses both spherical and elliptical particles and existing failure data of glass spheres on a metal surface to estimate the critical body force to cause the particles to release from the

- by Russell Crook
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- Optics, Remote Sensing, Systems Engineering, Satellite remote sensing