Three-dimensional Unit Cell Model Research Articles

Finite Element Analysis on the Behavior of Solidified Soil Embankments on Piled Foundations under Dynamic Traffic Loads

Most research conducted so far has primarily focused on pile-supported gravel embankments. The ability of solidified soil used as an embankment filling material has been verified, and a clear view on the performance of solidified soil embankments on piled foundations is rather limited. The three-dimensional unit cell models of pile-supported embankments are conducted to investigate the performance of solidified soil embankments in comparison to gravel embankments under static and dynamic loads. Then, a systematic parametric analysis is performed to investigate the effects of various factors, including the cohesion and friction of solidified soil, the velocity and wheel load of vehicles, the pile spacing, the height of embankments. The results show that, compared with the results of gravel embankments, the heights of the outer soil arch plane in solidified soil embankments reduces under static and dynamic loads, and the piles bear more load. In addition, the total settlements of solidified soil embankments decrease with increasing cohesions, and there is an economical cohesion of 25 kPa. The vehicle wheel load, pile spacing, and the height of embankment significantly influence the load transfer mechanism and total settlement of solidified soil embankment, while the friction angles and velocities have little effect on the total settlements and vertical stress. The relationship between the soil arch height and various parameters in solidified soil embankments is established by multiple regression analysis. This investigation highlights the advantage of solidified soil in reducing total settlement and provides an insightful understanding of the load transfer mechanism of solidified soil embankment on piled foundation.

Fretting Fatigue—An Integral Simulation Approach to Strengthening by Shot Peening

Abstract Fretting fatigue is a limiting factor in blade attachment design for turbomachinery. Shot peening is known to be a strength increasing measure against fatigue. It is applied not only to free surfaces of components under fatigue but also to contacting surfaces subject to fretting fatigue. The present work examines the effect of shot peening on fretting fatigue resistance in fixtures of rotor blades. The chosen integral approach allows the consideration of shot peening and subsequent fretting loading in one simulation. Thus, the residual stresses and material strengthening as well as the surface waviness due to the shot peening process are included in the fretting fatigue simulation. To achieve reasonable computation times a two-dimensioinal model, calibrated to a three-dimensional unit cell model, is employed. A comparative study on fatigue endurance limits is presented for the cases with and without shot peening. With view to the different failure mechanisms met in these two cases, an initiation evaluation is carried out with the Sines criterion for the unpeened condition; a fracture mechanics approach is shown to be necessary for the evaluation of the shot peened condition.

Recurrent neural network modeling of the large deformation of lithium-ion battery cells

As the automotive industry transitions from combustion to electric motors, there is a growing demand for efficient computational models that can describe the homogenized large deformation response of Li-ion batteries. Here, a detailed three-dimensional unit cell model with periodic boundary conditions is developed to describe the large deformation response of a typical anode-separator-cathode lay-up of a pouch cell. The model makes use of a Deshpande-Fleck foam model for the porous polymer separator and Drucker-Prager cap models of the granular cathode and anode coatings. Using the unit cell model, the stress-strain response of a battery cell is computed for 20’000 random loading paths in the six-dimensional strain space. Based on this data, a recurrent neural network (RNN) model is trained, validated and tested. It is found that an RNN model composed of two gated recurrent units in series with a deep fully connected network is capable to describe the large deformation response with a high level of accuracy. As a byproduct, it is shown that advanced conventional constitutive models such as the anisotropic Deshpande-Fleck model cannot provide any predictions of satisfactory accuracy.

Representative volume element based micromechanical modelling of rod shaped glass filled epoxy composites

In this study, Representative Volume Element based micromechanical modeling technique has been implemented to assess the mechanical properties of glass filled epoxy composites. Rod shaped glass fillers having an aspect ratio of 80 were used for preparing the epoxy composite. The three-dimensional unit cell model of representative volume element was prepared with finite element analysis tool ANSYS 19 using the periodic square and hexagonal array with an assumption that there is a perfect bonding between the filler and the epoxy matrix. Results revealed that the tensile modulus increases and Poisson’s ratio decreases with increase in the volume fraction of the filler. To study the effect of filler volume fraction, the pulse echo techniques were used to experimentally measure the tensile modulus and Poisson’s ratio for 5% to 15% volume fraction of the filler. A good agreement was found between the RVE based predicted values and the experimental results.

A three-dimensional unit cell model with controllable crimped structure for investigating finite strain response of collagen fiber reinforced biological composites

Composite materials reinforced by crimped fibers, such as collagen fibers, have a widely application in the advanced structures. Therefore, an effective and achievable model is significant for explicitly describing the geometry of the crimped fibers and evaluating their mechanical behaviors. Aiming at this purpose, a three-dimensional (3D) unit cell model (UCM) is developed based on the microstructure of the collagen fibers, in which a controllable modified sinusoidal waviness fiber is explicitly embedded into the soft matrix, and an effective periodic boundary condition is applied on the proposed 3D UCM by using the multi-points constraint equations. The accuracy and validity of the proposed model are verified by comparing with the existing experimental results. For investigating the influence of the geometric parameters on the mechanical responses of the crimped fiber reinforced composites, several numerical UCMs with different geometric parameters are presented. The obtained results reveal that the parameters of crimp amplitude H and waviness χ of the fibers mainly contribute to the flexibility of the materials. The parameter ω for characterizing the roughness of the fibers is associated with the size and position of largest stress region. Moreover, the fiber radius R plays an important role in determining the bearing capacity of the materials and an excellent mechanical property, e.g., not only withstands the large initial tensile load but also has a special ability to guarantee the flexibility of the materials, may be achieved by controlling the number of the fibers with big and small radii.

超音波処理ナノクレイ-ポリエチレンテレフタレート系複合材料の動的粘弾性特性

The objective of this study is to investigate the dynamic viscoelastic properties of poly (ethylene terephthalate) (PET) composites with ultrasonicated nanoclay. The nanoclays were ultrasonicated in solvent, and dried in an oven. The dispersion stability of nanoclay/solvent suspensions was observed to evaluate the degree of exfoliation of nanoclays. Morphology of ultrasonicated nanoclays was also examined using a scanning electron microscope (SEM). Specimens of PET composites with ultrasonicated nanoclays were then fabricated by melt blending. Dynamic viscoelastic tests were carried out, and the effects of ultrasonication time and nanoclay volume fraction on the temperature dependence of the storage and loss moduli of the composites were discussed. Morphology of nanoclays in the composites was also examined using a transmission electron microscope (TEM). In addition to conducting experiments, finite element analyses were performed using a three-dimensional unit cell model to predict the elastic properties of nanoclay/PET composites. The effect of nanoclay morphology on the elastic properties of the composites was examined.

Influence of the stress state on void nucleation and subsequent growth around inclusion in ductile material

A three-dimensional unit cell model with an inclusion is established, where an interfacial layer between the matrix and inclusion is modeled by a cohesive zone mode. This model is then used to investigate the effect of the stress state of the unit cell on the crack nucleation at the interface and subsequently the void growth, which gives the evolutions of the macro equivalent stress and relative void volume fraction associated with the macro equivalent strain. The interface debonding process indicates that both the stress triaxility and the Lode parameter play a remarkable role in the process and void nucleation and growth. Compared with the model of pure void, the inclusion increases the load carrying capacity and lowers the void growth rate for the same stress triaxiality. Meanwhile the inclusion causes a lag in the expansion of the void due to the interface fracture, which becomes significant as the stress triaxiality increases. The interfacial crack nucleates from different position for different Lode parameter and propagates in different pattern as the Lode parameter changes the principal stresses even for the same stress triaxiality. The two points, where the crack initiates and where the interface is fully debonded, vary with stress triaxiality and Lode parameter, and are getting closer for different Lode parameters when stress triaxiality increases.

The flatwise compressive properties of Nomex honeycomb core with debonding imperfections in the double cell wall

Mechanical properties of Nomex honeycomb core are governed by not only its global dimensions, cell topology, material properties and proportion of the aramid paper and phenolic resin, but also possible manufacturing imperfections, such as the debonding between the two aramid paper sheets in the double cell wall. To account for the layered feature of the cell walls and the bonding conditions between aramid paper sheets, a three-dimensional unit cell model was proposed and developed in this study. The aramid paper sheets, the phenolic resin coating, the adhesive between the aramid paper sheets, and their bonding relationships were all explicitly modelled in accordance with their actual geometry and material parameters. The model was validated by comparing the predicted load-displacement curves and failure modes with the test results. The effects of representative bonding imperfections on both the collapse load and the related displacement of the honeycomb core under flatwise compression were evaluated. Through the analyses, it was found that the debonding imperfections have significant effects on the mechanical behaviour of the honeycomb core and that with the same debonding area the debonding at the outside edge of the adhesive printing line is the most critical. It was also found that debonding fracture may occur if adhesive is not strong enough or the debonding imperfection area is large.

Effects of constructing different unit cells on predicting composite viscoelastic properties

A computational algorithm of volume average for three-dimensional unit cell model is established to predict the viscoelastic properties of composite materials consisting of linear viscoelastic matrix and transversely isotropic elastic fibers. Several repeating unit cells (RUCs) are constructed with square, hexagonal and random fiber packing to compare the predicted results of composite viscoelastic properties. Proper periodic boundary conditions and necessary physical constraints which are used to stop rigid body motions of the RUCs are implemented. The influences of the ways to construct the RUCs on the predicted results of composite viscoelastic properties are discussed. Some interesting remarks are drawn from the present study.

Computational Fluid Dynamics Analysis for Asymmetric Power Generation in a Prismatic Fuel Block of Fluoride-Salt-Cooled High-Temperature Test Reactor

Abstract The fluoride-salt-cooled high-temperature reactor (FHR) is an advanced reactor concept that uses tristructural isotropic (TRISO) high-temperature fuel and low-pressure liquid salt coolant. A 20-MWth test reactor, as the key step in demonstrating the technical feasibility, is currently under design at Massachusetts Institute of Technology. This study focuses on the coupled conduction and convection heat transfer adopting a three-dimensional unit-cell model with one coolant channel and six one-third fuel compacts. The laminar, transitional, and turbulent flows are investigated with the use of computational fluid dynamic (CFD) software, CD-adapco STARCCM+. The model is validated against theory for developing laminar flow in the benchmark study with excellent agreement. The model is also benchmarked for transitional and turbulent flows by Hausen, Gnielinski, Dittus-Boelter, and Sieder-Tate correlations. Azimuthal distributions of temperature, heat flux, and heat transfer coefficient along the coolant-graphite interface were obtained for the asymmetric heat source, graphite materials, and two different types of salt coolant. The results show that the asymmetric power generation has little impact on peak fuel temperature, interface temperature, and heat transfer coefficient for a unit-cell module in laminar flow regime due to effective thermal conduction of the graphite matrix. In the turbulent flow regime, the effect on the azimuthal heat flux and heat transfer coefficient is more pronounced.

Finite element modeling of polymer matrix nano-composites reinforced by nano-cylindrical fillers

A new three-dimensional unit cell model has been developed for modeling three constituent phases including inclusion, interphase and matrix. The total elastic modulus of nano-composite is evaluated. Numerical results are in good agreement with the previous proposed theoretical modeling. Higher matrix and inclusion elastic modulus both can dramatically influence the total elastic modulus.

Evaluation of Simulation Models of Lateral Spread Sites Treated with Prefabricated Vertical Drains

AbstractFinite-element analyses are performed of centrifuge tests consisting of untreated and drain-treated lateral spread sites, with the goal of evaluating the ability of numerical simulations to predict the response of sites improved with prefabricated vertical drains. Finite-element models of varying complexity are analyzed: a two-dimensional model of the full centrifuge test, a three-dimensional unit cell model around a single drain, and a two-dimensional unit cell model. All the finite-element models predict pore pressures consistent with the centrifuge tests. The deformation responses of the finite-element models show that unit cell analyses produce significantly larger deformations than those observed in the centrifuge. This result is caused by the fact that the centrifuge test geometry is not well represented by the infinite slope condition assumed in a unit cell. The full two-dimensional model predicts deformations that are more consistent with those of the centrifuge because it can capture the ...

Elastic modulus measurement of polymer matrix nano- composites reinforced by platelet nano-clays

Polymer-clay nano-composite materials, in which nano-meter thick layers of clay dispersed in polymer matrix, have generally higher mechanical properties than normal polymeric materials. A new threedimensional unit cell model has been developed for modeling three constituent phases including inclusion, interphase and matrix. The total elastic modulus of nano-composite is evaluated. Numerical results are in good agreement with the previous proposed theoretical modeling. Higher matrix and inclusion elastic modulus both can dramatically increase the total elastic modulus.

Prediction of equibiaxial loading stress in collagen-based extracellular matrix using a three-dimensional unit cell model

Mechanical signals are important factors in determining cell fate. Therefore, insights as to how mechanical signals are transferred between the cell and its surrounding three-dimensional collagen fibril network will provide a basis for designing the optimum extracellular matrix (ECM) microenvironment for tissue regeneration. Previously we described a cellular solid model to predict fibril microstructure–mechanical relationships of reconstituted collagen matrices due to unidirectional loads (Acta Biomater 2010;6:1471–86). The model consisted of representative volume elements made up of an interconnected network of flexible struts. The present study extends this work by adapting the model to account for microstructural anisotropy of the collagen fibrils and a biaxial loading environment. The model was calibrated based on uniaxial tensile data and used to predict the equibiaxial tensile stress–stretch relationship. Modifications to the model significantly improved its predictive capacity for equibiaxial loading data. With a comparable fibril length (model 5.9–8μm, measured 7.5μm) and appropriate fibril anisotropy the anisotropic model provides a better representation of the collagen fibril microstructure. Such models are important tools for tissue engineering because they facilitate prediction of microstructure–mechanical relationships for collagen matrices over a wide range of microstructures and provide a framework for predicting cell–ECM interactions.

Application of stochastic finite element method in estimation of elastic constants for NCF composites

The main aim of this paper is to evaluate the effect of micro-structure variations on elastic constants of NCF (non-crimp fabric) composites. To reach this aim, a three-dimensional unit cell model is developed by the finite element code ABAQUS and mean value of elastic constants in NCF composites are determined by analytical and unit cell based methods with various boundary conditions. In addition, first- and second-order stochastic finite element formulations are derived and variances of elastic constants are computed with respect to the dispersion in length and width of the voids. Results show up to 9.1% scattering in the elastic constants.

204 カーボンナノコイル強化ポリマーの損傷特性に関する有限要素解析(OS2-1 先端材料システムの力学とメゾスケールモデリング)

The damage properties of carbon nanocoil(CNC)/polymer composites have been investigated numerically. To predict the damage evolution in CNC/polymer composites, the finite element analyses were performed using a three-dimensional unit cell model of the composites with aligned straight CNCs. Matrix microcracking was detected by the von Mises criterion. The effects of the helical geometries of CNCs on the damage properties are examined. Similar calculations were also made for carbon nanotube (CNT)/polymer composites. The results for NC/polymer composites were compared with those for CNT/polymer composites.

OS0414 界面層を有するカーボンナノコイル強化ポリマーの有効弾性・熱伝導特性の評価(先端材料システムの力学とメゾスケールモデリング,オーガナイズドセッション)

The effective elastic and thermal transport properties of carbon nanocoil(CNC)/polymer composites has been investigated numerically. To determine the effective properties, the finite element analyzes were performed using a three-dimensional unit cell model taking into account the interface layer formed around the CNC. The effective properties of the composites with aligned straight CNCs were firstly calculated and the effective properties of the composite with randomly oriented straight CNCs were then predicted by the results for unit cell model. Similar calculations were also made for CNT/polymer composites. The results for CNC/polymer composites were compared with those for CNT/polymer composites.

Multiple void interaction of pipeline steel in triaxial stress fields

Three-dimensional unit cell models were developed to study the damage induced by void growth in ductile materials. Special emphasis is given to the influence of the void shape and random spatial void arrangements. The periodical void arrays of body centered cubic are investigated by analyzing representative unit cells. The isotropic behavior of the matrix material is modeled using v. Mises plasticity. The cell models are analyzed by the large strain finite element method under monotonic loading while keeping the constant stress triaxiality. Results showed that when void density increased, effects of void aspects on void growth gradually diminished.

Analytical and Experimental Characterization of Stiffness and Damping in Carbon Nanocoil Reinforced Polymer Composites

This study focuses on understanding the stiffness and damping characteristics of carbon nanocoil (CNC)/polymer composites. To determine the effective elastic and viscoelastic properties of a polymer reinforced with aligned CNCs, the finite element analysis was performed using a three-dimensional unit cell model. The coil morphology of CNCs was examined using a scanning electron microscope. The effects of coil diameter, tube diameter, coil pitch and number of coil turns on the effective properties are discussed. The effective properties of a polymer reinforced with randomly oriented CNCs were also predicted by the results for the unit cell model. The tradeoffs between stiffness and damping characteristics are assessed by changing the volume fraction and geometrical parameters of CNCs. Additionally, experimental measurements of the elastic modulus and the loss factor of the manufactured CNC/polymer composites were carried out by using dynamic mechanical analysis. The predictions were then compared with the experimental results. Furthermore, scanning electron microscopy was performed to observe the fracture surface of CNC/polymer composites.

Effect of Filler Shape and Volume Fraction on Strain Damage of Particulate-Reinforced Dental Composites

The effect of filler shape and volume fraction on the micromechanical damage behavior of particulate-reinforced dental composites was investigated using the finite element method. Threedimensional unit cell models for various filler volumes and shapes, using hydroxyapatite in Bis- GMA as a model system, were used. Young’s modulus and stress concentration factor were calculated. The effects of filler shape on the ease of initiation of strain damage in the matrix and onset of particle-matrix debonding are discussed.