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We use the bond fluctuation model (BFM) to study the pore-blockade times of a translocating polymer of length N in two dimensions, in the absence of external forces on the polymer (i.e., unbiased translocation) and hydrodynamic interactions (i.e., the polymer is a Rouse polymer), through a narrow pore. Earlier studies using the BFM concluded that the pore-blockade time scales with polymer length as τd∼Nβ, with β=1+2ν, whereas some recent studies using different polymer models produce results consistent with β=2+ν, originally predicted by us. Here ν is the Flory exponent of the polymer; ν=0.75 in 2D. In this paper we show that for the BFM if the simulations are extended to longer polymers, the purported scaling τd∼N1+2ν ceases to hold. We characterize the finite-size effects, and study the mobility of individual monomers in the BFM. In particular, we find that in the BFM, in the vicinity of the pore the individual monomeric mobilities are heavily suppressed in the direction perpendicular to the membrane. After a modification of the BFM which counters this suppression (but possibly introduces other artifacts in the dynamics), the apparent exponent β increases significantly. Our conclusion is that BFM simulations do not rule out our theoretical prediction for unbiased translocation, namely, β=2+ν. [ABSTRACT FROM AUTHOR]

This paper investigates the conformational and scaling properties of long linear polymer chains. These investigations are done with the aid of Monte Carlo (MC) and molecular dynamics (MD) simulations. Chain lengths that comprise several orders of magnitude to reduce errors of finite size scaling, including the effect of solvent quality, ranging from the athermal limit over the θ-transition to the collapsed state of chains are investigated. Also the effect of polydispersity on linear chains is included which is an important issue in the real fabrication of polymers. A detailed account of the hybrid MD and MC simulation model and the exploited numerical methods is given. Many results of chain properties in the extrapolated limit of infinite chain lengths are documented and universal properties of the chains within their universality class are given. An example of the difference between scaling exponents observed in actual solvents and those observed in the extremes of “good solvents” and “θ-solvents” in simulations is provided by comparing simulation results with experimental data on low density polyethylene. This paper is concluded with an outlook on the extension of this study to branched chain systems of many different branching types. [ABSTRACT FROM AUTHOR]

This paper discusses the evolution of longitudinal train dynamics (LTD) simulations, which covers numerical solvers, vehicle connection systems, air brake systems, wagon dumper systems and locomotives, resistance forces and gravitational components, vehicle in-train instabilities, and computing schemes. A number of potential research topics are suggested, such as modelling of friction, polymer, and transition characteristics for vehicle connection simulations, studies of wagon dumping operations, proper modelling of vehicle in-train instabilities, and computing schemes for LTD simulations. Evidence shows that LTD simulations have evolved with computing capabilities. Currently, advanced component models that directly describe the working principles of the operation of air brake systems, vehicle connection systems, and traction systems are available. Parallel computing is a good solution to combine and simulate all these advanced models. Parallel computing can also be used to conduct three-dimensional long train dynamics simulations. [ABSTRACT FROM AUTHOR]

Morphology of symmetric ABCD tetrablock quaterpolymers in melt was studied by the Monte Carlo (MC) simulation, where the volume fractions of the block chains, f, kept the relationships of fA = fD and fB = fC, and the volume fraction of the two mid-blocks φ was defined as φ = fB + fC. Previous self-consistent field theory for ABCD reported morphological change including several structures; however, the scope was limited within a two-dimensional system. To the contrary, in this paper, MC simulations were carried out in three dimensions with changing the φ value finely, which resulted in finding a tetracontinuous structure in the range of 0.625 ⩽ φ ⩽ 0.75. Moreover the tetracontinuous structure has been found to be the gyroid structure, and the mean curvature of the B/C interface is nearly zero. We concluded that the B/C interface must be the Schoen gyroid surface, one of three-dimensional periodic minimal surfaces. The geometrical nature of the A/B interface should be equivalent to that of the C/D interface, and they stand as level surfaces to the Schoen gyroid surface. [ABSTRACT FROM AUTHOR]

During the manufacturing of printed circuit boards (PCBs) for a Flight Project, it was found that a European manufacturer was building its boards to a European standard that had no requirement for copper wrap on the vias. The amount of copper wrap that was measured on coupons from the panel containing the boards of interest was less than the amount specified in IPC-6012 Rev B, Class 3. To help determine the reliability and usability of the boards, three sets of tests and a simulation were run. The test results, along with results of simulation and destructive physical analysis, are presented in this paper. The first experiment involved subjecting coupons from the panels supplied by the European manufacturer to thermal cycling. After 17 000 cycles, the test was stopped with no failures. A second set of accelerated tests involved comparing the thermal fatigue life of test samples made from FR4 and polyimide with varying amounts of copper wrap. Again, the testing did not reveal any failures. The third test involved using interconnect stress test coupons with through-hole vias and blind vias that were subjected to elevated temperatures to accelerate fatigue failures. While there were failures, as expected, the failures were at barrel cracks. In addition to the experiments, this paper also discusses the results of finite-element analysis using simulation software that was used to model plated-through holes under thermal stress using a steady-state analysis, also showing the main failure mode was barrel cracking. The tests show that although copper wrap was sought as a better alternative to butt joints between barrel plating and copper foil layers, manufacturability remains challenging and attempts to meet the requirements often result in features that reduce the reliability of the boards. Experimental and simulation work discussed in this paper indicate that the standard requirements for copper wrap are not contributing to the overall board reliability, although it should be added that a design with a butt joint is going to be a higher risk than a reduced copper wrap design. The study further shows that procurement requirements for wrap plating thickness from Class 3 to Class 2 would pose little risk to reliability (minimum 5 μm/0.197 mil for all via types). Experimental results corroborated by modeling indicate that the stress maxima are internal to the barrels rather than at the wrap location. In fact, the existence of Cu wrap was determined to have no appreciable effect on reliability. [ABSTRACT FROM AUTHOR]

Anisotropic conductive film (ACF) consists of an adhesive polymer matrix with dispersed conductive particles. In flip-chip technology, ACF has been used in place of solder and underfill for chip attachment to glass or organic substrates. The filler particles establish the electrical contacts between the interconnecting areas. ACF tip-chip bonding provides finer pitch, higher package density, reduced package size and improved lead-free compatibility. Nevertheless, the interconnection is different from traditional solder joints, the integrity and durability of the ACF interconnects have major concerns. Failures in anisotropic conductive film (ACF) parts have been reported after temperature cycling, moisture preconditioning and autoclave. The failures have not been well understood and have been attributed to a wide variety of causes. This paper investigates the failure mechanism of ACF using finite element simulation. From a failure-initiation point of view, the response of ACF packages to environmental (temperature and humidity) exposure is very different from standard underfilled packages. These differences cause the ACF package to fail in different ways from an underfilled package. Simulation results have shown that moisture-induced ACF swelling and delamination is the major cause of ACF failure. With moisture absorption, the loading condition at the interface is tensile-dominant, which corresponds to lower interface toughness (or fracture resistance). This condition is more prone to interface delamination. Therefore, the reliability of ACF packages is highly dependent on the ACF materials. The paper suggests a new approach toward material selection for reliable ACF packages. This approach has very good correlation with experimental results and... [ABSTRACT FROM AUTHOR]

In this paper, we construct an effective model for the dynamics of an excluded-volume chain under confinement by extending the formalism of Rouse modes. We make specific predictions about the behavior of the modes for a single polymer confined to a tube. The results are tested against Monte Carlo simulations using the bond-fluctuation algorithm which uses a lattice representation of the polymer chain with excluded-volume effects. [ABSTRACT FROM AUTHOR]

Molecular mechanisms of crystal growth and homogeneous nucleation from the melt of polyethylene-like linear polymer are investigated by molecular dynamics simulations. The present paper is aimed at extending our previous work with respect to the system size and the boundary condition, thereby enabling detailed studies on the structures of sufficiently large lamellae and fully equilibrated melt. Lamellae of uniform thickness but with marked tapered edges are found to grow at constant velocity from the substrate. Three-dimensional shape of the growing lamellae exhibits peculiar undulation at the growth front, the origin of which is suggested to be the inhomogeneous thickness distribution within the lamellae. Trajectories of chains crystallizing onto the growth front reveal an unexpected pathway for chain folding, where a partially attached chain stem forms a new fold by plunging its head back into a neighboring stem position through slithering snake motions of the chain. Detailed statistics of folds and cilia show that the folds are rather neat and mostly make re-entries into the nearest or the second or third nearest neighboring stem positions, whereas the cilia are generally short but with a small number of longer cilia forming thick amorphous layers. Structure of supercooled melt investigated versus temperature reveals that, at moderate degree of supercooling, the overall chain conformation remains Gaussian random coil but the persistent length of chains increases monotonically with increasing supercooling. Exceptions are at the largest supercooling where homogeneous nucleation takes place; usual melt structure becomes rapidly unstable and emerges many crystallites of random orientations. During early 10–20 ns after the quench, density of melt, radius of gyration of chains, and fraction of kinked bonds show marked alterations. These structural changes are highly cooperative and are considered simply due to the emergence of many embryonic crystals in the melt. Conformations of the chains forming nuclei are also traced to reveal that the homogeneous nuclei are fringed micelle like aggregates of chains, but the chains as a whole have folded conformations, which are similar to those reported in previous simulations on a single polyethylene in a vacuum. [ABSTRACT FROM AUTHOR]

We present a computer simulation model of polymer melts representing each chain as one single particle. Besides the position coordinate of each particle, we introduce a parameter nij for each pair of particles i and j within a specified distance from each other. These numbers, called entanglement numbers, describe the deviation of the system of ignored coordinates from its equilibrium state for the given configuration of the centers of mass of the polymers. The deviations of the entanglement numbers from their equilibrium values give rise to transient forces, which, together with the conservative forces derived from the potential of mean force, govern the displacements of the particles. We have applied our model to a melt of C800H1602 chains at 450 K and have found good agreement with experiments and more detailed simulations. Properties addressed in this paper are radial distribution functions, dynamic structure factors, and linear as well as nonlinear rheological properties. [ABSTRACT FROM AUTHOR]

It is the purpose of this paper to establish a bottom-up multiscale approach for dendronized polymers. Based on our understanding of the phenomenology of an atomistic model for this class of polymers, we introduce a “Janus chain” (JC) model which adds a vectorial degree of freedom (Janus vector)—related to the sectorial amphiphilicity—to each segment of the linear backbone of a (classical) uncharged, semiflexible, and multibead chain representation of a polymer. The JC features induced polymeric curvature and ultimately triggers complexation. JC parameters related to the topology and chemical details are obtained from the atomistic level. Available experimental observations including the formation of superstructures and double helical conformations are well reproduced by the JC model. JC is efficiently solved via Brownian dynamics simulation and can be seen as a member of a universality class which is one (two) level(s) above the magnetic (semiflexible) chain model. It therefore should allow to model not only dendronized polymers but also structures belonging to the same class—exhibiting induced (or spontaneous) curvature—such as single stranded DNA and actin filaments. [ABSTRACT FROM AUTHOR]

This paper is aimed to develop a Brownian dynamics simulation method for strongly confined semiflexible polymers where numerical simulation plays an indispensable role in complementing theory and experiments. A wormlike chain under strong confinement is modeled as a string of virtual spherical beads connected by inextensible rods with length varying according to the confinement intensity of the chain measured by the Odijk deflection length. The model takes hydrodynamic interactions into account. The geometrical constraints associated with the inextensible rods are realized by the so-called linear constraint solver. The model parameters are studied by quantitatively comparing the simulated properties of a double-stranded DNA chain with available experimental data and theoretical predictions. [ABSTRACT FROM AUTHOR]

It has been suggested that, due to topological constraints, rings in the melt may assume a more compact shape than Gaussian chains. In this paper, we exploit the availability of narrow fractions of perdeuterated linear and cyclic polydimethylsiloxane (PDMS) and, through the analysis of the small angle neutron scattering (SANS) profiles, demonstrate the difference in scattering properties of linear and cyclic PDMS molecules. As expected for Gaussian chains, for the H/D linear PDMS samples, log-log plots of the scattered intensity versus scattering vector Q display a Q(-2) dependence. However, for H/D cyclic blends, the scaling exponent is higher than 2, as predicted by computer simulations reported in the literature. We show that cyclic molecules in bulk display the characteristic maximum in plots of scattered intensity versus Q(-2) that is expected on the basis of Monte Carlo calculations and from the Casassa equation [E. F. Casassa, J. Polym. Sci. A 3, 605 (1965)]. It is also shown that, for rings, the Debye equation [P. Debye, J. Appl. Phys. 15, 338 (1944)] is no longer appropriate to describe the SANS profiles of H/D cyclic blends, at least up to Mw≈10 000. For these samples, the Casassa form factor gives a better representation of the SANS data and we show that this function which was developed for monodisperse cyclics is still adequate to describe our slightly polydisperse samples. Deviations from all above observations are noted for Mw>11 000 and are attributed to partial contamination of cyclic samples with linear chains. The failure of both the Debye and the Casassa form factors could be due to contamination of the cyclic fractions by linear polymers or to a real conformational change. [ABSTRACT FROM AUTHOR]

Using methods adapted from the simulation of suspension dynamics, we have developed a Brownian dynamics algorithm with multibody hydrodynamic interactions for simulating the dynamics of polymer molecules. The polymer molecule is modeled as a chain composed of a series of inextensible, rigid rods with constraints at each joint to ensure continuity of the chain. The linear and rotational velocities of each segment of the polymer chain are described by the slender-body theory of Batchelor [J. Fluid Mech. 44, 419 (1970)]. To include hydrodynamic interactions between the segments of the chain, the line distribution of forces on each segment is approximated by making a Legendre polynomial expansion of the disturbance velocity on the segment, where the first two terms of the expansion are retained in the calculation. Thus, the resulting linear force distribution is specified by a center of mass force, couple, and stresslet on each segment. This method for calculating the hydrodynamic interactions has been successfully used to simulate the dynamics of noncolloidal suspensions of rigid fibers [O. G. Harlen, R. R. Sundararajakumar, and D. L. Koch, J. Fluid Mech. 388, 355 (1999); J. E. Butler and E. S. G. Shaqfeh, J. Fluid Mech. 468, 204 (2002)]. The longest relaxation time and center of mass diffusivity are among the quantities calculated with the simulation technique. Comparisons are made for different levels of approximation of the hydrodynamic interactions, including multibody interactions, two-body interactions, and the “freely draining” case with no interactions. For the short polymer chains studied in this paper, the results indicate a difference in the apparent scaling of diffusivity with polymer length for the multibody versus two-body level of approximation for the hydrodynamic interactions.© 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Large scale molecular dynamics and grand canonical Monte Carlo simulation techniques are used to study the behavior of the interdiffusion of a solvent into an entangled polymer matrix as the state of the polymer changes from a melt to a glass. The weight gain by the polymer increases with time t as t1/2 in agreement with Fickian diffusion for all cases studied, although the diffusivity is found to be strongly concentration dependent especially as one approaches the glass transition temperature of the polymer. The diffusivity as a function of solvent concentration determined using the one-dimensional Fick’s model of the diffusion equation is compared to the diffusivity calculated using the Darken equation from simulations of equilibrated solvent-polymer solutions. The diffusivity calculated using these two different approaches are in good agreement. The behavior of the diffusivity strongly depends on the state of the polymer and is related to the shape of the solvent concentration profile.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper describes, and gives a mathematical analysis of the performance of two makes of CRT bleed resistors which exhibit markedly different characteristics under heat soak conditions. By examining the observed resistance changes with temperature, and relating these to the Arrhenius equation, the reaction activation energies can be determined. Further analysis of the power consumption characteristics of the resistors leads to the establishment of resistance-time curves for both makes of resistor. These indicate very different conclusions than might otherwise have been drawn from initial test data. Finally the 'Monte Carlo' simulation technique is used to determine the most likely survival characteristics in a Field situation, and a quantitative assessment of the reliability of CRTs using these bleed resistors is given. The construction of the resistor body is common to both makes and comprises a resistor substrate enclosed within an overcoat which is in turn encapsulated in epoxy. One make (type A) is a glass thick film structure, whereas the other is a polymer thick film system. [ABSTRACT FROM AUTHOR]

We present the results of numerical simulations of the irreversible aggregation process for self-avoiding flexible polymers in three dimensions. We have paid special attention to two experimentally interesting systems: telechelic ionomers and reverse micelles. The dynamics used in this paper to simulate the clustering process is based on Eden’s method. This dynamics was previously introduced by us for two-dimensional systems. We find a scaling relation between the radius of gyration of the cluster Rg, the chain length n and the number of chains N in the cluster in the form Rg∼nαNβ. The values of the exponents α and β calculated from the numerical simulations are somewhat lower than those predicted by Flory’s classical theory. We argue that the lower values of the exponents are possibly due to the finite size of the clusters and the presence of higher order interaction terms not considered in Flory’s theory. [ABSTRACT FROM AUTHOR]

This paper compares the performance of chip seals constructed with polymer-modified emulsion (PME; CRS-2L) versus those constructed with unmodified emulsion (CRS-2). The overall performance evaluation is based on aggregate retention performance. The adhesion of the emulsions is examined using the Vialit test with various curing times and temperature conditions. To evaluate the aggregate retention performance of the chip seals, we used the Vialit test, the flip-over test and the third-scale Model Mobile Loading Simulator (MMLS3). The results from these tests indicate that the PME (CRS-2L) enhances aggregate retention performance, and does so more significantly in the early stages and at low temperatures. [ABSTRACT FROM AUTHOR]

Atomic-scale molecular modeling and simulation are powerful tools for computational biology. However, constructing models with large, densely packed molecules, non-water solvents, or with combinations of multiple biomembranes, polymers, and nanomaterials remains challenging and requires significant time and expertise. Furthermore, existing tools do not support such assemblies under the periodic boundary conditions (PBC) necessary for molecular simulation. Here, we describe Multicomponent Assembler in CHARMM-GUI that automates complex molecular assembly and simulation input preparation under the PBC. In this work, we demonstrate its versatility by preparing 6 challenging systems with varying density of large components: (1) solvated proteins, (2) solvated proteins with a pre-equilibrated membrane, (3) solvated proteins with a sheet-like nanomaterial, (4) solvated proteins with a sheet-like polymer, (5) a mixed membrane-nanomaterial system, and (6) a sheet-like polymer with gaseous solvent. Multicomponent Assembler is expected to be a unique cyberinfrastructure to study complex interactions between small molecules, biomacromolecules, polymers, and nanomaterials. Building atomistic models with molecules of varying size and density requires significant time and expertize. Here, authors describe CHARMM-GUI Multicomponent Assembler that guides complex molecular assembly and simulation input preparation under periodic boundary conditions. [ABSTRACT FROM AUTHOR]

Further exploitation of the residual oil underground in post-polymer flooded reservoirs is attractive and challenging. Microbial-enhanced oil recovery (MEOR) is a promising strategy to enhance the recovery of residual oil in post-polymer flooded reservoirs. Identifying and selectively activating indigenous microorganisms with oil displacement capabilities is an urgent requirement in the current design of efficient microbial-enhanced oil recovery technologies. This study combines high-throughput sequencing with functional network analysis to identify the core functional microbes within the reservoirs. Concurrently, it devises targeted activation strategies tailored to oligotrophic conditions through an analysis of environmental factor influences. The feasibility of these strategies is then validated through physical simulation experiments. With nutrient stimulation, the overall diversity of microorganisms decreases while the abundance of functional microorganisms increases. The core displacement results showed that the oil recovery factor increased by 3.82% on the basis of polymer flooding. In summary, this research has established a system for the efficient activation of functional microorganisms under oligotrophic conditions by utilizing bioinformatics, network analysis, and indoor simulation systems. This achievement will undoubtedly lay a solid foundation for the practical implementation of microbial enhancement techniques in the field. [ABSTRACT FROM AUTHOR]

By employing the Massieu formalism presented in the preceding paper, Monte Carlo methods and extrapolation techniques are combined to simulate polymers with chain-length polydispersity. Semigrand canonical and grand canonical ensembles supplemented by identity exchange moves and expanded-ensemble moves have been tailored to simulate both thermodynamic properties and the structure of various coarse-grained model systems. It is demonstrated that the proposed methods can be used to simulate systems with arbitrary molecular weight distribution (e.g., to match experimental data), bulk-pore partitioning of polymer solutions, and liquid–liquid equilibrium of polydisperse polymer melts. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Polymeric materials reprocessing leads to modification of polymeric materials flow properties. In this paper there are summarized the correlations η - γ (obtained from previous experimental research), for several types of virgin and reprocessed polymeric materials, comparatively presented. Models and simulations were performed for the extruding polymeric materials reprocessing, the screw functional feature Q(Δp) - with and without considering the leaks over the screw helix flight tip - to assess changes in the performances. [ABSTRACT FROM AUTHOR]

This paper evaluates the seismic performance of reinforced concrete columns retrofitted with fibre reinforced polymer (FRP) sheets through numerical simulations of the load-deformation response using two-dimensional finite element analysis (2D-FEA). The relatively rational mesh configuration is verified through comparison of analysis results obtained from the different mesh configurations. The seismic performance of three reinforced concrete (RC) columns strengthened with FRP sheets is assessed through a series of parametric studies, and the applicability of existing crack models and constitutive relationships on crack discontinuity and concrete compressive behaviour are validated. Comparisons of analysis results with tests shows that an equivalent uniaxial strain model and a failure criterion can be used to accurately simulate nonlinear behaviour and the failure of concrete under a biaxial stress state, respectively. Moreover, it is shown that a modified confinement model can be simply adopted to evaluate confined effects from hoop steel and FRP on concrete, which generally operate in three-dimensional confinement. Lastly, the seismic retrofitting performance of RC columns wrapped with FRP sheets is verified by analysing load-deformation responses and the progression of stress-strain at inflection points and bottoms of the columns. [ABSTRACT FROM AUTHOR]

The mechanism of intercalation and the ability of double stranded DNA (dsDNA) to accommodate a variety of ligands in this manner has been well studied. Proposed mechanistic steps along this pathway for the classical intercalator ethidium have been discussed in the literature. Some previous studies indicate that the creation of an intercalation site may occur spontaneously, with the energy for this interaction arising either from solvent collisions or soliton propagation along the helical axis. A subsequent 1D diffusional search by the ligand along the helical axis of the DNA will allow the ligand entry to this intercalation site from its external, electrostatically stabilized position. Other mechanistic studies show that ethidium cation participates in the creation of the site, as a ligand interacting closely with the external surface of the DNA can cause unfavorable steric interactions depending on the ligands' orientation, which are relaxed during the creation of an intercalation site. Briefly, such a site is created by the lengthening of the DNA molecule via bond rotation between the sugars and phosphates along the DNA backbone, causing an unwinding of the dsDNA itself and separation between the adjacent base pairs local to the position of the ligand, which becomes the intercalation site. Previous experimental measurements of this interaction measure the enthalpic cost of this part of the mechanism to be about -8 kcal/mol. This paper reports the observation, during a computational study, of the spontaneous opening of an intercalation site in response to the presence of a single ethidium cation molecule in an externally bound configuration. The concerted motions between this ligand and the host, a dsDNA decamer, are clear. The dsDNA decamer AGGATGCCTG was studied; the central …GATG… site was the intercalation site. [ABSTRACT FROM AUTHOR]

Polymer processing industry can certainly benefit from recent improvements achieved in rheological modelling, numerical solvers and computer performances. This is also true in particular for profile extrusion, where the design of die lips is an important step. In the present paper, the authors show three-dimensional simulation results for the extrusion process of an industrial profile. Polymer melts are endowed with viscoelastic properties, and a multimode pom–pom model is used for describing the rheology of the selected melt. The calculation includes the prediction of the extrudate shape as well as that of the die lips. From the industrial point of view, this is the first technical paper where the algorithm and detailed simulation results are presented for the three-dimensional inverse extrusion flow of a multimode pom–pom model. [ABSTRACT FROM AUTHOR]

This paper presents a combined finite/discrete element method for 2D/3D modeling of composite specimens subjected to dynamic/impact loadings. Simulation of various composite failure modes, such as delamination and layer cracking, requires a sophisticated numerical approach capable of handling anisotropic behavior of individual layers as well as potential interaction phenomena. The combined finite/discrete element (FE/DE) methodology has proved to be an efficient approach for the simulation of progressive fracture in brittle and quasibrittle media. Therefore, an existing FE/DE approach has been adopted and modified in this study for the simulation of delamination and fracture in composites subjected to impact loadings. The paper comprises a section on fundamental aspects of adopted FE/DE algorithm and discusses the basics of a general node to face nonlinear frictional contact algorithm. It is followed by details of formulation for composite failure mechanisms, including the Hoffman material model and the 3D Hashin interface model. Several numerical simulations are then discussed to assess the performance of the proposed approach. Full progressive fracture and fragmentation behavior as well as potential post-cracking interactions caused by the newly created crack sides and segments are automatically controlled. The same procedure is capable of modeling the application of fiber reinforced polymer (FRP) layers to other engineering structures in order to improve their flexible behavior in static and dynamic loading conditions. [ABSTRACT FROM AUTHOR]

This paper develops a modified nucleation theory and examines its application to simulate the bubble nucleating phenomena in polymeric foaming processes. Bubbles typically nucleate homogeneously in the bulk phase of the polymer/gas solution and heterogeneously at the boundaries between the bulk phase and the nucleating agents. Although past research had attempted to consider the heterogeneous nucleation to simulate the plastic foaming process, the assumption of a flat nucleating surface might not be realistic. In this context, the authors have modified the heterogeneous nucleation theory by considering random surface geometries, and have developed a computer simulation program to predict the cell nuclei density based on this heterogeneous nucleation scheme with random surface geometries. Homogeneous cell nucleation was also included in the simulation. The simulation results obtained in this study are compared with the experimentally observed data from a batch foaming process to evaluate the validity of the theory proposed herein. It is found that the modified theory does in fact account for the quantitative aspects of the experimental observations when an iterative approach is used to determine the contact angle θc. Although the appropriateness of the values selected for θc requires further investigation from both experimental and theoretical points of view, this study illustrated that the modified nucleation theory can represent a new access point for exploring the cell nucleating phenomena in plastic foaming processes. [ABSTRACT FROM AUTHOR]

A dynamic model of polymer wet spinning coagulation process is proposed in this article. The model is based on the double diffusion phenomenon, phase separation process, continuity balance, and momentum balance of the entire coagulation process. The uniqueness of the model lies in its dynamic feature. The model can simulate the system's dynamic response to variations in system inputs/parameters. Steady-state system solutions can also be produced as the long-time solutions of the dynamic model; a settling time can be observed at the same time. This paper employs a computationally efficient method of lines numerical algorithm for solving the dynamic model. A simulation experiment on a selected non-solvent-solvent-polymer ternary system is carried out to verify the model as well as the numerical method. The dynamic simulation results are analyzed and discussed. At the end of the article, h-refinement and p-refinement are used to confirm the spatial convergence of the numerical solutions. © 2016 American Institute of Chemical Engineers AIChE J, 62: 3432-3440, 2016 [ABSTRACT FROM AUTHOR]

The paper presents an attempt of temperature distribution simulation of a polymer bearing. In order to create model, tribological tests were performed and thermal behavior of the bearing was observed until temperature constant values were achieved. Thermal simulations were done with commercial software package ANSYS Fluent for 3D geometrical model that included polymer bearing, its housing, shaft and some volume of the surrounding air. The heat generation caused by friction forces was implemented by volumetric heat source. The heat transfer and dissipation was through conduction, radiation and convection. The numerical model included all three mechanisms and in case of convection the heat transfer coefficient was not estimated by directly solved basing on the air flow around the bearing and adjacent parts. [ABSTRACT FROM AUTHOR]

This paper describes 3D particle-in-cell (PIC) simulation of charge injection and transport through ferroelectric semicrystalline polymer (e.g. PVDF) film comprised of nanocrystallites in an amorphous matrix with varying degrees of crystallinity. The classical electrical double layer (EDL) model for a monopolar core is extended (eEDL) to represent the nanocrystallite by replacing it with a dipolar core. Charge injection at the electrodes assumes metal-polymer Schottky emission at low to moderate fields and Fowler-Nordheim tunneling at high fields. Injected particles propagate via field-dependent Poole-Frenkel mobility. In the eEDL model, the initial attachment of charge particles forms the bound Stern-Helmholtz layer leading to Maxwell-Wagner-Sillars polarization. Subsequent waves of charge particles are repelled by the attached charge resulting in the diffuse Gouy- Chapman transport layer. The simulation algorithm uses a boundary integral equation method (BIEM) for solution of the Poisson equation coupled with a second-order predictorcorrector scheme for robust time integration of the equations of motion. The stability criterion of the explicit algorithm conforms to the Courant-Friedrichs-Levy (CFL) limit assuring robust and rapid convergence. The model is capable of simulating a wide dynamic range spanning leakage current to pre-breakdown levels. Simulation results for semicrystalline film with varying degrees of crystallinity indicate that charge transport behavior depends on nanoparticle polarization with anti-parallel orientation showing the highest conduction and therefore lowest level of charge trapping in the interaction zone. Charge attachment to nanocrystallites increase with vol% loading or degree of crystallinity, and saturates at 40 vol% for the set of simulation parameters. The eEDL model predicts the intuitive meandering pathways of charge particle trajectories, which get progressively more inclined from normal incidence with increasing vol% loading. [ABSTRACT FROM AUTHOR]

This paper presents a model for an elastomeric isolation system consisting of a three degree-of-freedom (DOF) rigid body assembled to a frame through multiple isolators. Each elastomeric isolator is either represented by a Maxwell-Voigt (MV) model consisting of two Maxwell elements or by a Maxwell ladder (ML) model consisting of three Maxwell elements. The MV models and the ML models are characterized by using experimental data that are collected at multiple excitation frequencies. The characterized models are evaluated and used to simulate the peiformance of the isolation system. The models developed in this paper are capable of representing frequency-dependent behavior that is exhibited by elastomeric isolators and the overall isolation system. Furthermore, the proposed model is capable of directly associating the behavior of the isolation system with physical and geometrical properties of each isolator. The proposed model is expected to be a useful tool for the analysis and design optimization of elastomeric isolation systems. Most of the isolation systems in practical applications exhibit multiple DOF, this model will be particularly useful in such applications since it does not constrain motion to translation only. This is a shortcoming of the models in the current literature that the proposed model attempts to overcome. [ABSTRACT FROM AUTHOR]

We propose a novel path sampling method based on the Onsager-Machlup (OM) action by generalizing the multiscale enhanced sampling technique suggested by Moritsugu and co-workers [J. Chem. Phys. 133, 224105 (2010)]. The basic idea of this method is that the system we want to study (for example, some molecular system described by molecular mechanics) is coupled to a coarse-grained (CG) system, which can move more quickly and can be computed more efficiently than the original system. We simulate this combined system (original + CG system) using Langevin dynamics where different heat baths are coupled to the two systems. When the coupling is strong enough, the original system is guided by the CG system, and is able to sample the configuration and path space with more efficiency. We need to correct the bias caused by the coupling, however, by employing the Hamiltonian replica exchange, where we prepare many path replicas with different coupling strengths. As a result, an unbiased path ensemble for the original system can be found in the weakest coupling path ensemble. This strategy is easily implemented because a weight for a path calculated by the OM action is formally the same as the Boltzmann weight if we properly define the path 'Hamiltonian.' We apply this method to a model polymer with Asakura-Oosawa interaction, and compare the results with the conventional transition path sampling method. [ABSTRACT FROM AUTHOR]

We present a theoretical approach to scale the artificially fast dynamics of simulated coarse-grained polymer liquids down to its realistic value. As coarse graining affects entropy and dissipation, two factors enter the rescaling: inclusion of intramolecular vibrational degrees of freedom and rescaling of the friction coefficient. Because our approach is analytical, it is general and transferable. Translational and rotational diffusion of unentangled and entangled polyethylene melts, predicted from mesoscale simulations of coarse-grained polymer melts using our rescaling procedure, are in quantitative agreement with united-atom simulations and with experiments. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we found the curves of infrared spectral intensity at specific wavenumbers of several polymer transitions can be accurately fitted by one of Boltzmann Sigmoid, Gaussian Cumulative, Lorentz Cumulative, or Asymmetric Sigmoid functions. These transitions include the melting of iPP, the Brill transition of PA66, the epoxy curing, the oxidation of SBS, and the melting of HDPE. These functions were obviously different from other important functions, which were earlier introduced into generalized 2D correlation spectroscopy, such as sinusoidal, exponential, and Lorentzian. The properties of the Boltzmann Sigmoid, Gaussian Cumulative, Lorentz Cumulative functions were studied using the simulated infrared spectra. The sequential order is only controlled by the parameter reflecting the center point location, while other parameter values have no relationship. The influences of the parameters in Asymmetric Sigmoid on the sequential order were also studied using the simulated IR spectra. Within the transition range, it was found the values of several waveform parameters co-determine the sequential order. We concluded that the MW2D or PCMW2D method should first be employed to determine a rational transition range before using 2D correlation infrared spectroscopy to study the mechanism of the polymer transitions. The clear physical meaning of the sequential order is the “earlier” or “later” of the transition points. As long as the experimental range (external perturbation) is wide enough and the data precision is good, the sequential order is absolutely reliable within the transition range. The results discussed throughout this paper have proven that the sequential order rules are absolutely correct. The content of the present study will solve the controversy on the sequential order rules to a large extent. [Copyright &y& Elsevier]

The alignment of polymer chains is a well-known microstructural evolution effect due to straining of polymers. This has a drastic influence on the macroscopic properties of the initially isotropic material, such as a pronounced strength in the loading direction of stretched films. For modeling the effect of strain-induced anisotropy, a macroscopic constitutive model is developed in this paper. Within a thermodynamic framework, an additive decomposition of the logarithmic Hencky strain tensor into elastic and inelastic parts is used to formulate the constitutive equations. As a key idea, weighting functions are introduced to represent a strain-softening/hardening effect to account for induced anisotropy. These functions represent the ratio between the total strain rate (representing the actual loading direction) and a structural tensor (representing the stretched polymer chains). In this way, we introduce material parameters as a sum of weighted direction-related quantities. The numerical implementation of the resulting set of constitutive is used to identify material parameters based on experimental data, exhibiting strain-induced anisotropy. In the finite-element examples, we simulate the cold-forming of amorphous thermoplastic films below the glass transition temperature subjected to different re-loading directions. [ABSTRACT FROM AUTHOR]

Abstract: Polymers are frequently used in applications in which they may be exposed to high rate or impact loading and there is growing industrial importance in understanding their mechanical behavior at different strain rates. This paper describes research that has been performed to better understand and predict the dependence on strain rate of mechanical properties such as yield and flow stress, by investigating the relationship between rate dependence and temperature dependence. In particular, the mechanical behavior of poly(vinyl chloride) with 20 wt% plasticizer has been studied at strain rates from 0.001 s−1 to 4700 s−1 and temperatures from −60 to +80 °C. In addition to the use of time–temperature superposition, this paper presents a novel experimental method in which the yield stress and the effects of adiabatic heating at high strain rates are simulated in the low rate loading. [Copyright &y& Elsevier]

In this paper, the molecular dynamics method was used to calculate the physical and mechanical properties of the cross-linked epoxy polymer composed of diglycidyl ether of bisphenol-A (DGEBA) as resin and diethylenetriamine (DETA) as curing agent. Calculation of the properties was performed using the constant- strain (static) approach. A series of independent simulations were carried out based on four widely used force fields; COMPASS, PCFF, UFF and Dreiding. Proper comparisons between the results and also with experimental observations were made to find the most suitable force field for molecular dynamics simulation of polymer materials. [ABSTRACT FROM AUTHOR]

In this paper, simulation studies are carried out to enhance the understanding of the mechanisms for the reported improvements in breakdown strength of nanocomposites. Electric field driven partial discharges and temperature rise can lead to electrical breakdown and hence it is important to study the electric field distribution and temperature rise in nanocomposites. An FEM based software, COMSOL V4.1, has been used to carry out the simulations. The nanocomposite has been modeled as two cores around the nanoparticle in a polymer. The interface between the particle and polymer is called as 1st core and a shell around the 1st core is called as 2nd core. The mechanisms in the 2nd core are characterized by its electrical conductivity and dielectric constant. Various models are used for modeling the 2nd core. The electric field, resistive losses and temperature rise have been computed for static and quasi-static fields for the linear and nonlinear materials. For many models, it is tough to simultaneously get both |E|-fields and resistive losses and hence temperature rise lower than unfilled material both inside and outside the 2nd core region. Based on the magnitude of electric field, resistive losses and temperature rise under transient fields, two linear models of 2nd core support the argument of enhanced dielectric strength whereas most other models do not. Possible hypotheses have been proposed. The results reinforce the idea that interfaces are critical for the reported breakdown strength improvements. [ABSTRACT FROM AUTHOR]

Polymer nanocomposites consist of nanoscale additives embedded in a polymer matrix and are widely used in the automobiles, optics and microelectronics industries. Since the composition and the morphology of the polymer nanocomposite impact its macroscopic properties, significant efforts have been made to understand how parameters, such as polymer and nanoparticle chemistries, molecular weight of the matrix polymers and nanoparticle size, help tune the morphology. Theory and simulations have proven to be useful tools in this field due to their ability to link molecular level interactions, the morphology and the macroscopic properties. Due to the computational intensity of molecular simulations of a dense polymer matrix, there has been a strong effort on the theoretical front to develop methodologies that map out equilibrium structure and phase behaviour of polymer nanocomposites over a large parameter space. In this paper, we review the details of the self-consistent polymer reference interaction site model (PRISM)–Monte Carlo (MC) simulation method which integrates theory and simulation to study phase behaviour in polymer nanocomposites. We discuss two specific cases of polymer nanocomposites containing polymer-grafted nanoparticles with chemical and physical heterogeneity in grafts in which this self-consistent PRISM–MC approach has been used to study effective inter-filler interactions and phase behaviour. [ABSTRACT FROM AUTHOR]

In general, polymers show time-dependent stress-strain responses. The responses can be measured in a time-based test (e.g. a stress relaxation test) or a frequency-based test (e.g. a rheometer test). In a stress relaxation test, it is easy to measure the long-term stress (i.e. the low frequency response) accurately, but it is very difficult, if not impossible, to measure the short-term stress (i.e. the high frequency response) accurately. In contrast, in a rheometer test it is easy to measure the high frequency response by lowering the temperature around the specimen, but it is almost impossible to measure the low frequency response by increasing the temperature over a threshold. Thus, in this paper, a method to combine the two test results was proposed to model a polyurethane stopper for a wide range of frequencies. This method was proven to be valid by showing that simulation results for a drop test and a torque test were in good agreement with test data for a polyurethane stopper used in a robot. [ABSTRACT FROM AUTHOR]

A phenomenologically motivated small strain model and a finite strain general framework to simulate the curing process of polymer have been developed and discussed in our recently published papers [1, 2, 3, 4]. In order to illustrate the capability of the finite strain framework proposed earlier, only the micromechanically-inspired 21-chain model and the phenomenologically motivated Neo-Hookean model (energy function) have been demonstrated so far. The Arruda--Boyce model (well-known as the 8-chain model in the elastic case and Bergström--Boyce model [5, 14] in the viscoelastic case) is a prototype hyperelastic model for polymeric materials. This follow-up contribution presents an extension of the Arruda--Boyce model [6] towards modelling the curing process of polymers. The necessary details, i.e. the stress tensor and the tangent operator, for the numerical implementation within the finite element method, are derived. The curing process of polymers is a complicated process where a series of chemical reactions have been activated, which will convert low molecular weight monomer solutions into more or less cross-linked solid macromolecular structures via the chemical conversion. This paper will model the elastic behaviour and shrinkage effects of the polymer curing process in the isothermal case using the Arruda--Boyce model. Several numerical examples have been demonstrated to verify our newly proposed, modified approach in case of curing process. [ABSTRACT FROM AUTHOR]

Nanoporous crystalline δe-form of syndiotactic polystyrene (sPS) is characterized by the rather peculiar behavior of being able to absorb considerable amounts of low molecular weight penetrants, in contrast to the general behavior reported for the crystalline phase of polymers that is impervious to penetrants. In particular, the δe nanoporous crystalline form of sPS displays a sorption capacity of penetrants that is several times higher than the one of the amorphous phase of sPS. In this paper, sorption thermodynamics of carbon dioxide in the δe nanoporous crystalline form of semicrystalline sPS is analyzed by means of Grand Canonical Monte Carlo (GCMC) molecular simulation methods, evaluating sorption isotherms as well as isosteric heats of sorption based on a semi-empirical molecular force-field. In fact, in the last years, this technique has been successfully used to investigate sorption properties of periodic crystals of a wide range of materials, including zeolites and polymers, supplying reliable estimates and representing a valid support to the experimental activity. While computational techniques allow direct determination of sorption properties of purely crystalline systems, experimental characterization of sorption in a semicrystalline polymer, as is the case of sPS under investigation, does not give a straight estimation of sorption capacity of the crystalline phase since sorption measurement incorporates other contributions related to the amorphous phase and interphases, as well as to possible defects of the crystalline phase. However, in the case of sPS at the investigated gas pressures, contribution of the amorphous and non-crystalline phases to carbon dioxide sorption can be neglected, and it has been possible to directly compare simulation predictions with experimental results, showing that GCMC computations supply excellent estimates for sorption isotherms and isosteric heats of sorption. [ABSTRACT FROM AUTHOR]

Injection velocity profile is an important process parameter that affects the quality of injection-molded parts. In this paper, a fast optimization method for injection velocity profile is proposed, which aims at a constant melt-front-velocity throughout the filling stage. According to the relationship between cavity geometry and the melt-front-velocity, the ideal injection velocity is proportional to the melt-front-area. Through studying the filling behavior of molten polymer and the characteristic of 3D surface mesh model, a modified Dijkstra's algorithm is employed to predict the melt-front-area at different filling steps. Based on the predicted melt-front-area, a least square method is adopted to find out the optimum injection velocity profile by minimizing the difference of injection velocity and the ideal injection velocity. Finally, a short shot experiment and a Moldflow simulation experiment have been conducted to verify the proposed optimization method, which demonstrate that the proposed method is correct and effective. [ABSTRACT FROM AUTHOR]