Description Of Material Properties Research Articles

Analysis of macromolecular microtubules using the potential-based matrix displacement method

This work presents an efficient matrix displacement approach for simulation of microtubules, a typical polyatomic macromolecular bio-structure in eukaryotic cells. The microtubule is modeled as an interatomic potential-based mechanical system. Unlike most of the continuum-based methods, the description of material properties in this model is based on fictitious bond and the interatomic potential energy is considered as based on the atomic force integral between basic macromolecule components. Meanwhile, superior to the conventional atomic-based simulation, the equilibrium state is solved in an efficient matrix framework comparable to the continuum-based structural mechanics approach. Following this approach, free vibration behavior of microtubules is intensively investigated. Microtubules with different boundary restrictions are considered in case studies and vibration modes and frequencies are obtained and compared with available references. It is found that the proposed macromolecular model performs with both accuracy and efficiency, and is superior to the two simulation regimes in atomic scale and continuum level.

Material and Structural Properties for Creating High Performance Concrete Structures

HPC and UHPC concretes are finding their ways both to new structures and to retrofitting of existing structures. Herein specific material properties as well as structural examples are discussed. New Codes and Recommendations provide description of material properties and design rules for HPC/UHPC structures and structural elements.

Rotational Dynamics and Li+ Transport Pathways in [PF6][P1,2,2,4

Diethyl(methyl)(isobutyl)phosphonium hexafluorophosphate, [PF6][P1,2,2,4], is an organic ionic plastic crystal with potential uses as a solid electrolyte in Li-ion cells. Using molecular dynamics simulations we perform an exhaustive study of this material at temperatures spanning from 175 K to 500 K. The simulations predict the stability of the crystalline phase for temperatures lower than 197 K where a transition to a semi-plastic phase with rotations of the PF6 anion is observed. At 280 K the larger cations start to undergo jump-like rotations. A transition to a fully plastic phase is observed at 340 K, and melting occurs at 450 K. We have also studied the most favorable pathways for a single Li ion to move in the bulk of the material at each one of the different phases. Overall the results agree with previously reported experimental data and the simulations provide exquisite details on the atomistic rotational dynamics. Nevertheless, the simulations also reveal the shortcomings of current force fields to describe material properties in an extended temperature range and highlight the needs for further theoretical efforts in order to achieve predictive power in general systems.

Transient simulation of a tubular packed bed solar receiver for hydrogen generation via metal oxide thermochemical cycles

Theoretical performance of a 4kW multiple tube solar receiver is evaluated for a two-step thermochemical redox cycle using a transient computational fluid dynamics model coupling radiative transfer with fluid flow, heat transfer, mass transfer and chemical reaction kinetics. The solar receiver consists of an array of tubular absorbers, each containing a packed bed of active material and situated within an insulated outer cavity with a small aperture. Tubular array configurations amenable to either temperature swing or isothermal operation are included, though calculations predict temperature separation of at most 150–200K between reduction and oxidation tubes positioned within a single well-insulated reaction vessel. Sensitivity of receiver performance to parameters describing material properties, operating conditions, cycle time, solar profile shape, tube dimensions, and tubular array configuration is assessed. Simulations indicate that receiver performance is most sensitive to aperture size with emission losses accounting for more than 50% of the solar input. An array consisting of a large number of small-diameter tubes is preferred, though performance is minimally impacted by the physical positions of these tubes within the receiver cavity. Time-averaged solar-to-chemical efficiency as high as 14% is predicted after accounting for energy necessary for O2 separation and steam vaporization.

A Parametric Investigation on the Neo-Hookean Material Constant

This paper assesses the Neo-Hookean material parameters pertaining to deformation behaviour of hyperelastic material by means of numerical analysis. A mathematical model relating stress and stretch is derived based on Neo-Hookeans strain energy function to evaluate the contribution of the material constant, C1, in the constitutive equation by varying its value. A systematic parametric study was constructed and for that purpose, a Matlab programme was developed for execution. The results show that the parameter (C1) is significant in describing material properties behaviour. The results and findings of the current study further enhances the understanding of Neo-Hookean model and hyperelastic materials behaviour. The ultimate future aim of this study is to come up with an alternative constitutive equation that may describe skin behaviour accurately. This study is novel as no similar parametric study on Neo-Hookean model has been reported before.

Numerical Modelling of Manufacturing of Lightweight Components – Selected Issues

The main aim of the present paper is focused on reviewing various aspects of modern numerical modelling techniques used during the development of new metalforming operations dedicated e.g. to manufacturing lightweight components. Since modelling of metal forming processes requires detailed descriptions of material properties in various length scales, a particular emphasis is put on the development of the material models. Rheological models are discussed in three major groups with different level of complexity: conventional closed form equations, internal variable models and multi scale models. The application of the inverse analysis for the purposes of model parameters identification is also addressed within the paper. Finally, selected successful applications of the mentioned models in the development of innovative manufacturing metalforming operations are presented.

First-principles local stress in crystalline and amorphous metals

Atomic size is perhaps the most commonly used concept to describe material properties. Advances in the understanding of materials are hindered by the available choices of simplifying concepts that can be used. However, the precise definition of atomic size is not easy, and often controversial. Atomic level stress provides a new interpretive tool that draws on the rich formalism of solid mechanics for use with density functional calculations to advance a deeper understanding of the properties of materials. We discuss atomic level stresses in liquids and glasses and make comparisons with ordered and disordered crystals. Somewhat surprisingly, even ordered compounds that are under no macroscopic stress and whose individual atoms are completely relaxed, i.e., no force acting on them, can have substantial atomic level stresses. On top of concepts such as the ionicity or covalency, the atomic level stresses add to the arsenal of analysis tools that are available to interpret the results of density functional calculations.

Evaluation of anti-reflective cracking measures by laboratory test

A laboratory simulation of load-induced reflective cracking was carried out using Hamburg wheel tracking tester (HWTT). The simulation, compared with some previous fatigue tests, is more reasonable and applicable because, instead of static load, the cyclic dynamic load is applied to the specimens and the test is relatively time and cost saving. The purpose of this study was to evaluate the effectiveness of various stress-absorbing interlayers to retard the development of reflective cracking, including styrene-butadiene-styrene (SBS)-modified asphalt sand concrete interlayer, asphalt-rubber sand concrete interlayer, fibreglass-polyester paving mat interlayer and stress-absorbing membrane interlayer (SAMI). Specimens without any anti-reflective cracking measure were also included to serve as a control. This paper first describes material properties, aggregate gradations and the simulation apparatus. Then, it assesses the effectiveness of different measures to prevent reflective cracking based on laboratory test results. It reveals that asphalt-rubber sand concrete interlayer performed best and fibreglass-polyester paving mat interlayer ranked next, whereas both SBS-modified asphalt sand concrete interlayer and SAMI showed similar and less sound performances compared with the former two under laboratory test environments. However, SAMI may witness an improved field performance due to the limitation of laboratory test set-up and any of the four measures could prolong the fatigue life of the specimens substantially. A finite element model simulation was followed to explain the anti-reflective cracking mechanism and support the HWTT results.

Behavior of intumescent epoxy resins in fireproofing applications

The thermal degradation process of a commercial intumescent epoxy resin for fireproofing applications was investigated. The changes in the morphology of the material during exposure to fire-like conditions were interpreted in the light of the degradation of single material components and of the overall swelling mechanism. An apparent kinetic model was developed to describe the thermally activated conversion and the weight loss of the material. The dramatic change in the key properties of the material (thermal conductivity, volume swelling, and apparent density) was investigated and linked with the thermal degradation phenomena governing the swelling process. Models were developed to describe material properties as a function of temperature and material conversion. The models provide the simulation of the fire-triggered degradation of the sample material at the heating rates of interest, allowing a detailed analysis of fireproofing performance.

Dynamic analysis of an axially moving sandwich beam with viscoelastic core

A development of the beam model of the axially moving sandwich continua with elastic faces and the core characterized by viscoelastic properties is presented in this paper. Two-parameter Kelvin–Voigt rheological model is used to describe material properties of the core. The Galerkin method is used to solve the governing partial differential equation. Dynamic analysis of the composite with two aluminum facings and a polyurethane core is carried out. The effect of the transport speed, the core thickness and the internal damping of the core material on the dynamic behavior of the system is investigated in undercrtitical and supercritical range of transport speed.

High‐Resolution Scanning Transmission Electron Microscopy (HRSTEM) Techniques: High‐Resolution Imaging and Spectroscopy Side by Side

This work presents an overview of high-resolution scanning transmission electron microscopy (HRSTEM) techniques and exemplifies the novel quantitative characterization possibilities that have emerged from recent advances in these methods. The synergistic combination of atomic resolution imaging and spectroscopy provided by HRSTEM is highlighted as a unique feature that can provide a comprehensive analytical description of material properties at the nanoscale. State-of-the-art high-angle annular dark field and annular bright field examples are depicted as well as the use of X-ray energy-dispersive spectroscopy and electron energy-loss spectroscopy for probing samples properties at the atomic scale. In addition, promising techniques such as cathodoluminescence, confocal HRSTEM, and diffraction mapping are introduced. The presented examples and results indicate that HRSTEM-related techniques are fundamental tools for comprehensive assessment of properties at the atomic scale.

Advanced 3D indoor propagation model: calibration and implementation

A software tool, implementing a semi-deterministic model which provides swift predictions, accounts for all significant physical phenomena while utilising a clear-cut description of material properties, is presented in this article. The software can predict signal coverage, delay profiles and angle of arrivals for receivers located anywhere in a scenario using three probabilistic parameters to describe each of the materials. Probabilistic parameters can be efficiently optimised based on measured data by a genetic algorithm optimiser contained in the software tool enabling real material properties (constants) to be avoided. The semi-deterministic model is briefly described whereas its implementation into the tool is explained in greater detail. Measured narrowband, as well as wideband, data are presented, and the basic principles of the computer optimisation utilised in the tool are shown. Optimised results are compared with the measured ones and deviation is determined. The principle of a simple multi-threading algorithm which improves the tool performance while decreasing time consumption is presented along with computational times where a different number of threads are compared.

An Explicit Integration Algorithm for Introducing User-Defined Thermo-Viscoplastic Constitutive Models in FE Simulations

Material models in the libraries of commercially available finite element codes often cannot satisfy the needs of some special material property descriptions, such as those of materials under ultra-high-speed cutting. To overcome the difficulty, this paper introduces an efficient explicit algorithm to implement a generalized user-defined model of metal plasticity into the Abaqus/Explicit program. This algorithm makes the computation quite efficient by avoiding updating the tensor of elastic-plastic modulus in each increment.

Stochastic study of hygrothermal performance of a wall assembly—The influence of material properties and boundary coefficients

An accurate description of material properties and boundary conditions is the prerequisite to achieve reliable results of a hygrothermal performance simulation. However, the uncertainties widely exist in those input variables, e.g., due to the inhomogeneous nature of materials and discrepancies in material manufacturing and measurement processes, the material properties are subjected to considerable variation. Therefore, the simulation result may not be only a single value, but in a range of possibilities. In this article, a stochastic approach is developed and implemented by using uncertainty analysis which assesses the uncertainties of a model's input variables on that of the output variables, and sensitivity analysis, which identifies the most influential input variables. The hygrothermal performance of one typical wall assembly in North America is studied by applying this approach, considering the uncertainties of material properties of each individual layer and the uncertainties of the interior and exterior boundary coefficients. The influence of wall orientation is also presented. The results show that the effect of a single input variable on an output variable is not constant but varies with time. The key variables that affect the results are also different over time.

Numerical Simulation of UHPFRC-NSC Composite Beam with Diana

This paper presents three-dimensional numerical simulation of UHPFRC-NSC composite beam with Diana. An elastic-plastic fracture model is proposed to describe material properties of UHPFRC. Differing from other concrete constitutive model, this one considers strain hardening in tension because of characteristic of UHPFRC. A total strain rotating crack model is used to describe material properties of NSC. The results of relevant push-out tests are used to describe the shear force-slip relationship of shear connection between UHPFRC girder and NSC slab. The numerical investigation focuses on the evaluation of load-deflection behavior, failure mode and shear connection. The agreement of test results and numerical results indicates the reliability of model.

Bone Tissue as a Basis of Osteoplastic Materials for Bone Structure Restoration

Definition of reparative regeneration, description of material properties used for bone plastics, and analysis of bone regeneration mechanisms are presented in the review. It is demonstrated that bone tissue restoration could not be realized without consideration of implant properties. Bone transplantation may become one of the tools for biological stimulation of the bone reparative regeneration

Structural solution using molecular dynamics: Fundamentals and a case study of epoxy-silica interface

In this paper, the molecular dynamics (MD) simulation technique is described in the context of structural mechanics applications, providing a fundamental understanding of the atomistic approach, and demonstrating its applicability. Atomistic models provide a bottom-up description of material properties and processes, and MD simulation is capable of solving the dynamic evolution of equilibrium and non-equilibrium processes. The applicability of the technique to structural engineering problems is demonstrated through an interface debonding problem in a multi-layered material system usually encountered in composite structures. Interface debonding may lead to a possible premature failure of fiber reinforced polymer (FRP) bonded reinforced concrete (RC) structural elements subjected to moisture. Existing knowledge on meso-scale fracture mechanics may not fully explain the weakening of the interface between concrete and epoxy, when the interface is under moisture; there is a need to study the moisture affected debonding of the interface using a more fundamental approach that incorporates chemistry in the description of materials. The results of the atomistic modeling presented in this paper show that the adhesive strength (in terms of energy) between epoxy and silica is weakened in the presence of water through its interaction with epoxy. This is correlated with the existing meso-scale experimental data. This example demonstrates that MD simulation can be effectively used in studying the durability of the system through an understanding of how materials interact with the environment at the molecular level. In view of the limitation of MD simulation on both length- and time-scales, future research may focus on the development of a bridging technique between MD and finite element modeling (FEM) to be able to correlate the results from the nano- to the macro-scale.

Experimental design for optimizing drug release from silicone elastomer matrix and investigation of transdermal drug delivery

Silicone elastomers are commonly used for medical devices and external prosthesis. Recently, there has been growing interest in silicone-based medical devices with enhanced function that release drugs from the elastomer matrix. In the current study, an experimental design approach was used to optimize the release properties of the model drug diclofenac from medical silicone elastomer matrix, including a combination of four permeation enhancers as additives and allowing for constraints in the properties of the material. The D-optimal design included six factors and five responses describing material properties and release of the drug. The first experimental object was screening, to investigate the main and interaction effects, based on 29 experiments. All excipients had a significant effect and were therefore included in the optimization, which also allowed the possible contribution of quadratic terms to the model and was based on 38 experiments. Screening and optimization of release and material properties resulted in the production of two optimized silicone membranes, which were tested for transdermal delivery. The results confirmed the validity of the model for the optimized membranes that were used for further testing for transdermal drug delivery through heat-separated human skin. The optimization resulted in an excipient/drug/silicone composition that resulted in a cured elastomer with good tensile strength and a 4- to 7-fold transdermal delivery increase relative to elastomer that did not contain excipients.

Large‐scale, long‐term nonadiabatic electron molecular dynamics for describing material properties and phenomena in extreme environments

We describe the first principle-based electron force field (eFF) methodology for modeling the simultaneous dynamics of electrons and nuclei (eMD) evolving nonadiabatically under transient extreme conditions. We introduce the parallel implementation of eFF (pEFF) that makes it practical to perform simulations of the nonadiabatic dynamics of materials in extreme environments involving millions of nuclei and electrons, over multi-picoseconds time scales, and demonstrate its application to: (i) accurately determine density and predict percent ionization of hydrogen at high pressure (∼61 GPa) and temperatures up to 15,300 K and (ii) determine, the single shock Hugoniot for lithium metal directly from the shock wave kinematics, i.e., mass velocities (U(p) ) and shock wave velocities (U(s) ), and shock density data. For (i), the density and ionization fractions of hydrogen atoms were calculated using the isobaric-isothermal ensemble at an isotropic pressure of 61.4 GPa and for temperatures between 300 K and 15,300 K. The results at 15,300 K describe a molecular fluid with density ρ = 0.36 g/cm(3) , in close agreement with existing experiments and theory, and ∼0.5% ionization. This result provides no indication of the existence of a critical plasma phase-transition point at this particular temperature and pressure, as previously predicted by others. For (ii), the relationship between U(p) and U(s) was characterized to be linear and plastic in the range 1-20 km/s, and the single shock Hugoniot was determined in close agreement with published results for experimentally reported U(p) s. In addition to this, we provide a description of the materials' behavior for large U(p) s in terms of the appearance of a weak metallic plasma phase by U(p) = 10 km/s, with ≃ 8% ionization, gradually transitioning to a denser plasma with an estimated ≃ 35% ionization by U(p) = 15 km/s. Last but not least, we confirm the computational efficiency and scalability of pEFF by comparing its single processor performance against the fastest existing serial code, which results in a linear speedup ∼10× faster for every 16,000 particles in favor of pEFF, and by evaluating its parallel performance in terms of its strong and weak scaling capabilities. Our results, on Los Alamos's Lobo supercomputer (a 38TFLOPSs Linux HPC with Quad-core AMD Opteron nodes interconnected with an Infiniband), show strong scaling with near ideal speedups for loads >62 particles per processor. Weak scaling is shown to be close to linear under the same per-processor load range. As an absolute reference, an NVT run with 2 million particle lithium bulk system (0.5 M nuclei and 1.5 M electrons) on Lobo takes ∼0.44 s/timestep on 1024 processors (∼1 day/ps using an integration timestep of 0.005 fs).

A Predictive Coarse‐Grained Model for Semiflexible Polymers in Specific Solvents

AbstractA predictive CG model based on a conventional freely rotating chain was developed to describe semiflexible polymers on a relatively large length/time scale. Parameterization of the model requires only two material properties such as, the Kuhn length and coil density. The diameter of spherical “beads” employed in the model is used as an effective parameter that needs to be determined from preliminary data. Once determined for a particular solvent system, this parameter can then be used to model general solvent systems on a parameter‐free basis. Comparison with SANS data on dilute conjugated polymer solutions reveals that the CG polymer model can well describe material properties ranging from local rodlike segments to bulk interchain aggregates.magnified image