Science.gov

Sample records for material model modelling

  1. Mechanics of materials model

    NASA Technical Reports Server (NTRS)

    Meister, Jeffrey P.

    1987-01-01

    The Mechanics of Materials Model (MOMM) is a three-dimensional inelastic structural analysis code for use as an early design stage tool for hot section components. MOMM is a stiffness method finite element code that uses a network of beams to characterize component behavior. The MOMM contains three material models to account for inelastic material behavior. These include the simplified material model, which assumes a bilinear stress-strain response; the state-of-the-art model, which utilizes the classical elastic-plastic-creep strain decomposition; and Walker's viscoplastic model, which accounts for the interaction between creep and plasticity that occurs under cyclic loading conditions.

  2. Materials modelling in London

    NASA Astrophysics Data System (ADS)

    Ciudad, David

    2016-04-01

    Angelos Michaelides, Professor in Theoretical Chemistry at University College London (UCL) and co-director of the Thomas Young Centre (TYC), explains to Nature Materials the challenges in materials modelling and the objectives of the TYC.

  3. Cryogenic Model Materials

    NASA Technical Reports Server (NTRS)

    Kimmel, W. M.; Kuhn, N. S.; Berry, R. F.; Newman, J. A.

    2001-01-01

    An overview and status of current activities seeking alternatives to 200 grade 18Ni Steel CVM alloy for cryogenic wind tunnel models is presented. Specific improvements in material selection have been researched including availability, strength, fracture toughness and potential for use in transonic wind tunnel testing. Potential benefits from utilizing damage tolerant life-prediction methods, recently developed fatigue crack growth codes and upgraded NDE methods are also investigated. Two candidate alloys are identified and accepted for cryogenic/transonic wind tunnel models and hardware.

  4. Interfacing materials models with fire field models

    SciTech Connect

    Nicolette, V.F.; Tieszen, S.R.; Moya, J.L.

    1995-12-01

    For flame spread over solid materials, there has traditionally been a large technology gap between fundamental combustion research and the somewhat simplistic approaches used for practical, real-world applications. Recent advances in computational hardware and computational fluid dynamics (CFD)-based software have led to the development of fire field models. These models, when used in conjunction with material burning models, have the potential to bridge the gap between research and application by implementing physics-based engineering models in a transient, multi-dimensional tool. This paper discusses the coupling that is necessary between fire field models and burning material models for the simulation of solid material fires. Fire field models are capable of providing detailed information about the local fire environment. This information serves as an input to the solid material combustion submodel, which subsequently calculates the impact of the fire environment on the material. The response of the solid material (in terms of thermal response, decomposition, charring, and off-gassing) is then fed back into the field model as a source of mass, momentum and energy. The critical parameters which must be passed between the field model and the material burning model have been identified. Many computational issues must be addressed when developing such an interface. Some examples include the ability to track multiple fuels and species, local ignition criteria, and the need to use local grid refinement over the burning material of interest.

  5. Materials Informatics: Statistical Modeling in Material Science.

    PubMed

    Yosipof, Abraham; Shimanovich, Klimentiy; Senderowitz, Hanoch

    2016-12-01

    Material informatics is engaged with the application of informatic principles to materials science in order to assist in the discovery and development of new materials. Central to the field is the application of data mining techniques and in particular machine learning approaches, often referred to as Quantitative Structure Activity Relationship (QSAR) modeling, to derive predictive models for a variety of materials-related "activities". Such models can accelerate the development of new materials with favorable properties and provide insight into the factors governing these properties. Here we provide a comparison between medicinal chemistry/drug design and materials-related QSAR modeling and highlight the importance of developing new, materials-specific descriptors. We survey some of the most recent QSAR models developed in materials science with focus on energetic materials and on solar cells. Finally we present new examples of material-informatic analyses of solar cells libraries produced from metal oxides using combinatorial material synthesis. Different analyses lead to interesting physical insights as well as to the design of new cells with potentially improved photovoltaic parameters.

  6. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Ramaswamy, V. G.; Vanstone, R. H.; Dame, L. T.; Laflen, J. H.

    1984-01-01

    The unified constitutive theories for application to typical isotropic cast nickel base supperalloys used for air-cooled turbine blades were evaluated. The specific modeling aspects evaluated were: uniaxial, monotonic, cyclic, creep, relaxation, multiaxial, notch, and thermomechanical behavior. Further development of the constitutive theories to model thermal history effects, refinement of the material test procedures, evaluation of coating effects, and verification of the models in an alternate material will be accomplished in a follow-on for this base program.

  7. Constitutive model for porous materials

    SciTech Connect

    Weston, A.M.; Lee, E.L.

    1982-01-01

    A simple pressure versus porosity compaction model is developed to calculate the response of granular porous bed materials to shock impact. The model provides a scheme for calculating compaction behavior when relatively limited material data are available. While the model was developed to study porous explosives and propellants, it has been applied to a much wider range of materials. The early development of porous material models, such as that of Hermann, required empirical dynamic compaction data. Erkman and Edwards successfully applied the early theory to unreacted porous high explosives using a Gruneisen equation of state without yield behavior and without trapped gas in the pores. Butcher included viscoelastic rate dependance in pore collapse. The theoretical treatment of Carroll and Holt is centered on the collapse of a circular pore and includes radial inertia terms and a complex set of stress, strain and strain rate constitutive parameters. Unfortunately data required for these parameters are generally not available. The model described here is also centered on the collapse of a circular pore, but utilizes a simpler elastic-plastic static equilibrium pore collapse mechanism without strain rate dependence, or radial inertia terms. It does include trapped gas inside the pore, a solid material flow stress that creates both a yield point and a variation in solid material pressure with radius. The solid is described by a Mie-Gruneisen type EOS. Comparisons show that this model will accurately estimate major mechanical features which have been observed in compaction experiments.

  8. Materials Analysis and Modeling of Underfill Materials.

    SciTech Connect

    Wyatt, Nicholas B; Chambers, Robert S.

    2015-08-01

    The thermal-mechanical properties of three potential underfill candidate materials for PBGA applications are characterized and reported. Two of the materials are a formulations developed at Sandia for underfill applications while the third is a commercial product that utilizes a snap-cure chemistry to drastically reduce cure time. Viscoelastic models were calibrated and fit using the property data collected for one of the Sandia formulated materials. Along with the thermal-mechanical analyses performed, a series of simple bi-material strip tests were conducted to comparatively analyze the relative effects of cure and thermal shrinkage amongst the materials under consideration. Finally, current knowledge gaps as well as questions arising from the present study are identified and a path forward presented.

  9. Sample - Based Material Structure Modeling

    NASA Astrophysics Data System (ADS)

    Liu, Xingchen

    The paradigm of Sample-based Material Structure Modeling is proposed to facilitate the design and manufacturing of material structures towards desired mechanical properties. By modeling material structure samples via a Markov random field, the proposed paradigm views material structure as a collection of neighborhoods. The abstraction facilitates the reconstruction of both periodic and stochastic material structures and extends to the reconstruction and design of spatially varying material structures, a principal mechanism for creating and controlling spatially varying material properties in nature and engineering. The spatially varying material properties are represented and controlled using the notion of material descriptors which include common geometric, statistical, and topological measures such as correlation functions and Minkowski functionals. The proposed method is of particular advantage in preserving the microscopic geometry and related properties of the material structure sample while achieving target macroscopic property distributions during the design of material structures. For material structures that exhibit anisotropy, properly oriented neighborhoods could greatly enhance the efficiency of the material. The expansion of the design space to include the rotation of neighborhoods is appropriate when the properties that need to be preserved can be safely regarded as rotation invariant. With the assumption of orthotropic symmetry, an automatic way to determine the principal axes of neighborhoods for material structure samples with stochastic orientations is proposed. A Green's function based homogenization method is investigated for the efficient evaluation of the mechanical properties of neighborhoods. The formulated integral equation is converted into a system of linear equations which is shown to be symmetric and positive definite with the appropriate reference material properties and can be solved efficiently using the conjugate gradient method

  10. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Lindholm, U. S.; Bodner, S. R.

    1988-01-01

    The third and fourth years of a 4-year research program, part of the NASA HOST Program, are described. The program goals were: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analysis of hot section components of gas turbine engines. The unified models selected for development and evaluation were those of Bodner-Partom and of Walker. The unified approach for elastic-viscoplastic constitutive equations is a viable method for representing and predicting material response characteristics in the range where strain rate and temperature dependent inelastic deformations are experienced. This conclusion is reached by extensive comparison of model calculations against the experimental results of a test program of two high temperature Ni-base alloys, B1900+Hf and Mar-M247, over a wide temperature range for a variety of deformation and thermal histories including uniaxial, multiaxial, and thermomechanical loading paths. The applicability of the Bodner-Partom and the Walker models for structural applications has been demonstrated by implementing these models into the MARC finite element code and by performing a number of analyses including thermomechanical histories on components of hot sections of gas turbine engines and benchmark notch tensile specimens. The results of the 4-year program have been published in four annual reports. The results of the base program are summarized in this report. The tasks covered include: (1) development of material test procedures, (2) thermal history effects, and (3) verification of the constitutive model for an alternative material.

  11. Micromechanical modeling of advanced materials

    SciTech Connect

    Silling, S.A.; Taylor, P.A.; Wise, J.L.; Furnish, M.D.

    1994-04-01

    Funded as a laboratory-directed research and development (LDRD) project, the work reported here focuses on the development of a computational methodology to determine the dynamic response of heterogeneous solids on the basis of their composition and microstructural morphology. Using the solid dynamics wavecode CTH, material response is simulated on a scale sufficiently fine to explicitly represent the material`s microstructure. Conducting {open_quotes}numerical experiments{close_quotes} on this scale, the authors explore the influence that the microstructure exerts on the material`s overall response. These results are used in the development of constitutive models that take into account the effects of microstructure without explicit representation of its features. Applying this methodology to a glass-reinforced plastic (GRP) composite, the authors examined the influence of various aspects of the composite`s microstructure on its response in a loading regime typical of impact and penetration. As a prerequisite to the microscale modeling effort, they conducted extensive materials testing on the constituents, S-2 glass and epoxy resin (UF-3283), obtaining the first Hugoniot and spall data for these materials. The results of this work are used in the development of constitutive models for GRP materials in transient-dynamics computer wavecodes.

  12. Solvable models of material breakdown

    NASA Astrophysics Data System (ADS)

    Leath, P. L.; Duxbury, P. M.

    The history of the study of fracture of materials is briefly reviewed. Then the importance of analytically solvable models in understanding material breakdown is illustrated by a review of the work of Duxbury, Leath and Beale on simple analytically solvable models of fuse network breakdown in brittle systems. We then review recent work extending this analytically to include close pairs of clusters of defects or double clusters, which also exhibit the double-exponential failure distribution. Finally, a new analytic recursion method is presented for breakdown of systems with linear cracks, but a continuous distribution of breaking strengths. Remarkably, these systems exhibit an optimum sample size where the failure probability can, at low stress, be reduced by many orders of magnitude below that of a single bond.

  13. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Lindholm, Ulric S.

    1985-01-01

    The objective is to develop a unified constitutive model for finite element structural analysis of turbine engine hot-section components. This effort constitutes a different approach for non-linear finite-element computer codes which have heretofore been based on classical inelastic methods. The unified constitutive theory to be developed will avoid the simplifying assumptions of classical theory and should more accurately represent the behavior of superalloy materials under cyclic loading conditions and high temperature environments. During the first two years of the program, extensive experimental correlations were made with two representative unified models. The experiments were both uniaxial and biaxial at temperatures up to 1093 C (2000 F). In addition, the unified models were adopted to the MARC finite element code and used for stress analysis of notched bar and turbine blade geometries.

  14. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Lindholm, Ulric S.; Chan, Kwai S.

    1986-01-01

    The objective of the program is to evaluate and develop existing constitutive models for use in finite-element structural analysis of turbine engine hot section components. The class of constitutive equation studied is considered unified in that all inelastic deformation including plasticity, creep, and stress relaxation are treated in a single term rather than a classical separation of plasticity (time independent) and creep (time dependent) behavior. The unified theories employed also do not utilize the classical yield surface or plastic potential concept. The models are constructed from an appropriate flow law, a scalar kinetic relation between strain rate, temperature and stress, and evolutionary equations for internal variables describing strain or work hardening, both isotropic and directional (kinematic). This and other studies have shown that the unified approach is particularly suited for determining the cyclic behavior of superalloy type blade and vane materials and is entirely compatible with three-dimensional inelastic finite-element formulations. The behavior was examined of a second nickel-base alloy, MAR-M247, and compared it with the Bodner-Partom model, further examined procedures for determining the material-specific constants in the models, and exercised the MARC code for a turbine blade under simulated flight spectrum loading. Results are summarized.

  15. HYPERELASTIC MODELS FOR GRANULAR MATERIALS

    SciTech Connect

    Humrickhouse, Paul W; Corradini, Michael L

    2009-01-29

    A continuum framework for modeling of dust mobilization and transport, and the behavior of granular systems in general, has been reviewed, developed and evaluated for reactor design applications. The large quantities of micron-sized particles expected in the international fusion reactor design, ITER, will accumulate into piles and layers on surfaces, which are large relative to the individual particle size; thus, particle-particle, rather than particle-surface, interactions will determine the behavior of the material in bulk, and a continuum approach is necessary and justified in treating the phenomena of interest; e.g., particle resuspension and transport. The various constitutive relations that characterize these solid particle interactions in dense granular flows have been discussed previously, but prior to mobilization their behavior is not even fluid. Even in the absence of adhesive forces between particles, dust or sand piles can exist in static equilibrium under gravity and other forces, e.g., fluid shear. Their behavior is understood to be elastic, though not linear. The recent “granular elasticity” theory proposes a non-linear elastic model based on “Hertz contacts” between particles; the theory identifies the Coulomb yield condition as a requirement for thermodynamic stability, and has successfully reproduced experimental results for stress distributions in sand piles. The granular elasticity theory is developed and implemented in a stand- alone model and then implemented as part of a finite element model, ABAQUS, to determine the stress distributions in dust piles subjected to shear by a fluid flow. We identify yield with the onset of mobilization, and establish, for a given dust pile and flow geometry, the threshold pressure (force) conditions on the surface due to flow required to initiate it. While the granular elasticity theory applies strictly to cohesionless granular materials, attractive forces are clearly important in the interaction of

  16. Modeling Non-Linear Material Properties in Composite Materials

    DTIC Science & Technology

    2016-06-28

    Technical Report ARWSB-TR-16013 MODELING NON-LINEAR MATERIAL PROPERTIES IN COMPOSITE MATERIALS Michael F. Macri Andrew G...REPORT TYPE Technical 3. DATES COVERED (From - To) 4. TITLE AND SUBTITLE MODELING NON-LINEAR MATERIAL PROPERTIES IN COMPOSITE MATERIALS ...systems are increasingly incorporating composite materials into their design. Many of these systems subject the composites to environmental conditions

  17. EPR-based material modelling of soils

    NASA Astrophysics Data System (ADS)

    Faramarzi, Asaad; Alani, Amir M.

    2013-04-01

    In the past few decades, as a result of the rapid developments in computational software and hardware, alternative computer aided pattern recognition approaches have been introduced to modelling many engineering problems, including constitutive modelling of materials. The main idea behind pattern recognition systems is that they learn adaptively from experience and extract various discriminants, each appropriate for its purpose. In this work an approach is presented for developing material models for soils based on evolutionary polynomial regression (EPR). EPR is a recently developed hybrid data mining technique that searches for structured mathematical equations (representing the behaviour of a system) using genetic algorithm and the least squares method. Stress-strain data from triaxial tests are used to train and develop EPR-based material models for soil. The developed models are compared with some of the well-known conventional material models and it is shown that EPR-based models can provide a better prediction for the behaviour of soils. The main benefits of using EPR-based material models are that it provides a unified approach to constitutive modelling of all materials (i.e., all aspects of material behaviour can be implemented within a unified environment of an EPR model); it does not require any arbitrary choice of constitutive (mathematical) models. In EPR-based material models there are no material parameters to be identified. As the model is trained directly from experimental data therefore, EPR-based material models are the shortest route from experimental research (data) to numerical modelling. Another advantage of EPR-based constitutive model is that as more experimental data become available, the quality of the EPR prediction can be improved by learning from the additional data, and therefore, the EPR model can become more effective and robust. The developed EPR-based material models can be incorporated in finite element (FE) analysis.

  18. Modeling of laser interactions with composite materials

    SciTech Connect

    Rubenchik, Alexander M.; Boley, Charles D.

    2013-05-07

    In this study, we develop models of laser interactions with composite materials consisting of fibers embedded within a matrix. A ray-trace model is shown to determine the absorptivity, absorption depth, and optical power enhancement within the material, as well as the angular distribution of the reflected light. We also develop a macroscopic model, which provides physical insight and overall results. We show that the parameters in this model can be determined from the ray trace model.

  19. Modeling of laser interactions with composite materials

    DOE PAGES

    Rubenchik, Alexander M.; Boley, Charles D.

    2013-05-07

    In this study, we develop models of laser interactions with composite materials consisting of fibers embedded within a matrix. A ray-trace model is shown to determine the absorptivity, absorption depth, and optical power enhancement within the material, as well as the angular distribution of the reflected light. We also develop a macroscopic model, which provides physical insight and overall results. We show that the parameters in this model can be determined from the ray trace model.

  20. Modeling of materials supply, demand and prices

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The societal, economic, and policy tradeoffs associated with materials processing and utilization, are discussed. The materials system provides the materials engineer with the system analysis required for formulate sound materials processing, utilization, and resource development policies and strategies. Materials system simulation and modeling research program including assessments of materials substitution dynamics, public policy implications, and materials process economics was expanded. This effort includes several collaborative programs with materials engineers, economists, and policy analysts. The technical and socioeconomic issues of materials recycling, input-output analysis, and technological change and productivity are examined. The major thrust areas in materials systems research are outlined.

  1. Modeling of materials supply, demand and prices

    NASA Technical Reports Server (NTRS)

    1982-01-01

    The societal, economic, and policy tradeoffs associated with materials processing and utilization, are discussed. The materials system provides the materials engineer with the system analysis required for formulate sound materials processing, utilization, and resource development policies and strategies. Materials system simulation and modeling research program including assessments of materials substitution dynamics, public policy implications, and materials process economics was expanded. This effort includes several collaborative programs with materials engineers, economists, and policy analysts. The technical and socioeconomic issues of materials recycling, input-output analysis, and technological change and productivity are examined. The major thrust areas in materials systems research are outlined.

  2. Constitutive modeling for isotropic materials

    NASA Technical Reports Server (NTRS)

    Lindholm, U. S.

    1984-01-01

    A state-of-the-art review of applicable constitutive models with selection of two for detailed comparison with a wide range of experimental tests was conducted. The experimental matrix contained uniaxial and biaxial tensile, creep, stress relaxation, and cyclic fatigue tests at temperatures to 1093 C and strain rates from .0000001 to .001/sec. Some nonisothermal cycles will also be run. The constitutive models will be incorporated into the MARC finite element structural analysis program with a demonstration computation made for advanced turbine blade configuration. In the code development work, particular emphasis is being placed on developing efficient integration algorithms for the highly nonlinear and stiff constitutive equations. Another area of emphasis is the appropriate and efficient methodology for determing constitutive constants from a minimum extent of experimental data.

  3. Bilinear modelling of cellulosic orthotropic nonlinear materials

    Treesearch

    E.P. Saliklis; T. J. Urbanik; B. Tokyay

    2003-01-01

    The proposed method of modelling orthotropic solids that have a nonlinear constitutive material relationship affords several advantages. The first advantage is the application of a simple bilinear stress-strain curve to represent the material response on two orthogonal axes as well as in shear, even for markedly nonlinear materials. The second advantage is that this...

  4. Modeling of shear localization in materials

    SciTech Connect

    Lesuer, D.; LeBlanc, M.; Riddle, B.; Jorgensen, B.

    1998-02-11

    The deformation response of a Ti alloy, Ti-6Al-4V, has been studied during shear localization. The study has involved well-controlled laboratory tests involving a double-notch shear sample. The results have been used to provide a comparison between experiment and the predicted response using DYNA2D and two material models (the Johnson-Cook model and an isotropic elastic-plastic-hydrodynamic model). The work will serve as the basis for the development of a new material model which represents the different deformation mechanisms active during shear localization.

  5. Constitutive model development for isotropic materials

    NASA Technical Reports Server (NTRS)

    Kaufman, A.

    1982-01-01

    The objective is to develop a unified constitutive model for finite-element structural analysis of turbine engine hot section components. This effort constitutes a different approach for nonlinear finite-element computer codes which were heretofore based on classical inelastic methods. A unified constitutive theory will avoid the simplifying assumptions of classical theory and should more accurately represent the behavior of superalloy materials under cyclic loading conditions and high temperature environments. Model development will be directed toward isotropic, cast nickel-base alloys used for aircooled turbine blades and vanes. The contractor will select a base material for model development and an alternate material for verification purposes from a list of three alloys specified by NASA. The candidate alloys represent a cross-section of turbine blade and vane materials of interest to both large and small size engine manufacturers. Material stock for the base and alternate materials will be supplied to the Contractor by the government.

  6. A continuum thermomechanical model for energetic materials

    NASA Astrophysics Data System (ADS)

    Ruderman, Gregory Allen

    Thermomechanical modeling of energetic materials, for example solid rocket motor propellants and explosives, is a complex problem due to the large number of behaviors such a material may exhibit. Experiments have shown that these materials are nonlinearly viscoelastic, and may also experience plastic flow (permanent deformation), phase changes (melting and vaporization processes), and combustion. In addition, these phenomena are often strongly coupled, making modeling very difficult. Compounding the difficulty further, reliable experimental data on the properties of these types of materials are quite scarce. Applying advanced tools of continuum thermomechanics, we have developed a fully three-dimensional framework which, in the most general form, is able to model all the mentioned behaviors of energetic materials. The concept of a balance of microforces, forces which drive changes in material microstructure, is employed to generate thermomechanically consistent equations of evolution for combustion and phase transitions. The model is then simplified to a set of three model problems: the constant-volume thermal explosion, one-dimensional shear loading, and one dimensional longitudinal loading. These model problems were solved numerically using essentially non-oscillatory and total variation diminishing methods. The solutions reveal extremely rich behavior, including complex wave phenomena, strain localization phenomena, and changes of material phase.

  7. Improvements to constitutive material model for fabrics

    NASA Astrophysics Data System (ADS)

    Morea, Mihai I.

    2011-12-01

    The high strength to weight ratio of woven fabric offers a cost effective solution to be used in a containment system for aircraft propulsion engines. Currently, Kevlar is the only Federal Aviation Administration (FAA) approved fabric for usage in systems intended to mitigate fan blade-out events. This research builds on an earlier constitutive model of Kevlar 49 fabric developed at Arizona State University (ASU) with the addition of new and improved modeling details. Latest stress strain experiments provided new and valuable data used to modify the material model post peak behavior. These changes reveal an overall improvement of the Finite Element (FE) model's ability to predict experimental results. First, the steel projectile is modeled using Johnson-Cook material model and provides a more realistic behavior in the FE ballistic models. This is particularly noticeable when comparing FE models with laboratory tests where large deformations in projectiles are observed. Second, follow-up analysis of the results obtained through the new picture frame tests conducted at ASU provides new values for the shear moduli and corresponding strains. The new approach for analysis of data from picture frame tests combines digital image analysis and a two-level factorial optimization formulation. Finally, an additional improvement in the material model for Kevlar involves checking the convergence at variation of mesh density of fabrics. The study performed and described herein shows the converging trend, therefore validating the FE model.

  8. Material characterization and modeling with shear ography

    NASA Technical Reports Server (NTRS)

    Workman, Gary L.; Callahan, Virginia

    1993-01-01

    Shearography has emerged as a useful technique for nondestructible evaluation and materials characterization of aerospace materials. A suitable candidate for the technique is to determine the response of debonds on foam-metal interfaces such as the TPS system on the External Tank. The main thrust is to develop a model which allows valid interpretation of shearographic information on TPS type systems. Confirmation of the model with shearographic data will be performed.

  9. ASPH modeling of Material Damage and Failure

    SciTech Connect

    Owen, J M

    2010-04-30

    We describe our new methodology for Adaptive Smoothed Particle Hydrodynamics (ASPH) and its application to problems in modeling material failure. We find that ASPH is often crucial for properly modeling such experiments, since in most cases the strain placed on materials is non-isotropic (such as a stretching rod), and without the directional adaptability of ASPH numerical failure due to SPH nodes losing contact in the straining direction can compete with or exceed the physical process of failure.

  10. Modeling and Characterization of Recompressed Damaged Materials

    SciTech Connect

    Becker, R; Belak, J; Campbell, G

    2002-12-16

    Ductile metals subjected to shock loading can develop internal damage through nucleation growth and coalescence of voids. The extent of damage can range from a well-defined spall plane induced by light shocks to more widespread damage caused by strong shocks. Because damage materials are often part of a dynamic system, significant additional deformation can occur in extensively damaged materials. To represent material behavior in simulation codes for stockpile stewardship calculations, both the damage and the recompression processes must be modeled accurately. Currently, no experimentally based models of recompression behavior are available for use in numerical simulations. The goals of this project are to (1) perform recompression experiments on samples containing controlled and well-characterized damage, (2) develop a model capturing the recompression behavior and residual strength based on the experimental data and micro-mechanical models, and (3) implement the model in an Advanced Simulation and Computing (ASCI) code (ALE3D). The recompression model, together with failure models based on underlying physical mechanisms, will provide a more accurate representation of material behavior-information that is needed for simulations of explosively loaded materials such as those required by the Stockpile Stewardship Program.

  11. Constitutive Modeling of Crosslinked Nanotube Materials

    NASA Technical Reports Server (NTRS)

    Odegard, G. M.; Frankland, S. J. V.; Herzog, M. N.; Gates, T. S.; Fay, C. C.

    2004-01-01

    A non-linear, continuum-based constitutive model is developed for carbon nanotube materials in which bundles of aligned carbon nanotubes have varying amounts of crosslinks between the nanotubes. The model accounts for the non-linear elastic constitutive behavior of the material in terms of strain, and is developed using a thermodynamic energy approach. The model is used to examine the effect of the crosslinking on the overall mechanical properties of variations of the crosslinked carbon nanotube material with varying degrees of crosslinking. It is shown that the presence of the crosslinks has significant effects on the mechanical properties of the carbon nanotube materials. An increase in the transverse shear properties is observed when the nanotubes are crosslinked. However, this increase is accompanied by a decrease in axial mechanical properties of the nanotube material upon crosslinking.

  12. Ceramic materials testing and modeling

    SciTech Connect

    Wilfinger, K. R., LLNL

    1998-04-30

    corrosion by limiting the transport of water and oxygen to the ceramic-metal interface. Thermal spray techniques for ceramic coating metallic structures are currently being explored. The mechanics of thermal spray resembles spray painting in many respects, allowing large surfaces and contours to be covered smoothly. All of the relevant thermal spray processes use a high energy input to melt or partially melt a powdered oxide material, along with a high velocity gas to impinge the molten droplets onto a substrate where they conform, quench, solidify and adhere mechanically. The energy input can be an arc generated plasma, an oxy-fuel flame or an explosion. The appropriate feed material and the resulting coating morphologies vary with technique as well as with application parameters. To date on this project, several versions of arc plasma systems, a detonation coating system and two variations of high velocity oxy-fuel (HVOF) fired processes have been investigated, operating on several different ceramic materials.

  13. Multiscale Materials Modeling in an Industrial Environment.

    PubMed

    Weiß, Horst; Deglmann, Peter; In 't Veld, Pieter J; Cetinkaya, Murat; Schreiner, Eduard

    2016-06-07

    In this review, we sketch the materials modeling process in industry. We show that predictive and fast modeling is a prerequisite for successful participation in research and development processes in the chemical industry. Stable and highly automated workflows suitable for handling complex systems are a must. In particular, we review approaches to build and parameterize soft matter systems. By satisfying these prerequisites, efficiency for the development of new materials can be significantly improved, as exemplified here for formulation polymer development. This is in fact in line with recent Materials Genome Initiative efforts sponsored by the US government. Valuable contributions to product development are possible today by combining existing modeling techniques in an intelligent fashion, provided modeling and experiment work hand in hand.

  14. Materials and techniques for model construction

    NASA Technical Reports Server (NTRS)

    Wigley, D. A.

    1985-01-01

    The problems confronting the designer of models for cryogenic wind tunnel models are discussed with particular reference to the difficulties in obtaining appropriate data on the mechanical and physical properties of candidate materials and their fabrication technologies. The relationship between strength and toughness of alloys is discussed in the context of maximizing both and avoiding the problem of dimensional and microstructural instability. All major classes of materials used in model construction are considered in some detail and in the Appendix selected numerical data is given for the most relevant materials. The stepped-specimen program to investigate stress-induced dimensional changes in alloys is discussed in detail together with interpretation of the initial results. The methods used to bond model components are considered with particular reference to the selection of filler alloys and temperature cycles to avoid microstructural degradation and loss of mechanical properties.

  15. Material modeling of biofilm mechanical properties.

    PubMed

    Laspidou, C S; Spyrou, L A; Aravas, N; Rittmann, B E

    2014-05-01

    A biofilm material model and a procedure for numerical integration are developed in this article. They enable calculation of a composite Young's modulus that varies in the biofilm and evolves with deformation. The biofilm-material model makes it possible to introduce a modeling example, produced by the Unified Multi-Component Cellular Automaton model, into the general-purpose finite-element code ABAQUS. Compressive, tensile, and shear loads are imposed, and the way the biofilm mechanical properties evolve is assessed. Results show that the local values of Young's modulus increase under compressive loading, since compression results in the voids "closing," thus making the material stiffer. For the opposite reason, biofilm stiffness decreases when tensile loads are imposed. Furthermore, the biofilm is more compliant in shear than in compression or tension due to the how the elastic shear modulus relates to Young's modulus. Copyright © 2014 Elsevier Inc. All rights reserved.

  16. Modeling shocks in periodic lattice materials

    NASA Astrophysics Data System (ADS)

    Messner, Mark C.; Barham, Mathew I.; Kumar, Mukul; Barton, Nathan R.

    2017-01-01

    Periodic lattice materials are extremely light relative to their stiffness and strength. Developments in additive manufacturing technologies open the possibility of using periodic lattices as energy absorbers for impact loading. This work extends an equivalent continuum material model for periodic, stretch dominated lattices to shock compression by augmenting the model with an equation for the evolution of relative density under volumetric plastic deformation. When compared to detailed finite element simulations, this simple modification to the equivalent continuum model accurately captures some parts of the shock response, especially the behavior of elastic precursors. However, the model is less accurate for the properties of the compaction shock, reflecting inaccuracies in the final state of the material.

  17. Modeling ready biodegradability of fragrance materials.

    PubMed

    Ceriani, Lidia; Papa, Ester; Kovarich, Simona; Boethling, Robert; Gramatica, Paola

    2015-06-01

    In the present study, quantitative structure activity relationships were developed for predicting ready biodegradability of approximately 200 heterogeneous fragrance materials. Two classification methods, classification and regression tree (CART) and k-nearest neighbors (kNN), were applied to perform the modeling. The models were validated with multiple external prediction sets, and the structural applicability domain was verified by the leverage approach. The best models had good sensitivity (internal ≥80%; external ≥68%), specificity (internal ≥80%; external 73%), and overall accuracy (≥75%). Results from the comparison with BIOWIN global models, based on group contribution method, show that specific models developed in the present study perform better in prediction than BIOWIN6, in particular for the correct classification of not readily biodegradable fragrance materials. © 2015 SETAC.

  18. Modeling mechanical response of heterogeneous materials

    NASA Astrophysics Data System (ADS)

    Pal, Siladitya

    developed. It is found that two different material phases (collagens) of mussel byssus thread are optimally distributed along the thread. These applications demonstrate that the presence of heterogeneity in the system demands high computational resources for simulation and modeling. Thus, Higher Dimensional Model Representation (HDMR) based surrogate modeling concept has been proposed to reduce computational complexity. The applicability of such methodology has been demonstrated in failure envelope construction and in multiscale finite element techniques. It is observed that surrogate based model can capture the behavior of complex material systems with sufficient accuracy. The computational algorithms presented in this thesis will further pave the way for accurate prediction of macroscopic deformation behavior of various class of advanced materials from their measurable microstructural features at a reasonable computational cost.

  19. Mechanistic materials modeling for nuclear fuel performance

    DOE PAGES

    Tonks, Michael R.; Andersson, David; Phillpot, Simon R.; ...

    2017-03-15

    Fuel performance codes are critical tools for the design, certification, and safety analysis of nuclear reactors. However, their ability to predict fuel behavior under abnormal conditions is severely limited by their considerable reliance on empirical materials models correlated to burn-up (a measure of the number of fission events that have occurred, but not a unique measure of the history of the material). In this paper, we propose a different paradigm for fuel performance codes to employ mechanistic materials models that are based on the current state of the evolving microstructure rather than burn-up. In this approach, a series of statemore » variables are stored at material points and define the current state of the microstructure. The evolution of these state variables is defined by mechanistic models that are functions of fuel conditions and other state variables. The material properties of the fuel and cladding are determined from microstructure/property relationships that are functions of the state variables and the current fuel conditions. Multiscale modeling and simulation is being used in conjunction with experimental data to inform the development of these models. Finally, this mechanistic, microstructure-based approach has the potential to provide a more predictive fuel performance capability, but will require a team of researchers to complete the required development and to validate the approach.« less

  20. Modeling of a biological material nacre: Waviness stiffness model.

    PubMed

    Al-Maskari, N S; McAdams, D A; Reddy, J N

    2017-01-01

    Nacre is a tough yet stiff natural composite composed of microscopic mineral polygonal tablets bonded by a tough biopolymer. The high stiffness of nacre is known to be due to its high mineral content. However, the remarkable toughness of nacre is explained by its ability to deform past a yield point and develop large inelastic strain over a large volume around defects and cracks. The high strain is mainly due to sliding and waviness of the tablets. Mimicking nacre's remarkable properties, to date, is still a challenge due in part to fabrication challenges as well as a lack of models that can predict its properties or properties of a bulk material given specific constituent materials and material structure. Previous attempts to create analytical models for nacre include tablet sliding but don't account for the waviness of the tablets. In this work, a mathematical model is proposed to account for the waviness of the tablet. Using this model, a better prediction of the elastic modulus is obtained that agrees with experimental values found in the literature. In addition, the waviness angle can be predicted which is within the recommended range. Having a good representative model aids in designing a bio-mimicked nacre.

  1. Modeling and Simulation of Amorphous Materials

    NASA Astrophysics Data System (ADS)

    Pandey, Anup

    The general and practical inversion of diffraction data - producing a computer model correctly representing the material explored - is an important unsolved problem for disordered materials. Such modeling should proceed by using our full knowledge base, both from experiment and theory. In this dissertation, we introduce a robust method, Force-Enhanced Atomic Refinement (FEAR), which jointly exploits the power of ab initio atomistic simulation along with the information carried by diffraction data. As a preliminary trial, the method has been implemented using empirical potentials for amorphous silicon (a-Si) and silica ( SiO2). The models obtained are comparable to the ones prepared by the conventional approaches as well as the experiments. Using ab initio interactions, the method is applied to two very different systems: amorphous silicon (a-Si) and two compositions of a solid electrolyte memory material silver-doped GeSe3. It is shown that the method works well for both the materials. Besides that, the technique is easy to implement, is faster and yields results much improved over conventional simulation methods for the materials explored. It offers a means to add a priori information in first principles modeling of materials, and represents a significant step toward the computational design of non-crystalline materials using accurate interatomic interactions and experimental information. Moreover, the method has also been used to create a computer model of a-Si, using highly precise X-ray diffraction data. The model predicts properties that are close to the continuous random network models but with no a priori assumptions. In addition, using the ab initio molecular dynamics simulations (AIMD) we explored the doping and transport in hydrogenated amorphous silicon a-Si:H with the most popular impurities: boron and phosphorous. We investigated doping for these impurities and the role of H in the doping process. We revealed the network motion and H hopping induced by

  2. The Model 9977 Radioactive Material Packaging Primer

    SciTech Connect

    Abramczyk, G.

    2015-10-09

    The Model 9977 Packaging is a single containment drum style radioactive material (RAM) shipping container designed, tested and analyzed to meet the performance requirements of Title 10 the Code of Federal Regulations Part 71. A radioactive material shipping package, in combination with its contents, must perform three functions (please note that the performance criteria specified in the Code of Federal Regulations have alternate limits for normal operations and after accident conditions): Containment, the package must “contain” the radioactive material within it; Shielding, the packaging must limit its users and the public to radiation doses within specified limits; and Subcriticality, the package must maintain its radioactive material as subcritical

  3. Modeling of Irradiation Hardening of Polycrystalline Materials

    SciTech Connect

    Li, Dongsheng; Zbib, Hussein M.; Garmestani, Hamid; Sun, Xin; Khaleel, Mohammad A.

    2011-09-14

    High energy particle irradiation of structural polycrystalline materials usually produces irradiation hardening and embrittlement. The development of predict capability for the influence of irradiation on mechanical behavior is very important in materials design for next generation reactors. In this work a multiscale approach was implemented to predict irradiation hardening of body centered cubic (bcc) alpha-iron. The effect of defect density, texture and grain boundary was investigated. In the microscale, dislocation dynamics models were used to predict the critical resolved shear stress from the evolution of local dislocation and defects. In the macroscale, a viscoplastic self-consistent model was applied to predict the irradiation hardening in samples with changes in texture and grain boundary. This multiscale modeling can guide performance evaluation of structural materials used in next generation nuclear reactors.

  4. High performance computing for materials process modeling

    SciTech Connect

    Zacharia, T.; Bjerke, M.A.; Simunovic, S.

    1993-12-31

    Advanced mathematical techniques and computer simulation play a major role in providing enhanced understanding of conventional materials processing operations such as welding and joining. Many of these numerical models are highly compute-intensive. It is not unusual for an analysis to require several hours of computational time on current supercomputers despite the simplicity of the models being studied. As computer simulations and materials databases grow in complexity, massively parallel computers have become important tools. This paper briefly describes massively parallel computational research at the ORNL with the objective of providing fundamental insight into the welding process.

  5. Global nuclear material flow/control model

    SciTech Connect

    Dreicer, J.S.; Rutherford, D.S.; Fasel, P.K.; Riese, J.M.

    1997-10-01

    This is the final report of a two-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The nuclear danger can be reduced by a system for global management, protection, control, and accounting as part of an international regime for nuclear materials. The development of an international fissile material management and control regime requires conceptual research supported by an analytical and modeling tool which treats the nuclear fuel cycle as a complete system. The prototype model developed visually represents the fundamental data, information, and capabilities related to the nuclear fuel cycle in a framework supportive of national or an international perspective. This includes an assessment of the global distribution of military and civilian fissile material inventories, a representation of the proliferation pertinent physical processes, facility specific geographic identification, and the capability to estimate resource requirements for the management and control of nuclear material. The model establishes the foundation for evaluating the global production, disposition, and safeguards and security requirements for fissile nuclear material and supports the development of other pertinent algorithmic capabilities necessary to undertake further global nuclear material related studies.

  6. Computational Materials: Modeling and Simulation of Nanostructured Materials and Systems

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.; Hinkley, Jeffrey A.

    2003-01-01

    The paper provides details on the structure and implementation of the Computational Materials program at the NASA Langley Research Center. Examples are given that illustrate the suggested approaches to predicting the behavior and influencing the design of nanostructured materials such as high-performance polymers, composites, and nanotube-reinforced polymers. Primary simulation and measurement methods applicable to multi-scale modeling are outlined. Key challenges including verification and validation of models are highlighted and discussed within the context of NASA's broad mission objectives.

  7. Constitutive modeling for isotropic materials (HOST)

    NASA Technical Reports Server (NTRS)

    Chan, Kwai S.; Lindholm, Ulric S.; Bodner, S. R.; Hill, Jeff T.; Weber, R. M.; Meyer, T. G.

    1986-01-01

    The results of the third year of work on a program which is part of the NASA Hot Section Technology program (HOST) are presented. The goals of this program are: (1) the development of unified constitutive models for rate dependent isotropic materials; and (2) the demonstration of the use of unified models in structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are those of Bodner-Partom and of Walker. A test procedure was developed for assisting the generation of a data base for the Bodner-Partom model using a relatively small number of specimens. This test procedure involved performing a tensile test at a temperature of interest that involves a succession of strain-rate changes. The results for B1900+Hf indicate that material constants related to hardening and thermal recovery can be obtained on the basis of such a procedure. Strain aging, thermal recovery, and unexpected material variations, however, preluded an accurate determination of the strain-rate sensitivity parameter is this exercise. The effects of casting grain size on the constitutive behavior of B1900+Hf were studied and no particular grain size effect was observed. A systematic procedure was also developed for determining the material constants in the Bodner-Partom model. Both the new test procedure and the method for determining material constants were applied to the alternate material, Mar-M247 . Test data including tensile, creep, cyclic and nonproportional biaxial (tension/torsion) loading were collected. Good correlations were obtained between the Bodner-Partom model and experiments. A literature survey was conducted to assess the effects of thermal history on the constitutive behavior of metals. Thermal history effects are expected to be present at temperature regimes where strain aging and change of microstructure are important. Possible modifications to the Bodner-Partom model to account for these effects are outlined

  8. Multiscale modeling of shock-loaded materials

    NASA Astrophysics Data System (ADS)

    Ortiz, Michael

    2001-06-01

    I will describe efforts within Caltech's ASCI/ASAP Center to develop a Virtual Testing Facility (VTF) for investigating the dynamic properties of materials subjected to extreme conditions of pressure, temperature and strain rate. The facility combines an Eulerian description of HE materials, with a Lagrangian description of solids. We subscribe to the multiscale modeling paradigm as the means of developing material models with a minimum of empiricism by a systematic bridging of lengthscales, from atomistic to macroscopic. For instance, we have developed a multiscale model of bcc Ta in which we specifically consider the following unit processes: double-kink formation and thermally activated motion of kinks; the close-range interactions between primary and forest dislocation, leading to the formation of jogs; the percolation motion of dislocations through a random array of forest dislocations introducing short-range obstacles of different strengths; dislocation multiplication due to breeding by double cross-slip; and dislocation pair-annihilation. These models contained parameters representing well-characterized physical properties of the material. All essential parameters of the model have been determined by recourse to atomistic calculations based on empirical potentials fitted to first-principles quantum mechanical calculations. In addition, the volumetric equation of state and the pressure and temperature dependence of the material have been determined directly from first-principles quantum mechanical calculations. The model is found to capture salient experimentally observed features of the behavior of Ta crystals. The VTF also includes cohesive descriptions of fracture enabling the simulation of fragmentation. The performance and scalability of the VTF on ASCI platforms has been extensively assessed. As an overarching application which tests the integration of all its components, the VTF is being applied to the simulation of detonation-induced shock loading of

  9. Model of holographic recording in thermoplastic materials.

    PubMed

    Bányász, I

    1998-04-10

    A method for the evaluation of images reconstructed from holograms recorded in thermoplastic materials is reported. The method is based on the use of the experimental modulation transfer function and nonlinear holographic characteristics of the recording material. Calculations have been carried out for high-numerical-aperture holograms of a five-element Ronchi ruling. The quality of the reconstructed image as a function of the recording parameters has been computed. The model predicts that it is possible to optimize holographic recording in these materials.

  10. Multidimensional DDT modeling of energetic materials

    SciTech Connect

    Baer, M.R.; Hertel, E.S.; Bell, R.L.

    1995-07-01

    To model the shock-induced behavior of porous or damaged energetic materials, a nonequilibrium mixture theory has been developed and incorporated into the shock physics code, CTH. The foundation for this multiphase model is based on a continuum mixture formulation given by Baer and Nunziato. This multiphase mixture model provides a thermodynamic and mathematically-consistent description of the self-accelerated combustion processes associated with deflagration-to-detonation and delayed detonation behavior which are key modeling issues in safety assessment of energetic systems. An operator-splitting method is used in the implementation of this model, whereby phase diffusion effects are incorporated using a high resolution transport method. Internal state variables, forming the basis for phase interaction quantities, are resolved during the Lagrangian step requiring the use of a stiff matrix-free solver. Benchmark calculations are presented which simulate low-velocity piston impact on a propellant porous bed and experimentally-measured wave features are well replicated with this model. This mixture model introduces micromechanical models for the initiation and growth of reactive multicomponent flow that are key features to describe shock initiation and self-accelerated deflagration-to-detonation combustion behavior. To complement one-dimensional simulation, two-dimensional numerical calculations are presented which indicate wave curvature effects due to the loss of wall confinement. This study is pertinent for safety analysis of weapon systems.

  11. A material model driver for DYNA3D

    SciTech Connect

    Hallquist, J.O.; Whirley, R.G.

    1990-02-22

    This report describes a material model driver which has recently been implemented in the DYNA3D code. The material model driver allows plotting of the constitutive response predicted by a material model under a given load path. This capability is particularly useful when fitting complex material models to experimental data. The plotting capability of the material model driver facilitates comparison of the simulated material stress-strain behavior with actual material test results. 1 ref., 6 figs., 4 tabs.

  12. Parameter Estimation for Viscoplastic Material Modeling

    NASA Technical Reports Server (NTRS)

    Saleeb, Atef F.; Gendy, Atef S.; Wilt, Thomas E.

    1997-01-01

    A key ingredient in the design of engineering components and structures under general thermomechanical loading is the use of mathematical constitutive models (e.g. in finite element analysis) capable of accurate representation of short and long term stress/deformation responses. In addition to the ever-increasing complexity of recent viscoplastic models of this type, they often also require a large number of material constants to describe a host of (anticipated) physical phenomena and complicated deformation mechanisms. In turn, the experimental characterization of these material parameters constitutes the major factor in the successful and effective utilization of any given constitutive model; i.e., the problem of constitutive parameter estimation from experimental measurements.

  13. A Hysteresis Model for Piezoceramic Materials

    NASA Technical Reports Server (NTRS)

    Smith, Ralph C.; Ounaies, Zoubeida

    1999-01-01

    This paper addresses the modeling of nonlinear constitutive relations and hysteresis inherent to piezoceramic materials at moderate to high drive levels. Such models are, necessary to realize the, full potential of the materials in high performance control applications, and a necessary prerequisite is the development of techniques which permit control implementation. The approach employed here is based on the qualification of reversible and irreversible domain wall motion in response to applied electric fields. A comparison with experimental data illustrates that because the resulting ODE model is physics-based, it can be employed for both characterization and prediction of polarization levels throughout the range of actuator operation. Finally, the ODE formulation is amenable to inversion which facilitates the development of an inverse compensator for linear control design.

  14. Constitutive modeling for isotropic materials (HOST)

    NASA Technical Reports Server (NTRS)

    Lindholm, U. S.; Chan, K. S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.; Cassenti, B. N.

    1985-01-01

    This report presents the results of the second year of work on a problem which is part of the NASA HOST Program. Its goals are: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are that of Bodner-Partom and Walker. For model evaluation purposes, a large constitutive data base is generated for a B1900 + Hf alloy by performing uniaxial tensile, creep, cyclic, stress relation, and thermomechanical fatigue (TMF) tests as well as biaxial (tension/torsion) tests under proportional and nonproportional loading over a wide range of strain rates and temperatures. Systematic approaches for evaluating material constants from a small subset of the data base are developed. Correlations of the uniaxial and biaxial tests data with the theories of Bodner-Partom and Walker are performed to establish the accuracy, range of applicability, and integability of the models. Both models are implemented in the MARC finite element computer code and used for TMF analyses. Benchmark notch round experiments are conducted and the results compared with finite-element analyses using the MARC code and the Walker model.

  15. NUMERICAL MODELING OF CATHODE CONTACT MATERIAL DENSIFICATION

    SciTech Connect

    Koeppel, Brian J.; Liu, Wenning N.; Stephens, Elizabeth V.; Khaleel, Mohammad A.

    2011-11-01

    Numerical modeling was used to simulate the constrained sintering process of the cathode contact layer during assembly of solid oxide fuel cells (SOFCs). A finite element model based on the continuum theory for sintering of porous bodies was developed and used to investigate candidate low-temperature cathode contact materials. Constitutive parameters for various contact materials under investigation were estimated from dilatometry screening tests, and the influence of processing time, processing temperature, initial grain size, and applied compressive stress on the free sintering response was predicted for selected candidate materials. The densification behavior and generated stresses within a 5-cell planar SOFC stack during sintering, high temperature operation, and room temperature shutdown were predicted. Insufficient constrained densification was observed in the stack at the proposed heat treatment, but beneficial effects of reduced grain size, compressive stack preload, and reduced thermal expansion coefficient on the contact layer densification and stresses were observed.

  16. Stochastic multiscale modeling of polycrystalline materials

    NASA Astrophysics Data System (ADS)

    Wen, Bin

    provides a new outlook to multi-scale materials modeling accounting for microstructure and process uncertainties. Predictive materials modeling will accelerate the development of new materials and processes for critical applications in industry.

  17. Thermal Ablation Modeling for Silicate Materials

    NASA Technical Reports Server (NTRS)

    Chen, Yih-Kanq

    2016-01-01

    A general thermal ablation model for silicates is proposed. The model includes the mass losses through the balance between evaporation and condensation, and through the moving molten layer driven by surface shear force and pressure gradient. This model can be applied in the ablation simulation of the meteoroid and the glassy ablator for spacecraft Thermal Protection Systems. Time-dependent axisymmetric computations are performed by coupling the fluid dynamics code, Data-Parallel Line Relaxation program, with the material response code, Two-dimensional Implicit Thermal Ablation simulation program, to predict the mass lost rates and shape change. The predicted mass loss rates will be compared with available data for model validation, and parametric studies will also be performed for meteoroid earth entry conditions.

  18. Thermal Ablation Modeling for Silicate Materials

    NASA Technical Reports Server (NTRS)

    Chen, Yih-Kanq

    2016-01-01

    A thermal ablation model for silicates is proposed. The model includes the mass losses through the balance between evaporation and condensation, and through the moving molten layer driven by surface shear force and pressure gradient. This model can be applied in ablation simulations of the meteoroid or glassy Thermal Protection Systems for spacecraft. Time-dependent axi-symmetric computations are performed by coupling the fluid dynamics code, Data-Parallel Line Relaxation program, with the material response code, Two-dimensional Implicit Thermal Ablation simulation program, to predict the mass lost rates and shape change. For model validation, the surface recession of fused amorphous quartz rod is computed, and the recession predictions reasonably agree with available data. The present parametric studies for two groups of meteoroid earth entry conditions indicate that the mass loss through moving molten layer is negligibly small for heat-flux conditions at around 1 MW/cm(exp. 2).

  19. Computational modeling of composite material fires.

    SciTech Connect

    Brown, Alexander L.; Erickson, Kenneth L.; Hubbard, Joshua Allen; Dodd, Amanda B.

    2010-10-01

    Composite materials behave differently from conventional fuel sources and have the potential to smolder and burn for extended time periods. As the amount of composite materials on modern aircraft continues to increase, understanding the response of composites in fire environments becomes increasingly important. An effort is ongoing to enhance the capability to simulate composite material response in fires including the decomposition of the composite and the interaction with a fire. To adequately model composite material in a fire, two physical model development tasks are necessary; first, the decomposition model for the composite material and second, the interaction with a fire. A porous media approach for the decomposition model including a time dependent formulation with the effects of heat, mass, species, and momentum transfer of the porous solid and gas phase is being implemented in an engineering code, ARIA. ARIA is a Sandia National Laboratories multiphysics code including a range of capabilities such as incompressible Navier-Stokes equations, energy transport equations, species transport equations, non-Newtonian fluid rheology, linear elastic solid mechanics, and electro-statics. To simulate the fire, FUEGO, also a Sandia National Laboratories code, is coupled to ARIA. FUEGO represents the turbulent, buoyantly driven incompressible flow, heat transfer, mass transfer, and combustion. FUEGO and ARIA are uniquely able to solve this problem because they were designed using a common architecture (SIERRA) that enhances multiphysics coupling and both codes are capable of massively parallel calculations, enhancing performance. The decomposition reaction model is developed from small scale experimental data including thermogravimetric analysis (TGA) and Differential Scanning Calorimetry (DSC) in both nitrogen and air for a range of heating rates and from available data in the literature. The response of the composite material subject to a radiant heat flux boundary

  20. Computational Modeling in Structural Materials Processing

    NASA Technical Reports Server (NTRS)

    Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

    1997-01-01

    High temperature materials such as silicon carbide, a variety of nitrides, and ceramic matrix composites find use in aerospace, automotive, machine tool industries and in high speed civil transport applications. Chemical vapor deposition (CVD) is widely used in processing such structural materials. Variations of CVD include deposition on substrates, coating of fibers, inside cavities and on complex objects, and infiltration within preforms called chemical vapor infiltration (CVI). Our current knowledge of the process mechanisms, ability to optimize processes, and scale-up for large scale manufacturing is limited. In this regard, computational modeling of the processes is valuable since a validated model can be used as a design tool. The effort is similar to traditional chemically reacting flow modeling with emphasis on multicomponent diffusion, thermal diffusion, large sets of homogeneous reactions, and surface chemistry. In the case of CVI, models for pore infiltration are needed. In the present talk, examples of SiC nitride, and Boron deposition from the author's past work will be used to illustrate the utility of computational process modeling.

  1. Computational Modeling in Structural Materials Processing

    NASA Technical Reports Server (NTRS)

    Meyyappan, Meyya; Arnold, James O. (Technical Monitor)

    1997-01-01

    High temperature materials such as silicon carbide, a variety of nitrides, and ceramic matrix composites find use in aerospace, automotive, machine tool industries and in high speed civil transport applications. Chemical vapor deposition (CVD) is widely used in processing such structural materials. Variations of CVD include deposition on substrates, coating of fibers, inside cavities and on complex objects, and infiltration within preforms called chemical vapor infiltration (CVI). Our current knowledge of the process mechanisms, ability to optimize processes, and scale-up for large scale manufacturing is limited. In this regard, computational modeling of the processes is valuable since a validated model can be used as a design tool. The effort is similar to traditional chemically reacting flow modeling with emphasis on multicomponent diffusion, thermal diffusion, large sets of homogeneous reactions, and surface chemistry. In the case of CVI, models for pore infiltration are needed. In the present talk, examples of SiC nitride, and Boron deposition from the author's past work will be used to illustrate the utility of computational process modeling.

  2. Viscoelastic Models for Nearly Incompressible Materials

    DTIC Science & Technology

    2009-09-01

    4.4.2 One-Parameter Family of Functions: Part I . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 4.4.3 The Mooney - Rivlin Elastic...2µ0Ψ(ω0,C) (211) and G∞(E) = G∞(C) = 2µ∞Ψ(ω∞,C) . (212) This example is motivated by the Mooney - Rivlin model for incompressible elastic materials...We 45 give a brief discussion of that model in section 4.4.3 and then return to the discussion of the example above. 4.4.3 The Mooney - Rivlin Elastic

  3. Characterization and modeling of compliant active materials

    NASA Astrophysics Data System (ADS)

    Marra, S. P.; Ramesh, K. T.; Douglas, A. S.

    2003-09-01

    Active materials respond mechanically to changes in environmental conditions. One example of a compliant active material is a polymer gel. Active polymer gels expand and contract in response to certain environmental stimuli, such as the application of an electric field or a change in the pH level of the surroundings. This ability to achieve large, reversible deformations with no external mechanical loading has generated much interest in the use of these gels as actuators and "artificial muscles". While much work has been done to study the behavior and properties of these gels, little information is available regarding the full constitutive description of the mechanical and actuation properties. This work focuses on developing a means of characterizing the mechanical properties of compliant active materials. A thermodynamically consistent finite-elastic constitutive model was developed to describe the mechanical and actuation behaviors of these kinds of materials. The mechanical properties of compliant active materials are characterized by a free-energy function, and the model utilizes an evolving internal variable to describe the actuation state. A biaxial testing system has been developed which can measure stresses and deformations of polymer gel films in a variety of liquid environments. This testing system is used to determine the form and parameters of the free-energy function for a specific active polymer gel, poly(vinyl alcohol)-poly(acrylic acid) gel.

  4. Modeling Solid State Detonation and Reactive Materials

    DTIC Science & Technology

    2010-07-01

    observed in "ideal" explosives. How- ever the lead wave head is not a classical shock in the sense of ZND theory, but rather a subsonic compaction wave...case for the classical ZND model of detonation. For this discussion, we regard the SSD as a det- onation in reactive materials that nominally runs at...2.33 km/sec. If one assumes simply that the wave head is supersonic relative to the am- bient, fresh material as is the case for a classical ZND

  5. Dynamic material modeling in hot forging

    SciTech Connect

    El-Gizawy, A.S. )

    1992-03-01

    A dynamic material model that characterized flow behavior in the workpiece under forging conditions was required to optimize the process and produce defect-free product at minimum cost. Constitutive equations describe the relationship between stress, strain rate, and temperature under forging conditions. Using aluminum alloy 7050, numerous deformation experiments were conducted to fully characterize constitutive equation variables. A thorough description of the experimental arrangement was provided. Flow data and efficiency data were assembled into a three-dimensional plot of temperature vs. strain rate vs. deformation efficiency to produce an efficiency map. The efficiency map provided the information required for optimization of forging process design. The results of dynamic modeling of the material were used in simulating the isothermal forging of a particular part. Recommendations concerning optimum preform design and processing conditions were reported.

  6. Dynamic modelling of packaging material flow systems.

    PubMed

    Tsiliyannis, Christos A

    2005-04-01

    A dynamic model has been developed for reused and recycled packaging material flows. It allows a rigorous description of the flows and stocks during the transition to new targets imposed by legislation, product demand variations or even by variations in consumer discard behaviour. Given the annual reuse and recycle frequency and packaging lifetime, the model determines all packaging flows (e.g., consumption and reuse) and variables through which environmental policy is formulated, such as recycling, waste and reuse rates and it identifies the minimum number of variables to be surveyed for complete packaging flow monitoring. Simulation of the transition to the new flow conditions is given for flows of packaging materials in Greece, based on 1995--1998 field inventory and statistical data.

  7. Computational modeling of material aging effects

    SciTech Connect

    Fang, H.E.

    1996-07-01

    Progress is being made in our efforts to develop computational models for predicting material property changes in weapon components due to aging. The first version of a two-dimensional lattice code for modeling thermomechanical fatigue, such as has been observed in solder joints on electronic components removed from the stockpile, has been written and tested. The code does a good qualitative job of presenting intergranular and/or transgranular cracking in a polycrystalline material when under thermomechanical deformation. The current progress is an encouraging start for our long term effort to develop multi-level simulation capabilities, with the technology of high performance computing, for predicting age-related effects on the reliability of weapons.

  8. Modeling shock waves in orthotropic elastic materials

    NASA Astrophysics Data System (ADS)

    Vignjevic, Rade; Campbell, James C.; Bourne, Neil K.; Djordjevic, Nenad

    2008-08-01

    A constitutive relationship for modeling of shock wave propagation in orthotropic materials is proposed for nonlinear explicit transient large deformation computer codes (hydrocodes). A procedure for separation of material volumetric compression (compressibility effects equation of state) from deviatoric strain effects is formulated, which allows for the consistent calculation of stresses in the elastic regime as well as in the presence of shock waves. According to this procedure the pressure is defined as the state of stress that results in only volumetric deformation, and consequently is a diagonal second order tensor. As reported by Anderson et al. [Comput. Mech. 15, 201 (1994)], the shock response of an orthotropic material cannot be accurately predicted using the conventional decomposition of the stress tensor into isotropic and deviatoric parts. This paper presents two different stress decompositions based on the assumption that the stress tensor is split into two components: one component is due to volumetric strain and the other is due to deviatoric strain. Both decompositions are rigorously derived. In order to test their ability to describe shock propagation in orthotropic materials, both algorithms were implemented in a hydrocode and their predictions were compared to experimental plate impact data. The material considered was a carbon fiber reinforced epoxy material, which was tested in both the through-thickness and longitudinal directions. The ψ decomposition showed good agreement with the physical behavior of the considered material, while the ζ decomposition significantly overestimated the longitudinal stresses.

  9. Modeling Bamboo as a Functionally Graded Material

    NASA Astrophysics Data System (ADS)

    Silva, Emílio Carlos Nelli; Walters, Matthew C.; Paulino, Glaucio H.

    2008-02-01

    Natural fibers are promising for engineering applications due to their low cost. They are abundantly available in tropical and subtropical regions of the world, and they can be employed as construction materials. Among natural fibers, bamboo has been widely used for housing construction around the world. Bamboo is an optimized composite material which exploits the concept of Functionally Graded Material (FGM). Biological structures, such as bamboo, are composite materials that have complicated shapes and material distribution inside their domain, and thus the use of numerical methods such as the finite element method and multiscale methods such as homogenization, can help to further understanding of the mechanical behavior of these materials. The objective of this work is to explore techniques such as the finite element method and homogenization to investigate the structural behavior of bamboo. The finite element formulation uses graded finite elements to capture the varying material distribution through the bamboo wall. To observe bamboo behavior under applied loads, simulations are conducted considering a spatially-varying Young's modulus, an averaged Young's modulus, and orthotropic constitutive properties obtained from homogenization theory. The homogenization procedure uses effective, axisymmetric properties estimated from the spatially-varying bamboo composite. Three-dimensional models of bamboo cells were built and simulated under tension, torsion, and bending load cases.

  10. Modeling Bamboo as a Functionally Graded Material

    SciTech Connect

    Silva, Emilio Carlos Nelli; Walters, Matthew C.; Paulino, Glaucio H.

    2008-02-15

    Natural fibers are promising for engineering applications due to their low cost. They are abundantly available in tropical and subtropical regions of the world, and they can be employed as construction materials. Among natural fibers, bamboo has been widely used for housing construction around the world. Bamboo is an optimized composite material which exploits the concept of Functionally Graded Material (FGM). Biological structures, such as bamboo, are composite materials that have complicated shapes and material distribution inside their domain, and thus the use of numerical methods such as the finite element method and multiscale methods such as homogenization, can help to further understanding of the mechanical behavior of these materials. The objective of this work is to explore techniques such as the finite element method and homogenization to investigate the structural behavior of bamboo. The finite element formulation uses graded finite elements to capture the varying material distribution through the bamboo wall. To observe bamboo behavior under applied loads, simulations are conducted considering a spatially-varying Young's modulus, an averaged Young's modulus, and orthotropic constitutive properties obtained from homogenization theory. The homogenization procedure uses effective, axisymmetric properties estimated from the spatially-varying bamboo composite. Three-dimensional models of bamboo cells were built and simulated under tension, torsion, and bending load cases.

  11. Fatigue and hysteresis modeling of ferroelectric materials

    NASA Astrophysics Data System (ADS)

    Yoo, In. K.; Desu, Seshu B.

    1993-10-01

    Due to their nonlinear properties, ferroelectric materials are ideal candidates for smart materials. Degradation properties such as low voltage breakdown, fatigue, and aging have been major problems in commercial applications of these materials. Such degradations affect the lifetime of ferroelectric materials. Therefore, it is important to understand degradation for reliability improvement. In this article, recent studies on fatigue and hysteresis of ferroelectric ceramics such as Lead Zirconate Titanate (PZT) thin films is reviewed. A new fatigue model is discussed in detail which is based on effective one-directional movement of defects by internal field difference, defect entrapment at the ferroelectrics-electrode interface, and resultant polarization loss at the interface. A fatigue equation derived from this model is presented. Fatigue parameters such as initial polarization, piling constant, and decay constant are defined from the fatigue equation and voltage and temperature dependence of fatigue parameters are discussed. The jump distance of defect calculated from voltage dependence of the decay constant is close to the lattice constant of ferroelectric materials, which implies that oxygen or lead vacancies migrate either parallel or antiparallel to the polarization direction. From the temperature dependence of the decay constant, it is shown that the activation energy for domain wall movement plays an important role in fatigue. The hysteresis model of ferroelectrics is shown using polarization reversal. The hysteresis loop is made by four polarization stages: nucleation, growth, merging, and shrinkage of domains. The hysteresis equation confirms that dielectric viscosity controls hysteresis properties, and temperature dependence of the coefficient of dielectric viscosity is also discussed in conjunction with fatigue mechanism.

  12. Materials Database Development for Ballistic Impact Modeling

    NASA Technical Reports Server (NTRS)

    Pereira, J. Michael

    2007-01-01

    A set of experimental data is being generated under the Fundamental Aeronautics Program Supersonics project to help create and validate accurate computational impact models of jet engine impact events. The data generated will include material property data generated at a range of different strain rates, from 1x10(exp -4)/sec to 5x10(exp 4)/sec, over a range of temperatures. In addition, carefully instrumented ballistic impact tests will be conducted on flat plates and curved structures to provide material and structural response information to help validate the computational models. The material property data and the ballistic impact data will be generated using materials from the same lot, as far as possible. It was found in preliminary testing that the surface finish of test specimens has an effect on measured high strain rate tension response of AL2024. Both the maximum stress and maximum elongation are greater on specimens with a smoother finish. This report gives an overview of the testing that is being conducted and presents results of preliminary testing of the surface finish study.

  13. Modeling material failure with a vectorized routine

    NASA Technical Reports Server (NTRS)

    Cramer, S. M.; Goodman, J. R.

    1984-01-01

    The computational aspects of modelling material failure in structural wood members are presented with particular reference to vector processing aspects. Wood members are considered to be highly orthotropic, inhomogeneous, and discontinuous due to the complex microstructure of wood material and the presence of natural growth characteristics such as knots, cracks and cross grain in wood members. The simulation of strength behavior of wood members is accomplished through the use of a special purpose finite element/fracture mechanics routine, program STARW (Strength Analysis Routine for Wood). Program STARW employs quadratic finite elements combined with singular crack tip elements in a finite element mesh. Vector processing techniques are employed in mesh generation, stiffness matrix formation, simultaneous equation solution, and material failure calculations. The paper addresses these techniques along with the time and effort requirements needed to convert existing finite element code to a vectorized version. Comparisons in execution time between vectorized and nonvectorized routines are provided.

  14. Estimating proportions of materials using mixture models

    NASA Technical Reports Server (NTRS)

    Heydorn, R. P.; Basu, R.

    1983-01-01

    An approach to proportion estimation based on the notion of a mixture model, appropriate parametric forms for a mixture model that appears to fit observed remotely sensed data, methods for estimating the parameters in these models, methods for labelling proportion determination from the mixture model, and methods which use the mixture model estimates as auxiliary variable values in some proportion estimation schemes are addressed.

  15. Projective Peridynamics for Modeling Versatile Elastoplastic Materials.

    PubMed

    He, Xiaowei; Wang, Huamin; Wu, Enhua

    2017-09-22

    Unified simulation of versatile elastoplastic materials and different dimensions offers many advantages in animation production, contact handling, and hardware acceleration. The unstructured particle representation is particularly suitable for this task, thanks to its simplicity. However, previous meshless techniques either need too much computational cost for addressing stability issues, or lack physical meanings and fail to generate interesting deformation behaviors, such as the Poisson effect. In this paper, we study the development of an elastoplastic model under the state-based peridynamics framework, which uses integrals rather than partial derivatives in its formulation. To model elasticity, we propose a unique constitutive model and an efficient iterative simulator solved in a projective dynamics way. To handle plastic behaviors, we incorporate our simulator with the Drucker-Prager yield criterion and a reference position update scheme, both of which are implemented under peridynamics. Finally, we show how to strengthen the simulator by position-based constraints and spatially varying stiffness models, to achieve incompressibility, particle redistribution, cohesion, and friction effects in viscoelastic and granular flows. Our experiments demonstrate that our unified, meshless simulator is flexible, efficient, robust, and friendly with parallel computing.

  16. Modeling plasticity of materials with nanostructure

    NASA Astrophysics Data System (ADS)

    Kudinova, N. R.

    2017-02-01

    A new approach to modeling of the plasticity of materials with the particle size in the range from 3 to 20 nm (nanostructure) has been proposed. It is based on classical thermodynamic approach employing the surface tension of nanoparticles. Its main advantage is the minimum number of physical parameters in use. In the context of the proposed model, we calculated the dependence of the melting temperature on the nanoparticle size which is consistent with experimental data. The volume density of the surface energy of nanoparticles was also determined. This energy is assumed to be a significant part of the internal energy during deformation Yield point was interpreted as the result of changes of grains surface energy during the deformation. The obtained yield point dependence on the grain size was related to the Hall–Petch law, and this resulted in confirmation of the hypothesis on the crucial role of surface tension forces in the initial stage of plastic deformation of nanomaterials.

  17. Realistic modeling of complex oxide materials

    NASA Astrophysics Data System (ADS)

    Solovyev, I. V.

    2011-01-01

    Since electronic and magnetic properties of many transition-metal oxides can be efficiently controlled by external factors such as the temperature, pressure, electric or magnetic field, they are regarded as promising materials for various applications. From the viewpoint of the electronic structure, these phenomena are frequently related to the behavior of a small group of states located near the Fermi level. The basic idea of this project is to construct a model for the low-energy states, derive all the parameters rigorously on the basis of density functional theory (DFT), and to study this model by modern techniques. After a brief review of the method, the abilities of this approach will be illustrated on a number of examples, including multiferroic manganites and spin-orbital-lattice coupled phenomena in RVO 3 (where R is the three-valent element).

  18. A Generalized Cap Model for Geological Materials

    DTIC Science & Technology

    1974-11-14

    modified Drucker - Prager , Ref. [31, yield condition, denoted by f(lJ ) = 0 (1) in which J and J are the first and second invariants of the stress and...models, such as anistropy, rate dependence, and hardening of the modified Drucker - Prager portion of the yield surface (isotropic and/or kinematic... DRUCKER - PRAGER LINE 11-1 1 15 in which W, D, , D, D, W and D are material constants. The quantity R in Eqs. (15, 16) represents the ratio of the

  19. Analytical modeling of materialized view maintenance algorithms

    SciTech Connect

    Srivastava, J.; Rotem, D.

    1987-10-01

    In the recent past there has been increasing interest in the idea of maintaining materialized copies of views, and use them to process view queries (ADIB 80, LIND 86, BLAK 86, ROSS 86, HANS 87). Various algorithms have been proposed, and their performance analyzed. However, there does not exist a comprehensive analytical framework under which the problem can be systematically studied. We present a queueing model which facilitates both a systematic study of the problem, and provides a means to compare various proposed algorithms. Specifically, we propose a parametrized approach in which both the user and system viewpoints are integrated, and the setting of the parameter decides the relative importance of each table.

  20. A Continuum Damage Model for Viscoelastic Materials

    DTIC Science & Technology

    1987-11-01

    CLASSIFICATION AUTHORITY 3b. DECLASSIFICATION/OOWNGRAOING SCHEDULE 4. PERFORMING ORGANIZATION REPORT NUMBER(S) MM- 4762 -87-17 e«. NAME OF PERFORMING...ENGINEERING SCIENCES DIRECTORATE CONTACT N00014-82-K-0562 M M- 4762 -87-17, / NOVEMEBER 1987 A CONTINUUM DAMAGE MODEL FOR VISCOELASTIC MATERIALS by Y...Contract F33615-67-C-1412), In "Workshop on a Continuum Mechanics Approach to Damage and Life Prediction" NSF-Solid Mechanics Program, 119. ASTM STP

  1. Fire and materials modeling for transportation systems

    SciTech Connect

    Skocypec, R.D.; Gritzo, L.A.; Moya, J.L.; Nicolette, V.F.; Tieszen, S.R.; Thomas, R.

    1994-10-01

    Fire is an important threat to the safety of transportation systems. Therefore, understanding the effects of fire (and its interaction with materials) on transportation systems is crucial to quantifying and mitigating the impact of fire on the safety of those systems. Research and development directed toward improving the fire safety of transportation systems must address a broad range of phenomena and technologies, including: crash dynamics, fuel dispersion, fire environment characterization, material characterization, and system/cargo thermal response modeling. In addition, if the goal of the work is an assessment and/or reduction of risk due to fires, probabilistic risk assessment technology is also required. The research currently underway at Sandia National Laboratories in each of these areas is summarized in this paper.

  2. Modeling material interfaces with hybrid adhesion method

    DOE PAGES

    Brown, Nicholas Taylor; Qu, Jianmin; Martinez, Enrique

    2017-01-27

    A molecular dynamics simulation approach is presented to approximate layered material structures using discrete interatomic potentials through classical mechanics and the underlying principles of quantum mechanics. This method isolates the energetic contributions of the system into two pure material layers and an interfacial region used to simulate the adhesive properties of the diffused interface. The strength relationship of the adhesion contribution is calculated through small-scale separation calculations and applied to the molecular surfaces through an inter-layer bond criterion. By segregating the contributions into three regions and accounting for the interfacial excess energies through the adhesive surface bonds, it is possiblemore » to model each material with an independent potential while maintaining an acceptable level of accuracy in the calculation of mechanical properties. This method is intended for the atomistic study of the delamination mechanics, typically observed in thin-film applications. Therefore, the work presented in this paper focuses on mechanical tensile behaviors, with observations in the elastic modulus and the delamination failure mode. To introduce the hybrid adhesion method, we apply the approach to an ideal bulk copper sample, where an interface is created by disassociating the force potential in the middle of the structure. Various mechanical behaviors are compared to a standard EAM control model to demonstrate the adequacy of this approach in a simple setting. In addition, we demonstrate the robustness of this approach by applying it on (1) a Cu-Cu2O interface with interactions between two atom types, and (2) an Al-Cu interface with two dissimilar FCC lattices. These additional examples are verified against EAM and COMB control models to demonstrate the accurate simulation of failure through delamination, and the formation and propagation of dislocations under loads. Finally, the results conclude that by modeling the energy

  3. Colloid transport in model fracture filling materials

    NASA Astrophysics Data System (ADS)

    Wold, S.; Garcia-Garcia, S.; Jonsson, M.

    2010-12-01

    Colloid transport in model fracture filling materials Susanna Wold*, Sandra García-García and Mats Jonsson KTH Chemical Science and Engineering Royal Institute of Technology, SE-100 44 Stockholm, Sweden *Corresponding author: E-mail: wold@kth.se Phone: +46 8 790 6295 In colloid transport in water-bearing fractures, the retardation depends on interactions with the fracture surface by sorption or filtration. These mechanisms are difficult to separate. A rougher surface will give a larger area available for sorption, and also when a particle is physically hindered, it approaches the surface and enables further sorption. Sorption can be explained by electrostatics were the strongest sorption on minerals always is observed at pH below pHpzc (Filby et al., 2008). The adhesion of colloids to mineral surfaces is related to the surface roughness according to a recent study (Darbha et al., 2010). There is a large variation in the characteristics of water-bearing fractures in bedrock in terms of aperture distribution, flow velocity, surface roughness, mineral distributions, presence of fracture filling material, and biological and organic material, which is hard to implement in modeling. The aim of this work was to study the transport of negatively charged colloids in model fracture filling material in relation to flow, porosity, mineral type, colloid size, and surface charge distribution. In addition, the impact on transport of colloids of mixing model fracture filling materials with different retention and immobilization capacities, determined by batch sorption experiments, was investigated. The transport of Na-montmorillonite colloids and well-defined negatively charged latex microspheres of 50, 100, and 200 nm diameter were studied in either columns containing quartz or quartz mixed with biotite. The ionic strength in the solution was exclusively 0.001 and pH 6 or 8.5. The flow rates used were 0.002, 0.03, and 0.6 mL min-1. Sorption of the colloids on the model fracture

  4. Constitutive modeling for isotropic materials (HOST)

    NASA Technical Reports Server (NTRS)

    Lindholm, Ulric S.; Chan, Kwai S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.; Cassenti, B. N.

    1984-01-01

    The results of the first year of work on a program to validate unified constitutive models for isotropic materials utilized in high temperature regions of gas turbine engines and to demonstrate their usefulness in computing stress-strain-time-temperature histories in complex three-dimensional structural components. The unified theories combine all inelastic strain-rate components in a single term avoiding, for example, treating plasticity and creep as separate response phenomena. An extensive review of existing unified theories is given and numerical methods for integrating these stiff time-temperature-dependent constitutive equations are discussed. Two particular models, those developed by Bodner and Partom and by Walker, were selected for more detailed development and evaluation against experimental tensile, creep and cyclic strain tests on specimens of a cast nickel base alloy, B19000+Hf. Initial results comparing computed and test results for tensile and cyclic straining for temperature from ambient to 982 C and strain rates from 10(exp-7) 10(exp-3) s(exp-1) are given. Some preliminary date correlations are presented also for highly non-proportional biaxial loading which demonstrate an increase in biaxial cyclic hardening rate over uniaxial or proportional loading conditions. Initial work has begun on the implementation of both constitutive models in the MARC finite element computer code.

  5. Modeling Emerging Solar Cell Materials and Devices

    NASA Astrophysics Data System (ADS)

    Thongprong, Non

    Organic photovoltaics (OPVs) and perovskite solar cells are emerging classes of solar cell that are promising for clean energy alternatives to fossil fuels. Understanding fundamental physics of these materials is crucial for improving their energy conversion efficiencies and promoting them to practical applications. Current density-voltage (JV) curves; which are important indicators of OPV efficiency, have direct connections to many fundamental properties of solar cells. They can be described by the Shockley diode equation, resulting in fitting parameters; series and parallel resistance (Rs and Rp), diode saturation current ( J0) and ideality factor (n). However, the Shockley equation was developed specifically for inorganic p-n junction diodes, so it lacks physical meanings when it is applied to OPVs. Hence, the puRposes of this work are to understand the fundamental physics of OPVs and to develop new diode equations in the same form as the Shockley equation that are based on OPV physics. We develop a numerical drift-diffusion simulation model to study bilayer OPVs, which will be called the drift-diffusion for bilayer interface (DD-BI) model. The model solves Poisson, drift-diffusion and current-continuity equations self-consistently for charge densities and potential profiles of a bilayer device with an organic heterojunction interface described by the GWWF model. We also derive new diode equations that have JV curves consistent with the DD-BI model and thus will be called self-consistent diode (SCD) equations. Using the DD-BI and the SCD model allows us to understand working principles of bilayer OPVs and physical definitions of the Shockley parameters. Due to low carrier mobilities in OPVs, space charge accumulation is common especially near the interface and electrodes. Hence, quasi-Fermi levels (i.e. chemical potentials), which depend on charge densities, are modified around the interface, resulting in a splitting of quasi-Fermi levels that works as a driving

  6. Constitutive modeling of inelastic anisotropic material response

    NASA Technical Reports Server (NTRS)

    Stouffer, D. C.

    1984-01-01

    A constitutive equation was developed to predict the inelastic thermomechanical response of single crystal turbine blades. These equations are essential for developing accurate finite element models of hot section components and contribute significantly to the understanding and prediction of crack initiation and propagation. The method used was limited to unified state variable constitutive equations. Two approaches to developing an anisotropic constitutive equation were reviewed. One approach was to apply the Stouffer-Bodner representation for deformation induced anisotropy to materials with an initial anisotropy such as single crystals. The second approach was to determine the global inelastic strain rate from the contribution of the slip in each of the possible crystallographic slip systems. A three dimensional finite element is being developed with a variable constitutive equation link that can be used for constitutive equation development and to predict the response of an experiment using the actual specimen geometry and loading conditions.

  7. Radioactive materials in biosolids : dose modeling.

    SciTech Connect

    Wolbarst, A. B.; Chiu, W. A; Yu, C.; Aiello, K.; Bachmaier, J. T.; Bastian, R. K.; Cheng, J. -J.; Goodman, J.; Hogan, R.; Jones, A. R.; Kamboj, S.; Lenhartt, T.; Ott, W. R.; Rubin, A.; Salomon, S. N.; Schmidt, D. W.; Setlow, L. W.; Environmental Science Division; U.S. EPA; Middlesex County Utilities Authority; U.S. DOE; U.S. NRC; NE Ohio Regional Sewer District

    2006-01-01

    The Interagency Steering Committee on Radiation Standards (ISCORS) has recently completed a study of the occurrence within the United States of radioactive materials in sewage sludge and sewage incineration ash. One component of that effort was an examination of the possible transport of radioactivity from sludge into the local environment and the subsequent exposure of humans. A stochastic environmental pathway model was applied separately to seven hypothetical, generic sludge-release scenarios, leading to the creation of seven tables of Dose-to-Source Ratios (DSR), which can be used in translating from specific activity in sludge into dose to an individual. These DSR values were then combined with the results of an ISCORS survey of sludge and ash at more than 300 publicly owned treatment works, to explore the potential for radiation exposure of sludge workers and members of the public. This paper provides a brief overview of the pathway modeling methodology employed in the exposure and dose assessments and discusses technical aspects of the results obtained.

  8. Initial investigation of cryogenic wind tunnel model filler materials

    NASA Technical Reports Server (NTRS)

    Rush, H. F.; Firth, G. C.

    1985-01-01

    Various filler materials are being investigated for applicability to cryogenic wind tunnel models. The filler materials will be used to fill surface grooves, holes and flaws. The severe test environment of cryogenic models precludes usage of filler materials used on conventional wind tunnel models. Coefficients of thermal expansion, finishing characteristics, adhesion and stability of several candidate filler materials were examined. Promising filler materials are identified.

  9. Mathematical Modelling of Laser/Material Interactions.

    DTIC Science & Technology

    1983-11-25

    translated to the model input. Even an experimental mode print can also be digitalised for the model. In trying to describe high order modes matliematically...4. Mazumder J. Steen W.M. "Welding of Ti 6al - 4V by continuous wave CO2 laser". Metal construction Sept. 1980 pp423 - 427. 5. Kogelnik H, Li.T Proc

  10. Initial Investigation of Cryogenic Wind Tunnel Model Filler Materials

    NASA Technical Reports Server (NTRS)

    Firth, G. C.

    1985-01-01

    Filler materials are used for surface flaws, instrumentation grooves, and fastener holes in wind tunnel models. More stringent surface quality requirements and the more demanding test environment encountered by cryogenic wind tunnels eliminate filler materials such as polyester resins, plaster, and waxes used on conventional wind tunnel models. To provide a material data base for cryogenic models, various filler materials are investigated. Surface quality requirements and test temperature extremes require matching of coefficients of thermal expansion or interfacing materials. Microstrain versus temperature curves are generated for several candidate filler materials for comparison with cryogenically acceptable materials. Matches have been achieved for aluminum alloys and austenitic steels. Simulated model surfaces are filled with candidate filler materials to determine finishing characteristics, adhesion and stability when subjected to cryogenic cycling. Filler material systems are identified which meet requirements for usage with aluminum model components.

  11. Physical models of hydrofracturing across material interfaces

    SciTech Connect

    Blair, S.C.; Thorpe, R.K.; Heuze, F.E.

    1988-10-01

    We have performed a series of laboratory tests to study the propagation of a hydrofracture into and through an interface between two rock-like materials. The aim of this research is to provide improved diagnostics for stimulating lenticular gas sand reservoirs by interpreting features of the injection pressure-time record caused by interaction of a hydrofracture with a geologic discontinuity. Results will also be used to validate conceptual models of hydrofracture behavior in discontinuous media, such as are embodied in the LLNL FEFFLAP code, a two-dimensional fracture propagation computer program. We prepared test specimens by embedding sandstone tablets (lenses) in blocks of gypsum cement. These blocks were hydrofractured under true triaxial loading conditions, at a constant injection rate. The injection path was designed so that we obtained a single-wing fracture, propagating in a plane perpendicular to the interface. The vertical extent of the fractures was controlled by means of wire mesh screen embedded in the blocks, perpendicular to the injection tube. Growth of the fractures was tracked via extension failure of fine tungsten wires embedded in the gypsum. After testing, we dissected the blocks and recorded the extent of fracturing and fluid penetration. Cross-sections of the fractures indicate that they were of constant height and propagated through the sandstone tablet. All the fractures showed step-crack behavior upon entering or exiting the sandstone tablet. Pressure-time and fracture tracking data were consistent for all tests. Distinct step increases on the pressure- time record were also noted in all tests, and are related to the interaction of the hydrofracture with the sandstone lens. 16 refs., 19 figs., 4 tabs.

  12. Exploring the interdependencies between parameters in a material model.

    SciTech Connect

    Silling, Stewart Andrew; Fermen-Coker, Muge

    2014-01-01

    A method is investigated to reduce the number of numerical parameters in a material model for a solid. The basis of the method is to detect interdependencies between parameters within a class of materials of interest. The method is demonstrated for a set of material property data for iron and steel using the Johnson-Cook plasticity model.

  13. A Material Model for FE-Simulation of UD Composites

    NASA Astrophysics Data System (ADS)

    Fischer, Sebastian

    2016-04-01

    Composite materials are being increasingly used for industrial applications. CFRP is particularly suitable for lightweight construction due to its high specific stiffness and strength properties. Simulation methods are needed during the development process in order to reduce the effort for prototypes and testing. This is particularly important for CFRP, as the material is costly. For accurate simulations, a realistic material model is needed. In this paper, a material model for the simulation of UD-composites including non-linear material behaviour and damage is developed and implemented in Abaqus. The material model is validated by comparison with test results on a range of test specimens.

  14. SRM (Solid Rocket Motor) propellant and polymer materials structural modeling

    NASA Technical Reports Server (NTRS)

    Moore, Carleton J.

    1988-01-01

    The following investigation reviews and evaluates the use of stress relaxation test data for the structural analysis of Solid Rocket Motor (SRM) propellants and other polymer materials used for liners, insulators, inhibitors, and seals. The stress relaxation data is examined and a new mathematical structural model is proposed. This model has potentially wide application to structural analysis of polymer materials and other materials generally characterized as being made of viscoelastic materials. A dynamic modulus is derived from the new model for stress relaxation modulus and is compared to the old viscoelastic model and experimental data.

  15. Modeling

    SciTech Connect

    Loth, E.; Tryggvason, G.; Tsuji, Y.; Elghobashi, S. E.; Crowe, Clayton T.; Berlemont, A.; Reeks, M.; Simonin, O.; Frank, Th; Onishi, Yasuo; Van Wachem, B.

    2005-09-01

    Slurry flows occur in many circumstances, including chemical manufacturing processes, pipeline transfer of coal, sand, and minerals; mud flows; and disposal of dredged materials. In this section we discuss slurry flow applications related to radioactive waste management. The Hanford tank waste solids and interstitial liquids will be mixed to form a slurry so it can be pumped out for retrieval and treatment. The waste is very complex chemically and physically. The ARIEL code is used to model the chemical interactions and fluid dynamics of the waste.

  16. Modeling and characterization of recompressed damaged materials

    SciTech Connect

    Becker, R; Cazamias, J U; Kalantar, D H; LeBlanc, M M; Springer, H K

    2004-02-11

    Experiments have been performed to explore conditions under which spall damage is recompressed with the ultimate goal of developing a predictive model. Spall is introduced through traditional gas gun techniques or with laser ablation. Recompression techniques producing a uniaxial stress state, such as a Hopkinson bar, do not create sufficient confinement to close the porosity. Higher stress triaxialities achieved through a gas gun or laser recompression can close the spall. Characterization of the recompressed samples by optical metallography and electron microscopy reveal a narrow, highly deformed process zone. At the higher pressures achieved in the gas gun, little evidence of spall remains other than differentially etched features in the optical micrographs. With the very high strain rates achieved with laser techniques there is jetting from voids and other signs of turbulent metal flow. Simulations of spall and recompression on micromechanical models containing a single void suggest that it might be possible to represent the recompression using models similar to those employed for void growth. Calculations using multiple, randomly distributed voids are needed to determine if such models will yield the proper behavior for more realistic microstructures.

  17. Process modeling for carbon-phenolic nozzle materials

    NASA Technical Reports Server (NTRS)

    Letson, Mischell A.; Bunker, Robert C.; Remus, Walter M., III; Clinton, R. G.

    1989-01-01

    A thermochemical model based on the SINDA heat transfer program is developed for carbon-phenolic nozzle material processes. The model can be used to optimize cure cycles and to predict material properties based on the types of materials and the process by which these materials are used to make nozzle components. Chemical kinetic constants for Fiberite MX4926 were determined so that optimization of cure cycles for the current Space Shuttle Solid Rocket Motor nozzle rings can be determined.

  18. An efficient descriptor model for designing materials for solar cells

    NASA Astrophysics Data System (ADS)

    Alharbi, Fahhad H.; Rashkeev, Sergey N.; El-Mellouhi, Fedwa; Lüthi, Hans P.; Tabet, Nouar; Kais, Sabre

    2015-11-01

    An efficient descriptor model for fast screening of potential materials for solar cell applications is presented. It works for both excitonic and non-excitonic solar cells materials, and in addition to the energy gap it includes the absorption spectrum (α(E)) of the material. The charge transport properties of the explored materials are modelled using the characteristic diffusion length (Ld) determined for the respective family of compounds. The presented model surpasses the widely used Scharber model developed for bulk heterojunction solar cells. Using published experimental data, we show that the presented model is more accurate in predicting the achievable efficiencies. To model both excitonic and non-excitonic systems, two different sets of parameters are used to account for the different modes of operation. The analysis of the presented descriptor model clearly shows the benefit of including α(E) and Ld in view of improved screening results.

  19. Modeling of Nearshore-Placed Dredged Material

    DTIC Science & Technology

    2015-07-01

    and placement onshore. Mound sand was dyed to provide contrast and to differentiate it from the natural sand beach used in the model. Beach surveys...were performed intermittently during each 9-hour (prototype) experiment with a laser scanner. In addition to beach change elevations, the scanner...accumulation was observed on the beach onshore and updrift of the mounds. Beach response was similar to that of an offshore breakwater in which the mound

  20. Stochastic Multiscale Modeling of Polycrystalline Materials

    DTIC Science & Technology

    2013-01-01

    2.16 Explicit structure of a (γ+γ′) grain and its equivalent homoge- nized model. The gray background on the left grain represents γ matrix, while...effective strength . . . . . . . . . . . . . . . . . . . . . . . 129 3.14 Convergence test of the mean field of the properties of the forged product...microstructure input. The variabil- ity of strain, stress and strength fields over the workpiece after forging is inves- tigated. The microstructures in the

  1. Dynamic Characterization and Modeling of Potting Materials for Electronics Assemblies

    NASA Astrophysics Data System (ADS)

    Joshi, Vasant; Lee, Gilbert; Santiago, Jaime

    2015-06-01

    Prediction of survivability of encapsulated electronic components subject to impact relies on accurate modeling. Both static and dynamic characterization of encapsulation material is needed to generate a robust material model. Current focus is on potting materials to mitigate high rate loading on impact. In this effort, encapsulation scheme consists of layers of polymeric material Sylgard 184 and Triggerbond Epoxy-20-3001. Experiments conducted for characterization of materials include conventional tension and compression tests, Hopkinson bar, dynamic material analyzer (DMA) and a non-conventional accelerometer based resonance tests for obtaining high frequency data. For an ideal material, data can be fitted to Williams-Landel-Ferry (WLF) model. A new temperature-time shift (TTS) macro was written to compare idealized temperature shift factor (WLF model) with experimental incremental shift factors. Deviations can be observed by comparison of experimental data with the model fit to determine the actual material behavior. Similarly, another macro written for obtaining Ogden model parameter from Hopkinson Bar tests indicates deviations from experimental high strain rate data. In this paper, experimental results for different materials used for mitigating impact, and ways to combine data from resonance, DMA and Hopkinson bar together with modeling refinements will be presented.

  2. ADVANCED ELECTRIC AND MAGNETIC MATERIAL MODELS FOR FDTD ELECTROMAGNETIC CODES

    SciTech Connect

    Poole, B R; Nelson, S D; Langdon, S

    2005-05-05

    The modeling of dielectric and magnetic materials in the time domain is required for pulse power applications, pulsed induction accelerators, and advanced transmission lines. For example, most induction accelerator modules require the use of magnetic materials to provide adequate Volt-sec during the acceleration pulse. These models require hysteresis and saturation to simulate the saturation wavefront in a multipulse environment. In high voltage transmission line applications such as shock or soliton lines the dielectric is operating in a highly nonlinear regime, which require nonlinear models. Simple 1-D models are developed for fast parameterization of transmission line structures. In the case of nonlinear dielectrics, a simple analytic model describing the permittivity in terms of electric field is used in a 3-D finite difference time domain code (FDTD). In the case of magnetic materials, both rate independent and rate dependent Hodgdon magnetic material models have been implemented into 3-D FDTD codes and 1-D codes.

  3. Shock Propagation Modeling in Heterogeneous Materials

    NASA Astrophysics Data System (ADS)

    Haill, Thomas

    2013-06-01

    Shock compression of foams is an intriguing research area that challenges our abilities to model experiments using computer simulations that span 9 orders of magnitude in spatial scales from the atomistic scale through the mesoscale and up to the continuum levels. Experiments test shock compression of dense polymers, polymer foams, and high-Z doped foams. Random distributions of polymer fibers, variations in pore size, and non-uniformities in the bulk properties of the foam (such as mean density) lead to spread in the experimental data. Adding dopants to foams introduces new complexities and the effect of the distribution and sizes of dopant particles must be characterized and understood. Therefore we turn to computer simulation to illumine the intricacies of the experiments that cannot be directly measured. This paper overviews of our range of methods to model pure and platinum-doped poly-methyl-pentene (PMP) foams. At the nanometer scale, hydrodynamic simulations compare favorably to classical molecular dynamics (MD) simulations of porous foams, verifying models of foam vaporization under strong shock conditions. Inhomogeneous mesoscale and homogenized continuum simulations present contrasting pictures of shocked foams. Mesoscale simulations at the micron scale have diffuse shock widths that depend upon the pore size, and post-shock vorticity results in fluctuations about the mean post-shock state and lower mean pressures and temperatures. Homogenized simulations, in the limit of zero pore size, have narrow shock widths, steady post-shock states, and higher mean pressures and temperature that compare favorably with 1D analysis of experiments. We reconcile the contrasting mesoscale and continuum views using theoretical turbulent corrections to the Hugoniot jump condition to show a consistent picture of shocked foams over 9 orders of spatial scale. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned

  4. Process modelling for materials preparation experiments

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Alexander, J. Iwan D.

    1992-01-01

    The development is examined of mathematical tools and measurement of transport properties necessary for high fidelity modeling of crystal growth from the melt and solution, in particular for the Bridgman-Stockbarger growth of mercury cadmium telluride (MCT) and the solution growth of triglycine sulphate (TGS). The tasks include development of a spectral code for moving boundary problems, kinematic viscosity measurements on liquid MCT at temperatures close to the melting point, and diffusivity measurements on concentrated and supersaturated TGS solutions. A detailed description is given of the work performed for these tasks, together with a summary of the resulting publications and presentations.

  5. Process modelling for materials preparation experiments

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Alexander, J. Iwan D.

    1993-01-01

    The main goals of the research consist of the development of mathematical tools and measurement of transport properties necessary for high fidelity modeling of crystal growth from the melt and solution, in particular for the Bridgman-Stockbarger growth of mercury cadmium telluride (MCT) and the solution growth of triglycine sulphate (TGS). Of the tasks described in detail in the original proposal, two remain to be worked on: development of a spectral code for moving boundary problems, and diffusivity measurements on concentrated and supersaturated TGS solutions. During this eighth half-year period, good progress was made on these tasks.

  6. Process modelling for materials preparation experiments

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Alexander, J. Iwan D.

    1993-01-01

    The main goals of the research under this grant consist of the development of mathematical tools and measurement of transport properties necessary for high fidelity modeling of crystal growth from the melt and solution, in particular, for the Bridgman-Stockbarger growth of mercury cadmium telluride (MCT) and the solution growth of triglycine sulphate (TGS). Of the tasks described in detail in the original proposal, two remain to be worked on: (1) development of a spectral code for moving boundary problems; and (2) diffusivity measurements on concentrated and supersaturated TGS solutions. Progress made during this seventh half-year period is reported.

  7. Quality Assurance Model for Digital Adult Education Materials

    ERIC Educational Resources Information Center

    Dimou, Helen; Kameas, Achilles

    2016-01-01

    Purpose: This paper aims to present a model for the quality assurance of digital educational material that is appropriate for adult education. The proposed model adopts the software quality standard ISO/IEC 9126 and takes into account adult learning theories, Bloom's taxonomy of learning objectives and two instructional design models: Kolb's model…

  8. Quality Assurance Model for Digital Adult Education Materials

    ERIC Educational Resources Information Center

    Dimou, Helen; Kameas, Achilles

    2016-01-01

    Purpose: This paper aims to present a model for the quality assurance of digital educational material that is appropriate for adult education. The proposed model adopts the software quality standard ISO/IEC 9126 and takes into account adult learning theories, Bloom's taxonomy of learning objectives and two instructional design models: Kolb's model…

  9. Generating Finite-Element Models Of Composite Materials

    NASA Technical Reports Server (NTRS)

    Melis, M. E.

    1993-01-01

    Program starts at micromechanical level, from simple inputs supplied by user. COMGEN, COmposite Model GENerator, is interactive FORTRAN program used to create wide variety of finite-element models of continuous-fiber composite materials at micromechanical level. Quickly generates batch or "session files" to be submitted to finite-element preprocessor and postprocessor program, PATRAN. COMGEN requires PATRAN to complete model.

  10. Numerical Modeling for Combustion of Thermoplastic Materials in Microgravity

    NASA Technical Reports Server (NTRS)

    Butler, Kathryn M.

    1997-01-01

    A time-dependent, three-dimensional model is under development to predict the temperature field, burning rate, and bubble bursting characteristics of burning thermoplastic materials in microgravity. Model results will be compared with experiments performed under microgravity and normal gravity conditions. The model will then be used to study the effects of variations in material properties and combustion conditions on burning rate and combustion behavior.

  11. Compendium of Material Composition Data for Radiation Transport Modeling

    SciTech Connect

    Williams, Ralph G.; Gesh, Christopher J.; Pagh, Richard T.

    2006-10-31

    Computational modeling of radiation transport problems including homeland security, radiation shielding and protection, and criticality safety all depend upon material definitions. This document has been created to serve two purposes: 1) to provide a quick reference of material compositions for analysts and 2) a standardized reference to reduce the differences between results from two independent analysts. Analysts are always encountering a variety of materials for which elemental definitions are not readily available or densities are not defined. This document provides a location where unique or hard to define materials will be located to reduce duplication in research for modeling purposes. Additionally, having a common set of material definitions helps to standardize modeling across PNNL and provide two separate researchers the ability to compare different modeling results from a common materials basis.

  12. Design, Fabrication, Characterization and Modeling of Integrated Functional Materials

    DTIC Science & Technology

    2015-12-01

    Award Number: W81XWH-10-2-0101 TITLE: Design, Fabrication, Characterization and Modeling of Integrated Functional Materials PRINCIPAL INVESTIGATOR...SUBTITLE Design, Fabrication, Characterization and Modeling of Integrated Functional Materials 5a. CONTRACT NUMBER W81XWH-10-2-0101 5c. PROGRAM...mobile refrigeration. These technological advances are critically dependent on the development of new and currently non-existing materials . This

  13. Modeling of radiative - conductive heat transfer in compositing materials

    NASA Astrophysics Data System (ADS)

    Luchnikov, P. A.; Nefedov, V. I.; Trefilov, N. A.; Dementiev, A. N.; Surzhikov, A. P.

    2017-01-01

    A layer of composite material is investigated, which is heated one-sidedly with one-dimensional energy transfer accounting for thermal conductivity and radiation. A mathematical model is suggested for non-stationary coefficient thermophysical problem under radiative-conductive heat transfer in a material layer. Temperature dependencies of thermal capacity and thermal conductivity coefficient of composite radio-transparent material have been determined through numerical modeling by solving the coefficient reverse problem of thermal conductivity.

  14. Course Material Model in A&O Learning Environment.

    ERIC Educational Resources Information Center

    Levasma, Jarkko; Nykanen, Ossi

    One of the problematic issues in the content development for learning environments is the process of importing various types of course material into the environment. This paper describes a method for importing material into the A&O open learning environment by introducing a material model for metadata recognized by the environment. The first…

  15. Waste Reduction Model (WARM) Material Descriptions and Data Sources

    EPA Pesticide Factsheets

    This page provides a summary of the materials included in EPA’s Waste Reduction Model (WARM). The page includes a list of materials, a description of the material as defined in the primary data source, and citations for primary data sources.

  16. Dynamic characterization and modeling of potting materials for electronics assemblies

    NASA Astrophysics Data System (ADS)

    Joshi, Vasant S.; Lee, Gilbert F.; Santiago, Jaime R.

    2017-01-01

    Prediction of survivability of encapsulated electronic components subject to impact relies on accurate modeling, which in turn needs both static and dynamic characterization of individual electronic components and encapsulation material to generate reliable material parameters for a robust material model. Current focus is on potting materials to mitigate high rate loading on impact. In this effort, difficulty arises in capturing one of the critical features characteristic of the loading environment in a high velocity impact: multiple loading events coupled with multi-axial stress states. Hence, potting materials need to be characterized well to understand its damping capacity at different frequencies and strain rates. An encapsulation scheme to protect electronic boards consists of multiple layers of filled as well as unfilled polymeric materials like Sylgard 184 and Trigger bond Epoxy # 20-3001. A combination of experiments conducted for characterization of materials used Split Hopkinson Pressure Bar (SHPB), and dynamic material analyzer (DMA). For material which behaves in an ideal manner, a master curve can be fitted to Williams-Landel-Ferry (WLF) model. To verify the applicability of WLF model, a new temperature-time shift (TTS) macro was written to compare idealized temperature shift factor with experimental incremental shift factor. Deviations can be readily observed by comparison of experimental data with the model fit to determine if model parameters reflect the actual material behavior. Similarly, another macro written for obtaining Ogden model parameter from Hopkinson Bar tests can readily indicate deviations from experimental high strain rate data. Experimental results for different materials used for mitigating impact, and ways to combine data from DMA and Hopkinson bar together with modeling refinements are presented.

  17. Constitutive modeling of viscoplastic damage in solder material

    SciTech Connect

    WEI,YONG; CHOW,C.L.; NEILSEN,MICHAEL K.; FANG,HUEI ELIOT

    2000-04-17

    This paper presents a constitutive modeling of viscoplastic damage in 63Sn-37Pb solder material taking into account the effects of microstructural change in grain coarsening. Based on the theory of damage mechanics, a two-scalar damage model is developed by introducing the damage variables and the free energy equivalence principle. An inelastic potential function based on the concept of inelastic damage energy release rate is proposed and used to derive an inelastic damage evolution equation. The validation of the model is carried out for the viscoplastic material by predicting monotonic tensile behavior and tensile creep curves at different temperatures. The softening behavior of the material under monotonic tension loading can be characterized with the model. The results demonstrate adequately the validity of the proposed viscoplastic constitutive modeling for the solder material.

  18. Calibrating the Abaqus Crushable Foam Material Model using UNM Data

    SciTech Connect

    Schembri, Philip E.; Lewis, Matthew W.

    2014-02-27

    Triaxial test data from the University of New Mexico and uniaxial test data from W-14 is used to calibrate the Abaqus crushable foam material model to represent the syntactic foam comprised of APO-BMI matrix and carbon microballoons used in the W76. The material model is an elasto-plasticity model in which the yield strength depends on pressure. Both the elastic properties and the yield stress are estimated by fitting a line to the elastic region of each test response. The model parameters are fit to the data (in a non-rigorous way) to provide both a conservative and not-conservative material model. The model is verified to perform as intended by comparing the values of pressure and shear stress at yield, as well as the shear and volumetric stress-strain response, to the test data.

  19. Interatomic Potential Models for Ionic Materials

    NASA Astrophysics Data System (ADS)

    Gale, Julian D.

    Ionic materials are present in many key technological applications of the modern era, from solid state batteries and fuel cells, nuclear waste immobiliza tion, through to industrial heterogeneous catalysis, such as that found in automotive exhaust systems. With the boundless possibilities for their utilization, it is natural that there has been a long history of computer simulation of their structure and properties in order to understand the materials science of these systems at the atomic level.

  20. Modelling cohesive, frictional and viscoplastic materials

    NASA Astrophysics Data System (ADS)

    Alehossein, Habib; Qin, Zongyi

    2016-06-01

    Most materials in mining and civil engineering construction are not only viscoplastic, but also cohesive frictional. Fresh concrete, fly ash and mining slurries are all granular-frictional-visco-plastic fluids, although solid concrete is normally considered as a cohesive frictional material. Presented here is both a formulation of the pipe and disc flow rates as a function of pressure and pressure gradient and the CFD application to fresh concrete flow in L-Box tests.

  1. Modeling the dynamic crush of impact mitigating materials

    SciTech Connect

    Logan, R.W.; McMichael, L.D.

    1995-05-12

    Crushable materials are commonly utilized in the design of structural components to absorb energy and mitigate shock during the dynamic impact of a complex structure, such as an automobile chassis or drum-type shipping container. The development and application of several finite-element material models which have been developed at various times at LLNL for DYNA3D will be discussed. Between the models, they are able to account for several of the predominant mechanisms which typically influence the dynamic mechanical behavior of crushable materials. One issue we addressed was that no single existing model would account for the entire gambit of constitutive features which are important for crushable materials. Thus, we describe the implementation and use of an additional material model which attempts to provide a more comprehensive model of the mechanics of crushable material behavior. This model combines features of the pre-existing DYNA models and incorporates some new features as well in an invariant large-strain formulation. In addition to examining the behavior of a unit cell in uniaxial compression, two cases were chosen to evaluate the capabilities and accuracy of the various material models in DYNA. In the first case, a model for foam filled box beams was developed and compared to test data from a 4-point bend test. The model was subsequently used to study its effectiveness in energy absorption in an aluminum extrusion, spaceframe, vehicle chassis. The second case examined the response of the AT-400A shipping container and the performance of the overpack material during accident environments selected from 10CFR71 and IAEA regulations.

  2. Research on infrared imaging illumination model based on materials

    NASA Astrophysics Data System (ADS)

    Hu, Hai-he; Feng, Chao-yin; Guo, Chang-geng; Zheng, Hai-jing; Han, Qiang; Hu, Hai-yan

    2013-09-01

    In order to effectively simulate infrared features of the scene and infrared high light phenomenon, Based on the visual light illumination model, according to the optical property of all material types in the scene, the infrared imaging illumination models are proposed to fulfill different materials: to the smooth material with specular characteristic, adopting the infrared imaging illumination model based on Blinn-Phone reflection model and introducing the self emission; to the ordinary material which is similar to black body without highlight feature, ignoring the computation of its high light reflection feature, calculating simply the material's self emission and its reflection to the surrounding as its infrared imaging illumination model, the radiation energy under zero range of visibility can be obtained according to the above two models. The OpenGl rendering technology is used to construct infrared scene simulation system which can also simulate infrared electro-optical imaging system, then gets the synthetic infrared images from any angle of view of the 3D scenes. To validate the infrared imaging illumination model, two typical 3D scenes are made, and their infrared images are calculated to compare and contrast with the real collected infrared images obtained by a long wave infrared band imaging camera. There are two major points in the paper according to the experiment results: firstly, the infrared imaging illumination models are capable of producing infrared images which are very similar to those received by thermal infrared camera; secondly, the infrared imaging illumination models can simulate the infrared specular feature of relative materials and common infrared features of general materials, which shows the validation of the infrared imaging illumination models. Quantitative analysis shows that the simulation images are similar to the collected images in the aspects of main features, but their histogram distribution does not match very well, the

  3. User-Defined Material Model for Progressive Failure Analysis

    NASA Technical Reports Server (NTRS)

    Knight, Norman F. Jr.; Reeder, James R. (Technical Monitor)

    2006-01-01

    An overview of different types of composite material system architectures and a brief review of progressive failure material modeling methods used for structural analysis including failure initiation and material degradation are presented. Different failure initiation criteria and material degradation models are described that define progressive failure formulations. These progressive failure formulations are implemented in a user-defined material model (or UMAT) for use with the ABAQUS/Standard1 nonlinear finite element analysis tool. The failure initiation criteria include the maximum stress criteria, maximum strain criteria, the Tsai-Wu failure polynomial, and the Hashin criteria. The material degradation model is based on the ply-discounting approach where the local material constitutive coefficients are degraded. Applications and extensions of the progressive failure analysis material model address two-dimensional plate and shell finite elements and three-dimensional solid finite elements. Implementation details and use of the UMAT subroutine are described in the present paper. Parametric studies for composite structures are discussed to illustrate the features of the progressive failure modeling methods that have been implemented.

  4. Process modelling for materials preparation experiments

    NASA Technical Reports Server (NTRS)

    Rosenberger, Franz; Alexander, J. Iwan D.

    1994-01-01

    The main goals of the research under this grant consist of the development of mathematical tools and measurement techniques for transport properties necessary for high fidelity modelling of crystal growth from the melt and solution. Of the tasks described in detail in the original proposal, two remain to be worked on: development of a spectral code for moving boundary problems, and development of an expedient diffusivity measurement technique for concentrated and supersaturated solutions. We have focused on developing a code to solve for interface shape, heat and species transport during directional solidification. The work involved the computation of heat, mass and momentum transfer during Bridgman-Stockbarger solidification of compound semiconductors. Domain decomposition techniques and preconditioning methods were used in conjunction with Chebyshev spectral methods to accelerate convergence while retaining the high-order spectral accuracy. During the report period we have further improved our experimental setup. These improvements include: temperature control of the measurement cell to 0.1 C between 10 and 60 C; enclosure of the optical measurement path outside the ZYGO interferometer in a metal housing that is temperature controlled to the same temperature setting as the measurement cell; simultaneous dispensing and partial removal of the lower concentration (lighter) solution above the higher concentration (heavier) solution through independently motor-driven syringes; three-fold increase in data resolution by orientation of the interferometer with respect to diffusion direction; and increase of the optical path length in the solution cell to 12 mm.

  5. RADIOACTIVE MATERIALS IN BIOSOLIDS: DOSE MODELING

    EPA Science Inventory

    The Interagency Steering Committee on Radiation Standards (ISCORS) has recently completed a study of the occurrence within the United States of radioactive materials in sewage sludge and sewage incineration ash. One component of that effort was an examination of the possible tra...

  6. RADIOACTIVE MATERIALS IN BIOSOLIDS: DOSE MODELING

    EPA Science Inventory

    The Interagency Steering Committee on Radiation Standards (ISCORS) has recently completed a study of the occurrence within the United States of radioactive materials in sewage sludge and sewage incineration ash. One component of that effort was an examination of the possible tra...

  7. Developing Interactive Instructional Materials: A Model.

    ERIC Educational Resources Information Center

    Henderson, Craig; And Others

    Many colleges and departments at Tennessee Technological University, as well as most other major universities, are progressing toward more interactive instructional materials. The benefits of implementing instructional technology are numerous and diverse. However, because of increasingly austere budgets, a focused and cost-effective approach to…

  8. A generalized methodology to characterize composite materials for pyrolysis models

    NASA Astrophysics Data System (ADS)

    McKinnon, Mark B.

    The predictive capabilities of computational fire models have improved in recent years such that models have become an integral part of many research efforts. Models improve the understanding of the fire risk of materials and may decrease the number of expensive experiments required to assess the fire hazard of a specific material or designed space. A critical component of a predictive fire model is the pyrolysis sub-model that provides a mathematical representation of the rate of gaseous fuel production from condensed phase fuels given a heat flux incident to the material surface. The modern, comprehensive pyrolysis sub-models that are common today require the definition of many model parameters to accurately represent the physical description of materials that are ubiquitous in the built environment. Coupled with the increase in the number of parameters required to accurately represent the pyrolysis of materials is the increasing prevalence in the built environment of engineered composite materials that have never been measured or modeled. The motivation behind this project is to develop a systematic, generalized methodology to determine the requisite parameters to generate pyrolysis models with predictive capabilities for layered composite materials that are common in industrial and commercial applications. This methodology has been applied to four common composites in this work that exhibit a range of material structures and component materials. The methodology utilizes a multi-scale experimental approach in which each test is designed to isolate and determine a specific subset of the parameters required to define a material in the model. Data collected in simultaneous thermogravimetry and differential scanning calorimetry experiments were analyzed to determine the reaction kinetics, thermodynamic properties, and energetics of decomposition for each component of the composite. Data collected in microscale combustion calorimetry experiments were analyzed to

  9. A hydrodynamic model for granular material flows including segregation effects

    NASA Astrophysics Data System (ADS)

    Gilberg, Dominik; Klar, Axel; Steiner, Konrad

    2017-06-01

    The simulation of granular flows including segregation effects in large industrial processes using particle methods is accurate, but very time-consuming. To overcome the long computation times a macroscopic model is a natural choice. Therefore, we couple a mixture theory based segregation model to a hydrodynamic model of Navier-Stokes-type, describing the flow behavior of the granular material. The granular flow model is a hybrid model derived from kinetic theory and a soil mechanical approach to cover the regime of fast dilute flow, as well as slow dense flow, where the density of the granular material is close to the maximum packing density. Originally, the segregation model has been formulated by Thornton and Gray for idealized avalanches. It is modified and adapted to be in the preferred form for the coupling. In the final coupled model the segregation process depends on the local state of the granular system. On the other hand, the granular system changes as differently mixed regions of the granular material differ i.e. in the packing density. For the modeling process the focus lies on dry granular material flows of two particle types differing only in size but can be easily extended to arbitrary granular mixtures of different particle size and density. To solve the coupled system a finite volume approach is used. To test the model the rotational mixing of small and large particles in a tumbler is simulated.

  10. Material model validation for laser shock peening process simulation

    NASA Astrophysics Data System (ADS)

    Amarchinta, H. K.; Grandhi, R. V.; Langer, K.; Stargel, D. S.

    2009-01-01

    Advanced mechanical surface enhancement techniques have been used successfully to increase the fatigue life of metallic components. These techniques impart deep compressive residual stresses into the component to counter potentially damage-inducing tensile stresses generated under service loading. Laser shock peening (LSP) is an advanced mechanical surface enhancement technique used predominantly in the aircraft industry. To reduce costs and make the technique available on a large-scale basis for industrial applications, simulation of the LSP process is required. Accurate simulation of the LSP process is a challenging task, because the process has many parameters such as laser spot size, pressure profile and material model that must be precisely determined. This work focuses on investigating the appropriate material model that could be used in simulation and design. In the LSP process material is subjected to strain rates of 106 s-1, which is very high compared with conventional strain rates. The importance of an accurate material model increases because the material behaves significantly different at such high strain rates. This work investigates the effect of multiple nonlinear material models for representing the elastic-plastic behavior of materials. Elastic perfectly plastic, Johnson-Cook and Zerilli-Armstrong models are used, and the performance of each model is compared with available experimental results.

  11. Models for estimating organic emissions from building materials: Formaldehyde example

    NASA Astrophysics Data System (ADS)

    Hawthorne, Alan R.; Matthews, Thomas G.

    One important source of chronic exposure to low levels of organic compounds in the indoor environment is emissions from building materials. Because removal of offending products may be costly or otherwise impractical, it is important that the emissions of organic pollutants be understood prior to incorporation of these materials into buildings. Once the organic pollutants of concern are identified, based on potential health effects and emission potential from the building material, it is necessary that an emission model be developed to predict the behavior of emission rates under various indoor conditions. Examples of the type of requirements that must be addressed in developing models for estimating organic emissions from building materials into the indoor environment are presented. Important factors include the products' characteristic source strengths at standard test conditions, impact of variations in environmental conditions (such as temperature and humidity), concentrations of the modeled organic pollutants in indoor environments and product ages. Ideally, emission models should have physical/chemical bases so that the important physical factors can be identified and their relative importance quantified. Although a universal model describing organic emissions from all building materials may not be feasible due to the tremendous variety of organic products and building materials in use, the most studied of the volatile organic compounds from building materials, formaldehyde, is used to illustrate an approach to the development of a specific model for organic emissions.

  12. Modeling of sorption characteristics of backfill materials

    SciTech Connect

    Chitra, S.; Sasidhar, P.; Lal, K.B.; Ahmed, J.

    1998-06-01

    Sorption data analysis was carried out using the Freundlich, Langmuir, and Modified Freundlich isotherms for the uptake of sodium and potassium in an initial concentration range of 10--100 mg/L on backfill materials, viz., bentonite, vermiculite, and soil samples. The soil samples were collected from a shallow land disposal facility at Kalpakkam. The Freundlich isotherm equation is validated as a preferred general mathematical tool for representing the sorption of K{sup +} by all the selected backfill materials. The Modified Freundlich isotherm equation is validated as a preferred mathematical tool for representing the sorption of Na{sup +} by the soil samples. Since a negative sorption was observed for the uptake of Na{sup +} by commercial clay minerals (vermiculite and bentonite clay in the laboratory experiments), sorption analysis could not be carried out using the above-mentioned isotherm equations. Hill plots of the sorption data suggest that in the region of low saturation (10--40 mg/L), sorption of K{sup +} by vermiculite is impeded by interaction among sorption sites. In the region of higher saturation (60--100 mg/L), sorption of K{sup +} by all three backfill materials is enhanced by interaction among sorption sites. The Hill plot of the sorption data for Na{sup +} by soil suggests that irrespective of Na{sup +} concentration, sorption of Na{sup +} at one exchange size enhances sorption at other exchange sites.

  13. Material point method modeling in oil and gas reservoirs

    DOEpatents

    Vanderheyden, William Brian; Zhang, Duan

    2016-06-28

    A computer system and method of simulating the behavior of an oil and gas reservoir including changes in the margins of frangible solids. A system of equations including state equations such as momentum, and conservation laws such as mass conservation and volume fraction continuity, are defined and discretized for at least two phases in a modeled volume, one of which corresponds to frangible material. A material point model technique for numerically solving the system of discretized equations, to derive fluid flow at each of a plurality of mesh nodes in the modeled volume, and the velocity of at each of a plurality of particles representing the frangible material in the modeled volume. A time-splitting technique improves the computational efficiency of the simulation while maintaining accuracy on the deformation scale. The method can be applied to derive accurate upscaled model equations for larger volume scale simulations.

  14. A Model Framework for Science and Other Course Materials Construction.

    ERIC Educational Resources Information Center

    Schlenker, Richard M.

    A model is presented to provide guidance for Coast Guard writers, curriculum developers, course coordinators, and instructors who intend to update, or draft course materials. Detailed instructions are provided for developing instructor's guides and student's guides. (CS)

  15. A Model Framework for Science and Other Course Materials Construction.

    ERIC Educational Resources Information Center

    Schlenker, Richard M.

    A model is presented to provide guidance for Coast Guard writers, curriculum developers, course coordinators, and instructors who intend to update, or draft course materials. Detailed instructions are provided for developing instructor's guides and student's guides. (CS)

  16. Material Characterization and Modeling for Industrial Sheet Forming Simulations

    NASA Astrophysics Data System (ADS)

    Mattiasson, Kjell; Sigvant, Mats

    2004-06-01

    In the present paper a project carried out at Volvo Cars Corp. and Chalmers University of Technology, with the purpose of improving material characterization and modeling for sheet forming simulation, is described. One of the primary targets has been to identify a material testing procedure, which is capable of providing effective stress-strain data at considerably larger strains than what can be achieved in a standard uniaxial tensile test. Another objective has been to advance from the common Hill '48 material model to a more flexible one, and, furthermore, to identify suitable test procedures for determining the parameters of such a model. A third objective has been to find practical examples, in which the importance of a careful material modeling can be clearly demonstrated.

  17. Mathematical and Numerical Analyses of Peridynamics for Multiscale Materials Modeling

    SciTech Connect

    Du, Qiang

    2014-11-12

    The rational design of materials, the development of accurate and efficient material simulation algorithms, and the determination of the response of materials to environments and loads occurring in practice all require an understanding of mechanics at disparate spatial and temporal scales. The project addresses mathematical and numerical analyses for material problems for which relevant scales range from those usually treated by molecular dynamics all the way up to those most often treated by classical elasticity. The prevalent approach towards developing a multiscale material model couples two or more well known models, e.g., molecular dynamics and classical elasticity, each of which is useful at a different scale, creating a multiscale multi-model. However, the challenges behind such a coupling are formidable and largely arise because the atomistic and continuum models employ nonlocal and local models of force, respectively. The project focuses on a multiscale analysis of the peridynamics materials model. Peridynamics can be used as a transition between molecular dynamics and classical elasticity so that the difficulties encountered when directly coupling those two models are mitigated. In addition, in some situations, peridynamics can be used all by itself as a material model that accurately and efficiently captures the behavior of materials over a wide range of spatial and temporal scales. Peridynamics is well suited to these purposes because it employs a nonlocal model of force, analogous to that of molecular dynamics; furthermore, at sufficiently large length scales and assuming smooth deformation, peridynamics can be approximated by classical elasticity. The project will extend the emerging mathematical and numerical analysis of peridynamics. One goal is to develop a peridynamics-enabled multiscale multi-model that potentially provides a new and more extensive mathematical basis for coupling classical elasticity and molecular dynamics, thus enabling next

  18. Mechanical Constitutive Models for Engineering Materials

    DTIC Science & Technology

    1977-09-01

    peruendicular to the yield surface at point C. Drucker - Prager material 138. The Von Mises yield condition was modified by Drucker and Prager12 to include the...Substituting Equation 500 mu2 il @ / I // I oli IC’ Figure 19. Drucker - Prager yield surface in principal stress space ! ! into Equation 469 we obtain the...following stress-strain relationship associated with the Drucker - Prager yield function dS- WdE / iG G d~ de +21 ij 2G 9K ij + + G x ( f e1ij) (501) From

  19. Validation Testing and Numerical Modeling of Advanced Armor Materials

    DTIC Science & Technology

    2012-11-01

    constitutive material strength response with an appropriate yield surface model. The research is sub-divided into three areas: engineering design...and specimen preparation for Taylor impact testing, analytical solution for the dynamic yield strength of the materials used, and numerical modeling...aluminum alloy only. We perform a detailed analysis of the deformed specimen shapes to determine the dynamic yield strength . Additionally, hydrocode

  20. Strain Rate Dependant Material Model for Orthotropic Metals

    NASA Astrophysics Data System (ADS)

    Vignjevic, Rade

    2016-08-01

    In manufacturing processes anisotropic metals are often exposed to the loading with high strain rates in the range from 102 s-1 to 106 s-1 (e.g. stamping, cold spraying and explosive forming). These types of loading often involve generation and propagation of shock waves within the material. The material behaviour under such a complex loading needs to be accurately modelled, in order to optimise the manufacturing process and achieve appropriate properties of the manufactured component. The presented research is related to development and validation of a thermodynamically consistent physically based constitutive model for metals under high rate loading. The model is capable of modelling damage, failure and formation and propagation of shock waves in anisotropic metals. The model has two main parts: the strength part which defines the material response to shear deformation and an equation of state (EOS) which defines the material response to isotropic volumetric deformation [1]. The constitutive model was implemented into the transient nonlinear finite element code DYNA3D [2] and our in house SPH code. Limited model validation was performed by simulating a number of high velocity material characterisation and validation impact tests. The new damage model was developed in the framework of configurational continuum mechanics and irreversible thermodynamics with internal state variables. The use of the multiplicative decomposition of deformation gradient makes the model applicable to arbitrary plastic and damage deformations. To account for the physical mechanisms of failure, the concept of thermally activated damage initially proposed by Tuller and Bucher [3], Klepaczko [4] was adopted as the basis for the new damage evolution model. This makes the proposed damage/failure model compatible with the Mechanical Threshold Strength (MTS) model Follansbee and Kocks [5], 1988; Chen and Gray [6] which was used to control evolution of flow stress during plastic deformation. In

  1. 3D microstructure modeling of compressed fiber-based materials

    NASA Astrophysics Data System (ADS)

    Gaiselmann, Gerd; Tötzke, Christian; Manke, Ingo; Lehnert, Werner; Schmidt, Volker

    2014-07-01

    A novel parametrized model that describes the 3D microstructure of compressed fiber-based materials is introduced. It allows to virtually generate the microstructure of realistically compressed gas-diffusion layers (GDL). Given the input of a 3D microstructure of some fiber-based material, the model compresses the system of fibers in a uniaxial direction for arbitrary compression rates. The basic idea is to translate the fibers in the direction of compression according to a vector field which depends on the rate of compression and on the locations of fibers within the material. In order to apply the model to experimental 3D image data of fiber-based materials given for several compression states, an optimal vector field is estimated by simulated annealing. The model is applied to 3D image data of non-woven GDL in PEMFC gained by synchrotron tomography for different compression rates. The compression model is validated by comparing structural characteristics computed for experimentally compressed and virtually compressed microstructures, where two kinds of compression - using a flat stamp and a stamp with a flow-field profile - are applied. For both stamps types, a good agreement is found. Furthermore, the compression model is combined with a stochastic 3D microstructure model for uncompressed fiber-based materials. This allows to efficiently generate compressed fiber-based microstructures in arbitrary volumes.

  2. A bespoke single-band Hubbard model material

    NASA Astrophysics Data System (ADS)

    Griffin, S. M.; Staar, P.; Schulthess, T. C.; Troyer, M.; Spaldin, N. A.

    2016-02-01

    The Hubbard model, which augments independent-electron band theory with a single parameter to describe electron-electron correlations, is widely regarded to be the "standard model" of condensed-matter physics. The model has been remarkably successful at addressing a range of correlation phenomena in solids, but it neglects many behaviors that occur in real materials, such as phonons, long-range interactions, and, in its simplest form, multiorbital effects. Here, we use ab initio electronic structure methods to design a material whose Hamiltonian matches as closely as possible that of the single-band Hubbard model. Our motivation is to compare the measured properties of our new material to those predicted by reliable theoretical solutions of the Hubbard model to determine the relevance of the model in the description of real materials. After identifying an appropriate crystal class and several appropriate chemistries, we use density-functional theory and dynamical mean-field theory to screen for the desired electronic band structure and metal-insulator transition. We then explore the most promising candidates for structural stability and suitability for doping, and we propose specific materials for subsequent synthesis. Finally, we identify a regime—that should manifest in our bespoke material—in which the single-band Hubbard model on a triangular lattice exhibits exotic d -wave superconductivity.

  3. A Model for Heterogeneous Materials Undergoing Phase Transitions

    NASA Astrophysics Data System (ADS)

    Plohr, Jeeyeon

    2005-03-01

    We develop a macroscopic model for a heterogeneous material undergoing a phase transition. Such a continuum-level material model, which is needed in practical engineering calculations, must faithfully reflect the micromechanical response of the constituent materials. Using the method of cells, which is a homogenization technique, we derive the constitutive properties of a composite material, part of which undergoes a phase transition. Specifically, we study tungsten heavy alloy (WHA), in which tungsten grains are dispersed within a low-melting-temperature alloy matrix. This material has desirable static properties as a penetrator, but melting in the matrix occurs during loading. Simulations with our model predicts the properties of WHA with different compositions, which can then be optimized.

  4. Crashworthiness analysis using advanced material models in DYNA3D

    SciTech Connect

    Logan, R.W.; Burger, M.J.; McMichael, L.D.; Parkinson, R.D.

    1993-10-22

    As part of an electric vehicle consortium, LLNL and Kaiser Aluminum are conducting experimental and numerical studies on crashworthy aluminum spaceframe designs. They have jointly explored the effect of heat treat on crush behavior and duplicated the experimental behavior with finite-element simulations. The major technical contributions to the state of the art in numerical simulation arise from the development and use of advanced material model descriptions for LLNL`s DYNA3D code. Constitutive model enhancements in both flow and failure have been employed for conventional materials such as low-carbon steels, and also for lighter weight materials such as aluminum and fiber composites being considered for future vehicles. The constitutive model enhancements are developed as extensions from LLNL`s work in anisotropic flow and multiaxial failure modeling. Analysis quality as a function of level of simplification of material behavior and mesh is explored, as well as the penalty in computation cost that must be paid for using more complex models and meshes. The lightweight material modeling technology is being used at the vehicle component level to explore the safety implications of small neighborhood electric vehicles manufactured almost exclusively from these materials.

  5. A Model Framework for Course Materials Construction. Third Edition.

    ERIC Educational Resources Information Center

    Schlenker, Richard M.

    A model framework for course materials construction is presented as an aid to Coast Guard course writers and coordinators, curriculum developers, and instructors who must modify a course or draft a new one. The model assumes that the instructor or other designated person has: (1) completed a task analysis which identifies the competencies, skills…

  6. A Model Framework for Course Materials Construction (Second Edition).

    ERIC Educational Resources Information Center

    Schlenker, Richard M.

    Designed for use by Coast Guard course writers, curriculum developers, course coordinators, and instructors as a decision-support system, this publication presents a model that translates the Intraservices Procedures for Instructional Systems Development curriculum design model into materials usable by classroom teachers and students. Although…

  7. Multi-Scale Modeling of Cementitious Materials (Briefing Chart)

    DTIC Science & Technology

    2014-08-31

    FEA approach. Voxels are generated for a heterogeneous cementitious material (Type-I cement ) consisting of typical volume fractions of various...for public release; distribution is unlimited. Micromechanics Based Representative Volume Element Modeling of Heterogeneous Cement Paste The views...P.O. Box 12211 Research Triangle Park, NC 27709-2211 cement paste, microstructure, RVE modeling, micromechanics REPORT DOCUMENTATION PAGE 11. SPONSOR

  8. On the Thermal Model of Transverse Flow of Unidirectional Materials

    NASA Technical Reports Server (NTRS)

    Tai, Hsiang

    2002-01-01

    The thermal model for transverse heat flow of having single filament in a unit cell is extended. In this model, we proposed that two circular filaments in a unit cell of square packing array and obtained the transverse thermal conductivity of an unidirectional material.

  9. A Model Framework for Course Materials Construction. Third Edition.

    ERIC Educational Resources Information Center

    Schlenker, Richard M.

    A model framework for course materials construction is presented as an aid to Coast Guard course writers and coordinators, curriculum developers, and instructors who must modify a course or draft a new one. The model assumes that the instructor or other designated person has: (1) completed a task analysis which identifies the competencies, skills…

  10. Learning to Apply Models of Materials While Explaining Their Properties

    ERIC Educational Resources Information Center

    Karpin, Tiia; Juuti, Kalle; Lavonen, Jari

    2014-01-01

    Background: Applying structural models is important to chemistry education at the upper secondary level, but it is considered one of the most difficult topics to learn. Purpose: This study analyses to what extent in designed lessons students learned to apply structural models in explaining the properties and behaviours of various materials.…

  11. Stochastic Modeling of Radioactive Material Releases

    SciTech Connect

    Andrus, Jason; Pope, Chad

    2015-09-01

    Nonreactor nuclear facilities operated under the approval authority of the U.S. Department of Energy use unmitigated hazard evaluations to determine if potential radiological doses associated with design basis events challenge or exceed dose evaluation guidelines. Unmitigated design basis events that sufficiently challenge dose evaluation guidelines or exceed the guidelines for members of the public or workers, merit selection of safety structures, systems, or components or other controls to prevent or mitigate the hazard. Idaho State University, in collaboration with Idaho National Laboratory, has developed a portable and simple to use software application called SODA (Stochastic Objective Decision-Aide) that stochastically calculates the radiation dose associated with hypothetical radiological material release scenarios. Rather than producing a point estimate of the dose, SODA produces a dose distribution result to allow a deeper understanding of the dose potential. SODA allows users to select the distribution type and parameter values for all of the input variables used to perform the dose calculation. SODA then randomly samples each distribution input variable and calculates the overall resulting dose distribution. In cases where an input variable distribution is unknown, a traditional single point value can be used. SODA was developed using the MATLAB coding framework. The software application has a graphical user input. SODA can be installed on both Windows and Mac computers and does not require MATLAB to function. SODA provides improved risk understanding leading to better informed decision making associated with establishing nuclear facility material-at-risk limits and safety structure, system, or component selection. It is important to note that SODA does not replace or compete with codes such as MACCS or RSAC, rather it is viewed as an easy to use supplemental tool to help improve risk understanding and support better informed decisions. The work was

  12. Probabilistic constitutive relationships for cyclic material strength models

    NASA Technical Reports Server (NTRS)

    Boyce, L.; Chamis, C. C.

    1988-01-01

    A methodology is developed that provides a probabilistic treatment for the lifetime of structural components of aerospace propulsion systems subjected to fatigue. Material strength degradation models, based on primitive variables, include both a fatigue strength reduction model and a fatigue crack growth model. Probabilistic analysis is based on simulation, and both maximum entropy and maximum penalized likelihood methods are used for the generation of probability density functions. The resulting constitutive relationships are included in several computer programs.

  13. Models of material ejection. [of solar coronal mass

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.

    1990-01-01

    Some recently developed models related to the formation of a coronal mass ejection (CME) are reviewed. The models individually consider the stability of a prominence, the eruption of a coupled prominence and CME configuration with driven reconnection below the prominence, magnetic arcade equilibrium, and coronal evolution due to shear motion. No effort is made to critique the various models. Their relevance to actual observed material ejections will ultimately be determined by detailed comparison with present and future observations.

  14. A model of material flow during friction stir welding

    SciTech Connect

    Hamilton, Carter Dymek, Stanislaw; Blicharski, Marek

    2008-09-15

    Tin plated 6061-T6 aluminum extrusions were friction stir welded in a 90 deg. butt-weld configuration. A banded microstructure of interleaved layers of particle-rich and particle-poor material comprised the weld nugget. Scanning and transmission electron microscopy revealed the strong presence of tin within the particle-rich bands, but TEM foils taken from the TMAZ, HAZ and base material showed no indication of Sn-containing phases. Since tin is limited to the surface of the pre-weld extrusions, surface material flowed into the nugget region, forming the particle-rich bands. Similarly, the particle-poor bands with no tin originated from within the thickness of the extrusions. A model of material flow during friction stir welding is proposed for which the weld nugget forms as surface material extrudes from the retreating side into a plasticized zone surrounding the FSW pin. The extruded column buckles between the extrusion force driving the material into the zone and the drag force of the in-situ material resisting its entry. A banded microstructure of interleaved surface material and in-situ material, therefore, develops. The model successfully describes several of the experimentally observed weld characteristics, but the model is limited to specific conditions of material flow and assumptions regarding steady-state.

  15. A continuum theory for modeling the dynamics of crystalline materials.

    PubMed

    Xiong, Liming; Chen, Youping; Lee, James D

    2009-02-01

    This paper introduces a multiscale field theory for modeling and simulation of the dynamics of crystalline materials. The atomistic formulation of a multiscale field theory is briefly introduced. Its applicability is discussed. A few application examples, including phonon dispersion relations of ferroelectric materials BiScO3 and MgO nano dot under compression are presented.

  16. Modeling of porous elastic viscoplastic material with tensile failure

    SciTech Connect

    Glenn, L A; Rubin, M; Vorobiev, O

    1998-11-01

    This work describes simple but comprehensive constitutive equations that model a number of physical phenomena exhibited by dry porous geological materials and metals. Moreover, formulas have been developed for robust numerical integration of the evolution equations at the element level that can be easily implemented into standard computer programs for dynamic response of materials.

  17. A perspective on modeling the multiscale response of energetic materials

    NASA Astrophysics Data System (ADS)

    Rice, Betsy M.

    2017-01-01

    The response of an energetic material to insult is perhaps one of the most difficult processes to model due to concurrent chemical and physical phenomena occurring over scales ranging from atomistic to continuum. Unraveling the interdependencies of these complex processes across the scales through modeling can only be done within a multiscale framework. In this paper, I will describe progress in the development of a predictive, experimentally validated multiscale reactive modeling capability for energetic materials at the Army Research Laboratory. I will also describe new challenges and research opportunities that have arisen in the course of our development which should be pursued in the future.

  18. Breaking of rod-shaped model material during compression

    NASA Astrophysics Data System (ADS)

    Lukas, Kulaviak; Vera, Penkavova; Marek, Ruzicka; Miroslav, Puncochar; Petr, Zamostny; Zdenek, Grof; Frantisek, Stepanek; Marek, Schongut; Jaromir, Havlica

    2017-06-01

    The breakage of a model anisometric dry granular material caused by uniaxial compression was studied. The bed of uniform rod-like pasta particles (8 mm long, aspect ratio 1:8) was compressed (Gamlen Tablet Press) and their size distribution was measured after each run (Dynamic Image Analysing). The compression dynamics was recorded and the effect of several parameters was tested (rate of compression, volume of granular bed, pressure magnitude and mode of application). Besides the experiments, numerical modelling of the compressed breakable material was performed as well, employing the DEM approach (Discrete Element Method). The comparison between the data and the model looks promising.

  19. Influence of Material Models Used in Finite Element Modeling on Cutting Forces in Machining

    NASA Astrophysics Data System (ADS)

    Jivishov, Vusal; Rzayev, Elchin

    2016-08-01

    Finite element modeling of machining is significantly influenced by various modeling input parameters such as boundary conditions, mesh size and distribution, as well as properties of workpiece and tool materials. The flow stress model of the workpiece material is the most critical input parameter. However, it is very difficult to obtain experimental values under the same conditions as in machining operations.. This paper analyses the influence of different material models for two steels (AISI 1045 and hardened AISI 52100) in finite element modelling of cutting forces. In this study, the machining process is scaled by a constant ratio of the variable depth of cut h and cutting edge radius rβ. The simulation results are compared with experimental measurements. This comparison illustrates some of the capabilities and limitations of FEM modelling.

  20. Vector Preisach modeling of magnetic materials under stress

    NASA Astrophysics Data System (ADS)

    Ktena, A.

    2015-02-01

    The Preisach formalism is used to model magnetic hysteresis loops in soft magnetic materials subject to tensile stress. The model uses the Stoner-Wohlfarth mechanism of coherent rotation and dispersion of easy axes to capture the vector response of the magnetization. The Preisach density is constructed as the weighed sum of normal probability density functions (pdf) for the regions of high and low induction. The model parameters reflect the effect of strain: increased pinning, modelled by the central pdf parameters; enhanced anisotropy dispersion modelled by the angular dispersion of easy axes. Upon removal of the tensile stress, compressive residual stresses give rise to effective demagnetizing fields leading to lower differential permeability with a two-peak profile. As deformation levels increase, the amplitude of and the relative distance between the two permeability peaks changes which is reflected in the side density parameters. Modelling results are in qualitative agreement with the experimental data. The potential and limitations of the model are discussed.

  1. The Constitutive Modeling of Thin Films with Randon Material Wrinkles

    NASA Technical Reports Server (NTRS)

    Murphey, Thomas W.; Mikulas, Martin M.

    2001-01-01

    Material wrinkles drastically alter the structural constitutive properties of thin films. Normally linear elastic materials, when wrinkled, become highly nonlinear and initially inelastic. Stiffness' reduced by 99% and negative Poisson's ratios are typically observed. This paper presents an effective continuum constitutive model for the elastic effects of material wrinkles in thin films. The model considers general two-dimensional stress and strain states (simultaneous bi-axial and shear stress/strain) and neglects out of plane bending. The constitutive model is derived from a traditional mechanics analysis of an idealized physical model of random material wrinkles. Model parameters are the directly measurable wrinkle characteristics of amplitude and wavelength. For these reasons, the equations are mechanistic and deterministic. The model is compared with bi-axial tensile test data for wrinkled Kaptong(Registered Trademark) HN and is shown to deterministically predict strain as a function of stress with an average RMS error of 22%. On average, fitting the model to test data yields an RMS error of 1.2%

  2. Chemical vapor deposition modeling for high temperature materials

    NASA Technical Reports Server (NTRS)

    Goekoglu, Sueleyman

    1992-01-01

    The formalism for the accurate modeling of chemical vapor deposition (CVD) processes has matured based on the well established principles of transport phenomena and chemical kinetics in the gas phase and on surfaces. The utility and limitations of such models are discussed in practical applications for high temperature structural materials. Attention is drawn to the complexities and uncertainties in chemical kinetics. Traditional approaches based on only equilibrium thermochemistry and/or transport phenomena are defended as useful tools, within their validity, for engineering purposes. The role of modeling is discussed within the context of establishing the link between CVD process parameters and material microstructures/properties. It is argued that CVD modeling is an essential part of designing CVD equipment and controlling/optimizing CVD processes for the production and/or coating of high performance structural materials.

  3. Model of bidirectional reflectance distribution function for metallic materials

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Zhu, Jing-Ping; Liu, Hong; Hou, Xun

    2016-09-01

    Based on the three-component assumption that the reflection is divided into specular reflection, directional diffuse reflection, and ideal diffuse reflection, a bidirectional reflectance distribution function (BRDF) model of metallic materials is presented. Compared with the two-component assumption that the reflection is composed of specular reflection and diffuse reflection, the three-component assumption divides the diffuse reflection into directional diffuse and ideal diffuse reflection. This model effectively resolves the problem that constant diffuse reflection leads to considerable error for metallic materials. Simulation and measurement results validate that this three-component BRDF model can improve the modeling accuracy significantly and describe the reflection properties in the hemisphere space precisely for the metallic materials.

  4. A model for heterogeneous materials including phase transformations

    NASA Astrophysics Data System (ADS)

    Addessio, F. L.; Clements, B. E.; Williams, T. O.

    2005-04-01

    A model is developed for particulate composites, which includes phase transformations in one or all of the constituents. The model is an extension of the method of cells formalism. Representative simulations for a single-phase, brittle particulate (SiC) embedded in a ductile material (Ti), which undergoes a solid-solid phase transformation, are provided. Also, simulations for a tungsten heavy alloy (WHA) are included. In the WHA analyses a particulate composite, composed of tungsten particles embedded in a tungsten-iron-nickel alloy matrix, is modeled. A solid-liquid phase transformation of the matrix material is included in the WHA numerical calculations. The example problems also demonstrate two approaches for generating free energies for the material constituents. Simulations for volumetric compression, uniaxial strain, biaxial strain, and pure shear are used to demonstrate the versatility of the model.

  5. A physically-based abrasive wear model for composite materials

    SciTech Connect

    Lee, Gun Y.; Dharan, C.K.H.; Ritchie, Robert O.

    2001-05-01

    A simple physically-based model for the abrasive wear of composite materials is presented based on the mechanics and mechanisms associated with sliding wear in soft (ductile) matrix composites containing hard (brittle) reinforcement particles. The model is based on the assumption that any portion of the reinforcement that is removed as wear debris cannot contribute to the wear resistance of the matrix material. The size of this non-contributing portion of the reinforcement is estimated by modeling the three primary wear mechanisms, specifically plowing, interfacial cracking and particle removal. Critical variables describing the role of the reinforcement, such as its relative size and the nature of the matrix/reinforcement interface, are characterized by a single contribution coefficient, C. Predictions are compared with the results of experimental two-body (pin-on drum) abrasive wear tests performed on a model aluminum particulate-reinforced epoxy matrix composite material.

  6. A multifluid mix model with material strength effects

    SciTech Connect

    Chang, C. H.; Scannapieco, A. J.

    2012-04-23

    We present a new multifluid mix model. Its features include material strength effects and pressure and temperature nonequilibrium between mixing materials. It is applicable to both interpenetration and demixing of immiscible fluids and diffusion of miscible fluids. The presented model exhibits the appropriate smooth transition in mathematical form as the mixture evolves from multiphase to molecular mixing, extending its applicability to the intermediate stages in which both types of mixing are present. Virtual mass force and momentum exchange have been generalized for heterogeneous multimaterial mixtures. The compression work has been extended so that the resulting species energy equations are consistent with the pressure force and material strength.

  7. Computer-Aided Process Model For Carbon/Phenolic Materials

    NASA Technical Reports Server (NTRS)

    Letson, Mischell A.; Bunker, Robert C.

    1996-01-01

    Computer program implements thermochemical model of processing of carbon-fiber/phenolic-matrix composite materials into molded parts of various sizes and shapes. Directed toward improving fabrication of rocket-engine-nozzle parts, also used to optimize fabrication of other structural components, and material-property parameters changed to apply to other materials. Reduces costs by reducing amount of laboratory trial and error needed to optimize curing processes and to predict properties of cured parts.

  8. Computer-Aided Process Model For Carbon/Phenolic Materials

    NASA Technical Reports Server (NTRS)

    Letson, Mischell A.; Bunker, Robert C.

    1996-01-01

    Computer program implements thermochemical model of processing of carbon-fiber/phenolic-matrix composite materials into molded parts of various sizes and shapes. Directed toward improving fabrication of rocket-engine-nozzle parts, also used to optimize fabrication of other structural components, and material-property parameters changed to apply to other materials. Reduces costs by reducing amount of laboratory trial and error needed to optimize curing processes and to predict properties of cured parts.

  9. Recent atomistic modelling studies of energy materials: batteries included.

    PubMed

    Islam, M Saiful

    2010-07-28

    Advances in functional materials for energy conversion and storage technologies are crucial in addressing the global challenge of green sustainable energy. This article aims to demonstrate the valuable role that modern modelling techniques now play in providing deeper fundamental insight into novel materials for rechargeable lithium batteries and solid oxide fuel cells. Recent work is illustrated by studies on important topical materials encompassing transition-metal phosphates and silicates for lithium battery electrodes, and apatite-type silicates for fuel cell electrolytes.

  10. Material Models for Simulation of Superplastic Mg Alloy Sheet Forming

    NASA Astrophysics Data System (ADS)

    Taleff, Eric M.; Hector, Louis G.; Verma, Ravi; Krajewski, Paul E.; Chang, Jung-Kuei

    2010-06-01

    Accurate prediction of strain fields and cycle times for fine-grained Mg alloy sheet forming at high temperatures (400-500 °C) is severely limited by a lack of accurate material constitutive models. This paper details an important first step toward addressing this issue by evaluating material constitutive models, developed from tensile data, for high-temperature plasticity of a fine-grained Mg AZ31 sheet material. The finite element method was used to simulate gas pressure bulge forming experiments at 450 °C using four constant gas pressures. The applicability of the material constitutive models to a balanced-biaxial stress state was evaluated through comparison of simulation results with bulge forming data. Simulations based upon a phenomenological material constitutive model developed using data from both tensile elongation and strain-rate-change experiments were found to be in favorable accord with experiments. These results provide new insights specific to the construction and use of material constitutive models for hot deformation of wrought, fine-grained Mg alloys.

  11. Equivalent-Continuum Modeling of Nano-Structured Materials

    NASA Technical Reports Server (NTRS)

    Odegard, Gregory M.; Gates, Thomas S.; Nicholson, Lee M.; Wise, Kristopher E.

    2001-01-01

    A method has been developed for modeling structure-property relationships of nano-structured materials. This method serves as a link between computational chemistry and solid mechanics by substituting discrete molecular structures with an equivalent-continuum model. It has been shown that this substitution may be accomplished by equating the vibrational potential energy of a nano-structured material with the strain energy of representative truss and continuum models. As an important example with direct application to the development and characterization of single-walled carbon nanotubes, the model has been applied to determine the effective continuum geometry of a graphene sheet. A representative volume element of the equivalent-continuum model has been developed with an effective thickness. This effective thickness has been shown to be similar to, but slightly smaller than, the interatomic spacing of graphite.

  12. Nonequilibrium multiphase mixture modeling of energetic material response

    SciTech Connect

    Baer, M.R.; Hertel, E.; Bell, R.

    1995-12-31

    To model the shock-induced behavior of porous or damaged energetic materials, a nonequilibrium mixture theory has been developed and incorporated into the shock physics code, CTH. Foundation for this multiphase model is based on a continuum mixture formulation given by Baer and Nunziato. In this nonequilibrium approach, multiple thermodynamic and mechanics fields are resolved including the effects of material relative motion, rate-dependent compaction, drag and heat transfer interphase effects and multiple-step combustion. Benchmark calculations are presented which simulate low-velocity piston impact on a propellant porous bed and experimentally-measured wave features are well replicated with this model. This mixture model introduces micromechanical models for the initiation and growth of reactive multicomponent flow which are key features to describe shock initiation and self-accelerated deflagration-to-detonation combustion behavior. To complement one-dimensional simulation, two dimensional numerical simulations are presented which indicate wave curvature effects due to the loss of wall confinement.

  13. System level permeability modeling of porous hydrogen storage materials.

    SciTech Connect

    Kanouff, Michael P.; Dedrick, Daniel E.; Voskuilen, Tyler

    2010-01-01

    A permeability model for hydrogen transport in a porous material is successfully applied to both laboratory-scale and vehicle-scale sodium alanate hydrogen storage systems. The use of a Knudsen number dependent relationship for permeability of the material in conjunction with a constant area fraction channeling model is shown to accurately predict hydrogen flow through the reactors. Generally applicable model parameters were obtained by numerically fitting experimental measurements from reactors of different sizes and aspect ratios. The degree of channeling was experimentally determined from the measurements and found to be 2.08% of total cross-sectional area. Use of this constant area channeling model and the Knudsen dependent Young & Todd permeability model allows for accurate prediction of the hydrogen uptake performance of full-scale sodium alanate and similar metal hydride systems.

  14. Dynamic brittle material response based on a continuum damage model

    SciTech Connect

    Chen, E.P.

    1994-12-31

    The response of brittle materials to dynamic loads was studied in this investigation based on a continuum damage model. Damage mechanism was selected to be interaction and growth of subscale cracks. Briefly, the cracks are activated by bulk tension and the density of activated cracks are described by a Weibull statistical distribution. The moduli of a cracked solid derived by Budiansky and O`Connell are then used to represent the global material degradation due to subscale cracking. This continuum damage model was originally developed to study rock fragmentation and was modified in the present study to improve on the post-limit structural response. The model was implemented into a transient dynamic explicit finite element code PRONTO 2D and then used for a numerical study involving the sudden stretching of a plate with a centrally located hole. Numerical results characterizing the dynamic responses of the material were presented. The effect of damage on dynamic material behavior was discussed.

  15. Explicit Pore Pressure Material Model in Carbon-Cloth Phenolic

    NASA Technical Reports Server (NTRS)

    Gutierrez-Lemini, Danton; Ehle, Curt

    2003-01-01

    An explicit material model that uses predicted pressure in the pores of a carbon-cloth phenolic (CCP) composite has been developed. This model is intended to be used within a finite-element model to predict phenomena specific to CCP components of solid-fuel-rocket nozzles subjected to high operating temperatures and to mechanical stresses that can be great enough to cause structural failures. Phenomena that can be predicted with the help of this model include failures of specimens in restrained-thermal-growth (RTG) tests, pocketing erosion, and ply lifting

  16. Percolation modeling of self-damaging of composite materials

    NASA Astrophysics Data System (ADS)

    Domanskyi, Sergii; Privman, Vladimir

    2014-07-01

    We propose the concept of autonomous self-damaging in “smart” composite materials, controlled by activation of added nanosize “damaging” capsules. Percolation-type modeling approach earlier applied to the related concept of self-healing materials, is used to investigate the behavior of the initial material's fatigue. We aim at achieving a relatively sharp drop in the material's integrity after some initial limited fatigue develops in the course of the sample's usage. Our theoretical study considers a two-dimensional lattice model and involves Monte Carlo simulations of the connectivity and conductance in the high-connectivity regime of percolation. We give several examples of local capsule-lattice and capsule-capsule activation rules and show that the desired self-damaging property can only be obtained with rather sophisticated “smart” material's response involving not just damaging but also healing capsules.

  17. Local Debonding and Fiber Breakage in Composite Materials Modeled Accurately

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Arnold, Steven M.

    2001-01-01

    A prerequisite for full utilization of composite materials in aerospace components is accurate design and life prediction tools that enable the assessment of component performance and reliability. Such tools assist both structural analysts, who design and optimize structures composed of composite materials, and materials scientists who design and optimize the composite materials themselves. NASA Glenn Research Center's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) software package (http://www.grc.nasa.gov/WWW/LPB/mac) addresses this need for composite design and life prediction tools by providing a widely applicable and accurate approach to modeling composite materials. Furthermore, MAC/GMC serves as a platform for incorporating new local models and capabilities that are under development at NASA, thus enabling these new capabilities to progress rapidly to a stage in which they can be employed by the code's end users.

  18. New material model for simulating large impacts on rocky bodies

    NASA Astrophysics Data System (ADS)

    Tonge, A.; Barnouin, O.; Ramesh, K.

    2014-07-01

    Large impact craters on an asteroid can provide insights into its internal structure. These craters can expose material from the interior of the body at the impact site [e.g., 1]; additionally, the impact sends stress waves throughout the body, which interrogate the asteroid's interior. Through a complex interplay of processes, such impacts can result in a variety of motions, the consequence of which may appear as lineaments that are exposed over all or portions of the asteroid's surface [e.g., 2,3]. While analytic, scaling, and heuristic arguments can provide some insight into general phenomena on asteroids, interpreting the results of a specific impact event, or series of events, on a specific asteroid geometry generally necessitates the use of computational approaches that can solve for the stress and displacement history resulting from an impact event. These computational approaches require a constitutive model for the material, which relates the deformation history of a small material volume to the average force on the boundary of that material volume. In this work, we present a new material model that is suitable for simulating the failure of rocky materials during impact events. This material model is similar to the model discussed in [4]. The new material model incorporates dynamic sub-scale crack interactions through a micro-mechanics-based damage model, thermodynamic effects through the use of a Mie-Gruneisen equation of state, and granular flow of the fully damaged material. The granular flow model includes dilatation resulting from the mutual interaction of small fragments of material (grains) as they are forced to slide and roll over each other and includes a P-α type porosity model to account for compaction of the granular material in a subsequent impact event. The micro-mechanics-based damage model provides a direct connection between the flaw (crack) distribution in the material and the rate-dependent strength. By connecting the rate

  19. Calibration of an advanced material model for a shotcrete lining

    NASA Astrophysics Data System (ADS)

    Chalmovský, Juraj; Závacký, Martin; Miča, Lumír

    2017-09-01

    Proper choice of a constitutive model is an essential part of any successful application of numerical methods in geotechnical engineering. In most cases, attention is paid to the soil constitutive model. For structural elements, such as tunnel linings, retaining structures etc. elastic constitutive models are often used. These material models however do not involve many aspects of a real structural behavior such as limited tensile and compressive strength, strain softening and time dependent behavior during service life of a construction. In the proposed paper, an application of the novel constitutive model for shotcrete (Schädlich, Schweiger, 2014) is presented. The paper is focused at the process of determination of input parameters values of this model based on performed laboratory test. Section of the primary collector network in Brno was chosen for the purpose of obtaining shotcrete lining samples.

  20. A continuous fiber distribution material model for human cervical tissue.

    PubMed

    Myers, Kristin M; Hendon, Christine P; Gan, Yu; Yao, Wang; Yoshida, Kyoko; Fernandez, Michael; Vink, Joy; Wapner, Ronald J

    2015-06-25

    The uterine cervix during pregnancy is the vital mechanical barrier which resists compressive and tensile loads generated from a growing fetus. Premature cervical remodeling and softening is hypothesized to result in the shortening of the cervix, which is known to increase a woman׳s risk of preterm birth. To understand the role of cervical material properties in preventing preterm birth, we derive a cervical material model based on previous mechanical, biochemical and histological experiments conducted on nonpregnant and pregnant human hysterectomy cervical tissue samples. In this study we present a three-dimensional fiber composite model that captures the equilibrium material behavior of the tissue in tension and compression. Cervical tissue is modeled as a fibrous composite material, where a single family of preferentially aligned and continuously distributed collagen fibers are embedded in a compressible neo-Hookean ground substance. The total stress in the collagen solid network is calculated by integrating the fiber stresses. The shape of the fiber distribution is described by an ellipsoid where semi-principal axis lengths are fit to optical coherence tomography measurements. The composite material model is fit to averaged mechanical testing data from uni-axial compression and tension experiments, and averaged material parameters are reported for nonpregnant and term pregnant human cervical tissue. The model is then evaluated by investigating the stress and strain state of a uniform thick-walled cylinder under a compressive stress with collagen fibers preferentially aligned in the circumferential direction. This material modeling framework for the equilibrium behavior of human cervical tissue serves as a basis to determine the role of preferentially-aligned cervical collagen fibers in preventing cervical deformation during pregnancy.

  1. Modeling the self-assembly of ordered nanoporous materials

    NASA Astrophysics Data System (ADS)

    Jin, Lin

    Porous materials have long been a research interest due to their practical importance in traditional chemical industries such as catalysis and separation processes. The successful synthesis of porous materials requires further understanding of the fundamental physics that govern the formation of these materials. In this thesis, we apply molecular modeling methods and develop novel models to study the formation mechanism of ordered porous materials. The improved understanding provides an opportunity to rational control pore size, pore shape, surface reactivity and may lead to new design of tailor-made materials. To attain detailed structural evolution of silicate materials, an atomistic model with explicitly representation of silicon and oxygen atoms is developed. Our model is based on rigid tetrahedra (representing SiO4) occupying the sites of a body centered cubic (bcc) lattice. The model serves as the base model to study the formation of silica materials. We first carried out Monte Carlo simulations to describe the polymerization process of silica without template molecules starting from a solution of silicic acid in water at pH 2. We predicted Qn evolutions during silica polymerization and good agreement was found compared with experimental data, where Qn is the fraction of Si atoms with n bridging oxygens. The model captures the basic kinetics of silica polymerization and provides structural evolution information. Next we generalize the application of this atomic lattice model to materials with tetrahedral (T) and bridging (B) atoms and apply parallel tempering Monte Carlo methods to search for ground states. We show that the atomic lattice model can be applied to silica and related materials with a rich variety of structures including known chalcogenides, zeolite analogs, and layered materials. We find that whereas canonical Monte Carlo simulations of the model consistently produce the amorphous solids studied in our previous work, parallel tempering Monte

  2. Properties of granular analogue model materials: A community wide survey

    NASA Astrophysics Data System (ADS)

    Klinkmüller, M.; Schreurs, G.; Rosenau, M.; Kemnitz, H.

    2016-08-01

    We report the material properties of 26 granular analogue materials used in 14 analogue modelling laboratories. We determined physical characteristics such as bulk density, grain size distribution, and grain shape, and performed ring shear tests to determine friction angles and cohesion, and uniaxial compression tests to evaluate the compaction behaviour. Mean grain size of the materials varied between c. 100 and 400 μm. Analysis of grain shape factors shows that the four different classes of granular materials (14 quartz sands, 5 dyed quartz sands, 4 heavy mineral sands and 3 size fractions of glass beads) can be broadly divided into two groups consisting of 12 angular and 14 rounded materials. Grain shape has an influence on friction angles, with most angular materials having higher internal friction angles (between c. 35° and 40°) than rounded materials, whereas well-rounded glass beads have the lowest internal friction angles (between c. 25° and 30°). We interpret this as an effect of intergranular sliding versus rolling. Most angular materials have also higher basal friction angles (tested for a specific foil) than more rounded materials, suggesting that angular grains scratch and wear the foil. Most materials have an internal cohesion in the order of 20-100 Pa except for well-rounded glass beads, which show a trend towards a quasi-cohesionless (C < 20 Pa) Coulomb-type material. The uniaxial confined compression tests reveal that rounded grains generally show less compaction than angular grains. We interpret this to be related to the initial packing density after sifting, which is higher for rounded grains than for angular grains. Ring-shear test data show that angular grains undergo a longer strain-hardening phase than more rounded materials. This might explain why analogue models consisting of angular grains accommodate deformation in a more distributed manner prior to strain localisation than models consisting of rounded grains.

  3. Mechanical Properties of Nanostructured Materials Determined Through Molecular Modeling Techniques

    NASA Technical Reports Server (NTRS)

    Clancy, Thomas C.; Gates, Thomas S.

    2005-01-01

    The potential for gains in material properties over conventional materials has motivated an effort to develop novel nanostructured materials for aerospace applications. These novel materials typically consist of a polymer matrix reinforced with particles on the nanometer length scale. In this study, molecular modeling is used to construct fully atomistic models of a carbon nanotube embedded in an epoxy polymer matrix. Functionalization of the nanotube which consists of the introduction of direct chemical bonding between the polymer matrix and the nanotube, hence providing a load transfer mechanism, is systematically varied. The relative effectiveness of functionalization in a nanostructured material may depend on a variety of factors related to the details of the chemical bonding and the polymer structure at the nanotube-polymer interface. The objective of this modeling is to determine what influence the details of functionalization of the carbon nanotube with the polymer matrix has on the resulting mechanical properties. By considering a range of degree of functionalization, the structure-property relationships of these materials is examined and mechanical properties of these models are calculated using standard techniques.

  4. CTH Implementation of a Two-Phase Material Model With Strength: Application to Porous Materials

    DTIC Science & Technology

    2012-07-01

    those of the SESAME family [30]. The SESAME EOS database describes the material state response in a tabulated form with necessary interpolations...model from the SESAME database is the DRY SAND model (in fact, a table extrapolation) complemented with the P-alpha EOS reduction rule [3] used for...model (Fig. 7(b)) and P-λ model (Fig. 7(c)). It is seen that the tabular EOS response based on the SESAME approach in Fig. 7(b) manifests an

  5. Dynamic brittle material response based on a continuum damage model

    SciTech Connect

    Chen, E.P.

    1995-12-31

    Because of its potential utilization in energy exploration and defense applications, the phenomenon of brittle fracture in solids under dynamic loads has been an ongoing topic of interest. A continuum damage model was developed to simulate rock fragmentation induced by explosive blasts for in situ oil shale retorting. The model was based on the premise that the inelastic brittle response exhibited by rock under dynamic loads is due principally to the stress-induced sub-scale cracks. Locally, the growth and interaction of these sub-scale cracks relieve portions of the material volume and reduce its capability to carry load. Globally, this effect is reflected in the degradation of the material stiffness. In this manner, the dynamic fracture process was modeled as a continuous accrual of damage, where damage is considered to be the degree of reduction of the material stiffness. Reasonable correlations between calculated and measured data were obtained by this model. Although the model has achieved some degree of success, some deficiencies have been identified over the years. For example, the adequacy of representing the compressive response by perfect plasticity was questioned. Because of the damage formulation, strain-softening and localization are natural by-products of the model. Thus, a question on mesh-size dependency has also been raised. This investigation is concerned with the improvement of the damage model in by including the Drucker-Prager model to represent compressional response and nonlocal treatment to tensile damage. The inclusion of the Drucker-Prager model allows pressure-dependent yield strength representation. Although the rate-dependent nature of the model may alleviate the mesh-size dependence problem, a nonlocal formulation was also investigated to insure mesh-size independency. This treatment is based on the nonlocal representation with local strain.

  6. Vibro-acoustics of porous materials - waveguide modelling approach

    NASA Astrophysics Data System (ADS)

    Darula, R.; Sorokin, S.

    2016-09-01

    The porous material is considered as a compound multi-layered waveguide (i.e. a fluid layer surrounded with elastic layers) with traction free boundary conditions. The attenuation of the vibro-acoustic waves in such a material is assessed. This approach is compared with a conventional Biot's model and a qualitative agreement in phase velocities as well as damping estimates is found. The waveguide model predicts four waves, out of which two are attenuated when the viscous fluid is considered (while the elastic layer being ideally lossless). One of these waves is found to be significantly controlled by the fluid viscosity, while for the other the effect of viscosity was observed for very small frequencies. The Biot's model predicts only one of these attenuated waves, where the latter one is not predicted. Thus the proposed waveguide approach provide additional information about the wave propagation in porous materials.

  7. Finite Element Modeling of the Thermographic Inspection for Composite Materials

    NASA Technical Reports Server (NTRS)

    Bucinell, Ronald B.

    1996-01-01

    The performance of composite materials is dependent on the constituent materials selected, material structural geometry, and the fabrication process. Flaws can form in composite materials as a result of the fabrication process, handling in the manufacturing environment, and exposure in the service environment to anomalous activity. Often these flaws show no indication on the surface of the material while having the potential of substantially degrading the integrity of the composite structure. For this reason it is important to have available inspection techniques that can reliably detect sub-surface defects such as inter-ply disbonds, inter-ply cracks, porosity, and density changes caused by variations in fiber volume content. Many non-destructive evaluation techniques (NDE) are capable of detecting sub-surface flaws in composite materials. These include shearography, video image correlation, ultrasonic, acoustic emissions, and X-ray. The difficulty with most of these techniques is that they are time consuming and often difficult to apply to full scale structures. An NDE technique that appears to have the capability to quickly and easily detect flaws in composite structure is thermography. This technique uses heat to detect flaws. Heat is applied to the surface of a structure with the use of a heat lamp or heat gun. A thermographic camera is then pointed at the surface and records the surface temperature as the composite structure cools. Flaws in the material will cause the thermal-mechanical material response to change. Thus, the surface over an area where a flaw is present will cool differently than regions where flaws do not exist. This paper discusses the effort made to thermo-mechanically model the thermography process. First the material properties and physical parameters used in the model will be explained. This will be followed by a detailed discussion of the finite element model used. Finally, the result of the model will be summarized along with

  8. Macro material flow modeling for analyzing solid waste management options

    SciTech Connect

    Holter, G.M.; Pennock, K.A.; Shaver, S.R.

    1993-06-01

    A Macro Material Flow Modeling (MMFM) concept and approach are being adopted to develop a predictive modeling capability. This capability is intended to provide part of the basis for evaluating potential impacts from various solid waste management system configurations and operating scenarios, as well as evaluating the impacts of various policies on solid waste quantities and compositions. The MMFM capability, as part of a broader Solid Waste Initiative at Pacific Northwest Laboratory, is intended to provide an increased understanding of solid waste as a disposal, energy, and resource problem on a national and global scale, particularly over the long term. This model is a macro-level simulation of the flows of the various materials through the solid waste management system, and also through the associated materials production and use system. Inclusion of materials production and use within the modeling context allows a systems approach to be used, providing a much more complete understanding of the origins of the solid waste materials and also of possible options for materials recovery and reuse than if a more traditional ``end-of-pipe`` view of solid waste is adopted. The MMFM is expected to be useful in evaluating longer-term, broader-ranging solid waste impacts than are traditionally evaluated by decision-makers involved in implementing solutions to local or regional solid waste management problems. This paper discusses the types of questions of interest in evaluating long-term, broad-range impacts from solid waste. It then identifies the basic needs for predictive modeling capabilities like the MMFM, and provides a basic description of the conceptual framework for the model and the associated data. Status of the MMFM implementation is also discussed.

  9. Macro material flow modeling for analyzing solid waste management options

    SciTech Connect

    Holter, G.M.; Pennock, K.A.; Shaver, S.R.

    1993-06-01

    A Macro Material Flow Modeling (MMFM) concept and approach are being adopted to develop a predictive modeling capability. This capability is intended to provide part of the basis for evaluating potential impacts from various solid waste management system configurations and operating scenarios, as well as evaluating the impacts of various policies on solid waste quantities and compositions. The MMFM capability, as part of a broader Solid Waste Initiative at Pacific Northwest Laboratory, is intended to provide an increased understanding of solid waste as a disposal, energy, and resource problem on a national and global scale, particularly over the long term. This model is a macro-level simulation of the flows of the various materials through the solid waste management system, and also through the associated materials production and use system. Inclusion of materials production and use within the modeling context allows a systems approach to be used, providing a much more complete understanding of the origins of the solid waste materials and also of possible options for materials recovery and reuse than if a more traditional end-of-pipe'' view of solid waste is adopted. The MMFM is expected to be useful in evaluating longer-term, broader-ranging solid waste impacts than are traditionally evaluated by decision-makers involved in implementing solutions to local or regional solid waste management problems. This paper discusses the types of questions of interest in evaluating long-term, broad-range impacts from solid waste. It then identifies the basic needs for predictive modeling capabilities like the MMFM, and provides a basic description of the conceptual framework for the model and the associated data. Status of the MMFM implementation is also discussed.

  10. Modeling thermal/chemical/mechanical response of energetic materials

    SciTech Connect

    Baer, M.R.; Hobbs, M.L.; Gross, R.J.

    1995-07-01

    An overview of modeling at Sandia National Laboratories is presented which describes coupled thermal, chemical and mechanical response of energetic materials. This modeling addresses cookoff scenarios for safety assessment studies in systems containing energetic materials. Foundation work is discussed which establishes a method for incorporating chemistry and mechanics into multidimensional analysis. Finite element analysis offers the capabilities to simultaneously resolve reactive heat transfer and structural mechanics in complex geometries. Nonlinear conduction heat transfer, with multiple step finite-rate chemistry, is resolved using a thermal finite element code. Rate equations are solved element-by-element using a modified matrix-free stiff solver This finite element software was developed for the simulation of systems requiring large numbers of finite elements. An iterative implicit scheme, based on the conjugate gradient method, is used and a hemi-cube algorithm is employed for the determination of view factors in surface-to-surface radiation transfer The critical link between the reactive heat transfer and mechanics is the introduction of an appropriate constitutive material model providing a stress-strain relationship for quasi-static mechanics analysis. This model is formally derived from bubble nucleation theory, and parameter variations of critical model parameters indicate that a small degree of decomposition leads to significant mechanical response. Coupled thermal/chemical/mechanical analysis is presented which simulates experiments designed to probe cookoff thermal-mechanical response of energetic materials.

  11. Dynamic fragmentation of brittle materials: analytical mechanics-based models

    NASA Astrophysics Data System (ADS)

    Drugan, W. J.

    2001-06-01

    Two analytical mechanics-based models of dynamic fragmentation in brittle materials are proposed and solved to predict fragment size and time to fragmentation onset in terms of fundamental material properties and the applied strain rate. Previous widely adopted analytical models of dynamic fragmentation are based on relatively simple energy balance arguments, and assume that the fragmentation event occurs instantaneously. The present models account for the actual time-varying dynamic deformation that occurs prior to fragmentation onset. One of the models treats the fragmenting material as initially flaw-free, and determines the minimum fragment size predicted by a dynamic instability analysis. The second model accounts for initial flaw spacing (which may correlate physically with, for example, grain size), and a dynamic instability analysis is employed to determine which flaws become critical. The fragment size predictions of the present models and two previous energy-based models are found to agree at extremely high strain rates (≈5×10 7/s for dense alumina), but the present, more realistic analysis indicates that the regime of validity of the energy-based models is rather restricted. The predictions of the present models are also shown to agree with those of a recent numerical finite element simulation of dynamic fragmentation which applies to a lower strain rate regime. Comparisons of the two new models show that if a material contains initial flaws whose spacing is smaller than the predicted fragment size of an equivalent "unflawed" material, the fragment size of the preflawed material will be smaller in general, but usually not as small as the initial flaw spacing. The analysis also permits determination of the evolution of the strain rate distribution in a prospective fragment before and after fragmentation initiation; results are presented for some example cases. Finally, closed-form analytical results are derived for minimum fragment size and time to

  12. Modeling of metal cutting as purposeful fracture of work material

    NASA Astrophysics Data System (ADS)

    Abushawashi, Yalla Mussa

    Metal cutting, or simply machining, is one of the oldest processes for shaping components in the manufacturing industry. It is widely quoted that 15% of the value of all mechanical components manufactured worldwide is derived from machining operations. The most influential model for metal cutting is the single-shear plane model (SSPM) of chip formation. The common notion is that new surfaces are formed simply by `plastic flow around the tool tip' so that metal cutting is one of the deforming processes. A number of cutting theories and the finite element method (FEM) models have been developed based on this concept. Metal cutting simulation models are available in commercial FEM packages. However, these model predictions and numerical simulations do not agree with the trends and phenomena observed in metal cutting experiments. Therefore, it is of the utmost importance to have a physically sound model of metal cutting. This thesis is based on the concept that metal cutting is the purposeful fracture of the work material. To reduce the energy required for fracture, one should minimize the energy of plastic deformation of the work material in its transformation into the chip because this energy constitutes up to 80% of the total energy required by the cutting system. Increased tool life and machining efficiency are the outcomes of such an optimization. To investigate this concept requires a work material model which considers the entire process from plastic deformation, damage initiation to final fracture. In this thesis, a work material model was developed based on the recent advancement in ductile fracture of metals. The model parameters must be determined under conditions that are pertinent to metal cutting. In machining, the work material experiences a complex, evolving multi-axial stress history. The existing testing specimens such as the notched bars and flat grooved specimens do not cover the stress triaxiality range found in machining. To generate material

  13. Handbook of Format Models for Designers of Technical Training Materials.

    DTIC Science & Technology

    1982-08-01

    ADA 1429 HANDBOOK OF FORMAT MODELS FOR DESIGNERS OF TECHNL A TRAIN ING MATERIALS(U TRAINING ANALYSIS AND EVA UAON GROUP (NAVY ORLANDO FLR RRAR ET AL...TRAIINGTECHNICAL REPORT 129 £A HANDBOOK OF FORMAT MODELS FOR DESIGNERS OF TECHNICAL TRAINING MATERIALS ’Original contains colcr ’. plates: All DTIC reproduct- ions...will be in black andAUST18 white*’UUT18 FOCUS ON THE TRAINED P .I CL DTICELECTE C...) SF B 4 1983 B. 83 02 04 005 APPROVED FOR PUBLIC RELEASE

  14. Pore-scale Modelling of Capillarity in Swelling Granular Materials

    NASA Astrophysics Data System (ADS)

    Hassanizadeh, S. M.; Sweijen, T.; Nikooee, E.; Chareyre, B.

    2015-12-01

    Capillarity in granular porous media is a common and important phenomenon in earth materials and industrial products, and therefore has been studied extensively. To model capillarity in granular porous media, one needs to go beyond current models which simulate either two-phase flow in porous media or mechanical behaviour in granular media. Current pore-scale models for two-phase flow such as pore-network models are tailored for rigid pore-skeletons, even though in many applications, namely hydro-mechanical coupling in soils, printing, and hygienic products, the porous structure does change during two-phase flow. On the other hand, models such as Discrete Element Method (DEM), which simulate the deformable porous media, have mostly been employed for dry or saturated granular media. Here, the effects of porosity change and swelling on the retention properties was studied, for swelling granular materials. A pore-unit model that was capable to construct the capillary pressure - saturation curve was coupled to DEM. Such that the capillary pressure - saturation curve could be constructed for varying porosities and amounts of absorbed water. The study material was super absorbent polymer particles, which are capable to absorb water 10's to 200 times their initial weight. We have simulated quasi-static primary imbibition for different porosities and amounts of absorbed water. The results reveal a 3 dimensional surface between capillary pressure, saturation, and porosity, which can be normalized by means of the entry pressure and the effective water saturation to a unique curve.

  15. DEM modeling of flexible structures against granular material avalanches

    NASA Astrophysics Data System (ADS)

    Lambert, Stéphane; Albaba, Adel; Nicot, François; Chareyre, Bruno

    2016-04-01

    This article presents the numerical modeling of flexible structures intended to contain avalanches of granular and coarse material (e.g. rock slide, a debris slide). The numerical model is based on a discrete element method (YADE-Dem). The DEM modeling of both the flowing granular material and the flexible structure are detailed before presenting some results. The flowing material consists of a dry polydisperse granular material accounting for the non-sphericity of real materials. The flexible structure consists in a metallic net hanged on main cables, connected to the ground via anchors, on both sides of the channel, including dissipators. All these components were modeled as flexible beams or wires, with mechanical parameters defined from literature data. The simulation results are presented with the aim of investigating the variability of the structure response depending on different parameters related to the structure (inclination of the fence, with/without brakes, mesh size opening), but also to the channel (inclination). Results are then compared with existing recommendations in similar fields.

  16. An in silico skin absorption model for fragrance materials.

    PubMed

    Shen, Jie; Kromidas, Lambros; Schultz, Terry; Bhatia, Sneha

    2014-12-01

    Fragrance materials are widely used in cosmetics and other consumer products. The Research Institute for Fragrance Materials (RIFM) evaluates the safety of these ingredients and skin absorption is an important parameter in refining systemic exposure. Currently, RIFM's safety assessment process assumes 100% skin absorption when experimental data are lacking. This 100% absorption default is not supportable and alternate default values were proposed. This study aims to develop and validate a practical skin absorption model (SAM) specific for fragrance material. It estimates skin absorption based on the methodology proposed by Kroes et al. SAM uses three default absorption values based on the maximum flux (J(max)) - namely, 10%, 40%, and 80%. J(max) may be calculated by using QSAR models that determine octanol/water partition coefficient (K(ow)), water solubility (S) and permeability coefficient (K(p)). Each of these QSAR models was refined and a semi-quantitative mechanistic model workflow is presented. SAM was validated with a large fragrance-focused data set containing 131 materials. All resulted in predicted values fitting the three-tiered absorption scenario based on Jmax ranges. This conservative SAM may be applied when fragrance material lack skin absorption data.

  17. Mathematical modeling and stochastic simulation of soft materials

    NASA Astrophysics Data System (ADS)

    Zeng, Yun

    Soft materials are all around us; they may appear as consumer products, foods, or biological materials. The interest in studying the properties of soft materials both experimentally and theoretically has steadily increased due to their wide range of industrial applications. One example of a soft material is wormlike micellar solutions. Depending on the temperature and composition, these solvent-surfactant-salt mixtures may exhibit close to mono-exponential or, alternatively, power-law or stretched-exponential stress decay. Of particular interest to this thesis is the development of stochastic models that can capture the stress relaxation behavior of such materials in the small strain limit, which is non-exponential in time as opposed to exponential. Continuous time random walk (CTRW) or subordinated Langevin processes are utilized to model systems exhibiting non-exponential relaxation behavior or anomalous diffusion. Stochastic simulations using the CTRW approach or the subordination method are carried out in this thesis for one-dimensional systems in which the probability density distribution of particle positions is described by a fractional Fokker-Planck equation (FFPE). The equivalence of the CTRW simulation and the subordination simulation with that of the FFPE is analyzed through the simulation of an ensemble of particle trajectories. The simulated particle dynamics suggest that CTRW processes or subordinated Langevin dynamics can be included in soft material mesoscale dynamics to capture the anomalous transport. To model the non-exponential stress relaxation dynamics of soft gel systems (three-dimensional fluids), stochastic models are simulated using transient network theory as developed and combined with the CTRW and subordinated Langevin processes. This approach enables us to connect the microstructural dynamics of certain soft gel-like materials with macroscale experimental observations by examining the material properties under homogeneous shear flow

  18. Diffusion in energy materials: Governing dynamics from atomistic modelling

    NASA Astrophysics Data System (ADS)

    Parfitt, D.; Kordatos, A.; Filippatos, P. P.; Chroneos, A.

    2017-09-01

    Understanding diffusion in energy materials is critical to optimising the performance of solid oxide fuel cells (SOFCs) and batteries both of which are of great technological interest as they offer high efficiency for cleaner energy conversion and storage. In the present review, we highlight the insights offered by atomistic modelling of the ionic diffusion mechanisms in SOFCs and batteries and how the growing predictive capability of high-throughput modelling, together with our new ability to control compositions and microstructures, will produce advanced materials that are designed rather than chosen for a given application. The first part of the review focuses on the oxygen diffusion mechanisms in cathode and electrolyte materials for SOFCs and in particular, doped ceria and perovskite-related phases with anisotropic structures. The second part focuses on disordered oxides and two-dimensional materials as these are very promising systems for battery applications.

  19. Hysteresis Modeling in Magnetostrictive Materials Via Preisach Operators

    NASA Technical Reports Server (NTRS)

    Smith, R. C.

    1997-01-01

    A phenomenological characterization of hysteresis in magnetostrictive materials is presented. Such hysteresis is due to both the driving magnetic fields and stress relations within the material and is significant throughout, most of the drive range of magnetostrictive transducers. An accurate characterization of the hysteresis and material nonlinearities is necessary, to fully utilize the actuator/sensor capabilities of the magnetostrictive materials. Such a characterization is made here in the context of generalized Preisach operators. This yields a framework amenable to proving the well-posedness of structural models that incorporate the magnetostrictive transducers. It also provides a natural setting in which to develop practical approximation techniques. An example illustrating this framework in the context of a Timoshenko beam model is presented.

  20. Properties of granular analogue model materials: A community wide survey

    NASA Astrophysics Data System (ADS)

    Klinkmüller, Matthias; Schreurs, Guido; Rosenau, Matthias; Kemnitz, Helga

    2016-04-01

    We report the material properties of 26 granular analogue materials used in 14 analogue modelling laboratories. We determined physical characteristics such as bulk density, grain size distribution, and grain shape, and performed ring shear tests to determine friction angles and cohesion, and uniaxial compression tests to evaluate the compaction behaviour. Mean grain size of the materials varied between (c. 100 and 400 micrometer). Analysis of grain shape factors show that the four different classes of granular materials (14 quartz sands, 5 dyed quartz sands, 4 heavy mineral sands and 3 size fractions of glass beads) can be broadly divided into two groups consisting of 12 angular and 14 rounded materials. Grain shape has an influence on friction angles, with most angular materials having higher internal friction angles (between c. 35° and 40°) than rounded materials, whereas well-rounded glass beads have the lowest internal friction angles (between c. 25° and 30°). We interpret this as an effect of intergranular sliding versus rolling . Most angular materials have also higher basal friction angles (tested for a specific foil) than more rounded materials, suggesting that angular grains scratch and wear the foil., Most materials have a cohesion in the order of 10-100 Pa except for well-rounded glass beads, which show a trend towards a quasi-cohesionless (C <10 Pa) Coulomb-type material. The uniaxial confined compression tests reveal that rounded grains generally show less compaction than angular grains. We interpret this to be related to the initial packing density reached during sieving which is higher for rounded grains than for angular grains. Ring-shear test data show that angular grains undergo a longer strain-hardening phase than more rounded materials. This might explain why analogue models consisting of angular grains accommodate deformation in a more distributed manner prior to strain localisation than models consisting of rounded grains. Also, models

  1. Modeling Permanent Deformations of Superelastic and Shape Memory Materials.

    PubMed

    Urbano, Marco Fabrizio; Auricchio, Ferdinando

    2015-06-11

    In this paper we propose a modification of the polycrystalline shape memory alloy constitutive model originally proposed by Souza. By introducing a transformation strain energy with two different hardening coefficients, we are able to take into account the effect of the martensitic transformation of unfavorably oriented grains occurring after the main plateau. By choosing a proper second hardening coefficient, it is possible to reproduce the correct stress strain behavior of the material after the plateau without the need of introducing a much smaller Young modulus for martensite. The proposed modification is introduced in the model comprising permanent deformation effects. Model results for uniaxial stress tests are compared to experimental results showing good agreement.

  2. Expert model process control of composite materials in a press

    NASA Astrophysics Data System (ADS)

    Saliba, Tony E.; Quinter, Suzanne R.; Abrams, Frances L.

    An expert model for the control of the press processing of thermoset composite materials has been developed. The knowledge base written using the PC PLUS expert system shell was interfaced with models written in FORTRAN. The expert model, which is running on a single computer with a single processor, takes advantage of the symbol-crunching capability of LISP and the number crunching capability of FORTRAN. The Expert Model control system is a qualitative-quantitative process automation (QQPA) system since it includes both quantitative model-based and qualitative rule-based expert system operations. Various physical and mechanical properties were measured from panels processed using the two cycles. Using QQPA, processing time has been reduced significantly without altering product quality.

  3. Multi-length Scale Material Model Development for Armorgrade Composites

    DTIC Science & Technology

    2014-05-02

    performance of the 2 material. The main objective of the present work was to identify and quantify the contributions of the key molecule-/ fibril ...Kevlar® type fibers, there is a substantial experimental support for the existence of fibrils within the fibers. Fibrils are smaller bundles of...fibers, fibers can be considered as an assembly of fibrils . At this length-scale, the material is modeled using an all-atom/molecular approach within

  4. A Continuum Approach For Neural Network Modelling Of Anisotropic Materials

    NASA Astrophysics Data System (ADS)

    Man, Hou; Furukawa, Tomonari

    2010-05-01

    This paper presents an approach for constitutive modelling of anisotropic materials using neural networks on a continuum basis. The proposed approach develops the models by using an error function formulated from the minimum total potential energy principle. The variation of the strain energy of a deformed geometry is approximated by using the full field strain measurement with the neural network constitutive model (NNCM) and the coordinate frame transformation. It is subsequently compared with the variation of the applied external work, such that the discrepancy is fed back to update the model properties. The proposed approach is, therefore, able to develop the NNCM without the presence of stress data. This not only facilitates the use of multi-axial load tests and non-standard specimens to produce more realistic experimental results, but also reduces the number of different specimen configurations used for the model development. A numerical example is presented in this paper to validate the performance and applicability of the proposed approach by modelling a carbon fibre reinforced plastic (CFRP) lamina. Artificial experimental results of tensile tests with two different specimens are used to facilitate the validation. The results emphasise the flexibility and applicability of the proposed approach for constitutive modelling of anisotropic materials.

  5. Thermal modeling of wide bandgap materials for power MOSFETs

    NASA Astrophysics Data System (ADS)

    Manandhar, Mahesh B.; Matin, Mohammad A.

    2016-09-01

    This paper investigates the thermal performance of different wide bandgap (WBG) materials for their applicability as semiconductor material in power electronic devices. In particular, Silicon Carbide (SiC) and Gallium Nitride (GaN) are modeled for this purpose. These WBG materials have been known to show superior intrinsic material properties as compared to Silicon (Si), such as higher carrier mobility, lower electrical and thermal resistance. These unique properties have allowed for them to be used in power devices that can operate at higher voltages, temperatures and switching speeds with higher efficiencies. Digital prototyping of power devices have facilitated inexpensive and flexible methods for faster device development. The commercial simulation software COMSOL Multiphysics was used to simulate a 2-D model of MOSFETs of these WBG materials to observe their thermal performance under different voltage and current operating conditions. COMSOL is a simulation software that can be used to simulate temperature changes due to Joule heating in the case of power MOSFETs. COMSOL uses Finite Element/Volume Analysis methods to solve for variables in complex geometries where multiple material properties and physics are involved. The Semiconductor and Heat Transfer with Solids modules of COMSOL were used to study the thermal performance of the MOSFETs in steady state conditions. The results of the simulations for each of the two WBG materials were compared with that of Silicon to determine relative stability and merit of each material.

  6. Modelling of advanced structural materials for GEN IV reactors

    NASA Astrophysics Data System (ADS)

    Samaras, M.; Hoffelner, W.; Victoria, M.

    2007-09-01

    The choice of suitable materials and the assessment of long-term materials damage are key issues that need to be addressed for the safe and reliable performance of nuclear power plants. Operating conditions such as high temperatures, irradiation and a corrosive environment degrade materials properties, posing the risk of very expensive or even catastrophic plant damage. Materials scientists are faced with the scientific challenge to determine the long-term damage evolution of materials under service exposure in advanced plants. A higher confidence in life-time assessments of these materials requires an understanding of the related physical phenomena on a range of scales from the microscopic level of single defect damage effects all the way up to macroscopic effects. To overcome lengthy and expensive trial-and-error experiments, the multiscale modelling of materials behaviour is a promising tool, bringing new insights into the fundamental understanding of basic mechanisms. This paper presents the multiscale modelling methodology which is taking root internationally to address the issues of advanced structural materials for Gen IV reactors.

  7. Dynamical Models for the Origin of Iapetus' Dark Material

    NASA Astrophysics Data System (ADS)

    Tamayo, Daniel; Burns, J. A.; Denk, T.

    2009-09-01

    The stark albedo dichotomy on Iapetus has been known since 1671. Interestingly, recent Cassini ISS color observations have revealed a separate "color dichotomy"--color and slight albedo differences within the dark and within the bright terrains--seemingly determined by Iapetus’ orbital motion (Denk et al. 2009, Science, submitted). Spencer and Denk (2009, Science, submitted) have modeled how such a color dichotomy could result in thermally-driven runaway migration of water ice leading to the global albedo distribution observed today. This scenario seems very reasonable, but the (likely exogenous) source for the reddish material required to form the color dichotomy and initiate the runaway ice migration remains open. We model dust particles from all the irregular moons as the source for the dark material by numerically integrating the effect of radiation forces on their orbits and calculating their cumulative probability of collision with Iapetus. This work is an extension of Burns et al. (1996) aimed at resolving the inconsistencies mentioned therein with regard to the distribution and supply of dark material. We evaluate Soter's model (1974) proposing Phoebe as the source of the dark material, as well as models where dust originates from irregular moons discovered more recently. Our calculations show that only particles on high-eccentricity orbits (induced by radiation pressure) are capable of striking Iapetus. We will discuss such a model's implications for the longitudinal coverage of dark material, as well as the importance of thermal processes for the latitudinal segregation of ice. Finally, we will address whether Phoebe and the outer irregular satellites can collectively account for a sufficient supply of material to darken and redden the leading-side polar areas relative to their trailing-side counterparts, thereby creating the color dichotomy. This would initiate the proposed thermally-driven migration process and lead to the presently observed global

  8. Modeling the Reactions of Energetic Materials in the Condensed Phase

    SciTech Connect

    Fried, L E; Manaa, M R; Lewis, J P

    2003-12-03

    High explosive (HE) materials are unique for having a strong exothermic reactivity, which has made them desirable for both military and commercial applications. Although the history of HE materials is long, condensed-phase properties are poorly understood. Understanding the condensed-phase properties of HE materials is important for determining stability and performance. Information regarding HE material properties (for example, the physical, chemical, and mechanical behaviors of the constituents in plastic-bonded explosive, or PBX, formulations) is necessary in efficiently building the next generation of explosives as the quest for more powerful energetic materials (in terms of energy per volume) moves forward. In addition, understanding the reaction mechanisms has important ramifications in disposing of such materials safely and cheaply, as there exist vast stockpiles of HE materials with corresponding contamination of earth and groundwater at these sites, as well as a military testing sites The ability to model chemical reaction processes in condensed phase energetic materials is rapidly progressing. Chemical equilibrium modeling is a mature technique with some limitations. Progress in this area continues, but is hampered by a lack of knowledge of condensed phase reaction mechanisms and rates. Atomistic modeling is much more computationally intensive, and is currently limited to very short time scales. Nonetheless, this methodology promises to yield the first reliable insights into the condensed phase processes responsible for high explosive detonation. Further work is necessary to extend the timescales involved in atomistic simulations. Recent work in implementing thermostat methods appropriate to shocks may promise to overcome some of these difficulties. Most current work on energetic material reactivity assumes that electronically adiabatic processes dominate. The role of excited states is becoming clearer, however. These states are not accessible in perfect

  9. Modeling

    NASA Technical Reports Server (NTRS)

    Zook, H. A.

    1985-01-01

    A prediction of the future population of satellites, satellite fragments, and assorted spacecraft debris in Earth orbit can be reliably made only after three conditions are satisfied: (1) the size and spatial distributions of these Earth-orbiting objects are established at some present-day time; (2) the processes of orbital evolution, explosions, hypervelocity impact fragmentation, and atmospheric drag are understood; and (3) a reasonable traffic model for the future launch rate of Earth-orbiting objects is assumed. The theoretician will then take these three quantities as input data and will carry through the necessary mathematica and numerical analyses to project the present-day orbital population into the future.

  10. Numerical model for thermal parameters in optical materials

    NASA Astrophysics Data System (ADS)

    Sato, Yoichi; Taira, Takunori

    2016-04-01

    Thermal parameters of optical materials, such as thermal conductivity, thermal expansion, temperature coefficient of refractive index play a decisive role for the thermal design inside laser cavities. Therefore, numerical value of them with temperature dependence is quite important in order to develop the high intense laser oscillator in which optical materials generate excessive heat across mode volumes both of lasing output and optical pumping. We already proposed a novel model of thermal conductivity in various optical materials. Thermal conductivity is a product of isovolumic specific heat and thermal diffusivity, and independent modeling of these two figures should be required from the viewpoint of a clarification of physical meaning. Our numerical model for thermal conductivity requires one material parameter for specific heat and two parameters for thermal diffusivity in the calculation of each optical material. In this work we report thermal conductivities of various optical materials as Y3Al5O12 (YAG), YVO4 (YVO), GdVO4 (GVO), stoichiometric and congruent LiTaO3, synthetic quartz, YAG ceramics and Y2O3 ceramics. The dependence on Nd3+-doping in laser gain media in YAG, YVO and GVO is also studied. This dependence can be described by only additional three parameters. Temperature dependence of thermal expansion and temperature coefficient of refractive index for YAG, YVO, and GVO: these are also included in this work for convenience. We think our numerical model is quite useful for not only thermal analysis in laser cavities or optical waveguides but also the evaluation of physical properties in various transparent materials.

  11. 3D Microstructures for Materials and Damage Models

    DOE PAGES

    Livescu, Veronica; Bronkhorst, Curt Allan; Vander Wiel, Scott Alan

    2017-02-01

    Many challenges exist with regard to understanding and representing complex physical processes involved with ductile damage and failure in polycrystalline metallic materials. Currently, the ability to accurately predict the macroscale ductile damage and failure response of metallic materials is lacking. Research at Los Alamos National Laboratory (LANL) is aimed at building a coupled experimental and computational methodology that supports the development of predictive damage capabilities by: capturing real distributions of microstructural features from real material and implementing them as digitally generated microstructures in damage model development; and, distilling structure-property information to link microstructural details to damage evolution under a multitudemore » of loading states.« less

  12. Thermodynamic modeling of the sorption of radioelements onto cementitious materials

    SciTech Connect

    Heath, T.G.; Ilett, D.J.; Tweed, C.J.

    1996-08-01

    A model has been developed for the sorption of radioelements onto cementitious materials based on the diffuse-layer modeling approach. The model assumes that silicon sites (>SiOH) and calcium sites (>CaOH) dominate the surface chemistry and the sorption of radioelements onto the cementitious materials. Both types of site may undergo surface protonation and deprotonation reactions. Cement-based systems vary greatly in their chemistry depending on their calcium-to-silicon molar ratio, and the corresponding variation in the surface chemistry has been incorporated by allowing sorption of calcium ions onto silicon sites. This process results in a change from a silica-type surface, at very low calcium-silicon ratios, to a calcium hydroxide-type surface for high-calcium cement-based materials. The predicted variation in the surface chemistry is consistent with literature data on measured zeta potentials of cements. The model has been applied successfully to describe the sorption of simple caesium and iodide ions at varying calcium-silicon ratios. In a Nirex repository for low and intermediate level wastes, a high-calcium cementitious backfill would be specified. This model has allowed a consistent interpretation of experimental data for sorption of key radioelements, including uranium and plutonium, onto the backfill, under saline and non-saline conditions.

  13. DYNA3D Material Model 71 - Solid Element Test Problem

    SciTech Connect

    Zywicz, E

    2008-01-24

    A general phenomenological-based elasto-plastic nonlinear isotropic strain hardening material model was implemented in DYNA3D for use in solid, beam, truss, and shell elements. The constitutive model, Model 71, is based upon conventional J2 plasticity and affords optional temperature and rate dependence (visco-plasticity). The expressions for strain hardening, temperature dependence, and rate dependence allow it to represent a wide variety of material responses. Options to capture temperature changes due to adiabatic heating and thermal straining are incorporated into the constitutive framework as well. The verification problem developed for this constitutive model consists of four uni-axial right cylinders subject to constant true strain-rate boundary conditions. Three of the specimens have different constant strain rates imposed, while the fourth specimen is subjected to several strain rate jumps. The material parameters developed by Fehlmann (2005) for 21-6-9 Nitronic steel are utilized. As demonstrated below, the finite element (FE) simulations are in excellent agreement with the theoretical responses and indicated the model is functioning as desired. Consequently, this problem serves as both a verification problem and regression test problem for DYNA3D.

  14. Molecular modeling of protein materials: case study of elastin

    NASA Astrophysics Data System (ADS)

    Tarakanova, Anna; Buehler, Markus J.

    2013-09-01

    Molecular modeling of protein materials is a quickly growing area of research that has produced numerous contributions in fields ranging from structural engineering to medicine and biology. We review here the history and methods commonly employed in molecular modeling of protein materials, emphasizing the advantages for using modeling as a complement to experimental work. We then consider a case study of the protein elastin, a critically important ‘mechanical protein’ to exemplify the approach in an area where molecular modeling has made a significant impact. We outline the progression of computational modeling studies that have considerably enhanced our understanding of this important protein which endows elasticity and recoil to the tissues it is found in, including the skin, lungs, arteries and the heart. A vast collection of literature has been directed at studying the structure and function of this protein for over half a century, the first molecular dynamics study of elastin being reported in the 1980s. We review the pivotal computational works that have considerably enhanced our fundamental understanding of elastin's atomistic structure and its extraordinary qualities—focusing on two in particular: elastin's superb elasticity and the inverse temperature transition—the remarkable ability of elastin to take on a more structured conformation at higher temperatures, suggesting its effectiveness as a biomolecular switch. Our hope is to showcase these methods as both complementary and enriching to experimental approaches that have thus far dominated the study of most protein-based materials.

  15. Game-theoretic model of dispersed material drying process

    NASA Astrophysics Data System (ADS)

    Oleg, Malafeyev; Denis, Rylow; Irina, Zaitseva; Pavel, Zelenkovskii; Marina, Popova; Lydia, Novozhilova

    2017-07-01

    Continuous and discrete game-theoretic models of dispersed material drying process are formalized and studied in the paper. The existence of optimal drying strategies is shown through application of results from the theory of differential games and dynamic programming. These optimal strategies can be found numerically.

  16. Cataloging, Processing, Administering AV Materials. A Model for Wisconsin Schools.

    ERIC Educational Resources Information Center

    Little, Robert D., Ed.

    The objective of this cataloging manual is to recommend specific methods for cataloging audiovisual materials for use in individual school media centers. The following types of audiovisual aids are included: educational games, filmstrips, flat graphics, kits, models, motion pictures, realia, records, slides, sound filmstrips, tapes,…

  17. Physics and Process Modeling (PPM) and Other Propulsion R and T. Volume 1; Materials Processing, Characterization, and Modeling; Lifting Models

    NASA Technical Reports Server (NTRS)

    1997-01-01

    This CP contains the extended abstracts and presentation figures of 36 papers presented at the PPM and Other Propulsion R&T Conference. The focus of the research described in these presentations is on materials and structures technologies that are parts of the various projects within the NASA Aeronautics Propulsion Systems Research and Technology Base Program. These projects include Physics and Process Modeling; Smart, Green Engine; Fast, Quiet Engine; High Temperature Engine Materials Program; and Hybrid Hyperspeed Propulsion. Also presented were research results from the Rotorcraft Systems Program and work supported by the NASA Lewis Director's Discretionary Fund. Authors from NASA Lewis Research Center, industry, and universities conducted research in the following areas: material processing, material characterization, modeling, life, applied life models, design techniques, vibration control, mechanical components, and tribology. Key issues, research accomplishments, and future directions are summarized in this publication.

  18. Energy based model for temperature dependent behavior of ferromagnetic materials

    NASA Astrophysics Data System (ADS)

    Sah, Sanjay; Atulasimha, Jayasimha

    2017-03-01

    An energy based model for temperature dependent anhysteretic magnetization curves of ferromagnetic materials is proposed and benchmarked against experimental data. This is based on the calculation of macroscopic magnetic properties by performing an energy weighted average over all possible orientations of the magnetization vector. Most prior approaches that employ this method are unable to independently account for the effect of both inhomogeneity and temperature in performing the averaging necessary to model experimental data. Here we propose a way to account for both effects simultaneously and benchmark the model against experimental data from 5 K to 300 K for two different materials in both annealed (fewer inhomogeneities) and deformed (more inhomogeneities) samples. This demonstrates that this framework is well suited to simulate temperature dependent experimental magnetic behavior.

  19. Modeling plasma/material interactions during a tokamak disruption

    SciTech Connect

    Hassanein, A.; Konkashbaev, I.

    1994-10-01

    Disruptions in tokamak reactors are still of serious concern and present a potential obstacle for successful operation and reliable design. Erosion of plasma-facing materials due to thermal energy dump during a disruption can severely limit the lifetime of these components, therefore diminishing the economic feasibility of the reactor. A comprehensive disruption erosion model which takes into account the interplay of major physical processes during plasma-material interaction has been developed. The initial burst of energy delivered to facing-material surfaces from direct impact of plasma particles causes sudden ablation of these materials. As a result, a vapor cloud is formed in front of the incident plasma particles. Shortly thereafter, the plasma particles are stopped in the vapor cloud, heating and ionizing it. The energy transmitted to the material surfaces is then dominated by photon radiation. It is the dynamics and the evolution of this vapor cloud that finally determines the net erosion rate and, consequently, the component lifetime. The model integrates with sufficient detail and in a self-consistent way, material thermal evolution response, plasma-vapor interaction physics, vapor hydrodynamics, and radiation transport in order to realistically simulate the effects of a plasma disruption on plasma-facing components. Candidate materials such as beryllium and carbon have been analyzed. The dependence of the net erosion rate on disruption physics and various parameters was analyzed and is discussed.

  20. Test model designs for advanced refractory ceramic materials

    NASA Technical Reports Server (NTRS)

    Tran, Huy Kim

    1993-01-01

    The next generation of space vehicles will be subjected to severe aerothermal loads and will require an improved thermal protection system (TPS) and other advanced vehicle components. In order to ensure the satisfactory performance system (TPS) and other advanced vehicle materials and components, testing is to be performed in environments similar to space flight. The design and fabrication of the test models should be fairly simple but still accomplish test objectives. In the Advanced Refractory Ceramic Materials test series, the models and model holders will need to withstand the required heat fluxes of 340 to 817 W/sq cm or surface temperatures in the range of 2700 K to 3000 K. The model holders should provide one dimensional (1-D) heat transfer to the samples and the appropriate flow field without compromising the primary test objectives. The optical properties such as the effective emissivity, catalytic efficiency coefficients, thermal properties, and mass loss measurements are also taken into consideration in the design process. Therefore, it is the intent of this paper to demonstrate the design schemes for different models and model holders that would accommodate these test requirements and ensure the safe operation in a typical arc jet facility.

  1. High-Fidelity Micromechanics Model Enhanced for Multiphase Particulate Materials

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Arnold, Steven M.

    2003-01-01

    This 3-year effort involves the development of a comprehensive micromechanics model and a related computer code, capable of accurately estimating both the average response and the local stress and strain fields in the individual phases, assuming both elastic and inelastic behavior. During the first year (fiscal year 2001) of the investigation, a version of the model called the High-Fidelity Generalized Method of Cells (HFGMC) was successfully completed for the thermo-inelastic response of continuously reinforced multiphased materials with arbitrary periodic microstructures (refs. 1 and 2). The model s excellent predictive capability for both the macroscopic response and the microlevel stress and strain fields was demonstrated through comparison with exact analytical and finite element solutions. This year, HFGMC was further extended in two technologically significant ways. The first enhancement entailed the incorporation of fiber/matrix debonding capability into the two-dimensional version of HFGMC for modeling the response of unidirectionally reinforced composites such as titanium matrix composites, which exhibit poor fiber/matrix bond. Comparison with experimental data validated the model s predictive capability. The second enhancement entailed further generalization of HFGMC to three dimensions to enable modeling the response of particulate-reinforced (discontinuous) composites in the elastic material behavior domain. Next year, the three-dimensional version will be generalized to encompass inelastic effects due to plasticity, viscoplasticity, and damage, as well as coupled electromagnetothermomechanical (including piezoelectric) effects.

  2. Coupled transport/hyperelastic model for nastic materials

    NASA Astrophysics Data System (ADS)

    Homison, Chris; Weiland, Lisa M.

    2006-03-01

    Nastic materials are high energy density active materials that mimic processes used in the plant kingdom to produce large deformations through the conversion of chemical energy. These materials utilize the controlled transport of charge and fluid across a selectively-permeable membrane to achieve bulk deformation in a process referred to in the plant kingdom as nastic movements. The nastic material being developed consists of synthetic membranes containing biological ion pumps, ion channels, and ion exchangers surrounding fluid-filled cavities embedded within a polymer matrix. In this paper the formulation of a biological transport model and its coupling with a hyperelastic finite element model of the polymer matrix is discussed. The transport model includes contributions from ion pumps, ion exchangers, and solvent flux. This work will form the basis for a feedback loop in material synthesis efforts. The goal of these studies is to determine the relative importance of the various parameters associated with both the polymer matrix and the biological transport components.

  3. Stability of Li-carbon materials: a molecular modeling study

    NASA Astrophysics Data System (ADS)

    Nicolau, Dan V.

    2004-03-01

    Materials with exceptionally high content of carbon are used in technologies with various degrees of added value, from quasi-amorphous materials for carbon electrodes used in e.g. lithium batteries to highly-organized materials comprising e.g. nanotubes and fullerenes. The present study aims to test the feasibility of predicting the properties of carbon based materials using (i) molecular modeling and simulation techniques for prediction of compositional stability; and (ii) experimental data regarding materials used for lithium batteries as validation data. It has been found that a higher H/C atomic ratio has a complex influence on lithium uptake. The decrease of the number of the aromatic rings will limit the number of lithium ions allowed in the pore and the increase in pore flexibility will induce a more energetically favorable mechanism for lithium ions uptake (folding/house-of-cards formation against pore expansion).

  4. Modelling and Microstructural Characterization of Sintered Metallic Porous Materials.

    PubMed

    Depczynski, Wojciech; Kazala, Robert; Ludwinek, Krzysztof; Jedynak, Katarzyna

    2016-07-12

    This paper presents selected characteristics of the metallic porous materials produced by the sintering of metal powders. The authors focus on materials produced from the iron powder (Fe) of ASC 100.29 and Distaloy SE. ASC 100.29 is formed by atomization and has a characteristic morphology. It consists of spherical particles of different sizes forming agglomerates. Distaloy SE is also based on the sponge-iron. The porous material is prepared using the patented method of sintering the mixture of iron powder ASC 100.29, Fe(III) oxide, Distaloy SE and Fe(III) oxide in the reducing atmosphere of dissociated ammonia. As a result, the materials with open pores of micrometer sizes are obtained. The pores are formed between iron particles bonded by diffusion bridges. The modelling of porous materials containing diffusion bridges that allows for three-dimensional (3D) imaging is presented.

  5. Modelling and Microstructural Characterization of Sintered Metallic Porous Materials

    PubMed Central

    Depczynski, Wojciech; Kazala, Robert; Ludwinek, Krzysztof; Jedynak, Katarzyna

    2016-01-01

    This paper presents selected characteristics of the metallic porous materials produced by the sintering of metal powders. The authors focus on materials produced from the iron powder (Fe) of ASC 100.29 and Distaloy SE. ASC 100.29 is formed by atomization and has a characteristic morphology. It consists of spherical particles of different sizes forming agglomerates. Distaloy SE is also based on the sponge-iron. The porous material is prepared using the patented method of sintering the mixture of iron powder ASC 100.29, Fe(III) oxide, Distaloy SE and Fe(III) oxide in the reducing atmosphere of dissociated ammonia. As a result, the materials with open pores of micrometer sizes are obtained. The pores are formed between iron particles bonded by diffusion bridges. The modelling of porous materials containing diffusion bridges that allows for three-dimensional (3D) imaging is presented. PMID:28773690

  6. A note on the Mooney-Rivlin material model

    NASA Astrophysics Data System (ADS)

    Liu, I.-Shih

    2012-11-01

    In finite elasticity, the Mooney-Rivlin material model for the Cauchy stress tensor T in terms of the left Cauchy-Green strain tensor B is given by T = -pI + s_1 B + s_2 B^{-1}, where p is the pressure and s 1, s 2 are two material constants. It is usually assumed that s 1 > 0 and s 2 ≤ 0, known as E-inequalities, based on the assumption that the free energy function be positive definite for any deformation. In this note, we shall relax this assumption and with a thermodynamic stability analysis, prove that s 2 need not be negative so that some typical behavior of materials under contraction can also be modeled.

  7. Quantitative property-structural relation modeling on polymeric dielectric materials

    NASA Astrophysics Data System (ADS)

    Wu, Ke

    Nowadays, polymeric materials have attracted more and more attention in dielectric applications. But searching for a material with desired properties is still largely based on trial and error. To facilitate the development of new polymeric materials, heuristic models built using the Quantitative Structure Property Relationships (QSPR) techniques can provide reliable "working solutions". In this thesis, the application of QSPR on polymeric materials is studied from two angles: descriptors and algorithms. A novel set of descriptors, called infinite chain descriptors (ICD), are developed to encode the chemical features of pure polymers. ICD is designed to eliminate the uncertainty of polymer conformations and inconsistency of molecular representation of polymers. Models for the dielectric constant, band gap, dielectric loss tangent and glass transition temperatures of organic polymers are built with high prediction accuracy. Two new algorithms, the physics-enlightened learning method (PELM) and multi-mechanism detection, are designed to deal with two typical challenges in material QSPR. PELM is a meta-algorithm that utilizes the classic physical theory as guidance to construct the candidate learning function. It shows better out-of-domain prediction accuracy compared to the classic machine learning algorithm (support vector machine). Multi-mechanism detection is built based on a cluster-weighted mixing model similar to a Gaussian mixture model. The idea is to separate the data into subsets where each subset can be modeled by a much simpler model. The case study on glass transition temperature shows that this method can provide better overall prediction accuracy even though less data is available for each subset model. In addition, the techniques developed in this work are also applied to polymer nanocomposites (PNC). PNC are new materials with outstanding dielectric properties. As a key factor in determining the dispersion state of nanoparticles in the polymer matrix

  8. Modelling cavitation erosion using fluid–material interaction simulations

    PubMed Central

    Chahine, Georges L.; Hsiao, Chao-Tsung

    2015-01-01

    Material deformation and pitting from cavitation bubble collapse is investigated using fluid and material dynamics and their interaction. In the fluid, a novel hybrid approach, which links a boundary element method and a compressible finite difference method, is used to capture non-spherical bubble dynamics and resulting liquid pressures efficiently and accurately. The bubble dynamics is intimately coupled with a finite-element structure model to enable fluid/structure interaction simulations. Bubble collapse loads the material with high impulsive pressures, which result from shock waves and bubble re-entrant jet direct impact on the material surface. The shock wave loading can be from the re-entrant jet impact on the opposite side of the bubble, the fast primary collapse of the bubble, and/or the collapse of the remaining bubble ring. This produces high stress waves, which propagate inside the material, cause deformation, and eventually failure. A permanent deformation or pit is formed when the local equivalent stresses exceed the material yield stress. The pressure loading depends on bubble dynamics parameters such as the size of the bubble at its maximum volume, the bubble standoff distance from the material wall and the pressure driving the bubble collapse. The effects of standoff and material type on the pressure loading and resulting pit formation are highlighted and the effects of bubble interaction on pressure loading and material deformation are preliminarily discussed. PMID:26442140

  9. Modelling cavitation erosion using fluid-material interaction simulations.

    PubMed

    Chahine, Georges L; Hsiao, Chao-Tsung

    2015-10-06

    Material deformation and pitting from cavitation bubble collapse is investigated using fluid and material dynamics and their interaction. In the fluid, a novel hybrid approach, which links a boundary element method and a compressible finite difference method, is used to capture non-spherical bubble dynamics and resulting liquid pressures efficiently and accurately. The bubble dynamics is intimately coupled with a finite-element structure model to enable fluid/structure interaction simulations. Bubble collapse loads the material with high impulsive pressures, which result from shock waves and bubble re-entrant jet direct impact on the material surface. The shock wave loading can be from the re-entrant jet impact on the opposite side of the bubble, the fast primary collapse of the bubble, and/or the collapse of the remaining bubble ring. This produces high stress waves, which propagate inside the material, cause deformation, and eventually failure. A permanent deformation or pit is formed when the local equivalent stresses exceed the material yield stress. The pressure loading depends on bubble dynamics parameters such as the size of the bubble at its maximum volume, the bubble standoff distance from the material wall and the pressure driving the bubble collapse. The effects of standoff and material type on the pressure loading and resulting pit formation are highlighted and the effects of bubble interaction on pressure loading and material deformation are preliminarily discussed.

  10. Modeling of shape memory alloys and application to porous materials

    NASA Astrophysics Data System (ADS)

    Panico, Michele

    In the last two decades the number of innovative applications for advanced materials has been rapidly increasing. Shape memory alloys (SMAs) are an exciting class of these materials which exhibit large reversible stresses and strains due to a thermoelastic phase transformation. SMAs have been employed in the biomedical field for producing cardiovascular stents, shape memory foams have been successfully tested as bone implant material, and SMAs are being used as deployable switches in aerospace applications. The behavior of shape memory alloys is intrinsically complex due to the coupling of phase transformation with thermomechanical loading, so it is critical for constitutive models to correctly simulate their response over a wide range of stress and temperature. In the first part of this dissertation, we propose a macroscopic phenomenological model for SMAs that is based on the classical framework of thermodynamics of irreversible processes and accounts for the effect of multiaxial stress states and non-proportional loading histories. The model is able to account for the evolution of both self-accommodated and oriented martensite. Moreover, reorientation of the product phase according to loading direction is specifically accounted for. Computational tests demonstrate the ability of the model to simulate the main aspects of the shape memory response in a one-dimensional setting and some of the features that have been experimentally found in the case of multi-axial non-proportional loading histories. In the second part of this dissertation, this constitutive model has been used to study the mesoscopic behavior of porous shape memory alloys with particular attention to the mechanical response under cyclic loading conditions. In order to perform numerical simulations, the model was implemented into the commercial finite element code ABAQUS. Due to stress concentrations in a porous microstructure, the constitutive law was enhanced to account for the development of

  11. Multiscale and Multiphysics Modeling of Additive Manufacturing of Advanced Materials

    NASA Technical Reports Server (NTRS)

    Liou, Frank; Newkirk, Joseph; Fan, Zhiqiang; Sparks, Todd; Chen, Xueyang; Fletcher, Kenneth; Zhang, Jingwei; Zhang, Yunlu; Kumar, Kannan Suresh; Karnati, Sreekar

    2015-01-01

    The objective of this proposed project is to research and develop a prediction tool for advanced additive manufacturing (AAM) processes for advanced materials and develop experimental methods to provide fundamental properties and establish validation data. Aircraft structures and engines demand materials that are stronger, useable at much higher temperatures, provide less acoustic transmission, and enable more aeroelastic tailoring than those currently used. Significant improvements in properties can only be achieved by processing the materials under nonequilibrium conditions, such as AAM processes. AAM processes encompass a class of processes that use a focused heat source to create a melt pool on a substrate. Examples include Electron Beam Freeform Fabrication and Direct Metal Deposition. These types of additive processes enable fabrication of parts directly from CAD drawings. To achieve the desired material properties and geometries of the final structure, assessing the impact of process parameters and predicting optimized conditions with numerical modeling as an effective prediction tool is necessary. The targets for the processing are multiple and at different spatial scales, and the physical phenomena associated occur in multiphysics and multiscale. In this project, the research work has been developed to model AAM processes in a multiscale and multiphysics approach. A macroscale model was developed to investigate the residual stresses and distortion in AAM processes. A sequentially coupled, thermomechanical, finite element model was developed and validated experimentally. The results showed the temperature distribution, residual stress, and deformation within the formed deposits and substrates. A mesoscale model was developed to include heat transfer, phase change with mushy zone, incompressible free surface flow, solute redistribution, and surface tension. Because of excessive computing time needed, a parallel computing approach was also tested. In addition

  12. Life Modeling and Design Analysis for Ceramic Matrix Composite Materials

    NASA Technical Reports Server (NTRS)

    2005-01-01

    The primary research efforts focused on characterizing and modeling static failure, environmental durability, and creep-rupture behavior of two classes of ceramic matrix composites (CMC), silicon carbide fibers in a silicon carbide matrix (SiC/SiC) and carbon fibers in a silicon carbide matrix (C/SiC). An engineering life prediction model (Probabilistic Residual Strength model) has been developed specifically for CMCs. The model uses residual strength as the damage metric for evaluating remaining life and is posed probabilistically in order to account for the stochastic nature of the material s response. In support of the modeling effort, extensive testing of C/SiC in partial pressures of oxygen has been performed. This includes creep testing, tensile testing, half life and residual tensile strength testing. C/SiC is proposed for airframe and propulsion applications in advanced reusable launch vehicles. Figures 1 and 2 illustrate the models predictive capabilities as well as the manner in which experimental tests are being selected in such a manner as to ensure sufficient data is available to aid in model validation.

  13. Modeling of space environment impact on nanostructured materials. General principles

    NASA Astrophysics Data System (ADS)

    Voronina, Ekaterina; Novikov, Lev

    2016-07-01

    In accordance with the resolution of ISO TC20/SC14 WG4/WG6 joint meeting, Technical Specification (TS) 'Modeling of space environment impact on nanostructured materials. General principles' which describes computer simulation methods of space environment impact on nanostructured materials is being prepared. Nanomaterials surpass traditional materials for space applications in many aspects due to their unique properties associated with nanoscale size of their constituents. This superiority in mechanical, thermal, electrical and optical properties will evidently inspire a wide range of applications in the next generation spacecraft intended for the long-term (~15-20 years) operation in near-Earth orbits and the automatic and manned interplanetary missions. Currently, ISO activity on developing standards concerning different issues of nanomaterials manufacturing and applications is high enough. Most such standards are related to production and characterization of nanostructures, however there is no ISO documents concerning nanomaterials behavior in different environmental conditions, including the space environment. The given TS deals with the peculiarities of the space environment impact on nanostructured materials (i.e. materials with structured objects which size in at least one dimension lies within 1-100 nm). The basic purpose of the document is the general description of the methodology of applying computer simulation methods which relate to different space and time scale to modeling processes occurring in nanostructured materials under the space environment impact. This document will emphasize the necessity of applying multiscale simulation approach and present the recommendations for the choice of the most appropriate methods (or a group of methods) for computer modeling of various processes that can occur in nanostructured materials under the influence of different space environment components. In addition, TS includes the description of possible

  14. A Predictive Model of Fragmentation using Adaptive Mesh Refinement and a Hierarchical Material Model

    SciTech Connect

    Koniges, A E; Masters, N D; Fisher, A C; Anderson, R W; Eder, D C; Benson, D; Kaiser, T B; Gunney, B T; Wang, P; Maddox, B R; Hansen, J F; Kalantar, D H; Dixit, P; Jarmakani, H; Meyers, M A

    2009-03-03

    Fragmentation is a fundamental material process that naturally spans spatial scales from microscopic to macroscopic. We developed a mathematical framework using an innovative combination of hierarchical material modeling (HMM) and adaptive mesh refinement (AMR) to connect the continuum to microstructural regimes. This framework has been implemented in a new multi-physics, multi-scale, 3D simulation code, NIF ALE-AMR. New multi-material volume fraction and interface reconstruction algorithms were developed for this new code, which is leading the world effort in hydrodynamic simulations that combine AMR with ALE (Arbitrary Lagrangian-Eulerian) techniques. The interface reconstruction algorithm is also used to produce fragments following material failure. In general, the material strength and failure models have history vector components that must be advected along with other properties of the mesh during remap stage of the ALE hydrodynamics. The fragmentation models are validated against an electromagnetically driven expanding ring experiment and dedicated laser-based fragmentation experiments conducted at the Jupiter Laser Facility. As part of the exit plan, the NIF ALE-AMR code was applied to a number of fragmentation problems of interest to the National Ignition Facility (NIF). One example shows the added benefit of multi-material ALE-AMR that relaxes the requirement that material boundaries must be along mesh boundaries.

  15. Modeling organohalide perovskites for photovoltaic applications: From materials to interfaces

    NASA Astrophysics Data System (ADS)

    de Angelis, Filippo

    2015-03-01

    The field of hybrid/organic photovoltaics has been revolutionized in 2012 by the first reports of solid-state solar cells based on organohalide perovskites, now topping at 20% efficiency. First-principles modeling has been widely applied to the dye-sensitized solar cells field, and more recently to perovskite-based solar cells. The computational design and screening of new materials has played a major role in advancing the DSCs field. Suitable modeling strategies may also offer a view of the crucial heterointerfaces ruling the device operational mechanism. I will illustrate how simulation tools can be employed in the emerging field of perovskite solar cells. The performance of the proposed simulation toolbox along with the fundamental modeling strategies are presented using selected examples of relevant materials and interfaces. The main issue with hybrid perovskite modeling is to be able to accurately describe their structural, electronic and optical features. These materials show a degree of short range disorder, due to the presence of mobile organic cations embedded within the inorganic matrix, requiring to average their properties over a molecular dynamics trajectory. Due to the presence of heavy atoms (e.g. Sn and Pb) their electronic structure must take into account spin-orbit coupling (SOC) in an effective way, possibly including GW corrections. The proposed SOC-GW method constitutes the basis for tuning the materials electronic and optical properties, rationalizing experimental trends. Modeling charge generation in perovskite-sensitized TiO2 interfaces is then approached based on a SOC-DFT scheme, describing alignment of energy levels in a qualitatively correct fashion. The role of interfacial chemistry on the device performance is finally discussed. The research leading to these results has received funding from the European Union Seventh Framework Programme [FP7/2007 2013] under Grant Agreement No. 604032 of the MESO project.

  16. Multiscale Modeling of Irradiation effects in Fusion Materials

    SciTech Connect

    Hussein Zbib

    2004-12-23

    The aim of this collaborative research work was to apply predictive, physically based multiscale modeling to improve understanding of the underlying mechanisms of material changes in the fusion environment, with the ultimate objective to aid development of advanced materials. The multiscale modeling methodology involved a hierarchical approach, integrating ab initio electronic structure calculations, molecular dynamics (MD) simulations, kinetic Monte Carlo (KMC), and three dimensional dislocation dynamics (DD) simulations, over the relevant length and time scales to model the fates of defects and solutes (including hydrogen and helium) and thus, predict microstructural evolution in ferritic/martensitic and vanadium based alloys. The main task at WSU was to investigate changes in mechanical properties as a result of the production of a varied population of nanostructural features and to be obtained from three dimensional dislocation dynamics simulation (DD). The initial dislocation structure and microstructure could be obtained from electron microscopy characterization and the appropriate nanostructural features produced during irradiation are introduced from predictions of the multiscale modeling. The dislocation structure was then allowed to evolve under an applied load, taking into account all possible forces and reactions between the dislocations with the radiation induced nanostructure as well as network dislocations. In this manner, quantitative predictions of irradiation hardening would result without the use of empirical constants within the framework of dispersed barrier hardening models.

  17. Modeling multiscale evolution of numerous voids in shocked brittle material.

    PubMed

    Yu, Yin; Wang, Wenqiang; He, Hongliang; Lu, Tiecheng

    2014-04-01

    The influence of the evolution of numerous voids on macroscopic properties of materials is a multiscale problem that challenges computational research. A shock-wave compression model for brittle material, which can obtain both microscopic evolution and macroscopic shock properties, was developed using discrete element methods (lattice model). Using a model interaction-parameter-mapping procedure, qualitative features, as well as trends in the calculated shock-wave profiles, are shown to agree with experimental results. The shock wave splits into an elastic wave and a deformation wave in porous brittle materials, indicating significant shock plasticity. Void collapses in the deformation wave were the natural reason for volume shrinkage and deformation. However, media slippage and rotation deformations indicated by complex vortex patterns composed of relative velocity vectors were also confirmed as an important source of shock plasticity. With increasing pressure, the contribution from slippage deformation to the final plastic strain increased. Porosity was found to determine the amplitude of the elastic wave; porosity and shock stress together determine propagation speed of the deformation wave, as well as stress and strain on the final equilibrium state. Thus, shock behaviors of porous brittle material can be systematically designed for specific applications.

  18. Multi-Material ALE with AMR for Modeling Hot Plasmas and Cold Fragmenting Materials

    NASA Astrophysics Data System (ADS)

    Alice, Koniges; Nathan, Masters; Aaron, Fisher; David, Eder; Wangyi, Liu; Robert, Anderson; David, Benson; Andrea, Bertozzi

    2015-02-01

    We have developed a new 3D multi-physics multi-material code, ALE-AMR, which combines Arbitrary Lagrangian Eulerian (ALE) hydrodynamics with Adaptive Mesh Refinement (AMR) to connect the continuum to the microstructural regimes. The code is unique in its ability to model hot radiating plasmas and cold fragmenting solids. New numerical techniques were developed for many of the physics packages to work efficiently on a dynamically moving and adapting mesh. We use interface reconstruction based on volume fractions of the material components within mixed zones and reconstruct interfaces as needed. This interface reconstruction model is also used for void coalescence and fragmentation. A flexible strength/failure framework allows for pluggable material models, which may require material history arrays to determine the level of accumulated damage or the evolving yield stress in J2 plasticity models. For some applications laser rays are propagating through a virtual composite mesh consisting of the finest resolution representation of the modeled space. A new 2nd order accurate diffusion solver has been implemented for the thermal conduction and radiation transport packages. One application area is the modeling of laser/target effects including debris/shrapnel generation. Other application areas include warm dense matter, EUV lithography, and material wall interactions for fusion devices.

  19. Compendium of Material Composition Data for Radiation Transport Modeling

    SciTech Connect

    McConn, Ronald J.; Gesh, Christopher J.; Pagh, Richard T.; Rucker, Robert A.; Williams III, Robert

    2011-03-04

    Introduction Meaningful simulations of radiation transport applications require realistic definitions of material composition and densities. When seeking that information for applications in fields such as homeland security, radiation shielding and protection, and criticality safety, researchers usually encounter a variety of materials for which elemental compositions are not readily available or densities are not defined. Publication of the Compendium of Material Composition Data for Radiation Transport Modeling, Revision 0, in 2006 was the first step toward mitigating this problem. Revision 0 of this document listed 121 materials, selected mostly from the combined personal libraries of staff at the Pacific Northwest National Laboratory (PNNL), and thus had a scope that was recognized at the time to be limited. Nevertheless, its creation did provide a well-referenced source of some unique or hard-to-define material data in a format that could be used directly in radiation transport calculations being performed at PNNL. Moreover, having a single common set of material definitions also helped to standardize at least one aspect of the various modeling efforts across the laboratory by providing separate researchers the ability to compare different model results using a common basis of materials. The authors of the 2006 compendium understood that, depending on its use and feedback, the compendium would need to be revised to correct errors or inconsistencies in the data for the original 121 materials, as well as to increase (per users suggestions) the number of materials listed. This 2010 revision of the compendium has accomplished both of those objectives. The most obvious change is the increased number of materials from 121 to 372. The not-so-obvious change is the mechanism used to produce the data listed here. The data listed in the 2006 document were compiled, evaluated, entered, and error-checked by a group of individuals essentially by hand, providing no library

  20. Modeling Materials: Design for Planetary Entry, Electric Aircraft, and Beyond

    NASA Technical Reports Server (NTRS)

    Thompson, Alexander; Lawson, John W.

    2014-01-01

    NASA missions push the limits of what is possible. The development of high-performance materials must keep pace with the agency's demanding, cutting-edge applications. Researchers at NASA's Ames Research Center are performing multiscale computational modeling to accelerate development times and further the design of next-generation aerospace materials. Multiscale modeling combines several computationally intensive techniques ranging from the atomic level to the macroscale, passing output from one level as input to the next level. These methods are applicable to a wide variety of materials systems. For example: (a) Ultra-high-temperature ceramics for hypersonic aircraft-we utilized the full range of multiscale modeling to characterize thermal protection materials for faster, safer air- and spacecraft, (b) Planetary entry heat shields for space vehicles-we computed thermal and mechanical properties of ablative composites by combining several methods, from atomistic simulations to macroscale computations, (c) Advanced batteries for electric aircraft-we performed large-scale molecular dynamics simulations of advanced electrolytes for ultra-high-energy capacity batteries to enable long-distance electric aircraft service; and (d) Shape-memory alloys for high-efficiency aircraft-we used high-fidelity electronic structure calculations to determine phase diagrams in shape-memory transformations. Advances in high-performance computing have been critical to the development of multiscale materials modeling. We used nearly one million processor hours on NASA's Pleiades supercomputer to characterize electrolytes with a fidelity that would be otherwise impossible. For this and other projects, Pleiades enables us to push the physics and accuracy of our calculations to new levels.

  1. Fracture surfaces of heterogeneous materials: A 2D solvable model

    NASA Astrophysics Data System (ADS)

    Katzav, E.; Adda-Bedia, M.; Derrida, B.

    2007-05-01

    Using an elastostatic description of crack growth based on the Griffith criterion and the principle of local symmetry, we present a stochastic model describing the propagation of a crack tip in a 2D heterogeneous brittle material. The model ensures the stability of straight cracks and allows for the study of the roughening of fracture surfaces. When neglecting the effect of the nonsingular stress, the problem becomes exactly solvable and yields analytic predictions for the power spectrum of the paths. This result suggests an alternative to the conventional power law analysis often used in the analysis of experimental data.

  2. Force models for particle-dynamics simulations of granular materials

    SciTech Connect

    Walton, O.R.

    1994-12-01

    Engineering-mechanics contact models are utilized to describe the inelastic, frictional interparticle forces acting in dry granular systems. Simple analyses based on one-dimensional chains are utilized to illustrate wave propagation phenomena in dense and dilute discrete particulates. The variation of restitution coefficient with impact velocity is illustrated for a variety of viscous and hysteretic normal force models. The effects of interparticle friction on material strength in discrete-particle simulations are much closer to measured values than are theories that do not allow article rotations.

  3. Micromechanical modelling of quasi-brittle materials behavior

    SciTech Connect

    Li, V.C.

    1992-12-01

    This special issues on Micromechanical modelling of quasi-brittle materials behavior represents an outgrowth of presentations given at a symposium of the same title held at the 1991 ASME Applied Mechanics and Biomechanics Summer Conference at the Ohio State University. The symposium was organized to promote communication between researchers in three materials groups: rock, cementitious materials, ceramics and related composites. The enthusiastic response of both speakers and attendants at the ASME symposium convinced the organizer that it would be useful to put together a coherent volume which can reach a larger audience. It was decided that the papers individually and as a volume ought to provide a broader view, so that as much as possible, the work contained in each paper would be accessible to readers working in any of the three materials groups. Applied Mechanics Reviews presents an appropriate platform for achieving these objectives.

  4. An ion diffusion model in semi-permeable clay materials.

    PubMed

    Liu, Chongxuan

    2007-08-01

    Clay materials typically contain negative surface charges that induce electrostatic fields (or diffuse double layers) in electrolytes. During ion diffusion in a porous medium of clay materials, ions dynamically interact with the electrostatic fields associated with individual clay grains by depressing or expanding the electrostatic double layers, which subsequently affects ionic fluxes. Current theory of ion transport in porous media, however, cannot explicitly account for the dynamic interactions. Here we proposed a model by coupling electrodynamics and nonequilibrium thermodynamics (EDNT) to describe ion diffusion in clay materials as a complex function of factors including clay surface charge density, tortuosity, porosity, chemicoosmotic coefficient, and ion self-diffusivity. The model was validated by comparing the calculated and measured apparent ion diffusion coefficients in clay materials as a function of ionic strength. At transitional states, ion diffusive fluxes are dynamically related to the electrostatic fields, which shrink or expand as ion diffusion occurs. At steady states, the electrostatic fields are time-invariant and ion diffusive fluxes conform to flux and concentration gradient relationships; and apparent diffusivity can be approximated by the ion diffusivity in bulk electrolytes corrected by a tortuosity factor and macroscopic concentration discontinuities at the interfaces between clay materials and bulk solutions.

  5. A 3D Orthotropic Elastic Continuum Damage Material Model

    SciTech Connect

    English, Shawn Allen; Brown, Arthur A.

    2013-08-01

    A three dimensional orthotropic elastic constitutive model with continuum damage is implemented for polymer matrix composite lamina. Damage evolves based on a quadratic homogeneous function of thermodynamic forces in the orthotropic planes. A small strain formulation is used to assess damage. In order to account for large deformations, a Kirchhoff material formulation is implemented and coded for numerical simulation in Sandia’s Sierra Finite Element code suite. The theoretical formulation is described in detail. An example of material parameter determination is given and an example is presented.

  6. Verification of a Finite Element Model for Pyrolyzing Ablative Materials

    NASA Technical Reports Server (NTRS)

    Risch, Timothy K.

    2017-01-01

    Ablating thermal protection system (TPS) materials have been used in many reentering spacecraft and in other applications such as rocket nozzle linings, fire protection materials, and as countermeasures for directed energy weapons. The introduction of the finite element model to the analysis of ablation has arguably resulted in improved computational capabilities due the flexibility and extended applicability of the method, especially to complex geometries. Commercial finite element codes often provide enhanced capability compared to custom, specially written programs based on versatility, usability, pre- and post-processing, grid generation, total life-cycle costs, and speed.

  7. Lifelong modelling of properties for materials with technological memory

    NASA Astrophysics Data System (ADS)

    Falaleev, AP; Meshkov, VV; Vetrogon, AA; Ogrizkov, SV; Shymchenko, AV

    2016-10-01

    An investigation of real automobile parts produced from dual phase steel during standard periods of life cycle is presented, which considers such processes as stamping, exploitation, automobile accident, and further repair. The development of the phenomenological model of the mechanical properties of such parts was based on the two surface plastic theory of Chaboche. As a consequence of the composite structure of dual phase steel, it was shown that local mechanical properties of parts produced from this material change significantly their during their life cycle, depending on accumulated plastic deformations and thermal treatments. Such mechanical property changes have a considerable impact on the accuracy of the computer modelling of automobile behaviour. The most significant errors of modelling were obtained at the critical operating conditions, such as crashes and accidents. The model developed takes into account the kinematics (Bauschinger effect), isotropic hardening, non-linear elastic steel behaviour and changes caused by the thermal treatment. Using finite element analysis, the model allows the evaluation of the passive safety of a repaired car body, and enables increased restoration accuracy following an accident. The model was confirmed experimentally for parts produced from dual phase steel DP780.

  8. Fatigue life prediction modeling for turbine hot section materials

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

    1988-01-01

    A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

  9. Fatigue life prediction modeling for turbine hot section materials

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

    1988-01-01

    A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

  10. Fatigue life prediction modeling for turbine hot section materials

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

    1989-01-01

    A major objective of the fatigue and fracture efforts under the NASA Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

  11. Material instability in granular assemblies from fundamentally different models

    NASA Astrophysics Data System (ADS)

    Sibille, L.; Nicot, F.; Donzé, F. V.; Darve, F.

    2007-03-01

    Three fundamentally different models: a phenomenological constitutive relation, a micro-mechanical model and direct numerical simulations by Distinct Element Method (DEM) are compared in this paper. In addition, the local form of Hill's sufficient condition of stability (i.e. the vanishing of the second-order work d2W) is considered to describe material instabilities in granular assemblies. Stress probes in the axisymmetric plane of stress increments are achieved with all three models to check whether d2W vanishes at different stress-strain states. For all the models, cones of unstable stress directions (cones of stress probe directions for which d2W = 0) are found and they appear for stress states strictly inside the plastic limit condition. Thus, independently of the model, a bifurcation domain exists inside the plastic limit condition which can describe the sudden collapses of sand samples observed in laboratory tests before reaching the Mohr-Coulomb criterion. Taking advantage of the different models considered, the vanishing of the second-order work is linked to the existence of non-associated plastic strains and to micro-mechanical bases. Copyright

  12. Bayesian methods for characterizing unknown parameters of material models

    SciTech Connect

    Emery, J. M.; Grigoriu, M. D.; Field Jr., R. V.

    2016-02-04

    A Bayesian framework is developed for characterizing the unknown parameters of probabilistic models for material properties. In this framework, the unknown parameters are viewed as random and described by their posterior distributions obtained from prior information and measurements of quantities of interest that are observable and depend on the unknown parameters. The proposed Bayesian method is applied to characterize an unknown spatial correlation of the conductivity field in the definition of a stochastic transport equation and to solve this equation by Monte Carlo simulation and stochastic reduced order models (SROMs). As a result, the Bayesian method is also employed to characterize unknown parameters of material properties for laser welds from measurements of peak forces sustained by these welds.

  13. Bayesian methods for characterizing unknown parameters of material models

    DOE PAGES

    Emery, J. M.; Grigoriu, M. D.; Field Jr., R. V.

    2016-02-04

    A Bayesian framework is developed for characterizing the unknown parameters of probabilistic models for material properties. In this framework, the unknown parameters are viewed as random and described by their posterior distributions obtained from prior information and measurements of quantities of interest that are observable and depend on the unknown parameters. The proposed Bayesian method is applied to characterize an unknown spatial correlation of the conductivity field in the definition of a stochastic transport equation and to solve this equation by Monte Carlo simulation and stochastic reduced order models (SROMs). As a result, the Bayesian method is also employed tomore » characterize unknown parameters of material properties for laser welds from measurements of peak forces sustained by these welds.« less

  14. Dynamic material modeling in hot forging. Progress report 4

    SciTech Connect

    El-Gizawy, A.S.

    1992-03-01

    A dynamic material model that characterized flow behavior in the workpiece under forging conditions was required to optimize the process and produce defect-free product at minimum cost. Constitutive equations describe the relationship between stress, strain rate, and temperature under forging conditions. Using aluminum alloy 7050, numerous deformation experiments were conducted to fully characterize constitutive equation variables. A thorough description of the experimental arrangement was provided. Flow data and efficiency data were assembled into a three-dimensional plot of temperature vs. strain rate vs. deformation efficiency to produce an efficiency map. The efficiency map provided the information required for optimization of forging process design. The results of dynamic modeling of the material were used in simulating the isothermal forging of a particular part. Recommendations concerning optimum preform design and processing conditions were reported.

  15. Arctic sea ice modeling with the material-point method.

    SciTech Connect

    Peterson, Kara J.; Bochev, Pavel Blagoveston

    2010-04-01

    Arctic sea ice plays an important role in global climate by reflecting solar radiation and insulating the ocean from the atmosphere. Due to feedback effects, the Arctic sea ice cover is changing rapidly. To accurately model this change, high-resolution calculations must incorporate: (1) annual cycle of growth and melt due to radiative forcing; (2) mechanical deformation due to surface winds, ocean currents and Coriolis forces; and (3) localized effects of leads and ridges. We have demonstrated a new mathematical algorithm for solving the sea ice governing equations using the material-point method with an elastic-decohesive constitutive model. An initial comparison with the LANL CICE code indicates that the ice edge is sharper using Materials-Point Method (MPM), but that many of the overall features are similar.

  16. Computational modelling of cohesive cracks in material structures

    NASA Astrophysics Data System (ADS)

    Vala, J.; Jarošová, P.

    2016-06-01

    Analysis of crack formation, considered as the creation of new surfaces in a material sample due to its microstructure, leads to nontrivial physical, mathematical and computational difficulties even in the rather simple case of quasistatic cohesive zone modelling inside the linear elastic theory. However, quantitative results from such evaluations are required in practice for the development and design of advanced materials, structures and technologies. Although most available software tools apply ad hoc computational predictions, this paper presents the proper formulation of such model problem, including its verification, and sketches the more-scale construction of finite-dimensional approximation of solutions, utilizing the finite element or similar techniques, together with references to original simulations results from engineering practice.

  17. Multiscale modeling for materials design: Molecular square catalysts

    NASA Astrophysics Data System (ADS)

    Majumder, Debarshi

    In a wide variety of materials, including a number of heterogeneous catalysts, the properties manifested at the process scale are a consequence of phenomena that occur at different time and length scales. Recent experimental developments allow materials to be designed precisely at the nanometer scale. However, the optimum design of such materials requires capabilities to predict the properties at the process scale based on the phenomena occurring at the relevant scales. The thesis research reported here addresses this need to develop multiscale modeling strategies for the design of new materials. As a model system, a new system of materials called molecular squares was studied in this research. Both serial and parallel multiscale strategies and their components were developed as parts of this work. As a serial component, a parameter estimation tool was developed that uses a hierarchical protocol and consists of two different search elements: a global search method implemented using a genetic algorithm that is capable of exploring large parametric space, and a local search method using gradient search techniques that accurately finds the optimum in a localized space. As an essential component of parallel multiscale modeling, different standard as well as specialized computational fluid dynamics (CFD) techniques were explored and developed in order to identify a technique that is best suited to solve a membrane reactor model employing layered films of molecular squares as the heterogeneous catalyst. The coupled set of non-linear partial differential equations (PDEs) representing the continuum model was solved numerically using three different classes of methods: a split-step method using finite difference (FD); domain decomposition in two different forms, one involving three overlapping subdomains and the other involving a gap-tooth scheme; and the multiple-timestep method that was developed in this research. The parallel multiscale approach coupled continuum

  18. Turning statistical physics models into materials design engines.

    PubMed

    Miskin, Marc Z; Khaira, Gurdaman; de Pablo, Juan J; Jaeger, Heinrich M

    2016-01-05

    Despite the success statistical physics has enjoyed at predicting the properties of materials for given parameters, the inverse problem, identifying which material parameters produce given, desired properties, is only beginning to be addressed. Recently, several methods have emerged across disciplines that draw upon optimization and simulation to create computer programs that tailor material responses to specified behaviors. However, so far the methods developed either involve black-box techniques, in which the optimizer operates without explicit knowledge of the material's configuration space, or require carefully tuned algorithms with applicability limited to a narrow subclass of materials. Here we introduce a formalism that can generate optimizers automatically by extending statistical mechanics into the realm of design. The strength of this approach lies in its capability to transform statistical models that describe materials into optimizers to tailor them. By comparing against standard black-box optimization methods, we demonstrate how optimizers generated by this formalism can be faster and more effective, while remaining straightforward to implement. The scope of our approach includes possibilities for solving a variety of complex optimization and design problems concerning materials both in and out of equilibrium.

  19. Turning statistical physics models into materials design engines

    SciTech Connect

    Miskin, Marc Z.; Khaira, Gurdaman; de Pablo, Juan J.; Jaeger, Heinrich M.

    2015-12-18

    Despite the success statistical physics has enjoyed at predicting the properties of materials for given parameters, the inverse problem, identifying which material parameters produce given, desired properties, is only beginning to be addressed. Recently, several methods have emerged across disciplines that draw upon optimization and simulation to create computer programs that tailor material responses to specified behaviors. However, so far the methods developed either involve black-box techniques, in which the optimizer operates without explicit knowledge of the material's configuration space, or require carefully tuned algorithms with applicability limited to a narrow subclass of materials. Here we introduce a formalism that can generate optimizers automatically by extending statistical mechanics into the realm of design. The strength of this approach lies in its capability to transform statistical models that describe materials into optimizers to tailor them. By comparing against standard black-box optimization methods, we demonstrate how optimizers generated by this formalism can be faster and more effective, while remaining straightforward to implement. The scope of our approach includes possibilities for solving a variety of complex optimization and design problems concerning materials both in and out of equilibrium.

  20. Material-specific transfer function model and SNR in CT.

    PubMed

    Brunner, Claudia C; Kyprianou, Iacovos S

    2013-10-21

    This study presents an analytical model for the edge spread function (ESF) of a clinical CT system that allows reliable fits of noisy ESF data. The model was used for the calculation of the material-specific transfer function TF and an estimation of the signal transfer and the signal-to-noise ratio (SNR) in 2D. Images of the Catphan phantom were acquired with a clinical Siemens Somatom Sensation Cardiac 64 CT scanner combining four different x-ray tube outputs (40, 150, 250 and 350 mAs) with four different reconstruction filters, which covered the range from very smooth (B10s) to very sharp (B70s). The images of the high- and mid-contrast cylinders of the phantom's 'Geometry and Sensitometry' module (air, Teflon, Delrin and PMP) were used to sample material-specific ESF curves. The ESF curves were fitted with the analytical model we developed based on a linear combination of Boltzmann and Gaussian functions. The analytical model of the ESF was used to obtain the Fourier-based material-specific transfer function TF, as well as the spatial-domain point spread function (PSF). TF was subsequently used to estimate the signal transfer, which was compared to the actual reconstructed image of a 3.0 mm diameter Teflon pin. The noise power spectrum (NPS) was calculated from images of a uniform water phantom under the same technique parameters. The task-specific SNR was calculated for all technique parameters from the model-based TF, the measured NPS and simulated 3 mm diameter disc signals modeling the aforementioned materials. Bootstrapping was performed to estimate the standard deviation of the TF and the SNR. The analytical model we developed accurately captured the features of the CT ESF data. The coefficient of determination R(2), a metric that describes the goodness of the fit, had a median value of 0.9995, and decreased for low tube output, low contrast and the sharp reconstruction filter. Our analysis showed that ESF, PSF and TF depended not only on the

  1. Material-specific transfer function model and SNR in CT

    NASA Astrophysics Data System (ADS)

    Brunner, Claudia C.; Kyprianou, Iacovos S.

    2013-10-01

    This study presents an analytical model for the edge spread function (ESF) of a clinical CT system that allows reliable fits of noisy ESF data. The model was used for the calculation of the material-specific transfer function TF and an estimation of the signal transfer and the signal-to-noise ratio (SNR) in 2D. Images of the Catphan phantom were acquired with a clinical Siemens Somatom Sensation Cardiac 64 CT scanner combining four different x-ray tube outputs (40, 150, 250 and 350 mAs) with four different reconstruction filters, which covered the range from very smooth (B10s) to very sharp (B70s). The images of the high- and mid-contrast cylinders of the phantom’s ‘Geometry and Sensitometry’ module (air, Teflon, Delrin and PMP) were used to sample material-specific ESF curves. The ESF curves were fitted with the analytical model we developed based on a linear combination of Boltzmann and Gaussian functions. The analytical model of the ESF was used to obtain the Fourier-based material-specific transfer function TF, as well as the spatial-domain point spread function (PSF). TF was subsequently used to estimate the signal transfer, which was compared to the actual reconstructed image of a 3.0 mm diameter Teflon pin. The noise power spectrum (NPS) was calculated from images of a uniform water phantom under the same technique parameters. The task-specific SNR was calculated for all technique parameters from the model-based TF, the measured NPS and simulated 3 mm diameter disc signals modeling the aforementioned materials. Bootstrapping was performed to estimate the standard deviation of the TF and the SNR. The analytical model we developed accurately captured the features of the CT ESF data. The coefficient of determination R2, a metric that describes the goodness of the fit, had a median value of 0.9995, and decreased for low tube output, low contrast and the sharp reconstruction filter. Our analysis showed that ESF, PSF and TF depended not only on the

  2. Modeling of Impact Properties of Auxetic Materials Phase 2

    DTIC Science & Technology

    2014-03-01

    Modeling of Impact Properties of Auxetic Materials – Phase 2 Lei Jiang, Dustin Pearson, Tim Dunbar Martec Limited Prepared By: Martec Limited 400...Manager: Lei Jiang, 902-425-5101 PWGSC Contract Number: W7707-135609/001/HAL CSA: Dr. Jeff Szabo, Defence Scientist, 902-427-3427 The scientific or...specifies the in-plane integration rule for 4-node shell elements. With IRQUAD = 2, “2×2 Gauss quadrature integration is employed”. The

  3. Materials constitutive models for nonlinear analysis of thermally cycled structures

    NASA Technical Reports Server (NTRS)

    Kaufman, A.; Hunt, L. E.

    1982-01-01

    Effects of inelastic materials models on computed stress-strain solutions for thermally loaded structures were studied by performing nonlinear (elastoplastic creep) and elastic structural analyses on a prismatic, double edge wedge specimen of IN 100 alloy that was subjected to thermal cycling in fluidized beds. Four incremental plasticity creep models (isotropic, kinematic, combined isotropic kinematic, and combined plus transient creep) were exercised for the problem by using the MARC nonlinear, finite element computer program. Maximum total strain ranges computed from the elastic and nonlinear analyses agreed within 5 percent. Mean cyclic stresses, inelastic strain ranges, and inelastic work were significantly affected by the choice of inelastic constitutive model. The computing time per cycle for the nonlinear analyses was more than five times that required for the elastic analysis.

  4. A Thermal Model Preprocessor For Graphics And Material Database Generation

    NASA Astrophysics Data System (ADS)

    Jones, Jack C.; Gonda, Teresa G.

    1989-08-01

    The process of developing a physical description of a target for thermal models is a time consuming and tedious task. The problem is one of data collection, data manipulation, and data storage. Information on targets can come from many sources and therefore could be in any form (2-D drawings, 3-D wireframe or solid model representations, etc.). TACOM has developed a preprocessor that decreases the time involved in creating a faceted target representation. This program allows the user to create the graphics for the vehicle and to assign the material properties to the graphics. The vehicle description file is then automatically generated by the preprocessor. By containing all the information in one database, the modeling process is made more accurate and data tracing can be done easily. A bridge to convert other graphics packages (such as BRL-CAD) to a faceted representation is being developed. When the bridge is finished, this preprocessor will be used to manipulate the converted data.

  5. Modeling Permanent Deformations of Superelastic and Shape Memory Materials

    PubMed Central

    Urbano, Marco Fabrizio; Auricchio, Ferdinando

    2015-01-01

    In this paper we propose a modification of the polycrystalline shape memory alloy constitutive model originally proposed by Souza. By introducing a transformation strain energy with two different hardening coefficients, we are able to take into account the effect of the martensitic transformation of unfavorably oriented grains occurring after the main plateau. By choosing a proper second hardening coefficient, it is possible to reproduce the correct stress strain behavior of the material after the plateau without the need of introducing a much smaller Young modulus for martensite. The proposed modification is introduced in the model comprising permanent deformation effects. Model results for uniaxial stress tests are compared to experimental results showing good agreement. PMID:26110494

  6. Extended model of the photoinitiation mechanisms in photopolymer materials

    SciTech Connect

    Liu Shui; Gleeson, Michael R.; Sabol, Dusan; Sheridan, John T.

    2009-11-15

    In order to further improve photopolymer materials for applications such as data storage, a deeper understanding of the photochemical mechanisms which are present during the formation of holographic gratings has become ever more crucial. This is especially true of the photoinitiation processes, since holographic data storage requires multiple sequential short exposures. Previously, models describing the temporal variation in the photosensitizer (dye) concentration as a function of exposure have been presented and applied to two different types of photosensitizer, i.e., Methylene Blue and Erythrosine B, in a polyvinyl alcohol/acrylamide based photopolymer. These models include the effects of photosensitizer recovery and bleaching under certain limiting conditions. In this paper, based on a detailed study of the photochemical reactions, the previous models are further developed to more physically represent these effects. This enables a more accurate description of the time varying dye absorption, recovery, and bleaching, and therefore of the generation of primary radicals in photopolymers containing such dyes.

  7. Multi-Scale Modeling of Cross-Linked Nanotube Materials

    NASA Technical Reports Server (NTRS)

    Frankland, S. J. V.; Odegard, G. M.; Herzog, M. N.; Gates, T. S.; Fay, C. C.

    2005-01-01

    The effect of cross-linking single-walled carbon nanotubes on the Young's modulus of a nanotube-reinforced composite is modeled with a multi-scale method. The Young's modulus is predicted as a function of nanotube volume fraction and cross-link density. In this method, the constitutive properties of molecular representative volume elements are determined using molecular dynamics simulation and equivalent-continuum modeling. The Young's modulus is subsequently calculated for cross-linked nanotubes in a matrix which consists of the unreacted cross-linking agent. Two different cross-linking agents are used in this study, one that is short and rigid (Molecule A), and one that is long and flexible (Molecule B). Direct comparisons between the predicted elastic constants are made for the models in which the nanotubes are either covalently bonded or not chemically bonded to the cross-linking agent. At a nanotube volume fraction of 10%, the Young's modulus of Material A is not affected by nanotube crosslinking, while the Young's modulus of Material B is reduced by 64% when the nanotubes are cross-linked relative to the non-cross-linked material with the same matrix.

  8. Multi-Scale Modeling of Cross-Linked Nanotube Materials

    NASA Technical Reports Server (NTRS)

    Frankland, S. J. V.; Odegard, G. M.; Herzog, M. N.; Gates, T. S.; Fay, C. C.

    2005-01-01

    The effect of cross-linking single-walled carbon nanotubes on the Young's modulus of a nanotube-reinforced composite is modeled with a multi-scale method. The Young's modulus is predicted as a function of nanotube volume fraction and cross-link density. In this method, the constitutive properties of molecular representative volume elements are determined using molecular dynamics simulation and equivalent-continuum modeling. The Young's modulus is subsequently calculated for cross-linked nanotubes in a matrix which consists of the unreacted cross-linking agent. Two different cross-linking agents are used in this study, one that is short and rigid (Molecule A), and one that is long and flexible (Molecule B). Direct comparisons between the predicted elastic constants are made for the models in which the nanotubes are either covalently bonded or not chemically bonded to the cross-linking agent. At a nanotube volume fraction of 10%, the Young's modulus of Material A is not affected by nanotube crosslinking, while the Young's modulus of Material B is reduced by 64% when the nanotubes are cross-linked relative to the non-cross-linked material with the same matrix.

  9. Predictive modeling of infrared detectors and material systems

    NASA Astrophysics Data System (ADS)

    Pinkie, Benjamin

    Detectors sensitive to thermal and reflected infrared radiation are widely used for night-vision, communications, thermography, and object tracking among other military, industrial, and commercial applications. System requirements for the next generation of ultra-high-performance infrared detectors call for increased functionality such as large formats (> 4K HD) with wide field-of-view, multispectral sensitivity, and on-chip processing. Due to the low yield of infrared material processing, the development of these next-generation technologies has become prohibitively costly and time consuming. In this work, it will be shown that physics-based numerical models can be applied to predictively simulate infrared detector arrays of current technological interest. The models can be used to a priori estimate detector characteristics, intelligently design detector architectures, and assist in the analysis and interpretation of existing systems. This dissertation develops a multi-scale simulation model which evaluates the physics of infrared systems from the atomic (material properties and electronic structure) to systems level (modulation transfer function, dense array effects). The framework is used to determine the electronic structure of several infrared materials, optimize the design of a two-color back-to-back HgCdTe photodiode, investigate a predicted failure mechanism for next-generation arrays, and predict the systems-level measurables of a number of detector architectures.

  10. Constitutive model for fiber-reinforced materials with deformable matrices.

    PubMed

    Planas, J; Guinea, G V; Elices, M

    2007-10-01

    A great number of biological structures are composed of fibers (elastin, collagen, etc.) dispersed on an aqueous matrix in such a complex way that a detailed mechanical analysis based on microconstituents is, for practical purposes, out of reach. Consequently, the preferred approach to the mechanical behavior of these materials is based on setting up of constitutive equations that homogenize the behavior while capturing their main microstructural features. This work presents a simple macroscopic model for fiber-reinforced materials with deformable matrices, especially suited to many biological structural tissues. The constitutive equation is derived by imposing equivalence between the virtual works of both the fiber-reinforced and the equivalent continuum media, showing that it is independent of the control volume used for such equivalence. The model is particularized to incompressible materials, and an extension to orthotropic biological fibers is shown. Numerical simulations of uniaxial tests on silk fibers demonstrate the model's ability to capture the progressive alignment of the microconstituents under large deformations.

  11. Industrial application for the Los Alamos Materials Modeling Platform

    SciTech Connect

    Lesar, R.; Charbon, C.; Kothe, D.; Wu, D.; Reddy, A.

    1996-09-01

    This is the final report of a one-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Casting and solidification of molten metals and metal alloys is a critical step in the production of high-quality metal stock and in the fabrication of finished parts. Control of the casting process can be the determining factor in both the quality and cost of the final metal product. Major problems with the quality of cast stock or finished parts can arise because of the difficulty of preventing variations in the alloy content, the generation of porosity or poor surface finish, and the loss of microstructure controlled strength and toughness resulting from the poor understanding and design of the mold filling and solidification processes. In this project, we sought to develop a new set of applications focused on adding the ability to accurately model solidification and grain growth to casting simulations. We implemented these applications within the Los Alamos Materials Modeling Platform, LAMMP, a graphical-based materials, and materials modeling environment being created at the Computational Testbed for Industry.

  12. New kinetic model for thermal decomposition of heterogeneous materials

    SciTech Connect

    Caballero, J.A.; Font, R.; Marcilla, A.; Conesa, J.A.

    1995-03-01

    In the kinetic studies of thermal decomposition of lignocellulosic materials using dynamic TG, relationships between the biomass fraction ``w`` and the time ``t`` of the form dw/dt = {minus}k(w {minus} w{sub {infinity}}){sup n} are usually admitted, and the residue fraction at infinite time (w{sub {infinity}}) is considered constant. However, in heterogeneous solids such as lignocellulosic materials, the different polymers decompose at different temperatures, and so the value of w{sub {infinity}} is not constant, Therefore, the previous equation must be considered approximate. To illustrate this feature, experiments with kraft lignin, which decomposes in an interval of temperatures between 150 and 750 C, have been carried out. A kinetic model is proposed, bearing in mind that there is a maximum pyrolyzable fraction at each temperature. This model considers that the thermal decomposition of a heterogeneous material occurs through a great number of reactions and that at a given temperature only some fractions can decompose. The kinetic parameters (activation energy and preexponential factor) can change during the decomposition process as function of the reactions taking place. Under some assumptions, it is deduced that this model is equivalent to assume the kinetic law dw/dt = {minus}k(w{minus}w{sub {infinity}}) for first-order reaction, where the residue yield w{sub {infinity}} is a function of the temperature.

  13. Formability prediction for AHSS materials using damage models

    NASA Astrophysics Data System (ADS)

    Amaral, R.; Santos, Abel D.; José, César de Sá; Miranda, Sara

    2017-05-01

    Advanced high strength steels (AHSS) are seeing an increased use, mostly due to lightweight design in automobile industry and strict regulations on safety and greenhouse gases emissions. However, the use of these materials, characterized by a high strength to weight ratio, stiffness and high work hardening at early stages of plastic deformation, have imposed many challenges in sheet metal industry, mainly their low formability and different behaviour, when compared to traditional steels, which may represent a defying task, both to obtain a successful component and also when using numerical simulation to predict material behaviour and its fracture limits. Although numerical prediction of critical strains in sheet metal forming processes is still very often based on the classic forming limit diagrams, alternative approaches can use damage models, which are based on stress states to predict failure during the forming process and they can be classified as empirical, physics based and phenomenological models. In the present paper a comparative analysis of different ductile damage models is carried out, in order numerically evaluate two isotropic coupled damage models proposed by Johnson-Cook and Gurson-Tvergaard-Needleman (GTN), each of them corresponding to the first two previous group classification. Finite element analysis is used considering these damage mechanics approaches and the obtained results are compared with experimental Nakajima tests, thus being possible to evaluate and validate the ability to predict damage and formability limits for previous defined approaches.

  14. Mechanical model testing of rebreathing potential in infant bedding materials

    PubMed Central

    Carleton, J.; Donoghue, A.; Porter, W.

    1998-01-01

    Rebreathing of expired air may be a lethal hazard for prone sleeping infants. This paper describes a mechanical model to simulate infant breathing, and examines the effects of bedding on exhaled air retention. Under simulated rebreathing conditions, the model allows the monitoring of raised carbon dioxide (CO2) inside an artificial lung-trachea system. Resulting levels of CO2 (although probably exaggerated in the mechanical model compared with an infant, due to the model's fixed breathing rate and volume) suggest that common bedding materials vary widely in inherent rebreathing potential. In face down tests, maximum airway CO2 ranged from less than 5% on sheets and waterproof mattresses to over 25% on sheepskins, bean bag cushions, and some pillows and comforters. Concentrations of CO2 decreased with increasing head angle of the doll, away from the face down position. Recreations of 29infant death scenes also showed large CO2 increases on some bedding materials, suggesting these infants could have died while rebreathing.

 PMID:9623394

  15. Modelling dynamic compaction of porous materials with the overstress approach

    NASA Astrophysics Data System (ADS)

    Partom, Y.

    2014-05-01

    To model compaction of a porous material we need 1) an equation of state of the porous material in terms of the equation of state of its matrix, and 2) a compaction law. For an equation of state it is common to use Herrmann's suggestion, as in his Pα model. For a compaction law it is common to use a quasi-static compaction relation obtained from 1) a meso-scale model (as in Carroll and Holt's spherical shell model), or from 2) quasi-static tests. Here we are interested in dynamic compaction, like in a planar impact test. In dynamic compaction the state may change too fast for the state point to follow the quasi-static compaction curve. We therefore get an overstress situation. The state point moves out of the quasi-static compaction boundary, and only with time collapses back towards it at a certain rate. In this way the dynamic compaction event becomes rate dependent. In the paper we first write down the rate equations for dynamic compaction according to the overstress approach. We then implement these equations in a hydro-code and run some examples. We show how the overstress rate parameter can be calibrated from tests.

  16. Accounting for nonlinear material characteristics in modeling ferroresonant transformers

    NASA Astrophysics Data System (ADS)

    Voisine, J. T.

    1985-04-01

    A mathematical model relating core material properties, including nonlinear magnetization characteristics, to the performance of ferroresonant transformers has been developed. In accomplishing this, other factors such as fabrication destruction factors, leakage flux, air gap characteristics, loading, and coil resistances and self-inductances are also accounted for. From a material manufacturer's view, knowing such information facilitates isolating sources of performance variations between units of similar design and is therefore highly desirable. The model predicts the primary induction necessary to establish a specified secondary induction and determines peak induction at other points in the magnetic circuit. A study comparing the model with a transformer indicated that each predicted peak induction was within ±5% of the corresponding measured peak induction. A generalized 4-node magnetic circuit having two shunt paths was chosen and modeled. Such a circuit is easily modified facilitating the analyses of numerous other core designs. A computer program designed to run on an HP-41 programmable calculator was also developed and is briefly described.

  17. Biomechanical Stability of Juvidur and Bone Models on Osteosyntesic Materials

    PubMed Central

    Grubor, Predrag; Mitković, Milorad; Grubor, Milan; Mitković, Milan; Meccariello, Luigi; Falzarano, Gabriele

    2016-01-01

    Introduction: Artificial models can be useful at approximate and qualitative research, which should give the preliminary results. Artificial models are usually made of photo-elastic plastic e.g.. juvidur, araldite in the three-dimensional contour shape of the bone. Anatomical preparations consist of the same heterogeneous, structural materials with extremely anisotropic and unequal highly elastic characteristics, which are embedded in a complex organic structure. The aim of the study: Examine the budget voltage and deformation of: dynamic compression plate (DCP), locking compression plate (LCP), Mitkovic internal fixator (MIF), Locked intramedullary nailing (LIN) on the compressive and bending forces on juvidur and veal bone models and compared the results of these two methods (juvidur, veal bone). Material and Methods: For the experimental study were used geometrically identical, anatomically shaped models of Juvidur and veal bones diameter of 30 mm and a length of 100 mm. Static tests were performed with SHIMADZU AGS-X testing machine, where the force of pressure (compression) increased from 0 N to 500 N, and then conducted relief. Bending forces grew from 0 N to 250 N, after which came into sharp relief. Results: On models of juvidur and veal bones studies have confirmed that uniform stability at the site of the fracture MIF with a coefficient ranking KMIF=0,1971, KLIN=0,2704, KDCP=0,2727 i KLCP=0,5821. Conclusion: On models of juvidur and veal bones working with Shimadzu AGS-X testing machine is best demonstrated MIF with a coefficient of 0.1971. PMID:27708489

  18. Chemical modeling of boron adsorption by humic materials using the constant capacitance model

    USDA-ARS?s Scientific Manuscript database

    The constant capacitance surface complexation model was used to describe B adsorption behavior on reference Aldrich humic acid, humic acids from various soil environments, and dissolved organic matter extracted from sewage effluents. The reactive surface functional groups on the humic materials wer...

  19. Texture synthesis models and material perception in the visual periphery

    NASA Astrophysics Data System (ADS)

    Balas, Benjamin

    2015-03-01

    The feature vocabularies used to support texture synthesis algorithms are increasingly being used to examine various aspects of human visual perception. These algorithms offer both a rich set of features that are typically sufficient to capture the appearance of complex natural inputs and a means of carrying out psychophysical experiments using synthetic textures as a proxy for the transformations ostensibly carried out by the visual system when processing natural images using summary statistics. Texture synthesis algorithms have recently been successfully applied to a wide range of visual tasks including texture perception, visual crowding, visual search, among others. Presently, we used both nonparametric and parametric texture synthesis models to investigate the nature of material perception in the visual periphery. We asked participants to classify images of four natural materials (metal, stone, water, and wood) when briefly presented in the visual periphery and compared the errors made under these viewing conditions to the errors made when judging the material category of synthetic images made from the original targets. We found that the confusions made under these two scenarios were substantially different, suggesting that these particular models do not appear to account for material perception in the periphery.

  20. Modeling failure of soft anisotropic materials with application to arteries.

    PubMed

    Volokh, K Y

    2011-11-01

    The arterial wall is a composite where the preferred orientation of collagen fibers induces anisotropy. Though the hyperelastic theories of fiber-reinforced composites reached a high level of sophistication and showed a reasonable correspondence with the available experimental data they are short of the failure description. Following the tradition of strength of materials the failure criteria are usually separated from stress analysis. In the present work we incorporate a failure description in the hyperelastic models of soft anisotropic materials by introducing energy limiters in the strain energy functions. The limiters provide the saturation value for the strain energy which indicates the maximum energy that can be stored and dissipated by an infinitesimal material volume. By using some popular constitutive models enhanced with the energy limiters we analyze rupture of a sheet of arterial material under the plane stress state varying from the uniaxial to equal biaxial tension. We calculate the local failure criteria including the maximum principal stress, the maximum principal stretch, the von Mises stress, and the strain energy at the moment of the sheet rupture. We find that the local failure criterion in the form of the critical strain energy is the most robust among the considered ones. We also find that the tensile strength-the maximum principal stress-that is usually obtained in uniaxial tension tests might not be appropriate as a failure indicator in the cases of the developed biaxiality of the stress-strain state. Copyright © 2011 Elsevier Ltd. All rights reserved.

  1. Plastometric tests for plasticine as physical modelling material

    NASA Astrophysics Data System (ADS)

    Wójcik, Łukasz; Lis, Konrad; Pater, Zbigniew

    2016-12-01

    This paper presents results of plastometric tests for plasticine, used as material for physical modelling of metal forming processes. The test was conducted by means of compressing by flat dies of cylindrical billets at various temperatures. The aim of the conducted research was comparison of yield stresses and course of material flow curves. Tests were made for plasticine in black and white colour. On the basis of the obtained experimental results, the influence of forming parameters change on flow curves course was determined. Sensitivity of yield stresses change in function of material deformation, caused by forging temperature change within the scope of 0&C ÷ 20&C and differentiation of strain rate for ˙ɛ = 0.563; ˙ɛ = 0.0563; ˙ɛ = 0.0056s-1,was evaluated. Experimental curves obtained in compression test were described by constitutive equations. On the basis of the obtained results the function which most favourably describes flow curves was chosen.

  2. Structure and Dynamics of a Model Discotic Organic Conducting Material

    NASA Astrophysics Data System (ADS)

    Zbiri, Mohamed; Haverkate, Lucas A.; Kearley, Gordon J.; Johnson, Mark R.; Mulder, Fokko M.

    2016-10-01

    Organic conducting materials exhibit promising functionalities, inducing hence a keen interest due to their potential use as a next generation photoconverters. However, unlike the more expensive inorganic analogues, the underlying properties that give rise to these advantages also cause organic materials to be inherently inefficient as photovoltaics. Understanding their properties at the microscopic level is a major step towards an efficient and targeted design. We probed the morphological and dynamical aspects of a model organic discotic liquid crystal material hexakis(n-hexyloxy)triphenylene (HAT6) by using neutron-based diffraction and quasielastic scattering techniques to gain deeper insights into structure and dynamics. The neutron measurements are accompanied, in a synergistic way, by molecular dynamics simulations for the sake of the analysis and interpretation of the observations

  3. Life prediction and constitutive models for anisotropic materials

    NASA Technical Reports Server (NTRS)

    Bill, R. C.

    1982-01-01

    The intent of this program is to develop a basic understanding of cyclic creep-fatigue deformation mechanisms and damage accumulation, a capability for reliable life prediction, and the ability to model the constitutive behavior of anisotropic single crystal (SC) and directionally solidified or recrystallized (DSR) comprise the program, and the work breakdown for each option reflects a distinct concern for two classes of anisotropic materials, SC and DSR materials, at temperatures encountered in the primary gas path (airfoil temperatures), and at temperatures typical of the blade root attachment and shank area. Work directed toward the higher temperature area of concern in the primary gas path includes effects of coatings on the behavior and properties of the materials of interest. The blade root attachment work areas will address the effects of stress concentrations associated with attachment features.

  4. Elevated Temperature Testing and Modeling of Advanced Toughened Ceramic Materials

    NASA Technical Reports Server (NTRS)

    Keith, Theo G.

    2005-01-01

    The purpose of this report is to provide a final report for the period of 12/1/03 through 11/30/04 for NASA Cooperative Agreement NCC3-776, entitled "Elevated Temperature Testing and Modeling of Advanced Toughened Ceramic Materials." During this final period, major efforts were focused on both the determination of mechanical properties of advanced ceramic materials and the development of mechanical test methodologies under several different programs of the NASA-Glenn. The important research activities made during this period are: 1. Mechanical properties evaluation of two gas-turbine grade silicon nitrides. 2) Mechanical testing for fuel-cell seal materials. 3) Mechanical properties evaluation of thermal barrier coatings and CFCCs and 4) Foreign object damage (FOD) testing.

  5. Exascale Co-design for Modeling Materials in Extreme Environments

    SciTech Connect

    Germann, Timothy C.

    2014-07-08

    Computational materials science has provided great insight into the response of materials under extreme conditions that are difficult to probe experimentally. For example, shock-induced plasticity and phase transformation processes in single-crystal and nanocrystalline metals have been widely studied via large-scale molecular dynamics simulations, and many of these predictions are beginning to be tested at advanced 4th generation light sources such as the Advanced Photon Source (APS) and Linac Coherent Light Source (LCLS). I will describe our simulation predictions and their recent verification at LCLS, outstanding challenges in modeling the response of materials to extreme mechanical and radiation environments, and our efforts to tackle these as part of the multi-institutional, multi-disciplinary Exascale Co-design Center for Materials in Extreme Environments (ExMatEx). ExMatEx has initiated an early and deep collaboration between domain (computational materials) scientists, applied mathematicians, computer scientists, and hardware architects, in order to establish the relationships between algorithms, software stacks, and architectures needed to enable exascale-ready materials science application codes within the next decade. We anticipate that we will be able to exploit hierarchical, heterogeneous architectures to achieve more realistic large-scale simulations with adaptive physics refinement, and are using tractable application scale-bridging proxy application testbeds to assess new approaches and requirements. Such current scale-bridging strategies accumulate (or recompute) a distributed response database from fine-scale calculations, in a top-down rather than bottom-up multiscale approach.

  6. Analytic Thermoelectric Couple Modeling: Variable Material Properties and Transient Operation

    NASA Technical Reports Server (NTRS)

    Mackey, Jonathan A.; Sehirlioglu, Alp; Dynys, Fred

    2015-01-01

    To gain a deeper understanding of the operation of a thermoelectric couple a set of analytic solutions have been derived for a variable material property couple and a transient couple. Using an analytic approach, as opposed to commonly used numerical techniques, results in a set of useful design guidelines. These guidelines can serve as useful starting conditions for further numerical studies, or can serve as design rules for lab built couples. The analytic modeling considers two cases and accounts for 1) material properties which vary with temperature and 2) transient operation of a couple. The variable material property case was handled by means of an asymptotic expansion, which allows for insight into the influence of temperature dependence on different material properties. The variable property work demonstrated the important fact that materials with identical average Figure of Merits can lead to different conversion efficiencies due to temperature dependence of the properties. The transient couple was investigated through a Greens function approach; several transient boundary conditions were investigated. The transient work introduces several new design considerations which are not captured by the classic steady state analysis. The work helps to assist in designing couples for optimal performance, and also helps assist in material selection.

  7. Turning statistical physics models into materials design engines

    PubMed Central

    Miskin, Marc Z.; Khaira, Gurdaman; de Pablo, Juan J.; Jaeger, Heinrich M.

    2016-01-01

    Despite the success statistical physics has enjoyed at predicting the properties of materials for given parameters, the inverse problem, identifying which material parameters produce given, desired properties, is only beginning to be addressed. Recently, several methods have emerged across disciplines that draw upon optimization and simulation to create computer programs that tailor material responses to specified behaviors. However, so far the methods developed either involve black-box techniques, in which the optimizer operates without explicit knowledge of the material’s configuration space, or require carefully tuned algorithms with applicability limited to a narrow subclass of materials. Here we introduce a formalism that can generate optimizers automatically by extending statistical mechanics into the realm of design. The strength of this approach lies in its capability to transform statistical models that describe materials into optimizers to tailor them. By comparing against standard black-box optimization methods, we demonstrate how optimizers generated by this formalism can be faster and more effective, while remaining straightforward to implement. The scope of our approach includes possibilities for solving a variety of complex optimization and design problems concerning materials both in and out of equilibrium. PMID:26684770

  8. Models for Multidimensional Tests and Hierarchically Structured Training Materials.

    DTIC Science & Technology

    1985-05-01

    Development and Evaluation of MIRT Models ........................ 2 Analysis of the General Rasch Model ......................... 6 Interpretation...multidimensional data. The first of the classes of models considered were extensions of the general model proposed by Rasch (1961). This model , in its most...r -- r r _ . . . .- . 5 , - ’ ,, " o 6 Analysis of the General Rasch Model The model presented in Equation I defines a very rich class of special

  9. Material Testing and Constitutive Modeling of Alaskan Frozen Soil

    NASA Astrophysics Data System (ADS)

    Lee, M. Y.; Fossum, A. F.; Bronowski, D. R.

    2002-12-01

    A series of laboratory tests, conducted using a unique high-pressure, low-temperature triaxial cell and the Split Hopkinson Pressure Bar (SHPB), provided data to construct a well-determined constitutive database for Alaskan frozen soil at confining pressures up to 100 MPa and temperatures down to -25 degree C. The test cell is capable of operating at temperatures as low as -65 degree C and confining pressures up to 500 MPa. The operating conditions of temperature and pressure were achieved using an externally cooled pressure vessel, composed of HP 9-4-20 alloy steel and equipped with 12 coaxial feed-throughs. Quasi-static compression tests and indirect tension (or Brazilian) tests constrain the variabilities of material properties of the frozen soil. The SHPB tests determine dynamic compression properties and the strain rate dependency of the frozen soil. The results from laboratory material testing showed that Alaskan frozen soil exhibits pressure and temperature dependence, rate sensitivity, anisotropy, brittle and ductile behavior, volumetric compaction, and dilation. The rate-sensitive and anisotropic form of a plasticity model, developed by Fossum and Fredrich (2000), captured the deformation behavior of this material very well. This model includes high strain-rate sensitivity and anisotropy in both the elastic and plastic regimes. The model comprises a continuous yield and loading surface for unified dilation and compaction phenomena. It is envisioned that this model will be used to predict the deformation and failure of frozen soil under the dynamic loading conditions resulting from projectile penetration into frozen soil targets.

  10. Material modeling for multistage tube hydroforming process simulation

    NASA Astrophysics Data System (ADS)

    Saboori, Mehdi

    strain on the nucleation, growth and coalescence of voids are investigated through a new user material for burst prediction during tube hydroforming. A numerical procedure for both plasticity and fracture is developed and implemented into 3D explicit commercial finite element software (LS-DYNA) through a new user material subroutine. The FLDs and predicted bursting pressure results are compared to the experimental data to validate the models. Finally, the new user material model is used to predict the bursting point of some real tube hydroforming parts such as round to square and round to V parts. Then, the predicted bursting pressure results are compared to the experimental data to validate the models in real and multistep tube hydroforming processes.

  11. Cubical Mass-Spring Model design based on a tensile deformation test and nonlinear material model.

    PubMed

    San-Vicente, Gaizka; Aguinaga, Iker; Tomás Celigüeta, Juan

    2012-02-01

    Mass-Spring Models (MSMs) are used to simulate the mechanical behavior of deformable bodies such as soft tissues in medical applications. Although they are fast to compute, they lack accuracy and their design remains still a great challenge. The major difficulties in building realistic MSMs lie on the spring stiffness estimation and the topology identification. In this work, the mechanical behavior of MSMs under tensile loads is analyzed before studying the spring stiffness estimation. In particular, the performed qualitative and quantitative analysis of the behavior of cubical MSMs shows that they have a nonlinear response similar to hyperelastic material models. According to this behavior, a new method for spring stiffness estimation valid for linear and nonlinear material models is proposed. This method adjusts the stress-strain and compressibility curves to a given reference behavior. The accuracy of the MSMs designed with this method is tested taking as reference some soft-tissue simulations based on nonlinear Finite Element Method (FEM). The obtained results show that MSMs can be designed to realistically model the behavior of hyperelastic materials such as soft tissues and can become an interesting alternative to other approaches such as nonlinear FEM.

  12. A Reproducible Oral Microcosm Biofilm Model for Testing Dental Materials

    PubMed Central

    Rudney, J.D.; Chen, R.; Lenton, P.; Li, J.; Li, Y.; Jones, R.S.; Reilly, C.; Fok, A.S.; Aparicio, C.

    2012-01-01

    Aims Most studies of biofilm effects on dental materials use single-species biofilms, or consortia. Microcosm biofilms grown directly from saliva or plaque are much more diverse, but difficult to characterize. We used the Human Oral Microbial Identification Microarray (HOMIM) to validate a reproducible oral microcosm model. Methods and Results Saliva and dental plaque were collected from adults and children. Hydroxyapatite and dental composite disks were inoculated with either saliva or plaque, and microcosm biofilms were grown in a CDC biofilm reactor. In later experiments, the reactor was pulsed with sucrose. DNA from inoculums and microcosms were analyzed by HOMIM for 272 species. Microcosms included about 60% of species from the original inoculum. Biofilms grown on hydroxyapatite and composites were extremely similar. Sucrose-pulsing decreased diversity and pH, but increased the abundance of Streptococcus and Veilonella. Biofilms from the same donor, grown at different times, clustered together. Conclusions This model produced reproducible microcosm biofilms that were representative of the oral microbiota. Sucrose induced changes associated with dental caries. Significance and Impact of the Study This is the first use of HOMIM to validate an oral microcosm model that can be used to study the effects of complex biofilms on dental materials. PMID:22925110

  13. Mooney-Rivlin biomechanical modeling of lung with Inhomogeneous material.

    PubMed

    Nasehi Tehrani, J; Wang, J

    2015-01-01

    In this study, the Mooney-Rivlin material with hyperelastic strain energy was proposed for biomechanical modeling of the lung. We modeled the lung as an inhomogeneous Mooney-Rivlin material with uncoupled deviatoric and volumetric behavior. The proposed method was evaluated on the lungs of eight lung cancer patients. For each patient, the lung was segmented from the 4D-CT images and tetrahedral volume mesh of the lung in phase 50% was created by using the adaptive mesh generation toolkit. The demons deformable registration algorithm was used to extract the displacement vector fields (DVFs). The Jacobian of the deformation gradient was calculated from DVFs, and the lung strain energy function was optimized to improve the tumor center of mass (TCM) motion simulation accuracy between respiratory phase 50% and 0%. The average TCM motion simulation error for the proposed strategy is 1.95 mm for eight patients. We observed 13% improvement in the TCM position prediction compared with the homogeneous Mooney-Rivlin modeling.

  14. Material Model Evaluation of a Composite Honeycomb Energy Absorber

    NASA Technical Reports Server (NTRS)

    Jackson, Karen E.; Annett, Martin S.; Fasanella, Edwin L.; Polanco, Michael A.

    2012-01-01

    A study was conducted to evaluate four different material models in predicting the dynamic crushing response of solid-element-based models of a composite honeycomb energy absorber, designated the Deployable Energy Absorber (DEA). Dynamic crush tests of three DEA components were simulated using the nonlinear, explicit transient dynamic code, LS-DYNA . In addition, a full-scale crash test of an MD-500 helicopter, retrofitted with DEA blocks, was simulated. The four material models used to represent the DEA included: *MAT_CRUSHABLE_FOAM (Mat 63), *MAT_HONEYCOMB (Mat 26), *MAT_SIMPLIFIED_RUBBER/FOAM (Mat 181), and *MAT_TRANSVERSELY_ANISOTROPIC_CRUSHABLE_FOAM (Mat 142). Test-analysis calibration metrics included simple percentage error comparisons of initial peak acceleration, sustained crush stress, and peak compaction acceleration of the DEA components. In addition, the Roadside Safety Verification and Validation Program (RSVVP) was used to assess similarities and differences between the experimental and analytical curves for the full-scale crash test.

  15. Model Stirrer Based on a Multi-Material Turntable for Microwave Processing Materials

    PubMed Central

    Ye, Jinghua; Hong, Tao; Wu, Yuanyuan; Wu, Li; Liao, Yinhong; Zhu, Huacheng; Yang, Yang; Huang, Kama

    2017-01-01

    Microwaves have been widely used in the treatment of materials, such as heating, drying, and sterilization. However, the heating in the commonly used microwave applicators is usually uneven. In this paper, a novel multi-material turntable structure is creatively proposed to improve the temperature uniformity in microwave ovens. Three customized turntables consisting of polyethylene (PE) and alumina, PE and aluminum, and alumina and aluminum are, respectively, utilized in a domestic microwave oven in simulation. During the heating process, the processed material is placed on a fixed Teflon bracket which covers the constantly rotating turntable. Experiments are conducted to measure the surface and point temperatures using an infrared thermal imaging camera and optical fibers. Simulated results are compared qualitatively with the measured ones, which verifies the simulated models. Compared with the turntables consisting of a single material, a 26%–47% increase in temperature uniformity from adapting the multi-material turntable can be observed for the microwave-processed materials. PMID:28772457

  16. Multiscale Modeling of Structurally-Graded Materials Using Discrete Dislocation Plasticity Models and Continuum Crystal Plasticity Models

    NASA Technical Reports Server (NTRS)

    Saether, Erik; Hochhalter, Jacob D.; Glaessgen, Edward H.

    2012-01-01

    A multiscale modeling methodology that combines the predictive capability of discrete dislocation plasticity and the computational efficiency of continuum crystal plasticity is developed. Single crystal configurations of different grain sizes modeled with periodic boundary conditions are analyzed using discrete dislocation plasticity (DD) to obtain grain size-dependent stress-strain predictions. These relationships are mapped into crystal plasticity parameters to develop a multiscale DD/CP model for continuum level simulations. A polycrystal model of a structurally-graded microstructure is developed, analyzed and used as a benchmark for comparison between the multiscale DD/CP model and the DD predictions. The multiscale DD/CP model follows the DD predictions closely up to an initial peak stress and then follows a strain hardening path that is parallel but somewhat offset from the DD predictions. The difference is believed to be from a combination of the strain rate in the DD simulation and the inability of the DD/CP model to represent non-monotonic material response.

  17. Mathematical modeling of material behaviors in the fracture process zone

    NASA Astrophysics Data System (ADS)

    Zhu, Mingcheng

    2000-10-01

    This Ph.D. research focuses on employing the cohesive crack models to investigate the fracture process zone behavior. The main contributions are summarized as the following: (1) A generalized mixed mode Dugdale model is developed. Research shows that the crack interaction will result in highly nonsymmetrical fracture process zone behavior. The nonsymmetrical fracture process zone behavior may be important in evaluation of effective properties of cracked materials if the local unsymmetrical loading induced by its neighbor crack interactions cannot be ignored. (2) A closed form solution of the stress history effect on the mixed mode Dugdale crack is obtained. Then a numerical procedure is proposed for studying the residual stress behavior of the loading and unloading path dependent Dugdale crack. (3) A general weight function method is developed for simulating the fracture process zone behavior. With this method the fracture process zone behavior can be easily simulated with singular solutions. (4) A numerical procedure is developed to investigate the strain-hardening or strain-softening effect on the Dugdale crack. Numerical examples show that, for a given Jc, the far-field failure stress of strain-hardening or strain-softening materials are very close to the Dugdale solution and this implies that the fracture failure criteria used in elastic-plastic material can be extended to the strain-hardening or strain-softening materials in the static loading situation. Stress distributions in the process zone have been calculated for several strain-hardening and strain-softening materials. An empirical equation of power-law type is proposed to represent the stress distribution as a function of the position in the process zone. It is shown that the power-law index varies linearly with the size of the fracture process zone. For static loading, Jc is the controlling parameter and the fracture process zone behavior is a secondary issue.

  18. Predictive Modeling of Terrestrial Radiation Exposure from Geologic Materials

    SciTech Connect

    Malchow, Russell L.; Haber, Daniel University of Nevada, Las Vegas; Burnley, Pamela; Marsac, Kara; Hausrath, Elisabeth; Adcock, Christopher

    2015-01-01

    Aerial gamma ray surveys are important for those working in nuclear security and industry for determining locations of both anthropogenic radiological sources and natural occurrences of radionuclides. During an aerial gamma ray survey, a low flying aircraft, such as a helicopter, flies in a linear pattern across the survey area while measuring the gamma emissions with a sodium iodide (NaI) detector. Currently, if a gamma ray survey is being flown in an area, the only way to correct for geologic sources of gamma rays is to have flown the area previously. This is prohibitively expensive and would require complete national coverage. This project’s goal is to model the geologic contribution to radiological backgrounds using published geochemical data, GIS software, remote sensing, calculations, and modeling software. K, U and Th are the three major gamma emitters in geologic material. U and Th are assumed to be in secular equilibrium with their daughter isotopes. If K, U, and Th abundance values are known for a given geologic unit the expected gamma ray exposure rate can be calculated using the Grasty equation or by modeling software. Monte Carlo N-Particle Transport software (MCNP), developed by Los Alamos National Laboratory, is modeling software designed to simulate particles and their interactions with matter. Using this software, models have been created that represent various lithologies. These simulations randomly generate gamma ray photons at energy levels expected from natural radiologic sources. The photons take a random path through the simulated geologic media and deposit their energy at the end of their track. A series of nested spheres have been created and filled with simulated atmosphere to record energy deposition. Energies deposited are binned in the same manner as the NaI detectors used during an aerial survey. These models are used in place of the simplistic Grasty equation as they take into account absorption properties of the lithology which the

  19. Modeling Dynamic Compaction of Porous Materials with the Overstress Approach

    NASA Astrophysics Data System (ADS)

    Partom, Yehuda

    2013-06-01

    To model compaction of a porous material (PM) we need 1) an equation of state (EOS) of the PM in terms of the EOS of its matrix, and 2) a compaction law. For the EOS it is common to use Herrmann's suggestion, as in his P α model. For a compaction law it is common to use a quasi-static compaction relation obtained from 1) a mezzo-scale model (as in Carroll and Holt's spherical shell model), or from 2) quasi-static tests. Here we are interested in dynamic compaction, like in a planar impact test. In dynamic compaction, the state may change too fast for the state point to follow the quasi-static compaction curve. We therefore get an overstress situation. The state point moves out of the quasi-static compaction boundary, and only with time collapses back towards it at a certain rate. In this way the dynamic compaction event becomes rate dependent. In the paper we first write down the rate equations for dynamic compaction according to this overstress approach. We then implement these equations in a hydro-code, and run some examples. We show how the overstress rate parameter can be calibrated from tests.

  20. Modelling challenges for battery materials and electrical energy storage

    NASA Astrophysics Data System (ADS)

    Muller, Richard P.; Schultz, Peter A.

    2013-10-01

    Many vital requirements in world-wide energy production, from the electrification of transportation to better utilization of renewable energy production, depend on developing economical, reliable batteries with improved performance characteristics. Batteries reduce the need for gasoline and liquid hydrocarbons in an electrified transportation fleet, but need to be lighter, longer-lived and have higher energy densities, without sacrificing safety. Lighter and higher-capacity batteries make portable electronics more convenient. Less expensive electrical storage accelerates the introduction of renewable energy to electrical grids by buffering intermittent generation from solar or wind. Meeting these needs will probably require dramatic changes in the materials and chemistry used by batteries for electrical energy storage. New simulation capabilities, in both methods and computational resources, promise to fundamentally accelerate and advance the development of improved materials for electric energy storage. To fulfil this promise significant challenges remain, both in accurate simulations at various relevant length scales and in the integration of relevant information across multiple length scales. This focus section of Modelling and Simulation in Materials Science and Engineering surveys the challenges of modelling for energy storage, describes recent successes, identifies remaining challenges, considers various approaches to surmount these challenges and discusses the potential of these methods for future battery development. Zhang et al begin with atoms and electrons, with a review of first-principles studies of the lithiation of silicon electrodes, and then Fan et al examine the development and use of interatomic potentials to the study the mechanical properties of lithiated silicon in larger atomistic simulations. Marrocchelli et al study ionic conduction, an important aspect of lithium-ion battery performance, simulated by molecular dynamics. Emerging high

  1. Damage Prediction Models for Advanced Materials and Composites

    NASA Technical Reports Server (NTRS)

    Xie, Ming; Ahmad, Jalees; Grady, Joseph E. (Technical Monitor)

    2005-01-01

    In the present study, the assessment and evaluation of various acoustic tile designs were conducted using three-dimensional finite element analysis, which included static analysis, thermal analysis and modal analysis of integral and non-integral tile design options. Various benchmark specimens for acoustic tile designs, including CMC integral T-joint and notched CMC plate, were tested in both room and elevated temperature environment. Various candidate ceramic matrix composite materials were used in the numerical modeling and experimental study. The research effort in this program evolved from numerical modeling and concept design to a combined numerical analysis and experimental study. Many subjects associated with the design and performance of the acoustic tile in jet engine exhaust nozzle have been investigated.

  2. Model of heterogeneous material dissolution in simulated biological fluid

    NASA Astrophysics Data System (ADS)

    Knyazeva, A. G.; Gutmanas, E. Y.

    2015-11-01

    In orthopedic research, increasing attention is being paid to bioresorbable/biodegradable implants as an alternative to permanent metallic bone healing devices. Biodegradable metal based implants possessing high strength and ductility potentially can be used in load bearing sites. Biodegradable Mg and Fe are ductile and Fe possess high strength, but Mg degrades too fast and Fe degrades too slow, Ag is a noble metal and should cause galvanic corrosion of the more active metallic iron - thus, corrosion of Fe can be increased. Nanostructuring should results in higher strength and can result in higher rate of dissolution/degradation from grain boundaries. In this work, a simple dissolution model of heterogeneous three phase nanocomposite material is considered - two phases being metal Fe and Ag and the third - nanopores. Analytical solution for the model is presented. Calculations demonstrate that the changes in the relative amount of each phase depend on mass exchange and diffusion coefficients. Theoretical results agree with preliminary experimental results.

  3. Chiral response in lattice models of Weyl materials

    NASA Astrophysics Data System (ADS)

    Gorbar, E. V.; Miransky, V. A.; Shovkovy, I. A.; Sukhachov, P. O.

    2017-09-01

    For a generic lattice Hamiltonian of the electron states in Weyl materials, we calculate analytically the chiral (or, equivalently, valley) charge and current densities in the first order in background electromagnetic and strain-induced pseudoelectromagnetic fields. We find that the chiral response induced by the pseudoelectromagnetic fields is not topologically protected. Although our calculations reproduce qualitatively the anomalous chiral Hall effect, the actual result for the conductivity depends on the definition of the chirality as well as on the parameters of the lattice model. In addition, while for the well-separated Fermi surfaces surrounding the individual Weyl nodes the current induced by the magnetic field coincides almost exactly with the current of the chiral separation effect in linearized models, there are clear deviations when the Fermi surfaces undergo the Lifshitz transition. In general, we find that all chiral response coefficients vanish at large chemical potential.

  4. Materials Processing Technology Initiatives. Delivery Order 0019-08: Material Behavior Modeling for Optimization of Thermomechanical Processes

    DTIC Science & Technology

    2000-11-01

    AFRL-RX-WP-TM-2008-4056 MATERIALS PROCESSING TECHNOLOGY INITIATIVES Delivery Order 0019-08: Material Behavior Modeling for Optimization of...5835-0019 5b. GRANT NUMBER 4. TITLE AND SUBTITLE MATERIALS PROCESSING TECHNOLOGY INITIATIVES Delivery Order 0019-08: Material Behavior Modeling

  5. A Material Model for the Cyclic Behavior of Nitinol

    NASA Astrophysics Data System (ADS)

    Rebelo, Nuno; Zipse, Achim; Schlun, Martin; Dreher, Gael

    2011-07-01

    The uniaxial behavior of Nitinol in different forms and at different temperatures has been well documented in the literature. Mathematical models for the three-dimensional behavior of this class of materials, covering superelasticity, plasticity, and shape memory effects have been previously developed. Phenomenological models embedded in FEA analysis are part of common practice today in the development of devices made out of Nitinol. In vivo loading of medical devices has cyclic characteristics. There have been some indications in the literature that cyclic loading of Nitinol modifies substantially its behavior. A consortium of several stent manufacturers, Safe Technology and Dassault Systèmes Simulia Corp., dedicated to the development of fatigue laws suitable for life prediction of Nitinol devices, has conducted an extensive experimental study of the modifications in uniaxial behavior of both Nitinol wire and tubing due to cyclic loading. The Abaqus Nitinol material model has been extended to capture some of the phenomena observed and is described in this article. Namely, a preload beyond 6% strain alters the transformation plateaus; if the cyclic load amplitude is large enough, permanent deformations (residual martensite) are observed; the lower plateau increases; and the upper plateau changes. The modifications to the upper plateau are very interesting in the sense that it appears broken: its start stress gets lowered creating a new plateau up to the highest level of cyclic strain, followed by resuming the original plateau until full transformation. Since quite often the geometry of a device at the point at which it is subjected to cyclic loading is very much dependent on the manufacturing, deployment, and preloading sequence, it is important that analyses be conducted with the original material behavior up to that point, and then with the cyclic behavior thereafter.

  6. CASTING DEFECT MODELING IN AN INTEGRATED COMPUTATIONAL MATERIALS ENGINEERING APPROACH

    SciTech Connect

    Sabau, Adrian S

    2015-01-01

    To accelerate the introduction of new cast alloys, the simultaneous modeling and simulation of multiphysical phenomena needs to be considered in the design and optimization of mechanical properties of cast components. The required models related to casting defects, such as microporosity and hot tears, are reviewed. Three aluminum alloys are considered A356, 356 and 319. The data on calculated solidification shrinkage is presented and its effects on microporosity levels discussed. Examples are given for predicting microporosity defects and microstructure distribution for a plate casting. Models to predict fatigue life and yield stress are briefly highlighted here for the sake of completion and to illustrate how the length scales of the microstructure features as well as porosity defects are taken into account for modeling the mechanical properties. Thus, the data on casting defects, including microstructure features, is crucial for evaluating the final performance-related properties of the component. ACKNOWLEDGEMENTS This work was performed under a Cooperative Research and Development Agreement (CRADA) with the Nemak Inc., and Chrysler Co. for the project "High Performance Cast Aluminum Alloys for Next Generation Passenger Vehicle Engines. The author would also like to thank Amit Shyam for reviewing the paper and Andres Rodriguez of Nemak Inc. Research sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office, as part of the Propulsion Materials Program under contract DE-AC05-00OR22725 with UT-Battelle, LLC. Part of this research was conducted through the Oak Ridge National Laboratory's High Temperature Materials Laboratory User Program, which is sponsored by the U. S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Program.

  7. Characterization and Modeling of Materials for Kr-Xe Separations

    SciTech Connect

    Forster, Paul; Naduvalath, Balakrishnan; Czerwinski, Ken

    2015-11-16

    We sought to identify practical adsorbents for the separation of Kr from Xe through pressure swing adsorption. We spent appreciable efforts on two categories of materials: metal-organic frameworks (MOFs) and zeolites. MOFs represent a new and exciting sorbent with numerous new framework topologies and surface chemistries. Zeolites are widely used and available commercial adsorbents. We have employed a combination of gas sorption analysis to analyze gas – surface interactions, computational modelling to both aid in interpreting experimental results and to predict practical adsorbents, and in-situ crystallographic studies to confirm specific experimental results.

  8. Neural Network method for Inverse Modeling of Material Deformation

    SciTech Connect

    Allen, J.D., Jr.; Ivezic, N.D.; Zacharia, T.

    1999-07-10

    A method is described for inverse modeling of material deformation in applications of importance to the sheet metal forming industry. The method was developed in order to assess the feasibility of utilizing empirical data in the early stages of the design process as an alternative to conventional prototyping methods. Because properly prepared and employed artificial neural networks (ANN) were known to be capable of codifying and generalizing large bodies of empirical data, they were the natural choice for the application. The product of the work described here is a desktop ANN system that can produce in one pass an accurate die design for a user-specified part shape.

  9. Towards enhancing Sandia's capabilities in multiscale materials modeling and simulation.

    SciTech Connect

    Aidun, John Bahram; Fang, Huei Eliot; Barbour, John Charles; Westrich, Henry Roger; Chen, Er-Ping

    2004-01-01

    We report our conclusions in support of the FY 2003 Science and Technology Milestone ST03-3.5. The goal of the milestone was to develop a research plan for expanding Sandia's capabilities in materials modeling and simulation. From inquiries and discussion with technical staff during FY 2003 we conclude that it is premature to formulate the envisioned coordinated research plan. The more appropriate goal is to develop a set of computational tools for making scale transitions and accumulate experience with applying these tools to real test cases so as to enable us to attack each new problem with higher confidence of success.

  10. First-principles modelling of materials: From polythiophene to phosphorene

    NASA Astrophysics Data System (ADS)

    Ziletti, Angelo

    As a result of the computing power provided by the current technology, computational methods now play an important role in modeling and designing materials at the nanoscale. The focus of this dissertation is two-fold: first, new computational methods to model nanoscale transport are introduced, then state-of-the-art tools based on density functional theory are employed to explore the properties of phosphorene, a novel low dimensional material with great potential for applications in nanotechnology. A Wannier function description of the electron density is combined with a generalized Slater-Koster interpolation technique, enabling the introduction of a new computational method for constructing first-principles model Hamiltonians for electron and hole transport that maintain the density functional theory accuracy at a fraction of the computational cost. As a proof of concept, this new approach is applied to model polythiophene, a polymer ubiquitous in organic photovoltaic devices. A new low dimensional material, phosphorene - a single layer of black phosphorous - the phosphorous analogue of graphene was first isolated in early 2014 and has attracted considerable attention. It is a semiconductor with a sizable band gap, which makes it a perfect candidate for ultrathin transistors. Multi-layer phosphorene transistors have already achieved the highest hole mobility of any two-dimensional material apart from graphene. Phosphorene is prone to oxidation, which can lead to degradation of electrical properties, and eventually structural breakdown. The calculations reported here are some of the first to explore this oxidation and reveal that different types of oxygen defects are readily introduced in the phosphorene lattice, creating electron traps in some situations. These traps are responsible for the non-ambipolar behavior observed by experimental collaborators in air-exposed few-layer black phosphorus devices. Calculation results predict that air exposure of phosphorene

  11. Characterization of Semicrystalline Polymeric Materials by Atomistic Models

    SciTech Connect

    Figueroa-Gerstenmaier, Susana; Milano, Giuseppe; Guerra, Gaetano

    2010-12-21

    Characterization of two crystalline phases ({delta} and {epsilon}) of syndiotactic polystyrene using molecular modeling are discussed. These two polymorphs present nanoporosity, being able to adsorb molecules of low molecular weight in their cavities ({delta}) or in their channels ({epsilon}). By means of Grand Canonical Monte Carlo molecular simulations, adsorption isotherms of nitrogen and hydrogen were calculated, exploring the possible utilization of these materials with storage purposes. Molecular Dynamics simulations were performed to determine self diffusion behavior of light gases and these results combined with a geometric method are being employed to measure the size of the nanochannels of the e polymorph.

  12. Computational Modeling of Multi-Scale Material Features in Cement Paste - An Overview

    DTIC Science & Technology

    2015-05-25

    material chemistry level config- uration of hydrated cement paste CSH Jennite structure. 3 MICRO SCALE MODELING The advent of scalable computing ...ABSTRACT 16. SECURITY CLASSIFICATION OF: Computational modeling of complex, heterogeneous, multi-scale features of cement paste requires starting from...that in-fluence the properties and behavior of materials through associated computational , material and mechanistic models. Such modeling starting

  13. Multiscale Modeling of Metallic Materials Containing Embedded Particles

    NASA Technical Reports Server (NTRS)

    Phillips, Dawn R.; Iesulauro, Erin; Glaessgen, Edward H.

    2004-01-01

    Multiscale modeling at small length scales (10(exp -9) to 10(exp -3) m) is discussed for aluminum matrices with embedded particles. A configuration containing one particle surrounded by about 50 grains and subjected to uniform tension and lateral constraint is considered. The analyses are performed to better understand the effects of material configuration on the initiation and progression of debonding of the particles from the surrounding aluminum matrix. Configurational parameters considered include particle aspect ratio and orientation within the surrounding matrix. Both configurational parameters are shown to have a significant effect on the behavior of the materials as a whole. For elliptical particles with the major axis perpendicular to the direction of loading, a particle with a 1:1 aspect ratio completely debonds from the surrounding matrix at higher loads than particles with higher aspect ratios. As the particle major axis is aligned with the direction of the applied load, increasing amounts of load are required to completely debond the particles.

  14. Mathematical model for radon diffusion in earthen materials

    SciTech Connect

    Nielson, K.K.; Rogers, V.C.

    1982-10-01

    Radon migration in porous, earthen materials is characterized by diffusion in both the air and water components of the system as well as by the interaction of the radon between the air and water. The size distribution and configuration of the pore spaces and their moisture distributions are key parameters in determining the radon diffusion coefficient for the bulk material. A mathematical model is developed and presented for calculating radon diffusion coefficients solely from the moisture content and pore size distribution of a soil, reducing the need for resorting to radon diffusion measurements. The resulting diffusion coefficients increase with the median pore diameter of the soil and decrease with increasing widths of the pore size distribution. The calculated diffusion coefficients are suitable for use in simple homogeneous-medium diffusion expressions for predicting radon transport and compare well with measured diffusion coefficients and with empirical diffusion coefficient correlations.

  15. Modeling the behaviour of shape memory materials under large deformations

    NASA Astrophysics Data System (ADS)

    Rogovoy, A. A.; Stolbova, O. S.

    2017-06-01

    In this study, the models describing the behavior of shape memory alloys, ferromagnetic materials and polymers have been constructed, using a formalized approach to develop the constitutive equations for complex media under large deformations. The kinematic and constitutive equations, satisfying the principles of thermodynamics and objectivity, have been derived. The application of the Galerkin procedure to the systems of equations of solid mechanics allowed us to obtain the Lagrange variational equation and variational formulation of the magnetostatics problems. These relations have been tested in the context of the problems of finite deformation in shape memory alloys and ferromagnetic materials during forward and reverse martensitic transformations and in shape memory polymers during forward and reverse relaxation transitions from a highly elastic to a glassy state.

  16. Kinetics Modeling and Numerical Simulation of Reactive Materials

    NASA Astrophysics Data System (ADS)

    Yoo, Sunhee; Stewart, D. Scott; Lambert, David E.; Choi, Sunjin

    2011-06-01

    Simulations with reduced kinetic models are used to study shock ignition and detonation in reactive materials that may support non-classical detonation. Porous aluminum Teflon oxidizer mixtures that support combustion reactions in air are considered, as a member of a class of materials with intrinsic interest. We recast a phenomenological theory with realistic kinetics with end products; AlF3, C and CO2. Intermediate products include at least thirty elementary reactions; a sub-set can be selected to simplify, but a hard problem remains. We use the multi-scale asymptotic ``G-scheme'' proposed by M. Valorani, S. Paolucci and reduce a dynamical system consisting of the intermediate reactions and rates, conservation laws and porosity evolution. Results of the multi-species evolution and its impact on rapid self-oxidizing combustion and possible detonation conditions and the computational methods are presented. Supported by AFRL/RW and DTRA.

  17. RECERTIFICATION OF THE MODEL 9977 RADIOACTIVE MATERIAL PACKAGING

    SciTech Connect

    Abramczyk, G.; Bellamy, S.; Loftin, B.; Nathan, S.

    2013-06-05

    The Model 9977 Packaging was initially issued a Certificate of Compliance (CoC) by the Department of Energy’s Office of Environmental Management (DOE-EM) for the transportation of radioactive material (RAM) in the Fall of 2007. This first CoC was for a single radioactive material and two packing configurations. In the five years since that time, seven Addendums have been written to the Safety Analysis Report for Packaging (SARP) and five Letter Amendments have been written that have authorized either new RAM contents or packing configurations, or both. This paper will discuss the process of updating the 9977 SARP to include all the contents and configurations, including the addition of a new content, and its submittal for recertification.

  18. Mathematical Models for the Education Sector, Supporting Material to the Survey. (Les Modeles Mathematiques du Secteur Enseignement. Annexes.) Technical Report.

    ERIC Educational Resources Information Center

    Organisation for Economic Cooperation and Development, Paris (France).

    This document contains supporting material for the survey on current practice in the construction and use of mathematical models for education. Two kinds of supporting material are included: (1) the responses to the questionnaire, and (2) supporting documents and other materials concerning the mathematical model-building effort in education.…

  19. Mathematical Models for the Education Sector, Supporting Material to the Survey. (Les Modeles Mathematiques du Secteur Enseignement. Annexes.) Technical Report.

    ERIC Educational Resources Information Center

    Organisation for Economic Cooperation and Development, Paris (France).

    This document contains supporting material for the survey on current practice in the construction and use of mathematical models for education. Two kinds of supporting material are included: (1) the responses to the questionnaire, and (2) supporting documents and other materials concerning the mathematical model-building effort in education.…

  20. Modeling Natural Space Ionizing Radiation Effects on External Materials

    NASA Technical Reports Server (NTRS)

    Alstatt, Richard L.; Edwards, David L.; Parker, Nelson C. (Technical Monitor)

    2000-01-01

    Predicting the effective life of materials for space applications has become increasingly critical with the drive to reduce mission cost. Programs have considered many solutions to reduce launch costs including novel, low mass materials and thin thermal blankets to reduce spacecraft mass. Determining the long-term survivability of these materials before launch is critical for mission success. This presentation will describe an analysis performed on the outer layer of the passive thermal control blanket of the Hubble Space Telescope. This layer had degraded for unknown reasons during the mission, however ionizing radiation (IR) induced embrittlement was suspected. A methodology was developed which allowed direct comparison between the energy deposition of the natural environment and that of the laboratory generated environment. Commercial codes were used to predict the natural space IR environment model energy deposition in the material from both natural and laboratory IR sources, and design the most efficient test. Results were optimized for total and local energy deposition with an iterative spreadsheet. This method has been used successfully for several laboratory tests at the Marshall Space Flight Center. The study showed that the natural space IR environment, by itself, did not cause the premature degradation observed in the thermal blanket.

  1. Mathematical and Numerical Analyses of Peridynamics for Multiscale Materials Modeling

    SciTech Connect

    Gunzburger, Max

    2015-02-17

    We have treated the modeling, analysis, numerical analysis, and algorithmic development for nonlocal models of diffusion and mechanics. Variational formulations were developed and finite element methods were developed based on those formulations for both steady state and time dependent problems. Obstacle problems and optimization problems for the nonlocal models were also treated and connections made with fractional derivative models.

  2. Modeling of fracture and damage in quasibrittle materials

    NASA Astrophysics Data System (ADS)

    Jirasek, Milan

    1993-02-01

    The dissertation presents several mathematical models useful for the simulation of fracture and damage propagation in quasi-brittle materials, which are characterized by the development of a large nonlinear process zone prior to failure. The simplest one is the R-curve model based on the replacement of the nonlinear fracture process zone by an equivalent linear elastic crack with a variable resistance against crack propagation. This approach is generalized by taking into account the effect of the loading rate. The emphasis is on the static loading rates rather than the dynamic ones, and creep in the bulk of the specimen is incorporated into the mathematical description. Another important class of models is based on the representation of a mechanical system by an assembly of interacting particles. A dynamic particle model is developed for the simulation of fracture of large sea ice floes during their impact on obstacles such as platforms or artificial islands. It is demonstrated that this model is capable of producing realistic results in terms of both the contact force history and the fracture pattern. Macroscopic fracture energy of random particle systems is studied as a function of the microscopic parameters using the size effect method. An effective numerical procedure for tracing a piecewise linear load-displacement curve is developed. The previously proposed continuum-based microplane model is carefully analyzed and shown to perform poorly in certain situations. The conditions under which the model gives unsatisfactory results are described and the reasons for the poor performance are explained. Modifications on the microscopic level do not remedy the situation and a macro-level modification is unavoidable. A promising concept of the revised version is advocated by presenting improvements of the behavior in several elementary situations. The dissertation is concluded by a localization analysis of a new concept of nonlocal averaging, strictly based on a

  3. Modeling of and experiments on electromagnetic levitation for materials processing

    NASA Astrophysics Data System (ADS)

    Hyers, Robert W.

    Electromagnetic levitation (EML) is an important experimental technique for research in materials processing. It has been applied for many years to a wide variety of research areas, including studies of nucleation and growth, phase selection, reaction kinetics, and thermophysical property measurements. The work presented here contributes to a more fundamental understanding of three aspects of levitation systems: modeling of electromagnetic effects, modeling of fluid flow characteristics, and experiments to measure surface tension and viscosity in microgravity. In this work, the interaction between the electromagnetic field and the sample were modeled, and experiments to measure the surface tension and viscosity of liquid metal droplets were performed. The models use a 2-D axisymmetric formulation, and use the method of mutual inductances to calculate the currents induced in the sample. The magnetic flux density was calculated from the Biot-Savart law, and the force distribution obtained. Parametric studies of the total force and induced heating on the sample were carried out, as well as a study of the influence of different parameters on the internal flows in a liquid droplet. The oscillating current frequency has an important effect on the feasible operating range of an EML system. Optimization of both heating and positioning are discussed, and the use of frequencies far from those in current use for levitation of small droplets provides improved results. The dependences of the force and induced power on current, frequency, sample conductivity, and sample size are given. A model coupling the magnetic force calculations to a commercial finite-element fluid dynamics program is used to characterize the flows in a liquid sample, including transitions in the flow pattern. The dependence of fluid flow velocity on positioning force, sample viscosity, and oscillating current frequency is presented. These models were applied to the design of thermophysical property

  4. Challenges in Modeling of the Plasma-Material Interface

    NASA Astrophysics Data System (ADS)

    Krstic, Predrag; Meyer, Fred; Allain, Jean Paul

    2013-09-01

    Plasma-Material Interface mixes materials of the two worlds, creating a new entity, a dynamical surface, which communicates between the two and represent one of the most challenging areas of multidisciplinary science, with many fundamental processes and synergies. How to build an integrated theoretical-experimental approach? Without mutual validation of experiment and theory chances very slim to have believable results? The outreach of the PMI science modeling at the fusion plasma facilities is illustrated by the significant step forward in understanding achieved recently by the quantum-classical modeling of the lithiated carbon surfaces irradiated by deuterium, showing surprisingly large role of oxygen in the deuterium retention and erosion chemistry. The plasma-facing walls of the next-generation fusion reactors will be exposed to high fluxes of neutrons and plasma-particles and will operate at high temperatures for thermodynamic efficiency. To this end we have been studying the evolution dynamics of vacancies and interstitials to the saturated dpa doses of tungsten surfaces bombarded by self-atoms, as well as the plasma-surface interactions of the damaged surfaces (erosion, hydrogen and helium uptake and fuzz formation). PSK and FWM acknowledge support of the ORNL LDRD program.

  5. Modeling and Characterization of Damage Processes in Metallic Materials

    NASA Technical Reports Server (NTRS)

    Glaessgen, E. H.; Saether, E.; Smith, S. W.; Hochhalter, J. D.; Yamakov, V. I.; Gupta, V.

    2011-01-01

    This paper describes a broad effort that is aimed at understanding the fundamental mechanisms of crack growth and using that understanding as a basis for designing materials and enabling predictions of fracture in materials and structures that have small characteristic dimensions. This area of research, herein referred to as Damage Science, emphasizes the length scale regimes of the nanoscale and the microscale for which analysis and characterization tools are being developed to predict the formation, propagation, and interaction of fundamental damage mechanisms. Examination of nanoscale processes requires atomistic and discrete dislocation plasticity simulations, while microscale processes can be examined using strain gradient plasticity, crystal plasticity and microstructure modeling methods. Concurrent and sequential multiscale modeling methods are being developed to analytically bridge between these length scales. Experimental methods for characterization and quantification of near-crack tip damage are also being developed. This paper focuses on several new methodologies in these areas and their application to understanding damage processes in polycrystalline metals. On-going and potential applications are also discussed.

  6. Computational Modeling of Ultrafast Pulse Propagation in Nonlinear Optical Materials

    NASA Technical Reports Server (NTRS)

    Goorjian, Peter M.; Agrawal, Govind P.; Kwak, Dochan (Technical Monitor)

    1996-01-01

    There is an emerging technology of photonic (or optoelectronic) integrated circuits (PICs or OEICs). In PICs, optical and electronic components are grown together on the same chip. rib build such devices and subsystems, one needs to model the entire chip. Accurate computer modeling of electromagnetic wave propagation in semiconductors is necessary for the successful development of PICs. More specifically, these computer codes would enable the modeling of such devices, including their subsystems, such as semiconductor lasers and semiconductor amplifiers in which there is femtosecond pulse propagation. Here, the computer simulations are made by solving the full vector, nonlinear, Maxwell's equations, coupled with the semiconductor Bloch equations, without any approximations. The carrier is retained in the description of the optical pulse, (i.e. the envelope approximation is not made in the Maxwell's equations), and the rotating wave approximation is not made in the Bloch equations. These coupled equations are solved to simulate the propagation of femtosecond optical pulses in semiconductor materials. The simulations describe the dynamics of the optical pulses, as well as the interband and intraband.

  7. Theoretical Models for Vibrational Lifetimes in Amorphous Materials.

    NASA Astrophysics Data System (ADS)

    Orbach, R.

    1996-03-01

    The lifetimes of high energy lattice vibrational states in amorphous or glassy materials are calculated on the basis of a model in which vibrational states are extended for energies ω < ω_c, and ``super-localized'' for ω > ω_c. This model can account for the plateau in the thermal conductivity κ(T), a feature which is nearly universal for amorphous and glassy materials. The increase of κ(T) for temperatures greater than the plateau temperature arises from anharmonicity-induced localized vibrational state hopping, the major contribution arising from states with energies in the vicinity of ω_c. The same anharmonicity vertex allows one to calculate the anharmonicity-induced vibrational lifetime τ(ω) which can be expressed in terms of the hopping contribution to the thermal conductivity. Though amorphous and glassy materials are certainly not in general mass fractals, the fracton model is a convenient approach to obtain quantitative results. At low temperatures, the high energy (ω>>ω_c) vibrational lifetime is found to be proportional to exp Bigl[Bigl(ω\\over ω_cBigr) ^d_φ/DBigr] where d_φ is the superlocalization exponent of the localized vibrational state, and D is the mass density scaling exponent (equal to the Euclidean dimension d for dense systems, and the fractal dimension for fractal systems). This behavior arises from the combined action of a decrease in localization length, and an increase in the most probable hop distance, with increasing ω. This dependence is quite opposite to that found for crystalline materials where τ(ω) ∝ ω-5. Experiments of Scholten et al.^1 on a-Si:H exhibit the predicted exponential increase of τ(ω) with increasing ω. Using measured values for the third order elastic constant C_111, quantitative agreement is obtained for the 480 cm-1 TO vibration, with τ(ω) = 70 ns. l *Supported by the National Science Foundation.l **In conjunction with Dr. A. Jagannathan, and dedicated to the memory of H. M. Rosenberg

  8. Computational modeling of multicellular constructs with the material point method.

    PubMed

    Guilkey, James E; Hoying, James B; Weiss, Jeffrey A

    2006-01-01

    Computational modeling of the mechanics of cells and multicellular constructs with standard numerical discretization techniques such as the finite element (FE) method is complicated by the complex geometry, material properties and boundary conditions that are associated with such systems. The objectives of this research were to apply the material point method (MPM), a meshless method, to the modeling of vascularized constructs by adapting the algorithm to accurately handle quasi-static, large deformation mechanics, and to apply the modified MPM algorithm to large-scale simulations using a discretization that was obtained directly from volumetric confocal image data. The standard implicit time integration algorithm for MPM was modified to allow the background computational grid to remain fixed with respect to the spatial distribution of material points during the analysis. This algorithm was used to simulate the 3D mechanics of a vascularized scaffold under tension, consisting of growing microvascular fragments embedded in a collagen gel, by discretizing the construct with over 13.6 million material points. Baseline 3D simulations demonstrated that the modified MPM algorithm was both more accurate and more robust than the standard MPM algorithm. Scaling studies demonstrated the ability of the parallel code to scale to 200 processors. Optimal discretization was established for the simulations of the mechanics of vascularized scaffolds by examining stress distributions and reaction forces. Sensitivity studies demonstrated that the reaction force during simulated extension was highly sensitive to the modulus of the microvessels, despite the fact that they comprised only 10.4% of the volume of the total sample. In contrast, the reaction force was relatively insensitive to the effective Poisson's ratio of the entire sample. These results suggest that the MPM simulations could form the basis for estimating the modulus of the embedded microvessels through a parameter

  9. Advances in design and modeling of porous materials

    NASA Astrophysics Data System (ADS)

    Ayral, André; Calas-Etienne, Sylvie; Coasne, Benoit; Deratani, André; Evstratov, Alexis; Galarneau, Anne; Grande, Daniel; Hureau, Matthieu; Jobic, Hervé; Morlay, Catherine; Parmentier, Julien; Prelot, Bénédicte; Rossignol, Sylvie; Simon-Masseron, Angélique; Thibault-Starzyk, Frédéric

    2015-07-01

    This special issue of the European Physical Journal Special Topics is dedicated to selected papers from the symposium "High surface area porous and granular materials" organized in the frame of the conference "Matériaux 2014", held on November 24-28, 2014 in Montpellier, France. Porous materials and granular materials gather a wide variety of heterogeneous, isotropic or anisotropic media made of inorganic, organic or hybrid solid skeletons, with open or closed porosity, and pore sizes ranging from the centimeter scale to the sub-nanometer scale. Their technological and industrial applications cover numerous areas from building and civil engineering to microelectronics, including also metallurgy, chemistry, health, waste water and gas effluent treatment. Many emerging processes related to environmental protection and sustainable development also rely on this class of materials. Their functional properties are related to specific transfer mechanisms (matter, heat, radiation, electrical charge), to pore surface chemistry (exchange, adsorption, heterogeneous catalysis) and to retention inside confined volumes (storage, separation, exchange, controlled release). The development of innovative synthesis, shaping, characterization and modeling approaches enables the design of advanced materials with enhanced functional performance. The papers collected in this special issue offer a good overview of the state-of-the-art and science of these complex media. We would like to thank all the speakers and participants for their contribution to the success of the symposium. We also express our gratitude to the organization committee of "Matériaux 2014". We finally thank the reviewers and the staff of the European Physical Journal Special Topics who made the publication of this special issue possible.

  10. Toward sustainable material usage: evaluating the importance of market motivated agency in modeling material flows.

    PubMed

    Gaustad, Gabrielle; Olivetti, Elsa; Kirchain, Randolph

    2011-05-01

    Increasing recycling will be a key strategy for moving toward sustainable materials usage. There are many barriers to increasing recycling, including quality issues in the scrap stream. Repeated recycling can compound this problem through the accumulation of tramp elements over time. This paper explores the importance of capturing recycler decision-making in accurately modeling accumulation and the value of technologies intended to mitigate it. A method was developed combining dynamic material flow analysis with allocation of those materials into production portfolios using blending models. Using this methodology, three scrap allocation methods were explored in the context of a case study of aluminum use: scrap pooling, pseudoclosed loop, and market-based. Results from this case analysis suggest that market-driven decisions and upgrading technologies can partially mitigate the negative impact of accumulation on scrap utilization, thereby increasing scrap use and reducing greenhouse gas emissions. A market-based allocation method for modeling material flows suggests a higher value for upgrading strategies compared to a pseudoclosed loop or pooling allocation method for the scenarios explored.

  11. Modeling Concrete Material Structure: A Two-Phase Meso Finite Element Model

    NASA Astrophysics Data System (ADS)

    Bonifaz, E. A.; Baus, Juan; Lantsoght, Eva O. L.

    Concrete is a compound material where aggregates are randomly placed within the cement paste. To describe the behavior of concrete structures at the ultimate, it is necessary to use nonlinear finite element models, which for shear and torsion problems do not always give satisfactory results. The current study aims at improving the modeling of concrete at the meso-level, which eventually can result in an improved assessment of existing structures. Concrete as a heterogeneous material is modeled consisting of hydrated cement paste and aggregates. The stress-strain curves of the hydrated cement paste and aggregates are described with results from the literature. A three-dimensional (3D) finite element model was developed to determine the influence of individual phases on the inelastic stress-strain distribution of concrete structures. A random distribution and morphology of the cement and aggregate fractions are achieved by using DREAM.3D. Two affordable computational dual-phase representative volume elements (RVEs) are imported to ABAQUS to be studied in compression and tension. The virtual specimens (concrete mesh) subjected to continuous monotonic strain loading conditions were constrained with 3D boundary conditions. Results demonstrate differences in stress-strain mechanical behavior in both compression and tension test simulations. A strong dependency of flow stress and plastic strain on phase type, aggregate (andesite) size, shape and distribution upon the composite local response are clearly observed. It is noted that the resistance to flow is higher in concrete meshes composed of finer and homogeneous aggregate particles because the Misses stresses and effective plastic strains are better distributed. This study shows that at the meso-level, concrete can be modeled consisting of aggregates and hydrated cement paste.

  12. Modeling of H2S migration through landfill cover materials.

    PubMed

    Xu, Qiyong; Powell, Jon; Jain, Pradeep; Townsend, Timothy

    2014-01-15

    The emission of H2S from landfills in the United States is an emergent problem because measured concentrations within the waste mass and in ambient air have been observed at potentially unsafe levels for on-site workers and at levels that can cause a nuisance and potentially deleterious health impacts to surrounding communities. Though recent research has provided data on H2S concentrations that may be observed at landfills, facility operators and landfill engineers have limited predictive tools to anticipate and plan for potentially harmful H2S emissions. A one-dimensional gas migration model was developed to assist engineers and practitioners better evaluate and predict potential emission levels of H2S based on four factors: concentration of H2S below the landfill surface (C0), advection velocity (v), H2S effective diffusion coefficient (D), and H2S adsorption coefficient of landfill cover soil (μ). Model simulations indicated that H2S migration into the atmosphere can be mitigated by reducing H2S diffusion and advection or using alternative cover soils with a high H2S adsorption coefficient. Laboratory column experiments were conducted to investigate the effects of the four parameters on H2S migration in cover soils and to calculate the adsorption coefficient of different cover materials. The model was validated by comparing results with laboratory column experiments. Based on the results, the laboratory column provides an effective way to estimate the H2S adsorption coefficient, which can then be incorporated into the developed model to predict the depth of cover soil required to reduce emitted H2S concentrations below a desired level. Copyright © 2013 Elsevier B.V. All rights reserved.

  13. Tight-binding model for materials at mesoscale

    SciTech Connect

    Tai, Yuan-Yen; Choi, Hongchul; Zhu, Wei; Zhu, Jian-Xin

    2016-12-21

    TBM3 is an open source package for computational simulations of quantum materials at multiple scales in length and time. The project originated to investigate the multiferroic behavior in transition-metal oxide heterostructures. The framework has also been designed to study emergent phemona in other quantum materials like 2-dimensional transition-metal dichalcogenides, graphene, topological insulators, and skyrmion in materials, etc. In the long term, we will enable the package for transport and time-resolved phenomena. TBM3 is currently a C++ based numerical tool package and framework for the design and construction of any kind of lattice structures with multi-orbital and spin degrees of freedom. The fortran based portion of the package will be added in the near future. The design of TBM3 is in a highly flexible and reusable framework and the tight-binding parameters can be modeled or informed by DFT calculations. It is currently GPU enabled and feature of CPU enabled MPI will be added in the future.

  14. Global Critical Materials Markets: An Agent-based Modeling Approach

    SciTech Connect

    Riddle, Matthew E.; Macal, Charles M.; Conzelmann, Guenter; Combs, Todd E.; Bauer, Diana; Fields, Fletcher

    2015-09-01

    As part of efforts to position the United States as a leader in clean energy technology production, the U. S. Department of Energy (DOE) issued two Critical Materials Strategy reports, which assessed 16 materials on the basis of their importance to clean energy development and their supply risk ( U.S. Department of Energy (DOE), 2010 and DOE, 2011). To understand the implications for clean energy of disruptions in supplies of critical materials, it is important to understand supply chain dynamics from mining to final product production. As a case study of critical material supply chains, we focus on the supply of two rare earth metals, neodymium (Nd) and dysprosium (Dy), for permanent magnets used in wind turbines, electric vehicles and other applications. We introduce GCMat, a dynamic agent-based model that includes interacting agents at five supply chain stages consisting of mining, metal refining, magnet production, final product production and demand. Agents throughout the supply chain make pricing, production and inventory management decisions. Deposit developers choose which deposits to develop based on market conditions and detailed data on 57 rare earth deposits. Wind turbine and electric vehicle producers choose from a set of possible production technologies that require different amounts of rare earths. We ran the model under a baseline scenario and four alternative scenarios with different demand and production technology inputs. Model results from 2010 to 2013 fit well with historical data. Projections through 2025 show a number of possible future price, demand, and supply trajectories. For each scenario, we highlight reasons for turning points under market conditions, for differences between Nd and Dy markets, and for differences between scenarios. Because GCMat can model causal dynamics and provide fine-grain representation of agents and their decisions, it provides explanations for turning points under market conditions that are not otherwise

  15. Computational modelling of Er(3+): Garnet laser materials

    NASA Technical Reports Server (NTRS)

    Spangler, Lee H.

    1994-01-01

    The Er(3+) ion has attracted a lot of interest for four reasons: (1) Its (4)I(sub 13/2) yields (4)I(sub 15/2) transition lases in the eyesafe region near 1.5 micron; (2) the (4)I(sub 13/2) transition lases near 2.8 micron, an important wavelength for surgical purposes; (3) it displays surprisingly efficient upconversion with lasing observed at 1.7, 1.2, 0.85, 0.56, 0.55, and 0.47 micron following 1.5 micron pumping; and (4) it has absorption bands at 0.96 and 0.81 micron and thus can be diode pumped. However, properties desirable for upconversion reduce the efficiency of 1.5 and 3 micron laser operation and vice versa. Since all of the processes are influenced by the host via the crystal field induced stark splittings in the Er levels, this project undertook modelling of the host influence on the Er lasinng behavior. While growth and measurement of all ten Er(3+) doped garnets is the surest way of identifying hosts which maximize upconversion (or conversly, 1.5 and 3 micron performance), it is also expensive - costing approximately $10,000/material or approximately $100,000 for the materials computationally investigated here. The calculations were performed using a quantum mechanical point charge model developed by Clyde Morrison at Harry Diamond Laboratories. The programs were used to fit the Er:YAG experimental energy levels so that the crystal field parameters, B(sub nm) could be extracted. From these radial factors, rho (sub n) were determined for Er(3+) in garnets. These, in combination with crystal field components, Anm, available from X-ray data, were used to predict energy levels for Er in the other nine garnet hosts. The levels in Er:YAG were fit with an rms error of 12.2/cm over a 22,000/cm range. Predicted levels for two other garnets for which literature values were available had rms errors of less than 17/cm , showing the calculations to be reliable. Based on resonances between pairs of calculated stark levels, the model predicts GSGG as the best host

  16. Predictive modeling of terrestrial radiation exposure from geologic materials

    NASA Astrophysics Data System (ADS)

    Haber, Daniel A.

    Aerial gamma ray surveys are an important tool for national security, scientific, and industrial interests in determining locations of both anthropogenic and natural sources of radioactivity. There is a relationship between radioactivity and geology and in the past this relationship has been used to predict geology from an aerial survey. The purpose of this project is to develop a method to predict the radiologic exposure rate of the geologic materials in an area by creating a model using geologic data, images from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), geochemical data, and pre-existing low spatial resolution aerial surveys from the National Uranium Resource Evaluation (NURE) Survey. Using these data, geospatial areas, referred to as background radiation units, homogenous in terms of K, U, and Th are defined and the gamma ray exposure rate is predicted. The prediction is compared to data collected via detailed aerial survey by our partner National Security Technologies, LLC (NSTec), allowing for the refinement of the technique. High resolution radiation exposure rate models have been developed for two study areas in Southern Nevada that include the alluvium on the western shore of Lake Mohave, and Government Wash north of Lake Mead; both of these areas are arid with little soil moisture and vegetation. We determined that by using geologic units to define radiation background units of exposed bedrock and ASTER visualizations to subdivide radiation background units of alluvium, regions of homogeneous geochemistry can be defined allowing for the exposure rate to be predicted. Soil and rock samples have been collected at Government Wash and Lake Mohave as well as a third site near Cameron, Arizona. K, U, and Th concentrations of these samples have been determined using inductively coupled mass spectrometry (ICP-MS) and laboratory counting using radiation detection equipment. In addition, many sample locations also have

  17. Predictive Multiscale Modeling of Nanocellulose Based Materials and Systems

    NASA Astrophysics Data System (ADS)

    Kovalenko, Andriy

    2014-08-01

    Cellulose Nanocrysals (CNC) is a renewable biodegradable biopolymer with outstanding mechanical properties made from highly abundant natural source, and therefore is very attractive as reinforcing additive to replace petroleum-based plastics in biocomposite materials, foams, and gels. Large-scale applications of CNC are currently limited due to its low solubility in non-polar organic solvents used in existing polymerization technologies. The solvation properties of CNC can be improved by chemical modification of its surface. Development of effective surface modifications has been rather slow because extensive chemical modifications destabilize the hydrogen bonding network of cellulose and deteriorate the mechanical properties of CNC. We employ predictive multiscale theory, modeling, and simulation to gain a fundamental insight into the effect of CNC surface modifications on hydrogen bonding, CNC crystallinity, solvation thermodynamics, and CNC compatibilization with the existing polymerization technologies, so as to rationally design green nanomaterials with improved solubility in non-polar solvents, controlled liquid crystal ordering and optimized extrusion properties. An essential part of this multiscale modeling approach is the statistical- mechanical 3D-RISM-KH molecular theory of solvation, coupled with quantum mechanics, molecular mechanics, and multistep molecular dynamics simulation. The 3D-RISM-KH theory provides predictive modeling of both polar and non-polar solvents, solvent mixtures, and electrolyte solutions in a wide range of concentrations and thermodynamic states. It properly accounts for effective interactions in solution such as steric effects, hydrophobicity and hydrophilicity, hydrogen bonding, salt bridges, buffer, co-solvent, and successfully predicts solvation effects and processes in bulk liquids, solvation layers at solid surface, and in pockets and other inner spaces of macromolecules and supramolecular assemblies. This methodology

  18. Fabrication, Characterization and Modeling of Functionally Graded Materials

    NASA Astrophysics Data System (ADS)

    Lee, Po-Hua

    In the past few decades, a number of theoretical and experimental studies for design, fabrication and performance analysis of solar panel systems (photovoltaic/thermal systems) have been documented. The existing literature shows that the use of solar energy provides a promising solution to alleviate the shortage of natural resources and the environmental pollution associated with electricity generation. A hybrid solar panel has been invented to integrate photovoltaic (PV) cells onto a substrate through a functionally graded material (FGM) with water tubes cast inside, through which water flow serves as both a heat sink and a solar heat collector. Due to the unique and graded material properties of FGMs, this novel design not only supplies efficient thermal harvest and electrical production, but also provides benefits such as structural integrity and material efficiency. In this work, a sedimentation method has been used to fabricate aluminum (Al) and high-density polyethylene (HDPE) FGMs. The size effect of aluminum powder on the material gradation along the depth direction is investigated. Aluminum powder or the mixture of Al and HDPE powder is thoroughly mixed and uniformly dispersed in ethanol and then subjected to sedimentation. During the sedimentation process, the concentration of Al and HDPE particles temporally and spatially changes in the depth direction due to the non-uniform motion of particles; this change further affects the effective viscosity of the suspension and thus changes the drag force of particles. A Stokes' law based model is developed to simulate the sedimentation process, demonstrate the effect of manufacturing parameters on sedimentation, and predict the graded microstructure of deposition in the depth direction. In order to improve the modeling for sedimentation behavior of particles, the Eshelby's equivalent inclusion method (EIM) is presented to determine the interaction between particles, which is not considered in a Stokes' law based

  19. Advanced numerical models and material characterisation techniques for composite materials subject to impact and shock wave loading

    NASA Astrophysics Data System (ADS)

    Clegg, R. A.; White, D. M.; Hayhurst, C.; Ridel, W.; Harwick, W.; Hiermaier, S.

    2003-09-01

    The development and validation of an advanced material model for orthotropic materials, such as fibre reinforced composites, is described. The model is specifically designed to facilitate the numerical simulation of impact and shock wave propagation through orthotropic materials and the prediction of subsequent material damage. Initial development of the model concentrated on correctly representing shock wave propagation in composite materials under high and hypervelocity impact conditions [1]. This work has now been extended to further concentrate on the development of improved numerical models and material characterisation techniques for the prediction of damage, including residual strength, in fibre reinforced composite materials. The work is focussed on Kevlar-epoxy however materials such as CFRP are also being considered. The paper describes our most recent activities in relation to the implementation of advanced material modelling options in this area. These enable refined non-liner directional characteristics of composite materials to be modelled, in addition to the correct thermodynamic response under shock wave loading. The numerical work is backed by an extensive experimental programme covering a wide range of static and dynamic tests to facilitate derivation of model input data and to validate the predicted material response. Finally, the capability of the developing composite material model is discussed in relation to a hypervelocity impact problem.

  20. Modeling, simulation and experimental verification of constitutive models for energetic materials

    NASA Astrophysics Data System (ADS)

    Haberman, K. S.; Bennett, J. G.; Asay, B. W.; Henson, B. F.; Funk, D. J.

    1998-07-01

    Simulation of the complete response of components and systems composed of energetic materials, such as PBX-9501 (1) is important in the determination of the safety of various explosive systems. For example, predicting the correct state of stress, rate of deformation and temperature during penetration is essential in the prediction of ignition. Such simulation requires accurate constitutive models. These models must also be computationally efficient to enable analysis of large scale three dimensional problems using explicit lagrangian finite element codes such as DYNA3D (2). However, to be of maximum utility, these predictions must be validated against robust dynamic experiments. In this paper, we report comparisons between experimental and predicted displacement fields in PBX-9501 during dynamic deformation, and describe the modeling approach. The predictions used Visco-SCRAM and the Generalized Method of Cells which have been implemented into DYNA3D. The experimental data were obtained using laser-induced fluorescence speckle photography. Results from this study have lead to more accurate models and have also guided further experimental work.

  1. Modeling, simulation and experimental verification of constitutive models for energetic materials

    SciTech Connect

    Haberman, K.S.; Bennett, J.G.; Assay, B.W.

    1997-09-01

    Simulation of the complete response of components and systems composed of energetic materials, such as PBX-9501 is important in the determination of the safety of various explosive systems. For example, predicting the correct state of stress, rate of deformation and temperature during penetration is essential in the prediction of ignition. Such simulation requires accurate constitutive models. These models must also be computationally efficient to enable analysis of large scale three dimensional problems using explicit lagrangian finite element codes such as DYNA3D. However, to be of maximum utility, these predictions must be validated against robust dynamic experiments. In this paper, the authors report comparisons between experimental and predicted displacement fields in PBX-9501 during dynamic deformation, and describe the modeling approach. The predictions used Visco-SCRAM and the Generalized Method of Cells which have been implemented into DYNA3D. The experimental data were obtained using laser-induced fluorescence speckle photography. Results from this study have lead to more accurate models and have also guided further experimental work.

  2. Sensitivity of hydrological performance assessment analysis to variations in material properties, conceptual models, and ventilation models

    SciTech Connect

    Sobolik, S.R.; Ho, C.K.; Dunn, E.; Robey, T.H.; Cruz, W.T.

    1996-07-01

    The Yucca Mountain Site Characterization Project is studying Yucca Mountain in southwestern Nevada as a potential site for a high-level nuclear waste repository. Site characterization includes surface- based and underground testing. Analyses have been performed to support the design of an Exploratory Studies Facility (ESF) and the design of the tests performed as part of the characterization process, in order to ascertain that they have minimal impact on the natural ability of the site to isolate waste. The information in this report pertains to sensitivity studies evaluating previous hydrological performance assessment analyses to variation in the material properties, conceptual models, and ventilation models, and the implications of this sensitivity on previous recommendations supporting ESF design. This document contains information that has been used in preparing recommendations for Appendix I of the Exploratory Studies Facility Design Requirements document.

  3. Growth and modelling of spherical crystalline morphologies of molecular materials.

    PubMed

    Shalev, O; Biswas, S; Yang, Y; Eddir, T; Lu, W; Clarke, R; Shtein, M

    2014-10-16

    Crystalline, yet smooth, sphere-like morphologies of small molecular compounds are desirable in a wide range of applications but are very challenging to obtain using common growth techniques, where either amorphous films or faceted crystallites are the norm. Here we show solvent-free, guard flow-assisted organic vapour jet printing of non-faceted, crystalline microspheroids of archetypal small molecular materials used in organic electronic applications. We demonstrate how process parameters control the size distribution of the spheroids and propose an analytical model and a phase diagram predicting the surface morphology evolution of different molecules based on processing conditions, coupled with the thermophysical and mechanical properties of the molecules. This experimental approach opens a path for exciting applications of small molecular organic compounds in optical coatings, textured surfaces with controlled wettability, pharmaceutical and food substance printing and others, where thick organic films and particles with high surface area are needed.

  4. Modelling and control of robotic arms fabricated from orthotropic materials

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, K.; Chandrashekhara, K.; Roy, S.

    1989-05-01

    A dynamic model for single-link robotic manipulators fabricated from orthotropic composite materials is presented. The equations of motion are derived using Hamilton's principle and include the coupling between the rigid body motion and elastic motion. An optimal controller is designed for rest-to-rest maneuvers without large starting or stopping transients and with minimum residual vibration. Results presented for aluminum, steel, graphite/epoxy, and boron/epoxy indicate that the motion induced vibration is significantly less for the composite robotic arms, and that substantial savings in energy are achieved. Furthermore, it was seen that the magnitude of the control spillover effects, an issue of great concern in designing control systems for flexible structures, was very small for the composite robotic arms.

  5. Modelling of tritium permeation through beryllium as plasma facing material

    NASA Astrophysics Data System (ADS)

    Berardinucci, L.

    1998-10-01

    Due to a number of technological properties and, first of all, to a low atomic number, beryllium will be used as plasma facing material in ITER. Tritium control, including both the permeation through and inventory in the beryllium, is of great importance for the safety of the device. Experimental data have shown that, under ITER-like plasma conditions, the plasma facing surfaces of the beryllium develop high porosity (bubbles) and become saturated with bubbles, leading to a strong uptake of tritium and deuterium ions almost independent of the incident flux. At fluxes typical of ITER, surface erosion of beryllium should be also taken into account. A computational model has been used with the computer code TMAP4 to reproduce the available experimental data concerning hydrogen ion implantation in beryllium. The results described in this paper refer to the first wall of the European Helium Cooled Pebble Bed Blanket (HCPB) Test Blanket Module (TBM-I).

  6. A quantification model for the structure of clay materials.

    PubMed

    Tang, Liansheng; Sang, Haitao; Chen, Haokun; Sun, Yinlei; Zhang, Longjian

    2016-07-04

    In this paper, the quantification for clay structure is explicitly explained, and the approach and goals of quantification are also discussed. The authors consider that the purpose of the quantification for clay structure is to determine some parameters that can be used to quantitatively characterize the impact of clay structure on the macro-mechanical behaviour. According to the system theory and the law of energy conservation, a quantification model for the structure characteristics of clay materials is established and three quantitative parameters (i.e., deformation structure potential, strength structure potential and comprehensive structure potential) are proposed. And the corresponding tests are conducted. The experimental results show that these quantitative parameters can accurately reflect the influence of clay structure on the deformation behaviour, strength behaviour and the relative magnitude of structural influence on the above two quantitative parameters, respectively. These quantitative parameters have explicit mechanical meanings, and can be used to characterize the structural influences of clay on its mechanical behaviour.

  7. High temperature viscoplastic ratchetting - Material response or modeling artifact

    NASA Technical Reports Server (NTRS)

    Freed, Alan D.

    1991-01-01

    Some of the basic issues of ratchetting behavior that are being addressed by the viscoplastic modeling community are discussed. Some of the shortcomings of existing viscoplastic models are examined in the light of the difficulty involved in using established viscoplastic modeling techniques to predict ratchetting accurately.

  8. Modeling the thermal properties and processing of composite materials

    SciTech Connect

    Pitchumani, R.

    1992-01-01

    The manufacture of partially cured, thermoset matrix composite systems is modeled. A generalized analysis, applicable to almost all the fiber-resin systems encountered in practice, is carried out in terms of four key dimensionless groups formed of the process and the product parameters - (1) the Damkohler number (K(sub o)) which is a relative measure of the conduction and the reaction time scales, (2) the dimensionless activation energy (E(sub o)), (3) the adiabatic reaction temperature (B(sub o)) which represents the temperature rise potential in the composite due to the heat of the cure reaction, and (4) the Biot number (B(sub i)) which characterizes the post-cure convective cooling of the composite product. Optimal cure cycles which yield a homogeneous cure in the composite, are obtained as a function of the dimensionless parameters. Design plots for the optimal cure temperature and duration are presented. Their use in practical situations is illustrated in the context of a commercially available graphite-epoxy prepreg from Hercules, which is widely used in the aerospace industry. The thermal properties of the composite namely, the transient thermal diffusivity and the steady state thermal conductivity, are essential parameters in the process modeling studies, as well for the design of composite materials for several high temperature applications. Transient heat conduction in fibrous composites is investigated with the aim of devising a criterion for the validity of the analysis of composite materials as homogeneous media having the effective thermal properties. A homogeneity criterion based on the composite thickness is derived in terms of the fiber volume fraction and the fiber diameter. The criterion, which is the first of its kind for fibrous composites, is valid in the practical range of composite parameters. An analytical means for evaluating the effective thermal diffusivity is also presented.

  9. Scaling in a Model of Material Damage with Healing

    NASA Astrophysics Data System (ADS)

    Gran, J. D.

    2009-12-01

    A variety of studies have modeled the physics of material deformation and damage as examples of generalized phase transitions, involving either critical phenomena or spinodal nucleation. Here we study a model for frictional sliding with interactions R>>1 and recurrent damage that is parameterized by a process of damage and partial healing during sliding. We define a mapping to a percolation transition, and show that the scaling exponents are, within measurement error, the same as for mean field percolation and spinodal nucleation. We also examine finite size effects, and show that the values of the scaling exponents correctly approach the values for spinodal nucleation as lattice size L is increased for fixed R. The probability of gridsize events vs the weakening parameter adjusted by the critical weakening value. The plot is on a logarithmic scale emphasizing the power-law dependence of P(h-hc) with a scaling exponent β = 1. The second region of increasing P(h-hc) is fit to an exponential curve. The inter-event intervals for the simulation with weakening parameter h = 0.074. An inter-event interval is defined as the number of micro-events occurring between two events whose area's are greater than a minimum cutoff size. The cutoff event size here is 15 sites. The plot shows the frequency of inter-event intervals has a power-law dependence on the size of the interval with a scaling exponent near 2.

  10. FEMA: a Finite Element Model of Material Transport through Aquifers

    SciTech Connect

    Yeh, G.T.; Huff, D.D.

    1985-01-01

    This report documents the construction, verification, and demonstration of a Finite Element Model of Material Transport through Aquifers (FEMA). The particular features of FEMA are its versatility and flexibility to deal with as many real-world problems as possible. Mechanisms included in FEMA are: carrier fluid advection, hydrodynamic dispersion and molecular diffusion, radioactive decay, sorption, source/sinks, and degradation due to biological, chemical as well as physical processes. Three optional sorption models are embodied in FEMA. These are linear isotherm and Freundlich and Langmuir nonlinear isotherms. Point as well as distributed source/sinks are included to represent artificial injection/withdrawals and natural infiltration of precipitation. All source/sinks can be transient or steady state. Prescribed concentration on the Dirichlet boundary, given gradient on the Neumann boundary segment, and flux at each Cauchy boundary segment can vary independently of each other. The aquifer may consist of as many formations as desired. Either completely confined or completely unconfined or partially confined and partially unconfined aquifers can be dealt with effectively. FEMA also includes transient leakage to or from the aquifer of interest through confining beds from or to aquifers lying below and/or above.

  11. Modeling plastic deformation effect on magnetization in ferromagnetic materials

    NASA Astrophysics Data System (ADS)

    Li, Jianwei; Xu, Minqiang; Leng, Jiancheng; Xu, Mingxiu

    2012-03-01

    Based on the Sablik-Landgraf model, an integrated model has been developed which provides a description of the effect of plastic deformation on magnetization. The modeling approach is to incorporate the effect of plastic deformation on the effective field and that on the model parameters. The effective field incorporates the contributions of residual stress, stress demagnetization term, and the plastic deformation. We also consider the effect of plastic deformation on the model parameters: pinning coefficient, the scaling constant and the interdomain coupling coefficient. The computed magnetization exhibits sharp change in the preliminary stage of plastic deformation, and then decreases slowly with the increase of plastic strain, in agreement with experimental results.

  12. Modeling of oxidation of structural materials in LBE systems

    NASA Astrophysics Data System (ADS)

    Steiner, H.; Schroer, C.; Voß, Z.; Wedemeyer, O.; Konys, J.

    2008-02-01

    In recent years, liquid metal alloys have been examined in the light of various applications in technical systems the most famous example is the sodium cooled Fast Breeder Reactor. One major problem in non-isothermal heavy liquid metal systems lies in the corrosion of their structural components. The formation of oxide scales on the structural components is considered as a viable measure in limiting the dissolution rates in the hot parts in lead and lead-bismuth loops. Models for oxide scale growth under the action of flowing liquid metals have been implemented in the newly developed code MATLIM, which allow calculating the evolution of the oxide scales on structural materials in multi-modular loops. There are thermo-hydraulic limitations on oxygen supply from the liquid metal to the structural materials, the oxygen mass transfer coefficient in the liquid metal, which depends on the flow conditions, being rate-determining. This seems to explain, for example, why in the first stage of oxidation of stainless steels slowly growing, dense single layer Fe/Cr spinel scales are formed.

  13. A Model of Research Paper Writing Instructional Materials for Academic Writing Course: "Needs & Documents Analysis and Model Design"

    ERIC Educational Resources Information Center

    Ghufron, M. Ali; Saleh, Mursid; Warsono; Sofwan, Ahmad

    2016-01-01

    This study aimed at designing a model of instructional materials for Academic Writing Course focusing on research paper writing. The model was designed based on the Curriculum at the English Education Study Program, Faculty of Language and Art Education of IKIP PGRI Bojonegoro, East Java, Indonesia. This model was developed in order to improve…

  14. Towards CFD modeling of turbulent pipeline material transportation

    NASA Astrophysics Data System (ADS)

    Shahirpour, Amir; Herzog, Nicoleta; Egbers, Cristoph

    2013-04-01

    Safe and financially efficient pipeline transportation of carbon dioxide is a critical issue in the developing field of the CCS Technology. In this part of the process, carbon dioxide is transported via pipes with diameter of 1.5 m and entry pressure of 150 bar, with Reynolds number of 107 and viscosity of 8×10(-5) Pa.s as dense fluid [1]. Presence of large and small scale structures in the pipeline, high Reynolds numbers at which CO2 should be transferred, and 3 dimensional turbulence caused by local geometrical modifications, increase the importance of simulation of turbulent material transport through the individual components of the CO2 chain process. In this study, incompressible turbulent channel flow and pipe flow have been modeled using OpenFoam, an open source CFD software. In the first step, simulation of a turbulent channel flow has been considered using LES for shear Reynolds number of 395. A simple geometry has been chosen with cyclic fluid inlet and outlet boundary conditions to simulate a fully developed flow. The mesh is gradually refined towards the wall to provide values close enough to the wall for the wall coordinate (y+). Grid resolution study has been conducted for One-Equation model. The accuracy of the results is analyzed with respect to the grid smoothness in order to reach an optimized resolution for carrying out the next simulations. Furthermore, three LES models, One-Equation, Smagorinsky and Dynamic Smagorinsky are applied for the grid resolution of (60 × 100 × 80) in (x, y, z) directions. The results are then validated with reference to the DNS carried out by Moser et al.[2] for the similar geometry using logarithmic velocity profile (U+) and Reynolds stress tensor components. In the second step the similar flow is modeled using Reynolds averaged method. Several RANS models, like K-epsilon and Launder-Reece-Rodi are applied and validated against DNS and LES results in a similar fashion. In the most recent step, it has been intended

  15. Inclusion of Material Non-Linearity and Inelasticity into a Continuum-Level Material Model for Soda-Lime Glass

    DTIC Science & Technology

    2012-01-01

    enhanced material model was coded using the Intel Fortran computational language and implemented as a VUMAT Material User Subroutine within the commercial...ABAQUS/Explicit finite- element solver with the VUMAT Material User Subroutine at each time increment at each integration point of each element can be...current time-step incremental strains are passed to the VUMAT by the ABAQUS/Explicit finite-element solver. Spe- cifically, the glass material model

  16. Modeling Spin Testing Using Location Specific Material Properties

    DTIC Science & Technology

    2012-04-01

    disc superalloy showed the highest departure from random uniform as a result of particle clustering associated with extensive thermomechanical...temperatures, a newer generation of nickel based superalloys such as LSHR, Alloy 10, Rene104 and RR1000 are being processed with dual microstructure...This model is derived from Tresa Pollocks’ nickel-base superalloy strength model. Strengthening model: Eq. 15 1. Solid solution

  17. Digital Learning Material for Model Building in Molecular Biology

    ERIC Educational Resources Information Center

    Aegerter-Wilmsen, Tinri; Janssen, Fred; Hartog, Rob; Bisseling, Ton

    2005-01-01

    Building models to describe processes forms an essential part of molecular biology research. However, in molecular biology curricula little attention is generally being paid to the development of this skill. In order to provide students the opportunity to improve their model building skills, we decided to develop a number of digital cases about…

  18. Digital Learning Material for Model Building in Molecular Biology

    ERIC Educational Resources Information Center

    Aegerter-Wilmsen, Tinri; Janssen, Fred; Hartog, Rob; Bisseling, Ton

    2005-01-01

    Building models to describe processes forms an essential part of molecular biology research. However, in molecular biology curricula little attention is generally being paid to the development of this skill. In order to provide students the opportunity to improve their model building skills, we decided to develop a number of digital cases about…

  19. Efficient material flow in mixed model assembly lines.

    PubMed

    Alnahhal, Mohammed; Noche, Bernd

    2013-01-01

    In this study, material flow from decentralized supermarkets to stations in mixed model assembly lines using tow (tugger) trains is investigated. Train routing, scheduling, and loading problems are investigated in parallel to minimize the number of trains, variability in loading and in routes lengths, and line-side inventory holding costs. The general framework for solving these problems in parallel contains analytical equations, Dynamic Programming (DP), and Mixed Integer Programming (MIP). Matlab in conjunction with LP-solve software was used to formulate the problem. An example was presented to explain the idea. Results which were obtained in very short CPU time showed the effect of using time buffer among routes on the feasible space and on the optimal solution. Results also showed the effect of the objective, concerning reducing the variability in loading, on the results of routing, scheduling, and loading. Moreover, results showed the importance of considering the maximum line-side inventory beside the capacity of the train in the same time in finding the optimal solution.

  20. Modeling the thermal characteristics of masonry mortar containing recycled materials

    NASA Astrophysics Data System (ADS)

    Laney, Morgan Gretchen

    As the building industry in the United States rapidly expands, the reuse of recycled demolition waste aggregates is becoming increasingly more important. Currently, the building industry is the largest consumer of natural resources. The constant use of raw virgin aggregate is resulting in depleting resources, lack of space for landfills, increasing costs, and heightened levels of pollution. The use of these recycled aggregates in building envelopes and the study of thermal properties are becoming a popular area of research in order to improve building energy usage. The construction of Zero Energy Buildings (ZEB) is encouraged by the United States government as a result of the unresolved finite resources and environmental pollution. The focus of this research is on the impact of using recycled demolition waste aggregates on thermal properties, including specific heat capacity and thermal conductivity, in masonry mortar applications. The new forms of aggregate were analyzed for efficiency and practical utilization in construction in seven locations across the United States by embedding the new material into the building envelope of a strip mall mercantile build model from the National Renewable Energy Laboratory (NREL) in the EnergyPlus Building Energy Simulation Program (BESP). It was determined that the recycled aggregate mortar mixtures performed as well as or better than the traditional mortar mix. Opportunities for future research in recycled aggregate mortar mixtures exist in a regional analysis, a regional recycled aggregate cost analysis, and a life cycled cost analysis (LCCA).

  1. Charge transport model to predict intrinsic reliability for dielectric materials

    SciTech Connect

    Ogden, Sean P.; Borja, Juan; Plawsky, Joel L. Gill, William N.; Lu, T.-M.; Yeap, Kong Boon

    2015-09-28

    Several lifetime models, mostly empirical in nature, are used to predict reliability for low-k dielectrics used in integrated circuits. There is a dispute over which model provides the most accurate prediction for device lifetime at operating conditions. As a result, there is a need to transition from the use of these largely empirical models to one built entirely on theory. Therefore, a charge transport model was developed to predict the device lifetime of low-k interconnect systems. The model is based on electron transport and donor-type defect formation. Breakdown occurs when a critical defect concentration accumulates, resulting in electron tunneling and the emptying of positively charged traps. The enhanced local electric field lowers the barrier for electron injection into the dielectric, causing a positive feedforward failure. The charge transport model is able to replicate experimental I-V and I-t curves, capturing the current decay at early stress times and the rapid current increase at failure. The model is based on field-driven and current-driven failure mechanisms and uses a minimal number of parameters. All the parameters have some theoretical basis or have been measured experimentally and are not directly used to fit the slope of the time-to-failure versus applied field curve. Despite this simplicity, the model is able to accurately predict device lifetime for three different sources of experimental data. The simulation's predictions at low fields and very long lifetimes show that the use of a single empirical model can lead to inaccuracies in device reliability.

  2. Charge transport model to predict intrinsic reliability for dielectric materials

    NASA Astrophysics Data System (ADS)

    Ogden, Sean P.; Borja, Juan; Plawsky, Joel L.; Lu, T.-M.; Yeap, Kong Boon; Gill, William N.

    2015-09-01

    Several lifetime models, mostly empirical in nature, are used to predict reliability for low-k dielectrics used in integrated circuits. There is a dispute over which model provides the most accurate prediction for device lifetime at operating conditions. As a result, there is a need to transition from the use of these largely empirical models to one built entirely on theory. Therefore, a charge transport model was developed to predict the device lifetime of low-k interconnect systems. The model is based on electron transport and donor-type defect formation. Breakdown occurs when a critical defect concentration accumulates, resulting in electron tunneling and the emptying of positively charged traps. The enhanced local electric field lowers the barrier for electron injection into the dielectric, causing a positive feedforward failure. The charge transport model is able to replicate experimental I-V and I-t curves, capturing the current decay at early stress times and the rapid current increase at failure. The model is based on field-driven and current-driven failure mechanisms and uses a minimal number of parameters. All the parameters have some theoretical basis or have been measured experimentally and are not directly used to fit the slope of the time-to-failure versus applied field curve. Despite this simplicity, the model is able to accurately predict device lifetime for three different sources of experimental data. The simulation's predictions at low fields and very long lifetimes show that the use of a single empirical model can lead to inaccuracies in device reliability.

  3. Probabilistic material degradation model for aerospace materials subjected to high temperature, mechanical and thermal fatigue, and creep

    NASA Astrophysics Data System (ADS)

    Boyce, L.

    1992-07-01

    A probabilistic general material strength degradation model has been developed for structural components of aerospace propulsion systems subjected to diverse random effects. The model has been implemented in two FORTRAN programs, PROMISS (Probabilistic Material Strength Simulator) and PROMISC (Probabilistic Material Strength Calibrator). PROMISS calculates the random lifetime strength of an aerospace propulsion component due to as many as eighteen diverse random effects. Results are presented in the form of probability density functions and cumulative distribution functions of lifetime strength. PROMISC calibrates the model by calculating the values of empirical material constants.

  4. Probabilistic material degradation model for aerospace materials subjected to high temperature, mechanical and thermal fatigue, and creep

    NASA Technical Reports Server (NTRS)

    Boyce, L.

    1992-01-01

    A probabilistic general material strength degradation model has been developed for structural components of aerospace propulsion systems subjected to diverse random effects. The model has been implemented in two FORTRAN programs, PROMISS (Probabilistic Material Strength Simulator) and PROMISC (Probabilistic Material Strength Calibrator). PROMISS calculates the random lifetime strength of an aerospace propulsion component due to as many as eighteen diverse random effects. Results are presented in the form of probability density functions and cumulative distribution functions of lifetime strength. PROMISC calibrates the model by calculating the values of empirical material constants.

  5. Application for managing model-based material properties for simulation-based engineering

    DOEpatents

    Hoffman, Edward L [Alameda, CA

    2009-03-03

    An application for generating a property set associated with a constitutive model of a material includes a first program module adapted to receive test data associated with the material and to extract loading conditions from the test data. A material model driver is adapted to receive the loading conditions and a property set and operable in response to the loading conditions and the property set to generate a model response for the material. A numerical optimization module is adapted to receive the test data and the model response and operable in response to the test data and the model response to generate the property set.

  6. Probabilistic Multi-Factor Interaction Model for Complex Material Behavior

    NASA Technical Reports Server (NTRS)

    Abumeri, Galib H.; Chamis, Christos C.

    2010-01-01

    Complex material behavior is represented by a single equation of product form to account for interaction among the various factors. The factors are selected by the physics of the problem and the environment that the model is to represent. For example, different factors will be required for each to represent temperature, moisture, erosion, corrosion, etc. It is important that the equation represent the physics of the behavior in its entirety accurately. The Multi-Factor Interaction Model (MFIM) is used to evaluate the divot weight (foam weight ejected) from the external launch tanks. The multi-factor has sufficient degrees of freedom to evaluate a large number of factors that may contribute to the divot ejection. It also accommodates all interactions by its product form. Each factor has an exponent that satisfies only two points - the initial and final points. The exponent describes a monotonic path from the initial condition to the final. The exponent values are selected so that the described path makes sense in the absence of experimental data. In the present investigation, the data used were obtained by testing simulated specimens in launching conditions. Results show that the MFIM is an effective method of describing the divot weight ejected under the conditions investigated. The problem lies in how to represent the divot weight with a single equation. A unique solution to this problem is a multi-factor equation of product form. Each factor is of the following form (1 xi/xf)ei, where xi is the initial value, usually at ambient conditions, xf the final value, and ei the exponent that makes the curve represented unimodal that meets the initial and final values. The exponents are either evaluated by test data or by technical judgment. A minor disadvantage may be the selection of exponents in the absence of any empirical data. This form has been used successfully in describing the foam ejected in simulated space environmental conditions. Seven factors were required

  7. December 2016 MOVES Model Review Work Group Meeting Materials

    EPA Pesticide Factsheets

    MOVES Model Review Work Group meeting on December 7th, 2016 included plans for updating running exhaust criteria pollutant emission rates for heavy-duty diesel vehicles, emission rates for extended idle and auxiliary power units, onroad vehicle population.

  8. March 2017 MOVES Model Review Work Group Meeting Materials

    EPA Pesticide Factsheets

    MOVES Model Review Work Group meeting on March 201 included plans for updating running exhaust criteria pollutant emission rates for heavy-duty diesel vehicles, emission rates for extended idle and auxiliary power units, onroad vehicle population.

  9. SLAC Model A, B, and C rf loads (Engineering Materials)

    SciTech Connect

    Not Available

    1983-01-01

    These three drawing lists and the drawings listed thereon provide the information and specifications for constructing the three types of high power rf loads used on the SLAC Linear Accelerator waveguide system. Drawing List DL-767-304-00-R1 Model B rf Load contains the largest number of drawings with Model A and C using some common parts therefrom. Model B load is used in other places requiring only a high power capability (water cooling) and the Model C load is used on the output of the 3 dB hybrid couplers used as power dividers and are not water cooled. Not all referenced drawings are included, however, all that are needed to construct the basic load assemblies are included.

  10. Simulation of human atherosclerotic femoral plaque tissue: the influence of plaque material model on numerical results

    PubMed Central

    2015-01-01

    Background Due to the limited number of experimental studies that mechanically characterise human atherosclerotic plaque tissue from the femoral arteries, a recent trend has emerged in current literature whereby one set of material data based on aortic plaque tissue is employed to numerically represent diseased femoral artery tissue. This study aims to generate novel vessel-appropriate material models for femoral plaque tissue and assess the influence of using material models based on experimental data generated from aortic plaque testing to represent diseased femoral arterial tissue. Methods Novel material models based on experimental data generated from testing of atherosclerotic femoral artery tissue are developed and a computational analysis of the revascularisation of a quarter model idealised diseased femoral artery from a 90% diameter stenosis to a 10% diameter stenosis is performed using these novel material models. The simulation is also performed using material models based on experimental data obtained from aortic plaque testing in order to examine the effect of employing vessel appropriate material models versus those currently employed in literature to represent femoral plaque tissue. Results Simulations that employ material models based on atherosclerotic aortic tissue exhibit much higher maximum principal stresses within the plaque than simulations that employ material models based on atherosclerotic femoral tissue. Specifically, employing a material model based on calcified aortic tissue, instead of one based on heavily calcified femoral tissue, to represent diseased femoral arterial vessels results in a 487 fold increase in maximum principal stress within the plaque at a depth of 0.8 mm from the lumen. Conclusions Large differences are induced on numerical results as a consequence of employing material models based on aortic plaque, in place of material models based on femoral plaque, to represent a diseased femoral vessel. Due to these large

  11. Comparison of responses of concrete damage material models with respect to optimization-based material parameter identification

    NASA Astrophysics Data System (ADS)

    Král, Petr; Hradil, Petr; Hušek, Martin; Hokeš, Filip

    2017-07-01

    Today, the inverse identification or optimization of material model parameters is very often used to find input parameter values for use in relevant nonlinear material models. These parameter values should enable the responses of structures obtained from numerical simulations to very closely approximate the real responses of such structures obtained from experiments. Due to the popularity of concrete as a construction material, much attention is paid to nonlinear material models that aim to describe its behavior. This paper is focused on the optimization-based inverse identification of the parameters of two related nonlinear concrete material models which are known as the Karagozian & Case Concrete model and the Karagozian & Case Concrete model - Release III. Within this paper, the identification of the material model parameters is performed on the basis of interaction between nonlinear numerical simulations, optimization algorithms and experimental data, the latter of which take the form of a loading curve measured during a triaxial compression test. A comparison of the responses of both of the used material models when the optimized parameters are employed is, of course, part of this paper.

  12. Material Models Used to Predict Spring-in of Composite Elements: a Comparative Study

    NASA Astrophysics Data System (ADS)

    Galińska, Anna

    2017-02-01

    There have been several approaches used in the modelling of the process-induced deformations of composite parts developed so far. The most universal and most frequently used approach is the FEM modelling. In the scope of the FEM modelling several material models have been used to model the composite behaviour. In the present work two of the most popular material models: elastic and CHILE (cure hardening instantaneous linear elastic) are used to model the spring-in deformations of composite specimens and a structure fragment. The elastic model is more effective, whereas the CHILE model is considered more accurate. The results of the models are compared with each other and with the measured deformations of the real composite parts. Such a comparison shows that both models allow to predict the deformations reasonably well and that there is little difference between their results. This leads to a conclusion that the use of the simpler elastic model is a valid engineering practice.

  13. Tunable polymeric sorbent materials for fractionation of model naphthenates.

    PubMed

    Mohamed, Mohamed H; Wilson, Lee D; Headley, John V

    2013-04-04

    The sorption properties are reported for several examples of single-component carboxylic acids representing naphthenic acids (NAs) with β-cyclodextrin (β-CD) based polyurethane sorbents. Seven single-component examples of NAs were chosen with variable z values, carbon number, and chemical structure as follows: 2-hexyldecanoic acid (z = 0 and C = 16; S1), n-caprylic acid (z = 0 and C = 8; S2), trans-4-pentylcyclohexanecarboxylic acid (z = -2 and C = 12; S3), 4-methylcyclohexanecarboxylic acid (z = -2 and C = 8; S4), dicyclohexylacetic acid (z = -4; C = 14; S5), 4-pentylbicyclo[2.2.2]octane-1-carboxylic acid (z = -4; C = 14; S6), and lithocholic acid (z = -6; C = 24; S7). The copolymer sorbents were synthesized at three relative β-CD:diisocyanate mole ratios (i.e., 1:1, 1:2, and 1:3) using 4,4'-dicyclohexylmethane diisocyanate (CDI) and 4,4'-diphenylmethane diisocyanate (MDI). The sorption properties of the copolymer sorbents were characterized using equilibrium sorption isotherms in aqueous solution at pH 9.00 with electrospray ionization mass spectrometry. The equilibrium fraction of the unbound carboxylate anions was monitored in the aqueous phase. The sorption properties of the copolymer sorbents (i.e., Qm) were obtained from the Sips isotherm model. The Qm values generally decrease as the number of accessible β-CD inclusion sites in the copolymer framework decreases. The chemical structure of the adsorbates played an important role in their relative uptake, as evidenced by the adsorbate lipophilic surface area (LSA) and the involvement of hydrophobic effects. The copolymers exhibit molecular selective sorption of the single-component carboxylates in mixtures which suggests their application as sorbents for fractionation of mixtures of NAs. By comparison, granular activated carbon (GAC) and chitosan sorbents did not exhibit any significant molecular selective sorption relative to the copolymer materials; however, evidence of variable sorption capacity was

  14. Assessing Models of Public Understanding In ELSI Outreach Materials

    SciTech Connect

    Bruce V. Lewenstein, Ph.D.; Dominique Brossard, Ph.D.

    2006-03-01

    issues has been used in educational public settings to affect public understanding of science. After a theoretical background discussion, our approach is three-fold. First, we will provide an overview, a ?map? of DOE-funded of outreach programs within the overall ELSI context to identify the importance of the educational component, and to present the criteria we used to select relevant and representative case studies. Second, we will document the history of the case studies. Finally, we will explore an intertwined set of research questions: (1) To identify what we can expect such projects to accomplish -in other words to determine the goals that can reasonably be achieved by different types of outreach, (2) To point out how the case study approach could be useful for DOE-ELSI outreach as a whole, and (3) To use the case study approach as a basis to test theoretical models of science outreach in order to assess to what extent those models accord with real world outreach activities. For this last goal, we aim at identifying what practices among ELSI outreach activities contribute most to dissemination, or to participation, in other words in which cases outreach materials spark action in terms of public participation in decisions about scientific issues.

  15. Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties

    ERIC Educational Resources Information Center

    Shaw, Stephanie M.; Thomson, Scott L.; Dromey, Christopher; Smith, Simeon

    2012-01-01

    Purpose: The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency (F[subscript 0]) during anterior-posterior stretching. Method: Three materially linear and 3 materially nonlinear models were…

  16. Cross Directorate Proposal: Nanostructured Materials for Munitions and Propellants-Production, Modeling, and Characterization

    DTIC Science & Technology

    2016-07-15

    AFRL-RW-EG-TR-2016-036 Cross Directorate Proposal: Nanostructured Materials for Munitions and Propellants – Production , Modeling, and...Directorate Proposal: Nanostructured Materials for Munitions and Propellants – Production , Modeling, and Characterization 5a. CONTRACT NUMBER 5b...LABORATORY TASK REPORT LRIR #: 14RW05COR Title: Cross Directorate Proposal: Nanostructured Materials for Munitions and Propellants – Production

  17. Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties

    ERIC Educational Resources Information Center

    Shaw, Stephanie M.; Thomson, Scott L.; Dromey, Christopher; Smith, Simeon

    2012-01-01

    Purpose: The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency (F[subscript 0]) during anterior-posterior stretching. Method: Three materially linear and 3 materially nonlinear models were…

  18. Implementation of a Tabulated Failure Model Into a Generalized Composite Material Model Suitable for Use in Impact Problems

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Carney, Kelly S.; Dubois, Paul; Hoffarth, Canio; Khaled, Bilal; Shyamsunder, Loukham; Rajan, Subramaniam; Blankenhorn, Gunther

    2017-01-01

    The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites under impact conditions is becoming critical as these materials are gaining increased use in the aerospace and automotive communities. The aerospace community has identified several key capabilities which are currently lacking in the available material models in commercial transient dynamic finite element codes. To attempt to improve the predictive capability of composite impact simulations, a next generation material model is being developed for incorporation within the commercial transient dynamic finite element code LS-DYNA. The material model, which incorporates plasticity, damage and failure, utilizes experimentally based tabulated input to define the evolution of plasticity and damage and the initiation of failure as opposed to specifying discrete input parameters such as modulus and strength. The plasticity portion of the orthotropic, three-dimensional, macroscopic composite constitutive model is based on an extension of the Tsai-Wu composite failure model into a generalized yield function with a non-associative flow rule. For the damage model, a strain equivalent formulation is used to allow for the uncoupling of the deformation and damage analyses. For the failure model, a tabulated approach is utilized in which a stress or strain based invariant is defined as a function of the location of the current stress state in stress space to define the initiation of failure. Failure surfaces can be defined with any arbitrary shape, unlike traditional failure models where the mathematical functions used to define the failure surface impose a specific shape on the failure surface. In the current paper, the complete development of the failure model is described and the generation of a tabulated failure surface for a representative composite material is discussed.

  19. Thermal-capillary model for Czochralski growth of semiconductor materials

    NASA Technical Reports Server (NTRS)

    Derby, J. J.; Brown, R. A.

    1985-01-01

    The success of efficiently calculating the temperature field, crystal radius, melt mensicus, and melt/solid interface in the Czochralski crystal growth system by full finite-element solution of the government thermal-capillary model is demonstrated. The model predicts realistic response to changes in pull rate, melt volume, and the thermal field. The experimentally observed phenomena of interface flipping, bumping, and the difficulty maintaining steady-state growth as the melt depth decreases are explained by model results. These calculations will form the basis for the first quantitative picture of Cz crystal growth. The accurate depiction of the melt meniscus is important in calculating the crystal radius and solidification interface. The sensitivity of the results to the equilibrium growth angle place doubt on less sophisticated attempts to model the process without inclusion of the meniscus. Quantitative comparison with experiments should be possible once more representation of the radiation and view factors in the thermal system and the crucible are included. Extensions of the model in these directions are underway.

  20. Enthalpy recovery in glassy materials: heterogeneous versus homogenous models.

    PubMed

    Mazinani, Shobeir K S; Richert, Ranko

    2012-05-07

    Models of enthalpy relaxations of glasses are the basis for understanding physical aging, scanning calorimetry, and other phenomena that involve non-equilibrium and non-linear dynamics. We compare models in terms of the nature of the relaxation dynamics, heterogeneous versus homogeneous, with focus on the Kovacs-Aklonis-Hutchinson-Ramos (KAHR) and the Tool-Narayanaswamy-Moynihan (TNM) approaches. Of particular interest is identifying the situations for which experimental data are capable of discriminating the heterogeneous from the homogeneous scenario. The ad hoc assumption of a single fictive temperature, T(f), is common to many models, including KAHR and TNM. It is shown that only for such single-T(f) models, enthalpy relaxation of a glass is a two-point correlation function in reduced time, implying that experimental results are not decisive regarding the underlying nature of the dynamics of enthalpy relaxation. We also find that the restriction of the common TNM model to a Kohlrausch-Williams-Watts type relaxation pattern limits the applicability of this approach, as the particular choice regarding the distribution of relaxation times is a more critical factor compared with isothermal relaxation experiments. As a result, significant improvements in fitting calorimetry data can be achieved with subtle adjustments in the underlying relaxation time distribution.

  1. Enthalpy recovery in glassy materials: Heterogeneous versus homogenous models

    NASA Astrophysics Data System (ADS)

    Mazinani, Shobeir K. S.; Richert, Ranko

    2012-05-01

    Models of enthalpy relaxations of glasses are the basis for understanding physical aging, scanning calorimetry, and other phenomena that involve non-equilibrium and non-linear dynamics. We compare models in terms of the nature of the relaxation dynamics, heterogeneous versus homogeneous, with focus on the Kovacs-Aklonis-Hutchinson-Ramos (KAHR) and the Tool-Narayanaswamy-Moynihan (TNM) approaches. Of particular interest is identifying the situations for which experimental data are capable of discriminating the heterogeneous from the homogeneous scenario. The ad hoc assumption of a single fictive temperature, Tf, is common to many models, including KAHR and TNM. It is shown that only for such single-Tf models, enthalpy relaxation of a glass is a two-point correlation function in reduced time, implying that experimental results are not decisive regarding the underlying nature of the dynamics of enthalpy relaxation. We also find that the restriction of the common TNM model to a Kohlrausch-Williams-Watts type relaxation pattern limits the applicability of this approach, as the particular choice regarding the distribution of relaxation times is a more critical factor compared with isothermal relaxation experiments. As a result, significant improvements in fitting calorimetry data can be achieved with subtle adjustments in the underlying relaxation time distribution.

  2. Analysis of forming characteristics of Ta EFP according to material model

    NASA Astrophysics Data System (ADS)

    Kim, H. J.; Yi, Y. S.; Park, L. J.

    2015-09-01

    This paper presents numerical analysis result of forming characteristics of Ta explosively formed penetrator (EFP) according to various material models and their values. Dynamic material properties of Ta were measured with static tensile testing machine and Hopkinson pressure bar tests. We used AUTODYN hydrodynamic code to simulate these phenomena. We used three material models, such as Von-Mises model, linear hardening model and Johnson-Cook model. We also compared the numerical results with the EFP forming test data. The numerical results show that material model and its parameter are so important to predict the shape of formed penetrator and Von-Mises model predicts the shape of the formed liner most well. We also analysed the influence of liner thickness on EFP formation using the verified numerical model.

  3. Sensitivity of WallDYN material migration modeling to uncertainties in mixed-material surface binding energies

    DOE PAGES

    Nichols, J. H.; Jaworski, M. A.; Schmid, K.

    2017-03-09

    The WallDYN package has recently been applied to a number of tokamaks to self-consistently model the evolution of mixed-material plasma facing surfaces. A key component of the WallDYN model is the concentration-dependent surface sputtering rate, calculated using SDTRIM.SP. This modeled sputtering rate is strongly influenced by the surface binding energies (SBEs) of the constituent materials, which are well known for pure elements but often are poorly constrained for mixed-materials. This work examines the sensitivity of WallDYN surface evolution calculations to different models for mixed-material SBEs, focusing on the carbon/lithium/oxygen/deuterium system present in NSTX. A realistic plasma background is reconstructed frommore » a high density, H-mode NSTX discharge, featuring an attached outer strike point with local density and temperature of 4 × 1020 m-3 and 4 eV, respectively. It is found that various mixed-material SBE models lead to significant qualitative and quantitative changes in the surface evolution profile at the outer divertor, with the highest leverage parameter being the C-Li binding model. Uncertainties of order 50%, appearing on time scales relevant to tokamak experiments, highlight the importance of choosing an appropriate mixed-material sputtering representation when modeling the surface evolution of plasma facing components. Lastly, these results are generalized to other fusion-relevant materials with different ranges of SBEs.« less

  4. Modeling micelle-templated mesoporous material SBA-15: atomistic model and gas adsorption studies.

    PubMed

    Bhattacharya, Supriyo; Coasne, Benoit; Hung, Francisco R; Gubbins, Keith E

    2009-05-19

    We report the development of a realistic molecular model for mesoporous silica SBA-15, which includes both the large cylindrical mesopores and the smaller micropores in the pore walls. The methodology for modeling the SBA-15 structure involves molecular and mesoscale simulations combined with geometrical interpolation techniques. First, a mesoscale model is prepared by mimicking the synthesis process using lattice Monte Carlo simulations. The main physical features of this mesoscale pore model are then carved out of an atomistic silica block; both the mesopores and the micropores are incorporated from the mimetic simulations. The calculated pore size distribution, surface area, and simulated TEM images of the model structure are in good agreement with those obtained from experimental samples of SBA-15. We then investigate the adsorption of argon in this structure using Grand Canonical Monte Carlo (GCMC) simulations. The adsorption results for our SBA-15 model are compared with those for a similar model that does not include the micropores; we also compare with results obtained in a regular cylindrical pore. The simulated adsorption isotherm for the SBA-15 model shows semiquantitative agreement with the experimental isotherm for a SBA-15 sample having a similar pore size. We observe that the presence of the micropores leads to increased adsorption at low pressure compared to the case of a model without micropores in the pore walls. At higher pressures, for all models, the filling proceeds via the monolayer-multilayer adsorption on the mesopore surface followed by capillary condensation, which is mainly controlled by the mesopore diameter and is not influenced by the presence of the micropores.

  5. Scarf Joint Modeling and Analysis of Composite Materials

    DTIC Science & Technology

    2009-06-01

    A. VIRTUAL CRACK CLOSURE TECHNIQUE ( VCCT ) .............5 B. MODIFIED VIRTUAL CRACK CLOSURE TECHNIQUE (MVCCT) ...5 C. VIRTUAL CRACK CLOSURE...TECHNIQUE ( VCCT ) .............7 D. CRACK CLOSURE AND FAILURE CRITERIA .................7 1. Interactive Biquadratic Formulation ...........9 E. CRACK...FAILURE LOAD MODELING A. VIRTUAL CRACK CLOSURE TECHNIQUE ( VCCT ) The virtual crack closure technique ( VCCT ) is a method used to extract Mode I and Mode

  6. Micromechanical model of crack growth in fiber reinforced brittle materials

    NASA Technical Reports Server (NTRS)

    Rubinstein, Asher A.; Xu, Kang

    1990-01-01

    A model based on the micromechanical mechanism of crack growth resistance in fiber reinforced ceramics is presented. The formulation of the model is based on a small scale geometry of a macrocrack with a bridging zone, the process zone, which governs the resistance mechanism. The effect of high toughness of the fibers in retardation of the crack advance, and the significance of the fiber pullout mechanism on the crack growth resistance, are reflected in this model. The model allows one to address issues such as influence of fiber spacing, fiber flexibility, and fiber matrix friction. Two approaches were used. One represents the fracture initiation and concentrated on the development of the first microcracks between fibers. An exact closed form solution was obtained for this case. The second case deals with the development of an array of microcracks between fibers forming the bridging zone. An implicit exact solution is formed for this case. In both cases, a discrete fiber distribution is incorporated into the solution.

  7. Simulation of active skeletal muscle tissue with a transversely isotropic viscohyperelastic continuum material model.

    PubMed

    Khodaei, Hamid; Mostofizadeh, Salar; Brolin, Karin; Johansson, Håkan; Osth, Jonas

    2013-05-01

    Human body models with biofidelic kinematics in vehicle pre-crash and crash simulations require a constitutive model of muscle tissue with both passive and active properties. Therefore, a transversely isotropic viscohyperelastic continuum material model with element-local fiber definition and activation capability is suggested for use with explicit finite element codes. Simulations of experiments with New Zealand rabbit's tibialis anterior muscle at three different strain rates were performed. Three different active force-length relations were used, where a robust performance of the material model was observed. The results were compared with the experimental data and the simulation results from a previous study, where the muscle tissue was modeled with a combination of discrete and continuum elements. The proposed material model compared favorably, and integrating the active properties of the muscle into a continuum material model opens for applications with complex muscle geometries.

  8. Theoretical Development of an Orthotropic Elasto-Plastic Generalized Composite Material Model

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Hoffarth, Canio; Harrington, Joseph; Subramanian, Rajan; Blankenhorn, Gunther

    2014-01-01

    The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites is becoming critical as these materials are gaining increased usage in the aerospace and automotive industries. While there are several composite material models currently available within LS-DYNA (Registered), there are several features that have been identified that could improve the predictive capability of a composite model. To address these needs, a combined plasticity and damage model suitable for use with both solid and shell elements is being developed and is being implemented into LS-DYNA as MAT_213. A key feature of the improved material model is the use of tabulated stress-strain data in a variety of coordinate directions to fully define the stress-strain response of the material. To date, the model development efforts have focused on creating the plasticity portion of the model. The Tsai-Wu composite failure model has been generalized and extended to a strain-hardening based orthotropic material model with a non-associative flow rule. The coefficients of the yield function, and the stresses to be used in both the yield function and the flow rule, are computed based on the input stress-strain curves using the effective plastic strain as the tracking variable. The coefficients in the flow rule are computed based on the obtained stress-strain data. The developed material model is suitable for implementation within LS-DYNA for use in analyzing the nonlinear response of polymer composites.

  9. A study for development of aerothermodynamic test model materials and fabrication technique

    NASA Technical Reports Server (NTRS)

    Dean, W. G.; Connor, L. E.

    1972-01-01

    A literature survey, materials reformulation and tailoring, fabrication problems, and materials selection and evaluation for fabricating models to be used with the phase-change technique for obtaining quantitative aerodynamic heat transfer data are presented. The study resulted in the selection of two best materials, stycast 2762 FT, and an alumina ceramic. Characteristics of these materials and detailed fabrication methods are presented.

  10. Time-Dependent Model for Fluid Flow in Porous Materials with Multiple Pore Sizes.

    PubMed

    Cummins, Brian M; Chinthapatla, Rukesh; Ligler, Frances S; Walker, Glenn M

    2017-04-18

    An understanding of fluid transport through porous materials is critical for the development of lateral flow assays and analytical devices based on paper microfluidics. Models of fluid transport within porous materials often assume a single capillary pressure and permeability value for the material, implying that the material comprises a single pore size and that the porous material is fully saturated behind the visible wetted front. As a result, current models can lead to inaccuracies when modeling transport over long distances and/or times. A new transport model is presented that incorporates a range of pore sizes to more accurately predict the capillary transport of fluid in porous materials. The model effectively predicts the time-dependent saturation of rectangular strips of Whatman filter no. 1 paper using the manufacturer's data, published pore-size distribution measurements, and the fluid's properties.

  11. Study of materials performance model for aircraft interiors

    NASA Technical Reports Server (NTRS)

    Leary, K.; Skratt, J.

    1980-01-01

    A demonstration version of an aircraft interior materials computer data library was developed and contains information on selected materials applicable to aircraft seats and wall panels, including materials for the following: panel face sheets, bond plies, honeycomb, foam, decorative film systems, seat cushions, adhesives, cushion reinforcements, fire blocking layers, slipcovers, decorative fabrics and thermoplastic parts. The information obtained for each material pertains to the material's performance in a fire scenario, selected material properties and several measures of processability.

  12. Calibrating corneal material model parameters using only inflation data: an ill-posed problem.

    PubMed

    Kok, S; Botha, N; Inglis, H M

    2014-12-01

    Goldmann applanation tonometry (GAT) is a method used to estimate the intraocular pressure by measuring the indentation resistance of the cornea. A popular approach to investigate the sensitivity of GAT results to material and geometry variations is to perform numerical modelling using the finite element method, for which a calibrated material model is required. These material models are typically calibrated using experimental inflation data by solving an inverse problem. In the inverse problem, the underlying material constitutive behaviour is inferred from the measured macroscopic response (chamber pressure versus apical displacement). In this study, a biomechanically motivated elastic fibre-reinforced corneal material model is chosen. The inverse problem of calibrating the corneal material model parameters using only experimental inflation data is demonstrated to be ill-posed, with small variations in the experimental data leading to large differences in the calibrated model parameters. This can result in different groups of researchers, calibrating their material model with the same inflation test data, drawing vastly different conclusions about the effect of material parameters on GAT results. It is further demonstrated that multiple loading scenarios, such as inflation as well as bending, would be required to reliably calibrate such a corneal material model.

  13. Thermomechanics of damageable materials under diffusion: modelling and analysis

    NASA Astrophysics Data System (ADS)

    Roubíček, Tomáš; Tomassetti, Giuseppe

    2015-12-01

    We propose a thermodynamically consistent general-purpose model describing diffusion of a solute or a fluid in a solid undergoing possible phase transformations and damage, beside possible visco-inelastic processes. Also heat generation/consumption/transfer is considered. Damage is modelled as rate-independent. The applications include metal-hydrogen systems with metal/hydride phase transformation, poroelastic rocks, structural and ferro/para-magnetic phase transformation, water and heat transport in concrete, and if diffusion is neglected, plasticity with damage and viscoelasticity, etc. For the ensuing system of partial differential equations and inclusions, we prove existence of solutions by a carefully devised semi-implicit approximation scheme of the fractional-step type.

  14. A Domain Wall Model for Hysteresis in Ferroelastic Materials

    DTIC Science & Technology

    2002-01-01

    are a distinguishable class of ferroelastics that recover from up to 10% deformations via stress and temperature-induced phase transformations. SMAs...simulations, and their solution requires techniques such as Monte Carlo methods that have a high computational cost. Another class of mesoscopic models...solely determines the symmetry-breaking mechanism, instead is expressed in terms of normal mode components of lattice modulation wave vectors [2, 3, 46

  15. Damage Mechanics of Composite Materials: Constitutive Modeling and Computational Algorithms

    DTIC Science & Technology

    1991-04-21

    Damage Mechanics", Appl. Mech. Rev., Vol. 37, Jan ., pp. 1-6. 15. KRAJCINOVIC, D., (1985), "Constitutive Theories for Solids with Defective Microstruc...damage models; see, e.g., Krajcinovic (1984,1986,1989) and Bazant (1986) for a comprehensive literature review. There are, however, some micromechanical...Solids, Vol. 37, No. 4, pp. 435-453. 5. BAZANT , Z., (1986), "Mechanics of Distributed Cracking",Appl. Mech. Rev., Vol. 39, No. 5 pp. 675-705. 6. BUDIANSKY

  16. PECASE - First Principles Modeling of Mechanics and Chemistry of Materials

    DTIC Science & Technology

    2013-01-18

    deformation kinetics of a component, but also the tuning of its physical and chemical properties by stress. Reaching ultrastrength enables ‘‘elastic strain...strength phenomena not only have to do with the shape stability and deformation kinetics of a component, but also the tuning of its physical and...processes that initiate and sustain plastic flow and fracture, and the mechanics and physics of both displacive and diffusive mechanisms are being modeled

  17. Kinetic modelling of molecular hydrogen transport in microporous carbon materials.

    PubMed

    Hankel, Marlies; Zhang, Hong; Nguyen, Thanh X; Bhatia, Suresh K; Gray, Stephen K; Smith, Sean C

    2011-05-07

    The proposal of kinetic molecular sieving of hydrogen isotopes is explored by employing statistical rate theory methods to describe the kinetics of molecular hydrogen transport in model microporous carbon structures. A Lennard-Jones atom-atom interaction potential is utilized for the description of the interactions between H(2)/D(2) and the carbon framework, while the requisite partition functions describing the thermal flux of molecules through the transition state are calculated quantum mechanically in view of the low temperatures involved in the proposed kinetic molecular sieving application. Predicted kinetic isotope effects for initial passage from the gas phase into the first pore mouth are consistent with expectations from previous modeling studies, namely, that at sufficiently low temperatures and for sufficiently narrow pore mouths D(2) transport is dramatically favored over H(2). However, in contrast to expectations from previous modeling, the absence of any potential barrier along the minimum energy pathway from the gas phase into the first pore mouth yields a negative temperature dependence in the predicted absolute rate coefficients-implying a negative activation energy. In pursuit of the effective activation barrier, we find that the minimum potential in the cavity is significantly higher than in the pore mouth for nanotube-shaped models, throwing into question the common assumption that passage through the pore mouths should be the rate-determining step. Our results suggest a new mechanism that, depending on the size and shape of the cavity, the thermal activation barrier may lie in the cavity rather than at the pore mouth. As a consequence, design strategies for achieving quantum-mediated kinetic molecular sieving of H(2)/D(2) in a microporous membrane will need, at the very least, to take careful account of cavity shape and size in addition to pore-mouth size in order to ensure that the selective step, namely passage through the pore mouth, is also

  18. Kinetic modelling of molecular hydrogen transport in microporous carbon materials.

    SciTech Connect

    Hankel, M.; Zhang, H.; Nguyen, T. X.; Bhatia, S. K.; Gray, S. K.; Smith, S. C.

    2011-01-01

    The proposal of kinetic molecular sieving of hydrogen isotopes is explored by employing statistical rate theory methods to describe the kinetics of molecular hydrogen transport in model microporous carbon structures. A Lennard-Jones atom-atom interaction potential is utilized for the description of the interactions between H{sub 2}/D{sub 2} and the carbon framework, while the requisite partition functions describing the thermal flux of molecules through the transition state are calculated quantum mechanically in view of the low temperatures involved in the proposed kinetic molecular sieving application. Predicted kinetic isotope effects for initial passage from the gas phase into the first pore mouth are consistent with expectations from previous modeling studies, namely, that at sufficiently low temperatures and for sufficiently narrow pore mouths D{sub 2} transport is dramatically favored over H{sub 2}. However, in contrast to expectations from previous modeling, the absence of any potential barrier along the minimum energy pathway from the gas phase into the first pore mouth yields a negative temperature dependence in the predicted absolute rate coefficients - implying a negative activation energy. In pursuit of the effective activation barrier, we find that the minimum potential in the cavity is significantly higher than in the pore mouth for nanotube-shaped models, throwing into question the common assumption that passage through the pore mouths should be the rate-determining step. Our results suggest a new mechanism that, depending on the size and shape of the cavity, the thermal activation barrier may lie in the cavity rather than at the pore mouth. As a consequence, design strategies for achieving quantum-mediated kinetic molecular sieving of H{sub 2}/D{sub 2} in a microporous membrane will need, at the very least, to take careful account of cavity shape and size in addition to pore-mouth size in order to ensure that the selective step, namely passage

  19. Numerical analysis and experimental verification of elastomer bending process with different material models

    NASA Astrophysics Data System (ADS)

    Kut, Stanislaw; Ryzinska, Grazyna; Niedzialek, Bernadetta

    2016-01-01

    The article presents the results of tests in order to verifying the effectiveness of the nine selected elastomeric material models (Neo-Hookean, Mooney with two and three constants, Signorini, Yeoh, Ogden, Arruda-Boyce, Gent and Marlow), which the material constants were determined in one material test - the uniaxial tension testing. The convergence assessment of nine analyzed models were made on the basis of their performance from an experimental bending test of the elastomer samples from the results of numerical calculations FEM for each material models. To calculate the material constants for the analyzed materials, a model has been generated by the stressstrain characteristics created as a result of experimental uniaxial tensile test with elastomeric dumbbell samples, taking into account the parameters received in its 18th cycle. Using such a calculated material constants numerical simulation of the bending process of a elastomeric, parallelepipedic sampleswere carried out using MARC / Mentat program.

  20. Modeling Mechanical Properties of Carbon Molecular Clusters and Carbon Nanostructural Materials

    DTIC Science & Technology

    2003-01-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP014264 TITLE: Modeling Mechanical Properties of Carbon Molecular...Clusters and Carbon Nanostructural Materials DISTRIBUTION: Approved for public release, distribution unlimited This paper is part of the following report...Res. Soc. Symp. Proc. Vol. 740 © 2003 Materials Research Society 17.2 Modeling mechanical properties of carbon molecular clusters and carbon

  1. A numerical model for the thermo-elasto-plastic behaviour of a material

    NASA Technical Reports Server (NTRS)

    Ray, Sujit K.; Utki, Senol

    1989-01-01

    This paper presents a numerical model for the thermo-elasto-plastic behavior of an isotropic material. The model is based on the assumption that the yielding of the material obeys von Mises distortion energy theory and the material exhibits isotropic strain hardening. This unique model can be used both for isothermal and non-isothermal cases. The original formulation for the non-isothermal three-dimensional case has been specialized for plane stress conditions and the equations for the computation of warping and thickness change are provided. The finite element implementation of this model is also outlined.

  2. A numerical model for the thermo-elasto-plastic behaviour of a material

    NASA Technical Reports Server (NTRS)

    Ray, Sujit K.; Utki, Senol

    1989-01-01

    This paper presents a numerical model for the thermo-elasto-plastic behavior of an isotropic material. The model is based on the assumption that the yielding of the material obeys von Mises distortion energy theory and the material exhibits isotropic strain hardening. This unique model can be used both for isothermal and non-isothermal cases. The original formulation for the non-isothermal three-dimensional case has been specialized for plane stress conditions and the equations for the computation of warping and thickness change are provided. The finite element implementation of this model is also outlined.

  3. Multi-scale modelling of rubber-like materials and soft tissues: an appraisal

    PubMed Central

    Puglisi, G.

    2016-01-01

    We survey, in a partial way, multi-scale approaches for the modelling of rubber-like and soft tissues and compare them with classical macroscopic phenomenological models. Our aim is to show how it is possible to obtain practical mathematical models for the mechanical behaviour of these materials incorporating mesoscopic (network scale) information. Multi-scale approaches are crucial for the theoretical comprehension and prediction of the complex mechanical response of these materials. Moreover, such models are fundamental in the perspective of the design, through manipulation at the micro- and nano-scales, of new polymeric and bioinspired materials with exceptional macroscopic properties. PMID:27118927

  4. The Effect of Orthodontic Model Fabrication Procedures on Gypsum Materials.

    DTIC Science & Technology

    1992-06-01

    and Grant, A. A.: The effect of model sealant solutions on the properties of gypsum. Journal of Dentistry (1980), 8(2)152-157. 35. Hollenback, G. M...Geriatric Dentistry for providing me the opportunity to earn a Master’s Degree, and lastly, my wife Pam, who has been most supportive and helpful throughout...evaluation and improvement of the properties of study casts. 2 Gypsum has been used in dentistry for over two and a half centuries.13 It is a white to

  5. Finite Element Modeling of Transient Thermography Inspection of Composite Materials

    NASA Technical Reports Server (NTRS)

    Chu, Tsuchin Philip

    1998-01-01

    Several finite element models of defects such as debond and void have been developed for composite panels subjected to transient thermography inspection. Since the exact nature of the heat generated from the flash lamps is unknown, direct comparison between FEA and experimental results is not possible. However, some similarity of the results has been observed. The shape of the time curve that simulates the heat flux from the flash lamps has minimal effect on the temperature profiles. Double the number of flash lamps could increase the contrast of thermal image and define the shape of defect better.

  6. Mechanical Property Characterization and Modeling of Structural Materials.

    DTIC Science & Technology

    1982-02-01

    Single Crystals," Philosophical Magazine A 41, 81 (1980). 32. N. J. Petch, J. Iron and Steel Institute 173, 25 (1953). 33. N. J. Petch, "The Lowering of...Simmons, Pao, and Wei 13 have studied the Stage II SCC behavior of 4340 steel in water vapor. They determined that dissociation of the water molecule...solution for the CCGR. They found that the deformation cavity-growth model of Hancock produced good agreement with CCG data for a Cr-Mo-V steel

  7. Digital Materials - Evaluation of the Possibilities of using Selected Hyperelastic Models to Describe Constitutive Relations

    NASA Astrophysics Data System (ADS)

    Mańkowski, J.; Lipnicki, J.

    2017-08-01

    The authors tried to identify the parameters of numerical models of digital materials, which are a kind of composite resulting from the manufacture of the product in 3D printers. With the arrangement of several heads of the printer, the new material can result from mixing of materials with radically different properties, during the process of producing single layer of the product. The new material has properties dependent on the base materials properties and their proportions. Digital materials tensile characteristics are often non-linear and qualify to be described by hyperelastic materials models. The identification was conducted based on the results of tensile tests models, its various degrees coefficients of the polynomials to various degrees coefficients of the polynomials. The Drucker's stability criterion was also examined. Fourteen different materials were analyzed.

  8. A sparse digital signal model for ultrasonic nondestructive evaluation of layered materials.

    PubMed

    Bochud, N; Gomez, A M; Rus, G; Peinado, A M

    2015-09-01

    Signal modeling has been proven to be an useful tool to characterize damaged materials under ultrasonic nondestructive evaluation (NDE). In this paper, we introduce a novel digital signal model for ultrasonic NDE of multilayered materials. This model borrows concepts from lattice filter theory, and bridges them to the physics involved in the wave-material interactions. In particular, the proposed theoretical framework shows that any multilayered material can be characterized by a transfer function with sparse coefficients. The filter coefficients are linked to the physical properties of the material and are analytically obtained from them, whereas a sparse distribution naturally arises and does not rely on heuristic approaches. The developed model is first validated with experimental measurements obtained from multilayered media consisting of homogeneous solids. Then, the sparse structure of the obtained digital filter is exploited through a model-based inverse problem for damage identification in a carbon fiber-reinforced polymer (CFRP) plate.

  9. Cookoff response of PBXN-109: material characterization and ALE3D model

    SciTech Connect

    McClelland, M A; Tran, T D; Cunningham, B J; Weese, R K; Maienschein, J L

    2000-10-24

    Materials properties measurements are made for the RDX-based explosive, PBXN-109, and an initial ALE3D model for cookoff is discussed. A significant effort is underway in the U.S. Navy and Department of Energy (DOE) laboratories to understand the thermal explosion behavior of this material. Benchmark cookoff experiments are being performed by the U.S. Navy to validate DOE materials models and computer codes. The ALE3D computer code can model the coupled thermal, mechanical, and chemical behavior of heating and ignition in cookoff tests. In order to provide a predictive capability, materials characterization measurements are being performed to specify parameters in these models. We report on progress in the development of these ALE3D materials models and present measurements as a function of temperature for thermal expansion, heat capacity, shear modulus, bulk modulus, and One-Dimensional-Time-to-Explosion (ODTX).

  10. Youngs-Type Material Strength Model in the Besnard-Harlow-Rauenzahn Turbulence Equations

    SciTech Connect

    Denissen, Nicholas Allen; Plohr, Bradley J.

    2015-08-17

    Youngs [AWE Report Number 96/96, 1992] has augmented a two-phase turbulence model to account for material strength. Here we adapt the model of Youngs to the turbulence model for the mixture developed by Besnard, Harlow, and Rauenzahn [LANL Report LA-10911, 1987].

  11. Experiments for calibration and validation of plasticity and failure material modeling: 304L stainless steel.

    SciTech Connect

    Lee, Kenneth L.; Korellis, John S.; McFadden, Sam X.

    2006-01-01

    Experimental data for material plasticity and failure model calibration and validation were obtained from 304L stainless steel. Model calibration data were taken from smooth tension, notched tension, and compression tests. Model validation data were provided from experiments using thin-walled tube specimens subjected to path dependent combinations of internal pressure, extension, and torsion.

  12. Heat Transfer Modeling of a Charring Material Using Isoconversional Kinetics (Pre-Print)

    DTIC Science & Technology

    2016-09-28

    been considered in the modeling of heat transfer and pyrolysis in a charring material. The isoconversional approach is appealing due to the use of...Aerospace Group, Brigham City, UT, 84302 Abstract An isoconversional modeling approach has been considered in the modeling of heat transfer and pyrolysis ...these materials often lose mass as they pyrolyze (char) internally, causing pyrolysis gases to escape through the porous char structure. As a result

  13. Failure Modeling of Titanium-6Al-4V and 2024-T3 Aluminum with the Johnson-Cook Material Model

    SciTech Connect

    Kay, G

    2002-09-16

    A validated Johnson-Cook model could be employed to perform simulations that conform to FAA standards for evaluating aircraft and engine designs for airworthiness and containment considerations. A previous LLNL report [1] described the motivation for using the Johnson-Cook material model in simulations involving engine containment and the effect of uncontained engine debris on aircraft structures. In that report, experimental studies of the deformation and failure behavior of Ti-6Al-4V and 2024-T3 aluminum at high strain rates and large strains were conducted. The report also describes the generation of material constants for the Johnson-Cook strength model. This report describes the determination and validation of parameters for Ti-6Al-4V and 2024-T3 aluminum that can be used in the failure portion of the Johnson-Cook material.

  14. Methodical fitting for mathematical models of rubber-like materials

    NASA Astrophysics Data System (ADS)

    Destrade, Michel; Saccomandi, Giuseppe; Sgura, Ivonne

    2017-02-01

    A great variety of models can describe the nonlinear response of rubber to uniaxial tension. Yet an in-depth understanding of the successive stages of large extension is still lacking. We show that the response can be broken down in three steps, which we delineate by relying on a simple formatting of the data, the so-called Mooney plot transform. First, the small-to-moderate regime, where the polymeric chains unfold easily and the Mooney plot is almost linear. Second, the strain-hardening regime, where blobs of bundled chains unfold to stiffen the response in correspondence to the `upturn' of the Mooney plot. Third, the limiting-chain regime, with a sharp stiffening occurring as the chains extend towards their limit. We provide strain-energy functions with terms accounting for each stage that (i) give an accurate local and then global fitting of the data; (ii) are consistent with weak nonlinear elasticity theory and (iii) can be interpreted in the framework of statistical mechanics. We apply our method to Treloar's classical experimental data and also to some more recent data. Our method not only provides models that describe the experimental data with a very low quantitative relative error, but also shows that the theory of nonlinear elasticity is much more robust that seemed at first sight.

  15. Shape memory behavior of epoxy-based model materials: Tailoring approaches and thermo-mechanical modeling

    NASA Astrophysics Data System (ADS)

    Pandini, Stefano; Avanzini, Andrea; Battini, Davide; Berardi, Mario; Baldi, Francesco; Bignotti, Fabio

    2016-05-01

    A series of structurally related epoxy resins were prepared as model systems for the investigation of the shape memory response, with the aim to assess the possibility of tailoring their thermo-mechanical response and conveniently describing their strain evolution under triggering stimuli with a simple thermoviscoelastic model. The resins formulation was varied in order to obtain systems with controlled glass transition temperature and crosslink density. The shape memory response was investigated by means of properly designed thermo-mechanical cycles, which allowed to measure both the ability to fully recover the applied strain and to exert a stress on a confining medium. The results were also compared with the predictions obtained by finite element simulations of the thermo-mechanical cycle by the employ of a model whose parameters were implemented from classical DMA analysis.

  16. Modeling the Creep of Rib-Reinforced Composite Media Made from Nonlinear Hereditary Phase Materials 2. Verification of the Model

    NASA Astrophysics Data System (ADS)

    Yankovskii, A. P.

    2015-05-01

    An indirect verification of a structural model describing the creep of a composite medium reinforced by honeycombs and made of nonlinear hereditary phase materials obeying the Rabotnov theory of creep is presented. It is shown that the structural model proposed is trustworthy and can be used in practical calculations. For different kinds of loading, creep curves for a honeycomb core made of a D16T aluminum alloy are calculated.

  17. Theoretical Development of an Orthotropic Elasto-Plastic Generalized Composite Material Model

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert; Carney, Kelly; DuBois, Paul; Hoffarth, Canio; Harrington, Joseph; Rajan, Subramaniam; Blankenhorn, Gunther

    2014-01-01

    The need for accurate material models to simulate the deformation, damage and failure of polymer matrix composites is becoming critical as these materials are gaining increased usage in the aerospace and automotive industries. While there are several composite material models currently available within LSDYNA (Livermore Software Technology Corporation), there are several features that have been identified that could improve the predictive capability of a composite model. To address these needs, a combined plasticity and damage model suitable for use with both solid and shell elements is being developed and is being implemented into LS-DYNA as MAT_213. A key feature of the improved material model is the use of tabulated stress-strain data in a variety of coordinate directions to fully define the stress-strain response of the material. To date, the model development efforts have focused on creating the plasticity portion of the model. The Tsai-Wu composite failure model has been generalized and extended to a strain-hardening based orthotropic yield function with a nonassociative flow rule. The coefficients of the yield function, and the stresses to be used in both the yield function and the flow rule, are computed based on the input stress-strain curves using the effective plastic strain as the tracking variable. The coefficients in the flow rule are computed based on the obtained stress-strain data. The developed material model is suitable for implementation within LS-DYNA for use in analyzing the nonlinear response of polymer composites.

  18. Simulation Toolkit for Renewable Energy Advanced Materials Modeling

    SciTech Connect

    Sides, Scott; Kemper, Travis; Larsen, Ross; Graf, Peter

    2013-11-13

    STREAMM is a collection of python classes and scripts that enables and eases the setup of input files and configuration files for simulations of advanced energy materials. The core STREAMM python classes provide a general framework for storing, manipulating and analyzing atomic/molecular coordinates to be used in quantum chemistry and classical molecular dynamics simulations of soft materials systems. The design focuses on enabling the interoperability of materials simulation codes such as GROMACS, LAMMPS and Gaussian.

  19. Presentation on the Modeling and Educational Demonstrations Laboratory Curriculum Materials Center (MEDL-CMC): A Working Model and Progress Report

    NASA Astrophysics Data System (ADS)

    Glesener, G. B.; Vican, L.

    2015-12-01

    Physical analog models and demonstrations can be effective educational tools for helping instructors teach abstract concepts in the Earth, planetary, and space sciences. Reducing the learning challenges for students using physical analog models and demonstrations, however, can often increase instructors' workload and budget because the cost and time needed to produce and maintain such curriculum materials is substantial. First, this presentation describes a working model for the Modeling and Educational Demonstrations Laboratory Curriculum Materials Center (MEDL-CMC) to support instructors' use of physical analog models and demonstrations in the science classroom. The working model is based on a combination of instructional resource models developed by the Association of College & Research Libraries and by the Physics Instructional Resource Association. The MEDL-CMC aims to make the curriculum materials available for all science courses and outreach programs within the institution where the MEDL-CMC resides. The sustainability and value of the MEDL-CMC comes from its ability to provide and maintain a variety of physical analog models and demonstrations in a wide range of science disciplines. Second, the presentation then reports on the development, progress, and future of the MEDL-CMC at the University of California Los Angeles (UCLA). Development of the UCLA MEDL-CMC was funded by a grant from UCLA's Office of Instructional Development and is supported by the Department of Earth, Planetary, and Space Sciences. Other UCLA science departments have recently shown interest in the UCLA MEDL-CMC services, and therefore, preparations are currently underway to increase our capacity for providing interdepartmental service. The presentation concludes with recommendations and suggestions for other institutions that wish to start their own MEDL-CMC in order to increase educational effectiveness and decrease instructor workload. We welcome an interuniversity collaboration to

  20. Using Supercomputers to Model and Design Novel Materials

    NASA Astrophysics Data System (ADS)

    Richardson, Steven L.

    1997-03-01

    Recent advances in computational materials science and theoretical condensed matter physics, coupled with the power and speed of modern supercomputers, have enabled scientists and engineers to design and study novel materials from a first-principles viewpoint. Such calculations have become increasingly useful in their ability to explain experimental properties of materials, as well as to predict novel behavior. As an example of such methods, we will discuss some of our recent calculations on the structural and electronic properties of the energetic material, solid cubane.(S. L. Richardson and J. L. Martins, submitted for publication.)

  1. Experimental modelling of material interfaces with ultracold atoms

    NASA Astrophysics Data System (ADS)

    Corcovilos, Theodore A.; Brooke, Robert W. A.; Gillis, Julie; Ruggiero, Anthony C.; Tiber, Gage D.; Zaccagnini, Christopher A.

    2014-05-01

    We present a design for a new experimental apparatus for studying the physics of junctions using ultracold potassium atoms (K-39 and K-40). Junctions will be modeled using holographically projected 2D optical potentials. These potentials can be engineered to contain arbitrary features such as junctions between dissimilar lattices or the intentional insertion of defects. Long-term investigation goals include edge states, scattering at defects, and quantum depletion at junctions. In this poster we show our overall apparatus design and our progress in building experimental subsystems including the vacuum system, extended cavity diode lasers, digital temperature and current control circuits for the lasers, and the saturated absorption spectroscopy system. Funding provided by the Bayer School of Natural and Environmental.

  2. Probabilistic Multi-Factor Interaction Model for Complex Material Behavior

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Abumeri, Galib H.

    2008-01-01

    The Multi-Factor Interaction Model (MFIM) is used to evaluate the divot weight (foam weight ejected) from the launch external tanks. The multi-factor has sufficient degrees of freedom to evaluate a large number of factors that may contribute to the divot ejection. It also accommodates all interactions by its product form. Each factor has an exponent that satisfies only two points the initial and final points. The exponent describes a monotonic path from the initial condition to the final. The exponent values are selected so that the described path makes sense in the absence of experimental data. In the present investigation, the data used was obtained by testing simulated specimens in launching conditions. Results show that the MFIM is an effective method of describing the divot weight ejected under the conditions investigated.

  3. Probabilistic Multi-Factor Interaction Model for Complex Material Behavior

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.; Abumeri, Galib H.

    2008-01-01

    The Multi-Factor Interaction Model (MFIM) is used to evaluate the divot weight (foam weight ejected) from the launch external tanks. The multi-factor has sufficient degrees of freedom to evaluate a large number of factors that may contribute to the divot ejection. It also accommodates all interactions by its product form. Each factor has an exponent that satisfies only two points, the initial and final points. The exponent describes a monotonic path from the initial condition to the final. The exponent values are selected so that the described path makes sense in the absence of experimental data. In the present investigation the data used was obtained by testing simulated specimens in launching conditions. Results show that the MFIM is an effective method of describing the divot weight ejected under the conditions investigated.

  4. Using JMatPro to model materials properties and behavior

    NASA Astrophysics Data System (ADS)

    Saunders, N.; Guo, U. K. Z.; Li, X.; Miodownik, A. P.; Schillé, J.-Ph.

    2003-12-01

    This article describes the development of a new multi-platform software program called JMatPro for calculating the properties and behavior of multi-component alloys. These properties are wide ranging, including thermophysical and physical properties (from room temperature to the liquid state), time-temperature-transformation/continuous-cooling transformation diagrams, stress/strain diagrams, proof and tensile stress, hardness, coarsening of γ' and γ″, and creep. A feature of the new program is that the calculations are based on sound physical principles rather than purely statistical methods. Thus, many of the shortcomings of methods such as regression analysis can be overcome. With this program, sensitivity to microstructure can be included for many of the properties and the true inter-relationship between properties can be developed, for example in the modeling of creep and precipitation hardening.

  5. A model identification technique to characterize the low frequency behaviour of surrogate explosive materials

    NASA Astrophysics Data System (ADS)

    Paripovic, Jelena; Davies, Patricia

    2016-09-01

    The mechanical response of energetic materials, especially those used in improvised explosive devices, is of great interest to improve understanding of how mechanical excitations may lead to improved detection or detonation. The materials are comprised of crystals embedded into a binder. Microstructural modelling can give insight into the interactions between the binder and the crystals and thus the mechanisms that may lead to material heating and but there needs to be validation of these models and they also require estimates of constituent material properties. Addressing these issues, nonlinear viscoelastic models of the low frequency behavior of a surrogate material-mass system undergoing base excitation have been constructed, and experimental data have been collected and used to estimate the order of components in the system model and the parameters in the model. The estimation technique is described and examples of its application to both simulated and experimental data are given. From the estimated system model the material properties are extracted. Material properties are estimated for a variety of materials and the effect of aging on the estimated material properties is shown.

  6. A novel criterion for determination of material model parameters

    NASA Astrophysics Data System (ADS)

    Andrade-Campos, A.; de-Carvalho, R.; Valente, R. A. F.

    2011-05-01

    Parameter identification problems have emerged due to the increasing demanding of precision in the numerical results obtained by Finite Element Method (FEM) software. High result precision can only be obtained with confident input data and robust numerical techniques. The determination of parameters should always be performed confronting numerical and experimental results leading to the minimum difference between them. However, the success of this task is dependent of the specification of the cost/objective function, defined as the difference between the experimental and the numerical results. Recently, various objective functions have been formulated to assess the errors between the experimental and computed data (Lin et al., 2002; Cao and Lin, 2008; among others). The objective functions should be able to efficiently lead the optimisation process. An ideal objective function should have the following properties: (i) all the experimental data points on the curve and all experimental curves should have equal opportunity to be optimised; and (ii) different units and/or the number of curves in each sub-objective should not affect the overall performance of the fitting. These two criteria should be achieved without manually choosing the weighting factors. However, for some non-analytical specific problems, this is very difficult in practice. Null values of experimental or numerical values also turns the task difficult. In this work, a novel objective function for constitutive model parameter identification is presented. It is a generalization of the work of Cao and Lin and it is suitable for all kinds of constitutive models and mechanical tests, including cyclic tests and Baushinger tests with null values.

  7. Sensitivity of Material Response Calculations to the Equation of State Model

    DTIC Science & Technology

    equation of state model. Three equation of state models, all...sources. The sensitivity of the calculated material response to the choice of equation of state model is characterized in terms of the generated impulse...and the peak propagating stress at the time the radiation source is cut off. For the calculations presented in this report, the three equation of state models are in fairly good

  8. Two-dimensional model of a plate made of an anisotropic inhomogeneous material

    NASA Astrophysics Data System (ADS)

    Tovstik, P. E.; Tovstik, T. P.

    2017-03-01

    We present an asymptotic derivation of the two-dimensional equations of equilibrium of a thin elastic inhomogeneous plate manufactured of an anisotropic material of general form with 21 moduli of elasticity. We also consider simplified models obtained under special assumptions on the moduli. We use test examples to illustrate the error estimate of the proposed model and discuss its scope. The model is compared with the classical Kirchhoff-Love and Timoshenko-Reissner models.

  9. Survey of Multi-Material Closure Models in 1D Lagrangian Hydrodynamics

    SciTech Connect

    Maeng, Jungyeoul Brad; Hyde, David Andrew Bulloch

    2015-07-28

    Accurately treating the coupled sub-cell thermodynamics of computational cells containing multiple materials is an inevitable problem in hydrodynamics simulations, whether due to initial configurations or evolutions of the materials and computational mesh. When solving the hydrodynamics equations within a multi-material cell, we make the assumption of a single velocity field for the entire computational domain, which necessitates the addition of a closure model to attempt to resolve the behavior of the multi-material cells’ constituents. In conjunction with a 1D Lagrangian hydrodynamics code, we present a variety of both the popular as well as more recently proposed multi-material closure models and survey their performances across a spectrum of examples. We consider standard verification tests as well as practical examples using combinations of fluid, solid, and composite constituents within multi-material mixtures. Our survey provides insights into the advantages and disadvantages of various multi-material closure models in different problem configurations.

  10. A "Layers of Negotiation" Model for Designing Constructivist Learning Materials.

    ERIC Educational Resources Information Center

    Cennamo, Katherine S.; And Others

    In designing materials for use in a contructivist learning environment, instructional designers still have a role in selecting the situations that may provide a stimulus for knowledge construction and providing features that support students and teachers in using these materials. This paper describes the process of designing a series of case-based…

  11. 3-D Nonlinear Constitutive Modeling Approach for Composite Materials

    DTIC Science & Technology

    1992-05-01

    material nonlinearities, damage , and interfacial debonding [1]. These nonlinearities must be considered for accurate prediction of strength or stability...the overall nonlinear behavior covers plasticity and damage effects, both of which could have significant impact on structural analysis results...through a user-written material ( UMAT ) subroutine. D Micromechanical Analyse Micromechanical methods and selective experimentation are used to develop an

  12. User-defined Material Model for Thermo-mechanical Progressive Failure Analysis

    NASA Technical Reports Server (NTRS)

    Knight, Norman F., Jr.

    2008-01-01

    Previously a user-defined material model for orthotropic bimodulus materials was developed for linear and nonlinear stress analysis of composite structures using either shell or solid finite elements within a nonlinear finite element analysis tool. Extensions of this user-defined material model to thermo-mechanical progressive failure analysis are described, and the required input data are documented. The extensions include providing for temperature-dependent material properties, archival of the elastic strains, and a thermal strain calculation for materials exhibiting a stress-free temperature.

  13. Material characterization and computer model simulation of low density polyurethane foam used in a rodent traumatic brain injury model.

    PubMed

    Zhang, Liying; Gurao, Manish; Yang, King H; King, Albert I

    2011-05-15

    Computer models of the head can be used to simulate the events associated with traumatic brain injury (TBI) and quantify biomechanical response within the brain. Marmarou's impact acceleration rodent model is a widely used experimental model of TBI mirroring axonal pathology in humans. The mechanical properties of the low density polyurethane (PU) foam, an essential piece of energy management used in Marmarou's impact device, has not been fully characterized. The foam used in Marmarou's device was tested at seven strain rates ranging from quasi-static to dynamic (0.014-42.86 s⁻¹) to quantify the stress-strain relationships in compression. Recovery rate of the foam after cyclic compression was also determined through the periods of recovery up to three weeks. The experimentally determined stress-strain curves were incorporated into a material model in an explicit Finite Element (FE) solver to validate the strain rate dependency of the FE foam model. Compression test results have shown that the foam used in the rodent impact acceleration model is strain rate dependent. The foam has been found to be reusable for multiple impacts. However the stress resistance of used foam is reduced to 70% of the new foam. The FU_CHANG_FOAM material model in an FE solver has been found to be adequate to simulate this rate sensitive foam.

  14. Material Characterization and Computer Model Simulation of Low Density Polyurethane Foam Used in a Rodent Traumatic Brain Injury Model

    PubMed Central

    Zhang, Liying; Gurao, Manish; Yang, King H.; King, Albert I.

    2011-01-01

    Computer models of the head can be used to simulate the events associated with traumatic brain injury (TBI) and quantify biomechanical response within the brain. Marmarou’s impact acceleration rodent model is a widely used experimental model of TBI mirroring axonal pathology in humans. The mechanical properties of the low density polyurethane (PU) foam, an essential piece of energy management used in Marmarou’s impact device, has not been fully characterized. The foam used in Marmarou’s device was tested at seven strain rates ranging from quasi-static to dynamic (0.014 ~ 42.86 s−1) to quantify the stress-strain relationships in compression. Recovery rate of the foam after cyclic compression was also determined through the periods of recovery up to three weeks. The experimentally determined stress-strain curves were incorporated into a material model in an explicit Finite Element (FE) solver to validate the strain rate dependency of the FE foam model. Compression test results have shown that the foam used in the rodent impact acceleration model is strain rate dependent. The foam has been found to be reusable for multiple impacts. However the stress resistance of used foam is reduced to 70% of the new foam. The FU_CHANG_FOAM material model in an FE solver has been found to be adequate to simulate this rate sensitive foam. PMID:21459114

  15. Computational Modeling of Heterogeneous Reactive Materials at the Mesoscale

    SciTech Connect

    BAER, MARVIN R.

    1999-09-22

    The mesoscopic processes of consolidation, deformation and reaction of shocked porous energetic materials are studied using shock physics analysis of impact on a collection of discrete ''crystals.'' Highly resolved three-dimensional CTH simulations indicate that rapid deformation occurs at material contact points causing large amplitude fluctuations of stress states with wavelengths of the order of several particle diameters. Localization of energy produces ''hot-spots'' due to shock focusing and plastic work near internal boundaries as material flows into interstitial regions. Numerical experiments indicate that ''hot-spots'' are strongly influenced by multiple crystal interactions. Chemical reaction processes also produce multiple wave structures associated with particle distribution effects. This study provides new insights into the micromechanical behavior of heterogeneous energetic materials strongly suggesting that initiation and sustained reaction of shocked heterogeneous materials involves states distinctly different from single jump state descriptions.

  16. Advances In High Temperature (Viscoelastoplastic) Material Modeling for Thermal Structural Analysis

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Saleeb, Atef F.

    2005-01-01

    Typical High Temperature Applications High Temperature Applications Demand High Performance Materials: 1) Complex Thermomechanical Loading; 2) Complex Material response requires Time-Dependent/Hereditary Models: Viscoelastic/Viscoplastic; and 3) Comprehensive Characterization (Tensile, Creep, Relaxation) for a variety of material systems.

  17. Calibration and Finite Element Implementation of an Energy-Based Material Model for Shape Memory Alloys

    NASA Astrophysics Data System (ADS)

    Junker, Philipp; Hackl, Klaus

    2016-09-01

    Numerical simulations are a powerful tool to analyze the complex thermo-mechanically coupled material behavior of shape memory alloys during product engineering. The benefit of the simulations strongly depends on the quality of the underlying material model. In this contribution, we discuss a variational approach which is based solely on energetic considerations and demonstrate that unique calibration of such a model is sufficient to predict the material behavior at varying ambient temperature. In the beginning, we recall the necessary equations of the material model and explain the fundamental idea. Afterwards, we focus on the numerical implementation and provide all information that is needed for programing. Then, we show two different ways to calibrate the model and discuss the results. Furthermore, we show how this model is used during real-life industrial product engineering.

  18. Fracture analysis for biological materials with an expanded cohesive zone model.

    PubMed

    An, Bingbing; Zhao, Xinluo; Arola, Dwayne; Zhang, Dongsheng

    2014-07-18

    In this study, a theoretical framework for simulation of fracture of bone and bone-like materials is provided. An expanded cohesive zone model with thermodynamically consistent framework has been proposed and used to investigate the crack growth resistance of bone and bone-like materials. The reversible elastic deformation, irreversible plastic deformation caused by large deformation of soft protein matrix, and damage evidenced by the material separation and crack nucleation in the cohesive zone, were all taken into account in the model. Furthermore, the key mechanisms in deformation of biocomposites consisting of mineral platelets and protein interfacial layers were incorporated in the fracture process zone in this model, thereby overcoming the limitations of previous cohesive zone modeling of bone fracture. Finally, applications to fracture of cortical bone and human dentin were presented, which showed good agreement between numerical simulation and reported experiments and substantiated the effectiveness of the model in investigating the fracture behavior of bone-like materials.

  19. A Model for Rate-Dependent Hysteresis in Piezoceramic Materials Operating at Low Frequencies

    NASA Technical Reports Server (NTRS)

    Smith, Ralph C.; Ounaies, Zoubeida; Wieman, Robert

    2001-01-01

    This paper addresses the modeling of certain rate-dependent mechanisms which contribute to hysteresis inherent to piezoelectric materials operating at low frequencies. While quasistatic models are suitable for initial material characterization in some applications, the reduction in coercive field and polarization values which occur as frequencies increase must be accommodated to achieve the full capabilities of the materials. The model employed here quantifies the hysteresis in two steps. In the first, anhysteretic polarization switching is modeled through the application of Boltzmann principles to balance the electrostatic and thermal energy. Hysteresis is then incorporated through the quantification of energy required to translate and bend domain walls pinned at inclusions inherent to the materials. The performance of the model is illustrated through a fit to low frequency data (0.1 Hz - 1 Hz) from a PZT5A wafer.

  20. Fatigue Crack Growth Analysis Models for Functionally Graded Materials

    SciTech Connect

    Dag, Serkan; Yildirim, Bora; Sabuncuoglu, Baris

    2008-02-15

    The objective of this study is to develop crack growth analysis methods for functionally graded materials (FGMs) subjected to mode I cyclic loading. The study presents finite elements based computational procedures for both two and three dimensional problems to examine fatigue crack growth in functionally graded materials. Developed methods allow the computation of crack length and generation of crack front profile for a graded medium subjected to fluctuating stresses. The results presented for an elliptical crack embedded in a functionally graded medium, illustrate the competing effects of ellipse aspect ratio and material property gradation on the fatigue crack growth behavior.

  1. Advanced Modeling and Materials in Kraft Pulp Mills

    SciTech Connect

    Keiser, J.R.; Gorog, J.P.

    2002-05-15

    This CRADA provided technical support to the Weyerhaeuser Company on a number of issues related to the performance and/or selection of materials at a number of locations in a pulp and paper mill. The studies related primarily to components for black liquor recovery boilers, but some effort was directed toward black liquor gasifiers and rolls for paper machines. The purpose of this CRADA was to assist Weyerhaeuser in the evaluation of materials exposed in various paper mill environments and to provide direction in the selection of alternate materials, when appropriate.

  2. A Short Review of Ablative-Material Response Models and Simulation Tools

    NASA Technical Reports Server (NTRS)

    Lachaud, Jean; Magin, Thierry E.; Cozmuta, Ioana; Mansour, Nagi N.

    2011-01-01

    A review of the governing equations and boundary conditions used to model the response of ablative materials submitted to a high-enthalpy flow is proposed. The heritage of model-development efforts undertaken in the 1960s is extremely clear: the bases of the models used in the community are mathematically equivalent. Most of the material-response codes implement a single model in which the equation parameters may be modified to model different materials or conditions. The level of fidelity of the models implemented in design tools only slightly varies. Research and development codes are generally more advanced but often not as robust. The capabilities of each of these codes are summarized in a color-coded table along with research and development efforts currently in progress.

  3. Effect of Material Property Heterogeneity on Biomechanical Modeling of Prostate under Deformation

    PubMed Central

    Samavati, Navid; McGrath, Deirdre M.; Jewett, Michael A.S.; van der Kwast, Theo; Ménard, Cynthia; Brock, Kristy K.

    2015-01-01

    Biomechanical model based deformable image registration has been widely used to account for prostate deformation in various medical imaging procedures. Biomechanical material properties are important components of a biomechanical model. In this study, the effect of incorporating tumor-specific material properties in the prostate biomechanical model was investigated to provide insight into the potential impact of material heterogeneity on the prostate deformation calculations First, a simple spherical prostate and tumor model was used to analytically describe the deformations and demonstrate the fundamental effect of changes in the tumor volume and stiffness in the modeled deformation. Next, using clinical prostate model, a parametric approach was used to describe the variations in the heterogeneous prostate model by changing tumor volume, stiffness, and location, to show the differences in the modeled deformation between heterogeneous and homogeneous prostate models. Finally, five clinical prostatectomy examples were used in separately performed homogeneous and heterogeneous biomechanical model based registrations to describe the deformations between 3D reconstructed histopathology images and ex vivo Magnetic Resonance Imaging (MRI), and examine the potential clinical impact of modeling biomechanical heterogeneity of the prostate. The analytical formulation showed that increasing the tumor volume and stiffness could significantly increase the impact of heterogeneous prostate model in the calculated displacement differences compared to homogeneous model. The parametric approach using a single prostate model indicated up to 4.8 mm of displacement difference at the tumor boundary compared to a homogeneous model. . Such differences in the deformation of prostate could bepotentially clinically significant given the voxel size of the ex vivo MR images (0.3×0.3×0.3 mm). However, no significant changes in the registration accuracy were observed using heterogeneous models

  4. Effect of material property heterogeneity on biomechanical modeling of prostate under deformation.

    PubMed

    Samavati, Navid; McGrath, Deirdre M; Jewett, Michael A S; van der Kwast, Theo; Ménard, Cynthia; Brock, Kristy K

    2015-01-07

    Biomechanical model based deformable image registration has been widely used to account for prostate deformation in various medical imaging procedures. Biomechanical material properties are important components of a biomechanical model. In this study, the effect of incorporating tumor-specific material properties in the prostate biomechanical model was investigated to provide insight into the potential impact of material heterogeneity on the prostate deformation calculations. First, a simple spherical prostate and tumor model was used to analytically describe the deformations and demonstrate the fundamental effect of changes in the tumor volume and stiffness in the modeled deformation. Next, using a clinical prostate model, a parametric approach was used to describe the variations in the heterogeneous prostate model by changing tumor volume, stiffness, and location, to show the differences in the modeled deformation between heterogeneous and homogeneous prostate models. Finally, five clinical prostatectomy examples were used in separately performed homogeneous and heterogeneous biomechanical model based registrations to describe the deformations between 3D reconstructed histopathology images and ex vivo magnetic resonance imaging, and examine the potential clinical impact of modeling biomechanical heterogeneity of the prostate. The analytical formulation showed that increasing the tumor volume and stiffness could significantly increase the impact of the heterogeneous prostate model in the calculated displacement differences compared to the homogeneous model. The parametric approach using a single prostate model indicated up to 4.8 mm of displacement difference at the tumor boundary compared to a homogeneous model. Such differences in the deformation of the prostate could be potentially clinically significant given the voxel size of the ex vivo MR images (0.3  ×  0.3  ×  0.3 mm). However, no significant changes in the registration accuracy were

  5. Material Modeling of Space Shuttle Leading Edge and External Tank Materials For Use in the Columbia Accident Investigation

    NASA Technical Reports Server (NTRS)

    Carney, Kelly; Melis, Matthew; Fasanella, Edwin L.; Lyle, Karen H.; Gabrys, Jonathan

    2004-01-01

    Upon the commencement of the analytical effort to characterize the impact dynamics and damage of the Space Shuttle Columbia leading edge due to External Tank insulating foam, the necessity of creating analytical descriptions of these materials became evident. To that end, material models were developed of the leading edge thermal protection system, Reinforced Carbon Carbon (RCC), and a low density polyurethane foam, BX-250. Challenges in modeling the RCC include its extreme brittleness, the differing behavior in compression and tension, and the anisotropic fabric layup. These effects were successfully included in LS-DYNA Material Model 58, *MAT_LAMINATED_ COMPOSITE_ FABRIC. The differing compression and tension behavior was modeled using the available damage parameters. Each fabric layer was given an integration point in the shell element, and was allowed to fail independently. Comparisons were made to static test data and coupon ballistic impact tests before being utilized in the full scale analysis. The foam's properties were typical of elastic automotive foams; and LS-DYNA Material Model 83, *MAT_FU_CHANG_FOAM, was successfully used to model its behavior. Material parameters defined included strain rate dependent stress-strain curves for both loading and un-loading, and for both compression and tension. This model was formulated with static test data and strain rate dependent test data, and was compared to ballistic impact tests on load-cell instrumented aluminum plates. These models were subsequently utilized in analysis of the Shuttle leading edge full scale ballistic impact tests, and are currently being used in the Return to Flight Space Shuttle re-certification effort.

  6. Computational Modeling and Design of Actively-Cooled Microvascular Materials

    DTIC Science & Technology

    2012-06-14

    autonomic healing and active cooling [1–3]. Recent advances in manufacturing techniques for microfluidic materials and devices [4,5] have extended the...application of such systems to a broad field including autonomic materials [6], biotechnology [7,8], chemical reactors [9], and microelectromechanical...1998) 484–487. [8] A. Strömberg, A. Karlsson, F. Ryttsén, M. Davidson, D.T. Chiu, O. Orwar, Microfluidic device for combinatorial fusion of liposomes and

  7. First-principles modeling of materials for nuclear energy applications

    SciTech Connect

    Dmitriev, Andrey I. Nikonov, Anton Yu.; Ponomareva, Alena V.; Abrikosov, Igor A.; Barannikova, Svetlana A.

    2014-11-14

    We discuss recent developments in the field of ab initio electronic structure theory and its use for studies of materials for nuclear energy applications. We review state-of-the-art simulation methods that allow for an efficient treatment of effects due to chemical and magnetic disorder, and illustrate their predictive power with examples of two materials systems, Fe-Cr-Ni alloys and Zr-Nb alloys.

  8. Cooperative Research Alliance Multiscale Modeling of Electronic Materials (MSME)

    DTIC Science & Technology

    2010-11-19

    Infrastructure & Capabilities Electro Optics & Photonics Bio & Nano Power & Energy • Time-Resolved Infrared Spectroscopy Facility • MOCVD, MBE semiconductor...Dielectric Deposition • LPCVD High Temperature Processing and Wafer Bonding • RIE/ICP • Auger /XPS • AFM • FIB • Micro Raman Electronic...Research of Materials Initiative Q. Wei, J. Mater Sci, 42, 2007 Tungsten Shear Bands Protection Materials Power & Energy Opto- electronics

  9. Computer Modelling of Cyclic Deformation of High-Temperature Materials

    DTIC Science & Technology

    1993-06-14

    precision. In this case the aim will be at least to eliminate functional empiricism. Restriction of empiricism to the choice of parameters to be input...deformation of dispersion-hardened materials. In the general case this will be done by a literature search. For specific materials, the micromechanisms...cross-slip and/or climb without the generation of appreciable back-stress. Task 112. Anisotropic dispersoids This task covers the case of dispersoids

  10. Verification and Validation of a Three-Dimensional Generalized Composite Material Model

    NASA Technical Reports Server (NTRS)

    Hoffarth, Canio; Harrington, Joseph; Rajan, Subramaniam D.; Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Blankenhorn, Gunther

    2015-01-01

    A general purpose orthotropic elasto-plastic computational constitutive material model has been developed to improve predictions of the response of composites subjected to high velocity impact. The three-dimensional orthotropic elasto-plastic composite material model is being implemented initially for solid elements in LS-DYNA as MAT213. In order to accurately represent the response of a composite, experimental stress-strain curves are utilized as input, allowing for a more general material model that can be used on a variety of composite applications. The theoretical details are discussed in a companion paper. This paper documents the implementation, verification and qualitative validation of the material model using the T800-F3900 fiber/resin composite material

  11. Verification and Validation of a Three-Dimensional Generalized Composite Material Model

    NASA Technical Reports Server (NTRS)

    Hoffarth, Canio; Harrington, Joseph; Subramaniam, D. Rajan; Goldberg, Robert K.; Carney, Kelly S.; DuBois, Paul; Blankenhorn, Gunther

    2014-01-01

    A general purpose orthotropic elasto-plastic computational constitutive material model has been developed to improve predictions of the response of composites subjected to high velocity impact. The three-dimensional orthotropic elasto-plastic composite material model is being implemented initially for solid elements in LS-DYNA as MAT213. In order to accurately represent the response of a composite, experimental stress-strain curves are utilized as input, allowing for a more general material model that can be used on a variety of composite applications. The theoretical details are discussed in a companion paper. This paper documents the implementation, verification and qualitative validation of the material model using the T800- F3900 fiber/resin composite material.

  12. Linear orthotropic viscoelasticity model for fiber reinforced thermoplastic material based on Prony series

    NASA Astrophysics Data System (ADS)

    Endo, Vitor Takashi; de Carvalho Pereira, José Carlos

    2017-05-01

    Material properties description and understanding are essential aspects when computational solid mechanics is applied to product development. In order to promote injected fiber reinforced thermoplastic materials for structural applications, it is very relevant to develop material characterization procedures, considering mechanical properties variation in terms of fiber orientation and loading time. Therefore, a methodology considering sample manufacturing, mechanical tests and data treatment is described in this study. The mathematical representation of the material properties was solved by a linear viscoelastic constitutive model described by Prony series, which was properly adapted to orthotropic materials. Due to the large number of proposed constitutive model coefficients, a parameter identification method was employed to define mathematical functions. This procedure promoted good correlation among experimental tests, and analytical and numerical creep models. Such results encourage the use of numerical simulations for the development of structural components with the proposed linear viscoelastic orthotropic constitutive model. A case study was presented to illustrate an industrial application of proposed methodology.

  13. Linear orthotropic viscoelasticity model for fiber reinforced thermoplastic material based on Prony series

    NASA Astrophysics Data System (ADS)

    Endo, Vitor Takashi; de Carvalho Pereira, José Carlos

    2016-09-01

    Material properties description and understanding are essential aspects when computational solid mechanics is applied to product development. In order to promote injected fiber reinforced thermoplastic materials for structural applications, it is very relevant to develop material characterization procedures, considering mechanical properties variation in terms of fiber orientation and loading time. Therefore, a methodology considering sample manufacturing, mechanical tests and data treatment is described in this study. The mathematical representation of the material properties was solved by a linear viscoelastic constitutive model described by Prony series, which was properly adapted to orthotropic materials. Due to the large number of proposed constitutive model coefficients, a parameter identification method was employed to define mathematical functions. This procedure promoted good correlation among experimental tests, and analytical and numerical creep models. Such results encourage the use of numerical simulations for the development of structural components with the proposed linear viscoelastic orthotropic constitutive model. A case study was presented to illustrate an industrial application of proposed methodology.

  14. Phase-field modeling of microstructure evolutions in magnetic materials

    PubMed Central

    Koyama, Toshiyuki

    2008-01-01

    Recently, the phase-field method has been extended and utilized across many fields of materials science. Since this method can incorporate, systematically, the effect of the coherency induced by lattice mismatch and the applied stress as well as the external electrical and magnetic fields, it has been applied to many material processes including solidification, solid-state phase transformations and various types of complex microstructure changes. In this paper, we focus on the recent phase-field simulations of real magnetic materials, and the simulation method for magnetic materials is explained comprehensively. Several applications of the phase-field method to clarifying the microstructure changes in magnetic materials, such as Ni2MnGa ferromagnetic shape memory alloy, FePt nanogranular thin film, Co–Sm–Cu rare-earth magnet, Fe–Cr–Co spinodal magnet, and Fe–C steel with external magnetic field, are demonstrated. Furthermore, the general concept of the effective strategy for controlling microstructure in magnetic materials is proposed. PMID:27877924

  15. Materials processing in a centrifuge - Numerical modeling of macrogravity effects

    NASA Technical Reports Server (NTRS)

    Ramachandran, N.; Downey, J. P.; Jones, J. C.; Curreri, P. A.

    1992-01-01

    The fluid mechanics associated with crystal growth processes on a centrifuge is investigated. A simple scaling analysis is used to examine the relative magnitudes of the forces acting on the system and good agreement is obtained with previous studies. A two-dimensional model of crystal growth on a centrifuge is proposed and calculations are undertaken to help in understanding the fundamental transport processes within the crystal growth cell. Results from three-dimensional calculations of actual centrifuge-based crystal growth systems are presented both for the thermodynamically stable and unstable configurations. The calculations show the existence of flow bifurcations in certain configurations but not in all instances. The numerical simulations also show that the centrifugal force is the dominant stabilizing force on fluid convection in the stable configuration. The stabilizing influence of the Coriolis force is found to be only secondary in nature. No significant impact of gravity gradient is found in the calculations. Simulations of unstable configurations show that the Coriolis force has a stabilizing influence on fluid motion by delaying the onset of unsteady convection. Detailed flow and thermal field characteristics are presented for all the different cases that are simulated.

  16. Coarse graining approach to First principles modeling of structural materials

    SciTech Connect

    Odbadrakh, Khorgolkhuu; Nicholson, Don M; Rusanu, Aurelian; Samolyuk, German D; Wang, Yang; Stoller, Roger E; Zhang, X.-G.; Stocks, George Malcolm

    2013-01-01

    Classical Molecular Dynamic (MD) simulations characterizing extended defects typically require millions of atoms. First principles calculations employed to understand these defect systems at an electronic level cannot, and should not deal with such large numbers of atoms. We present an e cient coarse graining (CG) approach to calculate local electronic properties of large MD-generated structures from the rst principles. We used the Locally Self-consistent Multiple Scattering (LSMS) method for two types of iron defect structures 1) screw-dislocation dipoles and 2) radiation cascades. The multiple scattering equations are solved at fewer sites using the CG. The atomic positions were determined by MD with an embedded atom force eld. The local moments in the neighborhood of the defect cores are calculated with rst-principles based on full local structure information, while atoms in the rest of the system are modeled by representative atoms with approximated properties. This CG approach reduces computational costs signi cantly and makes large-scale structures amenable to rst principles study. Work is sponsored by the USDoE, O ce of Basic Energy Sciences, Center for Defect Physics, an Energy Frontier Research Center. This research used resources of the Oak Ridge Leadership Computing Facility at the ORNL, which is supported by the O ce of Science of the USDoE under Contract No. DE-AC05-00OR22725.

  17. Modeling Material Properties of Lead-Free Solder Alloys

    NASA Astrophysics Data System (ADS)

    Guo, Zhanli; Saunders, Nigel; Miodownik, Peter; Schillé, Jean-Philippe

    2008-01-01

    A full set of physical and thermophysical properties for lead-free solder (LFS) alloys have been calculated, including liquidus/solidus temperatures, fraction solid, density, coefficient of thermal expansion, thermal conductivity, Young’s modulus, viscosity, and liquid surface tension, all as a function of composition and temperature (extending into the liquid state). The results have been extensively validated against data available in the literature. A detailed comparison of the properties of two LFS alloys Sn-20In-2.8Ag and Sn-5.5Zn-4.5In-3.5Bi with Sn-37Pb has been made to show the utility and need for calculations that cover a wide range of properties, including the need to consider the effect of nonequilibrium cooling. The modeling of many of these properties follows well-established procedures previously used in JMatPro software for a range of structural alloys. This paper describes an additional procedure for the calculation of the liquid surface tension for multicomponent systems, based on the Butler equation. Future software developments are reviewed, including the addition of mechanical properties, but the present calculations can already make a useful contribution to the selection of appropriate new LFS alloys.

  18. Hybrid Soft Soil Tire Model (HSSTM). Part 1: Tire Material and Structure Modeling

    DTIC Science & Technology

    2015-04-28

    efficiency [11-13]. The majority of the models in this field use the two-dimensional empirical formulation developed by Bekker and Wong [21-28]. In...Mechanical Engineers, Part D: Journal of Automobile Engineering, 2008. 222(11): p. 1939-1954. 21. Bekker , M.G., Introduction to Terrain-Vehicle System. 1969...Ann Arbor: The University of Michigan Press. 22. Bekker , M.G., Off the Road Locomotion. 1960, Ann Arbor, Michigan: University of Michigan Press

  19. High-Fidelity Micromechanics Model Developed for the Response of Multiphase Materials

    NASA Technical Reports Server (NTRS)

    Aboudi, Jacob; Pindera, Marek-Jerzy; Arnold, Steven M.

    2002-01-01

    A new high-fidelity micromechanics model has been developed under funding from the NASA Glenn Research Center for predicting the response of multiphase materials with arbitrary periodic microstructures. The model's analytical framework is based on the homogenization technique, but the method of solution for the local displacement and stress fields borrows concepts previously employed in constructing the higher order theory for functionally graded materials. The resulting closed-form macroscopic and microscopic constitutive equations, valid for both uniaxial and multiaxial loading of periodic materials with elastic and inelastic constitutive phases, can be incorporated into a structural analysis computer code. Consequently, this model now provides an alternative, accurate method.

  20. The use of kinetic modelling as a fast way to screen thermal endurance of space materials

    NASA Astrophysics Data System (ADS)

    Moser, M.; Heltzel, S.; Semprimoschnig, C.; Garcia Martin, G.

    2003-09-01

    Currently planned missions of ESA (European Space Agency) to the inner part of the solar system will require the use of materials at an extreme radiation and temperature environment. A major concern regarding the selection of these materials is the thermal behaviour and the thermal stability. In this paper two kinetic models, the one following the ASTM E 1641 and ASTM E 1877 standards and the other following the Model Free Kinetics (MFK) approach, are presented. These models allow an easy and fast way to screen the thermal endurance of organic materials by running Thermo Gravimetric Analyses (TGA) temperature scans.

  1. A distributional model for elastic-plastic behavior of shock loaded materials.

    SciTech Connect

    Vogler, Tracy John; Asay, James Russell

    2003-07-01

    To address known shortcomings of classical metal plasticity for describing material behavior under shock loading, a model which incorporates a distribution in the deviatoric stress state is developed. This distribution will translate in stress space under loading, and growth of the distribution can be included in the model as well. This proposed model is capable of duplicating the key features of a set of reshock and release experiments on 6061-T6 aluminum, many of which are not captured by classical plasticity. The model is relatively simple, is only moderately more computationally intensive, and requires few additional material parameters.

  2. Modeling of Slot Waveguide Sensors Based on Polymeric Materials

    PubMed Central

    Bettotti, Paolo; Pitanti, Alessandro; Rigo, Eveline; De Leonardis, Francesco; Passaro, Vittorio M. N.; Pavesi, Lorenzo

    2011-01-01

    Slot waveguides are very promising for optical sensing applications because of their peculiar spatial mode profile. In this paper we have carried out a detailed analysis of mode confinement properties in slot waveguides realized in very low refractive index materials. We show that the sensitivity of a slot waveguide is not directly related to the refractive index contrast of high and low materials forming the waveguide. Thus, a careful design of the structures allows the realization of high sensitivity devices even in very low refractive index materials (e.g., polymers) to be achieved. Advantages of low index dielectrics in terms of cost, functionalization and ease of fabrication are discussed while keeping both CMOS compatibility and integrable design schemes. Finally, applications of low index slot waveguides as substitute of bulky fiber capillary sensors or in ring resonator architectures are addressed. Theoretical results of this work are relevant to well established polymer technologies. PMID:22164020

  3. Modeling of slot waveguide sensors based on polymeric materials.

    PubMed

    Bettotti, Paolo; Pitanti, Alessandro; Rigo, Eveline; De Leonardis, Francesco; Passaro, Vittorio M N; Pavesi, Lorenzo

    2011-01-01

    Slot waveguides are very promising for optical sensing applications because of their peculiar spatial mode profile. In this paper we have carried out a detailed analysis of mode confinement properties in slot waveguides realized in very low refractive index materials. We show that the sensitivity of a slot waveguide is not directly related to the refractive index contrast of high and low materials forming the waveguide. Thus, a careful design of the structures allows the realization of high sensitivity devices even in very low refractive index materials (e.g., polymers) to be achieved. Advantages of low index dielectrics in terms of cost, functionalization and ease of fabrication are discussed while keeping both CMOS compatibility and integrable design schemes. Finally, applications of low index slot waveguides as substitute of bulky fiber capillary sensors or in ring resonator architectures are addressed. Theoretical results of this work are relevant to well established polymer technologies.

  4. Frequency response of synthetic vocal fold models with linear and nonlinear material properties.

    PubMed

    Shaw, Stephanie M; Thomson, Scott L; Dromey, Christopher; Smith, Simeon

    2012-10-01

    The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency (F0) during anterior-posterior stretching. Three materially linear and 3 materially nonlinear models were created and stretched up to 10 mm in 1-mm increments. Phonation onset pressure (Pon) and F0 at Pon were recorded for each length. Measurements were repeated as the models were relaxed in 1-mm increments back to their resting lengths, and tensile tests were conducted to determine the stress-strain responses of linear versus nonlinear models. Nonlinear models demonstrated a more substantial frequency response than did linear models and a more predictable pattern of F0 increase with respect to increasing length (although range was inconsistent across models). Pon generally increased with increasing vocal fold length for nonlinear models, whereas for linear models, Pon decreased with increasing length. Nonlinear synthetic models appear to more accurately represent the human vocal folds than do linear models, especially with respect to F0 response.

  5. Frequency Response of Synthetic Vocal Fold Models with Linear and Nonlinear Material Properties

    PubMed Central

    Shaw, Stephanie M.; Thomson, Scott L.; Dromey, Christopher; Smith, Simeon

    2014-01-01

    Purpose The purpose of this study was to create synthetic vocal fold models with nonlinear stress-strain properties and to investigate the effect of linear versus nonlinear material properties on fundamental frequency during anterior-posterior stretching. Method Three materially linear and three materially nonlinear models were created and stretched up to 10 mm in 1 mm increments. Phonation onset pressure (Pon) and fundamental frequency (F0) at Pon were recorded for each length. Measurements were repeated as the models were relaxed in 1 mm increments back to their resting lengths, and tensile tests were conducted to determine the stress-strain responses of linear versus nonlinear models. Results Nonlinear models demonstrated a more substantial frequency response than did linear models and a more predictable pattern of F0 increase with respect to increasing length (although range was inconsistent across models). Pon generally increased with increasing vocal fold length for nonlinear models, whereas for linear models, Pon decreased with increasing length. Conclusions Nonlinear synthetic models appear to more accurately represent the human vocal folds than linear models, especially with respect to F0 response. PMID:22271874

  6. Overall challenges in incorporating micro-mechanical models into materials design process

    NASA Astrophysics Data System (ADS)

    Bennoura, M.; Aboutajeddine, A.

    2016-10-01

    Using materials in engineering design has historically been handled using the paradigm of selecting appropriate materials from the finite set of available material databases. Recent trends, however, have moved toward the tailoring of materials that meet the overall system performance requirements, based on a process called material design. An important building block of this process is micromechanical models that relate microstructure to proprieties. Unfortunately, these models remain short and include a lot of uncertainties from assumptions and idealizations, which, unavoidably, impacts material design strategy. In this work, candidate methods to deal with micromechanical models uncertainties and their drawbacks in material design are investigated. Robust design methods for quantifying uncertainty and managing or mitigating its impact on design performances are reviewed first. These methods include principles for classifying uncertainty, mathematical techniques for evaluating its level degree, and design methods for performing and generating design alternatives, that are relatively insensitive to sources of uncertainty and flexible for admitting design changes or variations. The last section of this paper addresses the limits of the existing approaches from material modelling perspective and identifies the research opportunities to overcome the impediment of incorporating micromechanical models in material design process.

  7. Modeling Ablation of Fibrous Materials from Bulk to Knudsen Regime

    NASA Technical Reports Server (NTRS)

    Lachaud, Jean; Mansour, Nagi N.

    2008-01-01

    Material-environment interactions are analyzed at microscopic scale to explain the lower than expected density observed by post-flight analysis of the char layer on the Stardust shield. Mass transfer, ablation (oxidation), and surface recession of fibrous material is simulated in 3D using a Monte-Carlo simulation tool. Ablation is found to occur either at the surface or in volume depending on Knudsen and Thiele number values. This study supports the idea of volume ablation followed by possible carbon fiber spallation that may explain post-flight analyses.

  8. Predictive rendering for accurate material perception: modeling and rendering fabrics

    NASA Astrophysics Data System (ADS)

    Bala, Kavita

    2012-03-01

    In computer graphics, rendering algorithms are used to simulate the appearance of objects and materials in a wide range of applications. Designers and manufacturers rely entirely on these rendered images to previsualize scenes and products before manufacturing them. They need to differentiate between different types of fabrics, paint finishes, plastics, and metals, often with subtle differences, for example, between silk and nylon, formaica and wood. Thus, these applications need predictive algorithms that can produce high-fidelity images that enable such subtle material discrimination.

  9. Numerical modeling of cyclic strengthening and weaking of material

    NASA Astrophysics Data System (ADS)

    Dudda, Waldemar

    2007-04-01

    The study concerns analytical and numerical tools for description of strengthening and weakening effects of materials put under influence of cyclic mechanical loads. The paper presents formulas describing the change in material mechanical properties such as the yield point and strain hardening modulus depending on the number of load cycles and stress ratio. Numerical simulations for cases based on experimental studies presented in the existing literature were conducted. The results of numerical calculations and their comparison with the experimental data are presented in the form of stress-strain hysteresis loop graphs.

  10. Modeling of Micromechanisms of Fatigue and Fracture in Hybrid Materials

    DTIC Science & Technology

    1990-06-15

    titanium aluminides . Unclassified SECURITY CLASSIFICATION OF THIS PAGE Report No. UCB/R/90/A1065 Final Report to U.S. Air Force Office of Scientific...PARTICULATE-REINFORCED Ti-6AI-4V COMPOSITES ............... 52 5. TITANIUM ALUMINIDE INTERMETALLICS ............................................ 59 6...preliminary examination of the microstructure of titanium aluminides . V 1. INTRODUCTION In recent years, the need for lighter materials with high

  11. A Simple Ballistic Material Model for Soda-Lime Glass

    DTIC Science & Technology

    2009-01-01

    photo-elastic imaging mode, stress-induced birefringence in the target material gives rise to a 90 switching in the beam polarization vector producing...Guillemet C. In: Kurkjian CR, editor. Strength of inorganic glass. New York: Plenum; 1985. p. 1–26. [11] Gy R, Guillemet C. In: Pye LD, La Course WC

  12. An Overview of Mesoscale Modeling Software for Energetic Materials Research

    DTIC Science & Technology

    2010-03-01

    oceanography, microfluidics , chemical flow 7. traffic flow: air, vehicle, pedestrians, flow of people within a building Properties 1. Flow properties 2...0401073 (accessed 2004). 77. Workshop on Advanced Computational Materials Science: Application to Fusion and Generation IV Fission Reactors , U.S

  13. Anisotropic viscoelastic-viscoplastic continuum model for high-density cellulose-based materials

    NASA Astrophysics Data System (ADS)

    Tjahjanto, D. D.; Girlanda, O.; Östlund, S.

    2015-11-01

    A continuum material model is developed for simulating the mechanical response of high-density cellulose-based materials subjected to stationary and transient loading. The model is formulated in an infinitesimal strain framework, where the total strain is decomposed into elastic and plastic parts. The model adopts a standard linear viscoelastic solid model expressed in terms of Boltzmann hereditary integral form, which is coupled to a rate-dependent viscoplastic formulation to describe the irreversible plastic part of the overall strain. An anisotropic hardening law with a kinematic effect is particularly adopted in order to capture the complex stress-strain hysteresis typically observed in polymeric materials. In addition, the present model accounts for the effects of material densification associated with through-thickness compression, which are captured using an exponential law typically applied in the continuum description of elasticity in porous media. Material parameters used in the present model are calibrated to the experimental data for high-density (press)boards. The experimental characterization procedures as well as the calibration of the parameters are highlighted. The results of the model simulations are systematically analyzed and validated against the corresponding experimental data. The comparisons show that the predictions of the present model are in very good agreement with the experimental observations for both stationary and transient load cases.

  14. Physics-Based Multi-Scale Modeling of Shear Initiated Reactions in Energetic and Reactive Materials

    DTIC Science & Technology

    2010-04-01

    Physics-based Multi-scale Modeling of Shear Initiated Reactions in Energetic and Reactive Materials by John K. Brennan, Müge Fermen -Coker...Energetic and Reactive Materials John K. Brennan and Müge Fermen -Coker Weapons and Materials Research Directorate, ARL and Linhbao Tran Shock...Materials 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) John K. Brennan, Müge Fermen -Coker, and Linhbao Tran 5d

  15. Finite Element Micromechanics and Minimechanics Modeling of a Three- Dimensional Carbon-Carbon Composite Material

    DTIC Science & Technology

    1985-12-01

    9 2.4.1 Materials Science Corporation - DCAP .... ....... 9 2.4.2 Science Applications Inc. - APIC ... ......... ... 13 2.4.3...input material properties to a second level minimechanics analyses. 2.4 Minimechanics Analyses 2.4.1 Materials Science Corvoration - DCAP During the... DCAP , is probably the most versatile and useful predictive tool for modeling three-dimensional carbon-carbon composite materials developed to date

  16. Challenges in Integrated Computational Structure - Material Modeling of High Strain-Rate Deformation and Failure in Heterogeneous Materials

    DTIC Science & Technology

    2014-10-09

    author(s) and should not contrued as an official Department of the Army position, policy or decision, unless so designated by other documentation . 9...Structure Heterogeneous Material Models REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 10. SPONSOR/MONITOR’S ACRONYM(S) ARO 8...Bronkhorst of LANL . This was followed by a 30 min. panel discussion. (iv) Plenary session # 2 on Probabilistic Modeling & Uncertainty

  17. Modeling aerosol emissions from the combustion of composite materials

    NASA Technical Reports Server (NTRS)

    Roop, J. A.; Caldwell, D. J.; Kuhlmann, K. J.

    1994-01-01

    The use of advanced composite materials (ACM) in the B-2 bomber, composite armored vehicle, and F-22 advanced tactical fighter has rekindled interest concerning the health risk of burned or burning ACM. The objective of this work was to determine smoke production from burning ACM and its toxicity. A commercial version of the UPITT II combustion toxicity method developed at the University of Pittsburgh, and subsequently refined through a US Army-funded basic research project, was used to established controlled combustion conditions which were selected to evaluate real-world exposure scenarios. Production and yield of toxic species varied with the combustion conditions. Previous work with this method showed that the combustion conditions directly influenced the toxicity of the decomposition products from a variety of materials.

  18. Life prediction and constitutive models for engine hot section anisotropic materials program

    NASA Technical Reports Server (NTRS)

    Swanson, G. A.

    1985-01-01

    The purpose is to develop life prediction models for coated anisotropic materials used in gas temperature airfoils. Two single crystal alloys and two coatings are now being tested. These include PWA 1480; Alloy 185; overlay coating, PWA 286; and aluminide coating, PWA 273. Constitutive models are also being developed for these materials to predict the plastic and creep strain histories of the materials in the lab tests and for actual design conditions. This nonlinear material behavior is particularily important for high temperature gas turbine applications and is basic to any life prediction system.

  19. Electronic State Decomposition of Energetic Materials and Model Systems

    DTIC Science & Technology

    2010-11-17

    tetrazine1,4-dioxde ( DATO ), is investigated. Although these molecules are based on N -oxides of a tetrazine aromatic heterocyclic ring, their...nitramines, furazan, tetrazines, tetrazine-N oxides, terazoles, PETN, RDX,HMX,CL-20,DAATO,ACTO, DATO ,conical intersections Elliot R Bernstein Colorado State...Tetrazine-N-Oxide Based High Nitrogen Content Energetic Materials from Excited Electronic States," J. Chem. Phys. 131, 194304 (2009). A

  20. Pressure Modeling of Char-Forming and Laminated Materials.

    DTIC Science & Technology

    1983-06-01

    terms of rate of total mass loss, flame heighit, upward flame spread rate, and maximum lateral flame dimensions during the spread process . The cnar...flame extent during the spread process . The char-forming materials (pine-wood, particle-board and a rigid, polyurethane foam) are tested in a 900... processes occur. 2. The behavior of the flame spread process at elevated air pressures, for walls composed of a face layer of PMMA with a thick

  1. The Challenge for Materials Design. Integrating Modeling and Computation

    DTIC Science & Technology

    2007-11-02

    15+ yrs • Lightweight composites for army vehicles 15+ yrs • Gamma titanium aluminides ~30yrs and counting • Ceramics for engines - 30+++ ? yrs...suite of simulations and experiments to assess elastic moduli and anisotropic yield surfaces •Deploy around the Digital Material framework •Interface...Known alloy to reliable part ~36 months • Steels for navy landing gear 15+ yrs • Lightweight composites for army vehicles 15+ yrs • Gamma titanium

  2. Prediction of Fracture Behavior in Rock and Rock-like Materials Using Discrete Element Models

    NASA Astrophysics Data System (ADS)

    Katsaga, T.; Young, P.

    2009-05-01

    The study of fracture initiation and propagation in heterogeneous materials such as rock and rock-like materials are of principal interest in the field of rock mechanics and rock engineering. It is crucial to study and investigate failure prediction and safety measures in civil and mining structures. Our work offers a practical approach to predict fracture behaviour using discrete element models. In this approach, the microstructures of materials are presented through the combination of clusters of bonded particles with different inter-cluster particle and bond properties, and intra-cluster bond properties. The geometry of clusters is transferred from information available from thin sections, computed tomography (CT) images and other visual presentation of the modeled material using customized AutoCAD built-in dialog- based Visual Basic Application. Exact microstructures of the tested sample, including fractures, faults, inclusions and void spaces can be duplicated in the discrete element models. Although the microstructural fabrics of rocks and rock-like structures may have different scale, fracture formation and propagation through these materials are alike and will follow similar mechanics. Synthetic material provides an excellent condition for validating the modelling approaches, as fracture behaviours are known with the well-defined composite's properties. Calibration of the macro-properties of matrix material and inclusions (aggregates), were followed with the overall mechanical material responses calibration by adjusting the interfacial properties. The discrete element model predicted similar fracture propagation features and path as that of the real sample material. The path of the fractures and matrix-inclusion interaction was compared using computed tomography images. Initiation and fracture formation in the model and real material were compared using Acoustic Emission data. Analysing the temporal and spatial evolution of AE events, collected during the

  3. Material Properties from Air Puff Corneal Deformation by Numerical Simulations on Model Corneas

    PubMed Central

    Dorronsoro, Carlos; de la Hoz, Andrés; Marcos, Susana

    2016-01-01

    Objective To validate a new method for reconstructing corneal biomechanical properties from air puff corneal deformation images using hydrogel polymer model corneas and porcine corneas. Methods Air puff deformation imaging was performed on model eyes with artificial corneas made out of three different hydrogel materials with three different thicknesses and on porcine eyes, at constant intraocular pressure of 15 mmHg. The cornea air puff deformation was modeled using finite elements, and hyperelastic material parameters were determined through inverse modeling, minimizing the difference between the simulated and the measured central deformation amplitude and central-peripheral deformation ratio parameters. Uniaxial tensile tests were performed on the model cornea materials as well as on corneal strips, and the results were compared to stress-strain simulations assuming the reconstructed material parameters. Results The measured and simulated spatial and temporal profiles of the air puff deformation tests were in good agreement (< 7% average discrepancy). The simulated stress-strain curves of the studied hydrogel corneal materials fitted well the experimental stress-strain curves from uniaxial extensiometry, particularly in the 0–0.4 range. Equivalent Young´s moduli of the reconstructed material properties from air-puff were 0.31, 0.58 and 0.48 MPa for the three polymer materials respectively which differed < 1% from those obtained from extensiometry. The simulations of the same material but different thickness resulted in similar reconstructed material properties. The air-puff reconstructed average equivalent Young´s modulus of the porcine corneas was 1.3 MPa, within 18% of that obtained from extensiometry. Conclusions Air puff corneal deformation imaging with inverse finite element modeling can retrieve material properties of model hydrogel polymer corneas and real corneas, which are in good correspondence with those obtained from uniaxial extensiometry

  4. Material Properties from Air Puff Corneal Deformation by Numerical Simulations on Model Corneas.

    PubMed

    Bekesi, Nandor; Dorronsoro, Carlos; de la Hoz, Andrés; Marcos, Susana

    2016-01-01

    To validate a new method for reconstructing corneal biomechanical properties from air puff corneal deformation images using hydrogel polymer model corneas and porcine corneas. Air puff deformation imaging was performed on model eyes with artificial corneas made out of three different hydrogel materials with three different thicknesses and on porcine eyes, at constant intraocular pressure of 15 mmHg. The cornea air puff deformation was modeled using finite elements, and hyperelastic material parameters were determined through inverse modeling, minimizing the difference between the simulated and the measured central deformation amplitude and central-peripheral deformation ratio parameters. Uniaxial tensile tests were performed on the model cornea materials as well as on corneal strips, and the results were compared to stress-strain simulations assuming the reconstructed material parameters. The measured and simulated spatial and temporal profiles of the air puff deformation tests were in good agreement (< 7% average discrepancy). The simulated stress-strain curves of the studied hydrogel corneal materials fitted well the experimental stress-strain curves from uniaxial extensiometry, particularly in the 0-0.4 range. Equivalent Young´s moduli of the reconstructed material properties from air-puff were 0.31, 0.58 and 0.48 MPa for the three polymer materials respectively which differed < 1% from those obtained from extensiometry. The simulations of the same material but different thickness resulted in similar reconstructed material properties. The air-puff reconstructed average equivalent Young´s modulus of the porcine corneas was 1.3 MPa, within 18% of that obtained from extensiometry. Air puff corneal deformation imaging with inverse finite element modeling can retrieve material properties of model hydrogel polymer corneas and real corneas, which are in good correspondence with those obtained from uniaxial extensiometry, suggesting that this is a promising technique

  5. Modeling the Mechanical Behavior of Ceramic Matrix Composite Materials

    NASA Technical Reports Server (NTRS)

    Jordan, William

    1998-01-01

    Ceramic matrix composites are ceramic materials, such as SiC, that have been reinforced by high strength fibers, such as carbon. Designers are interested in using ceramic matrix composites because they have the capability of withstanding significant loads while at relatively high temperatures (in excess of 1,000 C). Ceramic matrix composites retain the ceramic materials ability to withstand high temperatures, but also possess a much greater ductility and toughness. Their high strength and medium toughness is what makes them of so much interest to the aerospace community. This work concentrated on two different tasks. The first task was to do an extensive literature search into the mechanical behavior of ceramic matrix composite materials. This report contains the results of this task. The second task was to use this understanding to help interpret the ceramic matrix composite mechanical test results that had already been obtained by NASA. Since the specific details of these test results are subject to the International Traffic in Arms Regulations (ITAR), they are reported in a separate document (Jordan, 1997).

  6. Microstructure-based modelling of multiphase materials and complex structures

    NASA Astrophysics Data System (ADS)

    Werner, Ewald; Wesenjak, Robert; Fillafer, Alexander; Meier, Felix; Krempaszky, Christian

    2016-09-01

    Micromechanical approaches are frequently employed to monitor local and global field quantities and their evolution under varying mechanical and/or thermal loading scenarios. In this contribution, an overview on important methods is given that are currently used to gain insight into the deformational and failure behaviour of multiphase materials and complex structures. First, techniques to represent material microstructures are reviewed. It is common to either digitise images of real microstructures or generate virtual 2D or 3D microstructures using automated procedures (e.g. Voronoï tessellation) for grain generation and colouring algorithms for phase assignment. While the former method allows to capture exactly all features of the microstructure at hand with respect to its morphological and topological features, the latter method opens up the possibility for parametric studies with respect to the influence of individual microstructure features on the local and global stress and strain response. Several applications of these approaches are presented, comprising low and high strain behaviour of multiphase steels, failure and fracture behaviour of multiphase materials and the evolution of surface roughening of the aluminium top metallisation of semiconductor devices.

  7. Geometry generation challenges for modelling and analysis of micro-structured materials

    NASA Astrophysics Data System (ADS)

    McMillan, A. J.

    2015-02-01

    Engineers evaluating the performance of a component at the design stage will typically convert Computer Aided Design (CAD) geometry into a Finite Element model, and run a Finite Element Analysis (FEA) to determine deformations and stress levels as a result of applied loads or displacements. The analysis results would then be interpreted by comparing them with the required duty of the component. For metallic components, homogeneous and isotropic material properties are generally assumed - "macro-scale" modelling. For components to be manufactured from composite materials, models may represent heterogeneity at the ply level, and orthotropic material properties applied with appropriate directionality. This ply-level modelling is often termed "meso-scale" modelling. Engineering interpretation of failure in materials is often based on empirical understanding of experimental data. This approach is generally robust: safety critical components would always be subject to validation by means of a suitable programme of testing. The aspect that is missing is the opportunity to improve understanding of the material performance by investigating the material performance at the "micro-scale". This paper describes computational algorithms for generating random geometries exhibiting similar characteristics to those seen at the "micro-scale" in real materials, and the use of these to predict the influence of the "micro-scale" structure on the "macro-scale" material performance.

  8. Fully scalable implementation of a volume coupling scheme for the modeling of multiscale materials

    NASA Astrophysics Data System (ADS)

    Schlittler, Thiago Milanetto; Cottereau, Régis

    2017-07-01

    We present in this paper a new implementation of a multi-scale, multi-model coupling algorithm, with a proposed parallelization scheme for the construction of the coupling terms between the models. This allows one to study such problems with a fully scalable algorithm on large computer clusters, even when the models and/or the coupling have a high number of degrees of freedom. As an application example, we will consider a system composed by an homogeneous, macroscopic Elastic model and an anisotropic polycrystalline material model, with a volume coupling based on the Arlequin framework.

  9. COMGEN-BEM: Boundary element model generation for composite materials micromechanical analysis

    NASA Technical Reports Server (NTRS)

    Goldberg, Robert K.

    1992-01-01

    Composite Model Generation-Boundary Element Method (COMGEN-BEM) is a program developed in PATRAN command language (PCL) which generates boundary element models of continuous fiber composites at the micromechanical (constituent) scale. Based on the entry of a few simple parameters such as fiber volume fraction and fiber diameter, the model geometry and boundary element model are generated. In addition, various mesh densities, material properties, fiber orientation angles, loads, and boundary conditions can be specified. The generated model can then be translated to a format consistent with a boundary element analysis code such as BEST-CMS.

  10. Atomistic simulation of nanoporous layered double hydroxide materials and their properties. I. Structural modeling.

    PubMed

    Kim, Nayong; Kim, Yongman; Tsotsis, Theodore T; Sahimi, Muhammad

    2005-06-01

    An atomistic model of layered double hydroxides, an important class of nanoporous materials, is presented. These materials have wide applications, ranging from adsorbents for gases and liquid ions to nanoporous membranes and catalysts. They consist of two types of metallic cations that are accommodated by a close-packed configuration of OH- and other anions in a positively charged brucitelike layer. Water and various anions are distributed in the interlayer space for charge compensation. A modified form of the consistent-valence force field, together with energy minimization and molecular dynamics simulations, is utilized for developing an atomistic model of the materials. To test the accuracy of the model, we compare the vibrational frequencies, x-ray diffraction patterns, and the basal spacing of the material, computed using the atomistic model, with our experimental data over a wide range of temperature. Good agreement is found between the computed and measured quantities.

  11. Atomistic simulation of nanoporous layered double hydroxide materials and their properties. I. Structural modeling

    NASA Astrophysics Data System (ADS)

    Kim, Nayong; Kim, Yongman; Tsotsis, Theodore T.; Sahimi, Muhammad

    2005-06-01

    An atomistic model of layered double hydroxides, an important class of nanoporous materials, is presented. These materials have wide applications, ranging from adsorbents for gases and liquid ions to nanoporous membranes and catalysts. They consist of two types of metallic cations that are accommodated by a close-packed configuration of OH- and other anions in a positively charged brucitelike layer. Water and various anions are distributed in the interlayer space for charge compensation. A modified form of the consistent-valence force field, together with energy minimization and molecular dynamics simulations, is utilized for developing an atomistic model of the materials. To test the accuracy of the model, we compare the vibrational frequencies, x-ray diffraction patterns, and the basal spacing of the material, computed using the atomistic model, with our experimental data over a wide range of temperature. Good agreement is found between the computed and measured quantities.

  12. Impact Testing of Aluminum 2024 and Titanium 6Al-4V for Material Model Development

    NASA Technical Reports Server (NTRS)

    Pereira, J. Michael; Revilock, Duane M.; Lerch, Bradley A.; Ruggeri, Charles R.

    2013-01-01

    One of the difficulties with developing and verifying accurate impact models is that parameters such as high strain rate material properties, failure modes, static properties, and impact test measurements are often obtained from a variety of different sources using different materials, with little control over consistency among the different sources. In addition there is often a lack of quantitative measurements in impact tests to which the models can be compared. To alleviate some of these problems, a project is underway to develop a consistent set of material property, impact test data and failure analysis for a variety of aircraft materials that can be used to develop improved impact failure and deformation models. This project is jointly funded by the NASA Glenn Research Center and the FAA William J. Hughes Technical Center. Unique features of this set of data are that all material property data and impact test data are obtained using identical material, the test methods and procedures are extensively documented and all of the raw data is available. Four parallel efforts are currently underway: Measurement of material deformation and failure response over a wide range of strain rates and temperatures and failure analysis of material property specimens and impact test articles conducted by The Ohio State University; development of improved numerical modeling techniques for deformation and failure conducted by The George Washington University; impact testing of flat panels and substructures conducted by NASA Glenn Research Center. This report describes impact testing which has been done on aluminum (Al) 2024 and titanium (Ti) 6Al-4vanadium (V) sheet and plate samples of different thicknesses and with different types of projectiles, one a regular cylinder and one with a more complex geometry incorporating features representative of a jet engine fan blade. Data from this testing will be used in validating material models developed under this program. The material

  13. Process Modeling of Composite Materials for Wind-Turbine Rotor Blades: Experiments and Numerical Modeling.

    PubMed

    Wieland, Birgit; Ropte, Sven

    2017-10-05

    The production of rotor blades for wind turbines is still a predominantly manual process. Process simulation is an adequate way of improving blade quality without a significant increase in production costs. This paper introduces a module for tolerance simulation for rotor-blade production processes. The investigation focuses on the simulation of temperature distribution for one-sided, self-heated tooling and thick laminates. Experimental data from rotor-blade production and down-scaled laboratory tests are presented. Based on influencing factors that are identified, a physical model is created and implemented as a simulation. This provides an opportunity to simulate temperature and cure-degree distribution for two-dimensional cross sections. The aim of this simulation is to support production processes. Hence, it is modelled as an in situ simulation with direct input of temperature data and real-time capability. A monolithic part of the rotor blade, the main girder, is used as an example for presenting the results.

  14. Tools for modeling radioactive contaminants in chip materials

    NASA Astrophysics Data System (ADS)

    Wrobel, F.; Kaouache, A.; Saigné, F.; Touboul, A. D.; Schrimpf, R. D.; Warot, G.; Bruguier, O.

    2017-03-01

    Radioactive pollutants are naturally present in microelectronic device materials and can be an issue for the reliability of devices. The main concern is alpha emitters that produce high-energy particles (a few MeV) that ionize the semiconductor and then trigger soft errors. The question is to know what kinds of radionuclides are present in the device, their location in the device and the abundance of each species. In this paper we describe tools that are required to address the issue of radioactive pollutants in electronic devices.

  15. Unexpected collapses during isotropic consolidation of model granular materials

    NASA Astrophysics Data System (ADS)

    Doanh, Thiep; Le Bot, Alain; Abdelmoula, Nouha; Gribaa, Lassad; Hans, Stéphane; Boutin, Claude

    2016-02-01

    This paper reports the unexpected instantaneous instabilities of idealized granular materials under simple isotropic drained compression. Specimens of monosized glass beads submitted to isotropic compression exhibit a series of local collapses under undetermined external stress with partial liquefaction, experience sudden volumetric compaction and axial contraction of various amplitude. Short-lived excess pore water pressure vibrates like an oscillating underdamped system in the first dynamic transient phase and rapidly disperses in the subsequent longer dissipation phase. However, very dense samples maintain a collapse-free behaviour below a threshold void ratio e0col at 30 kPa of stress. The potential mechanisms that could explain these spontaneous collapses are discussed.

  16. Strain-Path Modeling for Geo-Materials.

    DTIC Science & Technology

    1984-03-07

    Summary: Overview To compute the response of the earth to explosions below or near its surface, discrete analogs are written of equations that govern...fruitful application in other branches of materials science . 8 A... ... 8 . ... ,... .. ., ~ ~ ~ ~ ~ ~ ~ ~ .. . . . ...*- .. ._ , -. . . -- ~~t...4 @14 C4 1 1 IO > * AiW v4 14 C6 -1@ C4 Ř 4 U 4 0 04 o 0 w 00.to -4 o N Q-E 41 0 10. 0n.0 0 en44 Ai Zk o - .o . o _t $..4@ 010k ca 0 03 41 0 r W4 fn

  17. Rheological and physical characteristics of crustal-scaled materials for centrifuge analogue modelling

    NASA Astrophysics Data System (ADS)

    Waffle, Lindsay; Godin, Laurent; Harris, Lyal B.; Kontopoulou, M.

    2016-05-01

    We characterize a set of analogue materials used for centrifuge analogue modelling simulating deformation at different levels in the crust simultaneously. Specifically, we improve the rheological characterization in the linear viscoelastic region of materials for the lower and middle crust, and cohesive synthetic sands without petroleum-binding agents for the upper crust. Viscoelastic materials used in centrifuge analogue modelling demonstrate complex dynamic behaviour, so viscosity alone is insufficient to determine if a material will be an effective analogue. Two series of experiments were conducted using an oscillating bi-conical plate rheometer to measure the storage and loss moduli and complex viscosities of several modelling clays and silicone putties. Tested materials exhibited viscoelastic and shear-thinning behaviour. The silicone putties and some modelling clays demonstrated viscous-dominant behaviour and reached Newtonian plateaus at strain rates < 0.5 × 10-2 s-1, while other modelling clays demonstrated elastic-dominant power-law relationships. Based on these results, the elastic-dominant modelling clay is recommended as an analogue for basement cratons. Inherently cohesive synthetic sands produce fine-detailed fault and fracture patterns, and developed thrust, strike-slip, and extensional faults in simple centrifuge test models. These synthetic sands are recommended as analogues for the brittle upper crust. These new results increase the accuracy of scaling analogue models to prototype. Additionally, with the characterization of three new materials, we propose a complete lithospheric profile of analogue materials for centrifuge modelling, allowing future studies to replicate a broader range of crustal deformation behaviours.

  18. D2M2 Dredged-Material Disposal Management Model. User’s Manual

    DTIC Science & Technology

    1984-07-01

    developed by Rochelle Barkin and the network model and the branch-and-bound algorithm were formulated by David Ford and Darryl Davis, Chief, Planning...10 Appendix I: Reprint of "Dredged-material Disposal Management Model" by David T. Ford...By David T. Ford,’ M. ASCE Aae•mA: To identify efficient dredged-material disposal management strat- egies for the Delaware River navigation system

  19. Modeling and Analysis of Composite Wing Sections for Improved Aeroelastic and Vibration Characteristics Using Smart Materials

    NASA Technical Reports Server (NTRS)

    Chattopadhyay, Aditi

    1996-01-01

    The objective of this research is to develop analysis procedures to investigate the coupling of composite and smart materials to improve aeroelastic and vibratory response of aerospace structures. The structural modeling must account for arbitrarily thick geometries, embedded and surface bonded sensors and actuators and imperfections, such as delamination. Changes in the dynamic response due to the presence of smart materials and delaminations is investigated. Experiments are to be performed to validate the proposed mathematical model.

  20. Toward Technological Application of Non-Newtonian Fluids & Complex Materials/Modeling, Simulation, & Design of Experiments

    DTIC Science & Technology

    2007-11-02

    34Therrmanechanical Equations Governing a Material with Prescribed Temperature-Dependent Density, with Applications to Nonisothernal Plane Poiseuille Flow ", D...1-0431 Materials/Modeling, Simulation , & Design of Experiments 6. AUTHORS M. Gregory Forest & Stephen E. Bechtel 7. PERFORMING ORGANIZATION NAME(S...made significant progress in each of these general areas. We produced high resolution models and codes that simulate molten fiber manufacturing