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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Micromechanical modeling of damage growth in titanium based metal-matrix composites

The thermomechanical behavior of continuous-fiber reinforced titanium based metal-matrix composites (MMC) is studied using the finite element method. A thermoviscoplastic unified state variable constitutive theory is employed to capture inelastic and strain-rate sensitive behavior in the Timetal-21s matrix. The SCS-6 fibers are modeled as thermoplastic. The effects of residual stresses generated during the consolidation process on the tensile response of the composites are investigated. Unidirectional and cross-ply geometries are considered. Differences between the tensile responses in composites with perfectly bonded and completely debonded fiber/matrix interfaces are discussed. Model simulations for the completely debonded-interface condition are shown to correlate well with experimental results.

Sherwood, James A.↗
NASA NTRS2002

System Model for MEMS based Laser Ultrasonic Receiver

A need has been identified for more advanced nondestructive Evaluation technologies for assuring the integrity of airframe structures, wiring, etc. Laser ultrasonic inspection instruments have been shown to detect flaws in structures. However, these instruments are generally too bulky to be used in the confined spaces that are typical of aerospace vehicles. Microsystems technology is one key to reducing the size of current instruments and enabling increased inspection coverage in areas that were previously inaccessible due to instrument size and weight. This paper investigates the system modeling of a Micro OptoElectroMechanical System (MOEMS) based laser ultrasonic receiver. The system model is constructed in software using MATLAB s dynamical simulator, Simulink. The optical components are modeled using geometrical matrix methods and include some image processing. The system model includes a test bench which simulates input stimuli and models the behavior of the material under test.

Wilson, William C.↗
DOE OSTI2023

Modeling Workloads of a Linear Electromagnetic Code for Load Balancing Matrix Assembly

This report presents our work to model the workloads of a linear electromagnetic application based on the method of moments in the frequency domain to effectively load balance the matrix assembly. This application is particularly challenging to load balance due to its lack of persistent iterative behavior, its operation under tight memory constraint (where the matrix may fill 80% of memory on each node), and the algorithmic complexity of the computational method. This report describes the first step in our work to apply an inspector-executor approach for load balancing workloads where key parameters are exposed during the inspector phase and a pre-trained model is applied to predict relative task weights for the load balancer.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2022

Investigation of Coupled Processes in Fractures and the Bordering Matrix via a Micro‐Continuum Reactive Transport Model

Abstract In multi‐mineral fractured rocks, the altered porous layer on the fracture surface resulting from preferential dissolution of the fast‐reacting minerals can have profound impacts on subsequent chemical‐physical alteration of the fractures. This study adopts the micro‐continuum approach to provide further understanding of reactive transport processes in the altered layer (AL), and mass exchanges with the bordering matrix and fracture. The modeling framework couples the Darcy‐Brinkman‐Stokes (DBS) solver in COMSOL Multiphysics and the geochemical modeling capability of CrunchFlow. Three‐dimensional steady state simulations with systematically varied chemical‐physical parameters of the AL were performed to examine the impacts of individual factors and processes. Our simulation results confirm previous observations that dissolution of the fast‐reacting mineral (i.e., calcite) is largely controlled by diffusion across the AL. We also show that dissolution of the slow‐reacting mineral (i.e., dolomite), which controls AL development and fracture enlargement, increases with surface area and has a complex dependence on different local rate‐limiting processes. In particular, advection can result in evident spatial variations in the local dissolution rates of dolomite, although it does not affect the bulk chemistry significantly. The difference in the spatial patterns between simulations with and without advection in the AL is more noticeable in the locations with smaller apertures, with up to 20% difference in local reaction rates. Therefore, it is important to include a full depiction of advection, diffusion, and reactions for accurately capturing local dynamics that control long‐term fracture evolution.

58 GEOSCIENCES↗
NASA NTRS2017

Modeling of Different Fiber Type and Content SiC/SiC Minicomposites Creep Behavior

Silicon Carbide based Ceramic Matrix Composites (CMCs) are attractive materials for use in high-temperature applications in the aerospace and nuclear industries. However, creep damage mechanism in CMCs is the most dominant mechanism at elevated temperatures. Consequently, the tensile creep behavior of Hi-Nicalon, Hi-Nicalon Type S SiC fibers and Chemical vapor infiltrated Silicon Carbide matrix (CVI-SiC) were characterized and creep parameters were extracted from creep experiments. Some fiber creep tests were performed in inert environment at 1200 C on individual fibers. Creep behavior of different fiber content pristine and precracked Hi-Nicalon and Hi-Nicalon Type S reinforced minicomposites with BN interphases and CVI-SiC matrix were then modelled using the creep data found in this study and the literature and compared with creep experiments results for the pristine and precracked Hi-Nicalon and Hi-Nicalon Type S minicomposites. Finally, the effects of load-sharing and matrix cracking on CMC creep behavior will be discussed.

ceramic matrix minicomposites↗
NASA NTRS2003

Modeling of 3-D Woven Ceramic Matrix Composites

Three different approaches are being pursued at the NASA Glenn Research Center to predict the nanostructural behavior of three-dimensional woven ceramic matrix composites. These are: a micromechanics-based approach using W-CEMCAN (Woven Ceramic Matrix Composite Analyzer), a laminate analogy method and a structural frame approach (based on the finite element method). All three techniques are applied to predict the thermomechanical properties of a three-dimensional woven angle interlock C/SiC composite. The properties are predicted for room temperature and 1100 C and the predicted properties are compared to measurements. General observations regarding the three approaches for three-dimensional composite modeling are discussed.

Murthy, Pappu L. N.↗
DOE OSTI2020

Predicting ductility of Mg/SiCp nanocomposite under multiaxial loading conditions based on unit cell modeling

This article presents an investigation on the ductility of Mg/SiCp under nine different multiaxial loading conditions based on a unit cell (or called representative volumetric element, RVE) finite element model. The constitutive relationship of magnesium matrix is characterized by a model combined Lode angle dependent plasticity model with the CPB06 plasticity model, which is able to describe the tension-compression asymmetry in magnesium matrix. The debonding of the matrix-particle interface and matrix fracture are considered by the modified Mohr-Coulomb (MMC) fracture model. Simulation results show that the interface debonding and subsequent matrix fracture are responsible for the ductility and fracture of nanocomposite. The computational results with parametric studies are compared and well correlated with experimental data, and it finally gives a stress-based full fracture locus of Mg/SiCp nanocomposite.

42 ENGINEERING↗
NASA NTRS1980

Mechanisms of fatigue damage in boron/aluminum composites

Tensile fatigue tests were conducted on several laminates of boron/aluminum (6061-0). In laminates with 0 deg fibers on the outside, an analysis that identifies "shakedown" conditions predicted the stress amplitude below which no fatigue damage accumulated. A fatigue damage accumulation model which relates matrix fatigue cracking and the overall laminate properties is described. A model for the saturation damage stage development is presented, that identical laminates, tested in directions 90 deg apart (such that one layup has 90 deg outer plies and the other 0 deg), have different fatigue behaviors due to the stacking sequence. The 90 deg plies on the surface develop cracks earlier than predicted by shakedown. An attempt was made to explain this stacking sequence effect. Variable load history effects on the fatigue damage response were investigated. Tests reveal that for a given stress ratio the specimen seeks the saturation damage state for the largest stress range to which it is subjected. It was also found that little damage is generated by shifting a given stress range down, whereas significant damage may be created by shifting it upward. The laminate stresses were always tensile.

Johnson, W. S.↗
NASA NTRS1989

Modeling and control system design and analysis tools for flexible structures

Described here are Boeing software tools used for the development of control laws of flexible structures. The Boeing Company has developed a software tool called Modern Control Software Package (MPAC). MPAC provides the environment necessary for linear model development, analysis, and controller design for large models of flexible structures. There are two features of MPAC which are particularly appropriate for use with large models: (1) numerical accuracy and (2) label-driven nature. With the first feature MPAC uses double precision arithmetic for all numerical operations and relies on EISPAC and LINPACK for the numerical foundation. With the second feature, all MPAC model inputs, outputs, and states are referenced by user-defined labels. This feature allows model modification while maintaining the same state, input, and output names. In addition, there is no need for the user to keep track of a model variable's matrix row and colunm locations. There is a wide range of model manipulation, analysis, and design features within the numerically robust and flexible environment provided by MPAC. Models can be built or modified using either state space or transfer function representations. Existing models can be combined via parallel, series, and feedback connections; and loops of a closed-loop model may be broken for analysis.

Anissipour, Amir A.↗
NASA NTRS1983

Viscosity of rock-ice mixtures and applications to the evolution of icy satellites

Theory and experiments are used to establish lower and upper bounds on the ratio of actual viscosity to pure ice viscosity for a suspension of rock particles in a water ice matrix. A rheological model for rock-ice mixtures is described, establishing bounds for the range of possible viscosity enhancements provided by a suspension of silicate spheres in an ice matrix. A parametrized thermal convection model is described and used to determine a criterion for criticality, defined as the heat flow and/or silicate volume fraction for which the satellite temperature profile intercepts the melting curve of water ice. The consequences of achieving this critical state are examined, and it is shown that under certain circumstances a 'runaway' differentiation can occur in which the silicates settle to form a core and extensive melting of water ice takes place, the latent heat being supplied by the gravitational energy of differentiation. A possible application of these results to Ganymede and Callisto is described.

Friedson, A. J.↗
DOE OSTI2020

Modular Growth and Nucleation Formulations in Modular Plasticity Models

Recent investigations like the second and third Sandia Fracture Challenges have characterized and demonstrated the performance of a variety of failure techniques and models. These surveys have considered a wide breadth of models encapsulating both general failure criteria as well as those focusing on pore nucleation and growth. Extensive reviews exist on both topics. The former category generally consists of classic models like the Johnson-Cook or Wilkins criteria. These models were recently added to modular plasticity models in the Library of Advanced Materials for Engineering (LAME) as criteria for use with element death capabilities. The latter category was not treated in that effort. There exists a large class of failure models based on predicting the evolution of pores and failure associated with such microstructures. While the exact mechanisms and corresponding impact on the macroscale behavior remain an active area of research, a large suite of formulations have been proposed combining different features of both pore nucleation and subsequent growth. The most famous of these are based on the popular Gurson model of pore growth derived via micromechanical analysis assuming a plastically incompressible matrix. Numerous other models exist for both growth and nucleation and the Cocks-Ashby growth and Horstemeyer-Gokhale nucleation models have been used successfully in recent Sandia Fracture Challenges. This specific combination is colloquially referred to as the "BCJ-failure model as it has been frequently used with the Bammann-Chisea-Johnson plasticity model.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Bayesian Inference of State-Level COVID-19 Basic Reproduction Numbers across the United States

Although many persons in the United States have acquired immunity to COVID-19, either through vaccination or infection with SARS-CoV-2, COVID-19 will pose an ongoing threat to non-immune persons so long as disease transmission continues. We can estimate when sustained disease transmission will end in a population by calculating the population-specific basic reproduction number ℛ0, the expected number of secondary cases generated by an infected person in the absence of any interventions. The value of ℛ0 relates to a herd immunity threshold (HIT), which is given by 1−1/ℛ0. When the immune fraction of a population exceeds this threshold, sustained disease transmission becomes exponentially unlikely (barring mutations allowing SARS-CoV-2 to escape immunity). Here, we report state-level ℛ0 estimates obtained using Bayesian inference. Maximum a posteriori estimates range from 7.1 for New Jersey to 2.3 for Wyoming, indicating that disease transmission varies considerably across states and that reaching herd immunity will be more difficult in some states than others. ℛ0 estimates were obtained from compartmental models via the next-generation matrix approach after each model was parameterized using regional daily confirmed case reports of COVID-19 from 21 January 2020 to 21 June 2020. Our ℛ0 estimates characterize the infectiousness of ancestral strains, but they can be used to determine HITs for a distinct, currently dominant circulating strain, such as SARS-CoV-2 variant Delta (lineage B.1.617.2), if the relative infectiousness of the strain can be ascertained. On the basis of Delta-adjusted HITs, vaccination data, and seroprevalence survey data, we found that no state had achieved herd immunity as of 20 September 2021.

60 APPLIED LIFE SCIENCES↗
NASA NTRS1998

Modeling the Mechanical Behavior of Ceramic Matrix Composite Materials

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).

Jordan, William↗
NASA NTRS2003

Analytical Modeling of the High Strain Rate Deformation of Polymer Matrix Composites

The results presented here are part of an ongoing research program to develop strain rate dependent deformation and failure models for the analysis of polymer matrix composites subject to high strain rate impact loads. State variable constitutive equations originally developed for metals have been modified in order to model the nonlinear, strain rate dependent deformation of polymeric matrix materials. To account for the effects of hydrostatic stresses, which are significant in polymers, the classical 5 plasticity theory definitions of effective stress and effective plastic strain are modified by applying variations of the Drucker-Prager yield criterion. To verify the revised formulation, the shear and tensile deformation of a representative toughened epoxy is analyzed across a wide range of strain rates (from quasi-static to high strain rates) and the results are compared to experimentally obtained values. For the analyzed polymers, both the tensile and shear stress-strain curves computed using the analytical model correlate well with values obtained through experimental tests. The polymer constitutive equations are implemented within a strength of materials based micromechanics method to predict the nonlinear, strain rate dependent deformation of polymer matrix composites. In the micromechanics, the unit cell is divided up into a number of independently analyzed slices, and laminate theory is then applied to obtain the effective deformation of the unit cell. The composite mechanics are verified by analyzing the deformation of a representative polymer matrix composite (composed using the representative polymer analyzed for the correlation of the polymer constitutive equations) for several fiber orientation angles across a variety of strain rates. The computed values compare favorably to experimentally obtained results.

Goldberg, Robert K.↗