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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 991 records · Page 55

Environmental charging of spacecraft surfaces: Tests of thermal control materials for use on the global positioning system flight space vehicle. Part 1: Specimens 1 to 5

The NASA/USAF program on Environmental Charging of Spacecraft Surfaces consists of experimental efforts directed toward evaluating the response of materials to the environmental charged particle flux. Samples of thermal blankets and second surface mirrors of the type to be used on the Global Positioning System Flight Space Vehicle were tested to determine their response to electron flux. The primary result observed was that the ground connection of the metal layers of the blanket, as made by the baseline grounding technique using serrated washers and grommets, deteriorated with time at test. The discharges observed on the blankets were the glow type, not the 'lightning' strike observed on past specimens. Testing was performed at ambient laboratory temperatures.

Stevens, N. J.↗

ASC PEM Materials Modeling Overview: Focus on Predicting Response of Metals [Slides]

In general, the large / high rate deformation process involves high pressure and temperature, finite elasticity, phase change, localization, porosity initiation, porosity growth, and coalescence dominated by localized deformation. These physical events are statistical, coupled, occur over several length scales, and intimately involves the microstructure. Understanding these complex thermo-mechanical processes is critical to our ability to numerically represent and predict these deformation events. ASC Materials is generally responsible for the modeling of 12-15 different metallic materials subjected to a broad range of conditions. This talk discusses current approaches and unanswered questions in the areas of high rate strength, phase transformations, and damage and failure.

36 MATERIALS SCIENCE↗

Complex Functional Materials

Complex functional materials are materials comprised of multiple components or building blocks that are integrated or chemically bound together to achieve a desired function or response. Soft materials, such as polymers, as well as structural properties at the mesoscale and micro-scale that control materials function are particularly emphasized in this area of leadership. Further, complex functional materials must generally be developed to satisfy multiple criteria essential to the overall application. Thus, this area of leadership supports applications that are aligned with all three Los Alamos National Laboratory mission areas of energy security, global security, and nuclear deterrence.

36 MATERIALS SCIENCE↗

Complex Functional Materials

The Complex Functional Materials (CFM) area of leadership focuses on the identification and development of materials comprised of multiple components or building blocks that are integrated or chemically bound together to achieve a desired function or response. Soft materials, such as polymers, as well as structural properties at the meso- and micro-scale that control materials function are particularly emphasized in this leadership area. Further, complex functional materials are generally developed to satisfy multiple materials design criteria all of which are essential to the overall application. CFM supports applications that are aligned with all three Los Alamos National Laboratory mission areas. These mission areas are: materials for nuclear deterrence, materials for energy security, and materials for global security

36 MATERIALS SCIENCE↗

Fundamental aspects in the quantitative ultrasonic determination of fracture toughness: General equations

The problem of establishing a theoretical groundwork for experimentally-found correlations between ultrasonic and fracture toughness factors in polycrystalline metals is discussed. It is noted that the link between these material properties and ultrasonic factors are the microstructural parameters that interact with stress wave propagation during deformation and fracture. The dynamic response of material inhomogeneities and the strains and displacements they undergo under incident stress waves are considered. Dynamic strains and displacements inside and outside scatterers are treated. The underlying approach, the formulation and governing equations for the eigenstrains, and the determination of the energy due to the presence of inhomogeneities are presented. The stress wave interaction problem is presented in terms of the dynamic eigenstrain concept.

Fu, L. S.↗

Surface Engineering by Simultaneous Action of Multiple External Fields (Final Technical Report)

This research project aims at enabling surface engineering strategies based on the fundamental understanding and predictive modeling of the surface morphological response of solid materials subjected to the combined action of multiple external forces. Surface morphological response to mismatch strain in strained-layer heterostructures also is analyzed. Our research focuses on the surface morphological evolution and stability of electrically conducting (metallic, such as Cu) and semiconducting (such as Si) solids under the simultaneous application of mechanical stresses, electric fields, and temperature gradients. We emphasize on identifying the conditions under which the multiply driven surface morphology is stable and on exploring the complexity of the corresponding various morphologically stable surface patterns. We also emphasize on the driven evolution of nanoscale features aiming at stabilizing and controlling nanoscale patterns on surfaces by their manipulation through simultaneously applied multiple external forces. Specifically, we address systematically the morphological response to the combined action of multiple external forces of bulk solid surfaces, surfaces of thin films grown epitaxially on thick or thin substrates, as well as nanoscale surface features such as coherently strained islands grown epitaxially on substrate surfaces. The research is based on a modeling approach that combines theoretical analyses of surface morphological stability with self-consistent dynamical simulations of surface evolution based on properly parameterized continuum and multiscale surface transport models.

36 MATERIALS SCIENCE↗

Environmental charging of spacecraft-tests of thermal control materials for use on the global positioning system flight space vehicle. Part 2: Specimen 6 to 9

The NASA/USAF program on the Environmental Charging of Spacecraft Surfaces consists, in part, of experimental efforts directed toward evaluating the response of materials to the environmental charged particle flux. Samples of thermal blankets of the type to be used on the Global Positioning System Flight Space Vehicles were tested to determine their response to electron flux. The primary result observed was that no discharges were obtained with the quartz-fiber-fabric-covered multilayer insulation specimen. The taped aluminized polyester grounding system used on all specimens did not appear to grossly deteriorate with time; however, the specimens require specific external pressure to maintain constant grounding system resistance.

Stevens, N. J.↗

Cathodoluminescence for the 21st century: Learning more from light

Cathodoluminescence (CL) is the emission of light from a material in response to excitation by incident electrons. The technique has had significant impact in the characterization of semiconductors, minerals, ceramics, and many nanostructured materials. Since 2010, there have been a number of innovative developments that have revolutionized and expanded the information that can be gained from CL and broadened the areas of application. While the primary historical application of CL was for spatial mapping of luminescence variations (e.g., imaging dark line defects in semiconductor lasers or providing high resolution imaging of compositional variations in geological materials), new ways to collect and analyze the emitted light have expanded the science impact of CL, particularly at the intersection of materials science and nanotechnology. Current developments include (1) angular and polarized CL, (2) advances in time resolved CL, (3) far-field and near-field transport imaging that enable drift and diffusion information to be obtained through real space imaging, (4) increasing use of statistical analyses for the study of grain boundaries and interfaces, (5) 3D CL including tomography and combined work utilizing dual beam systems with CL, and (6) combined STEM/CL measurements that are reaching new levels of resolution and advancing single photon spectroscopy. This focused review will first summarize the fundamentals and then briefly describe the state-of-the-art in conventional CL imaging and spectroscopy. We also review these recent novel experimental approaches that enable added insight and information, providing a range of examples from nanophotonics, photovoltaics, plasmonics, and studies of individual defects and grain boundaries.

14 SOLAR ENERGY↗

Micromechanical properties of spherical and facetted He bubble loaded copper

Exploring new irradiation resistant materials requires understanding their mechanical responses to irradiation. Resistance to helium bubble formation and understanding bubble effects on the mechanical response of candidate materials are crucial factors to qualify materials as irradiation resistant. Here, in this paper, we explore the effect of spherical and facetted helium bubbles on the mechanical response of copper via in-situ micromechanical tensile testing at room temperature. Bubble formation and shape effects on strength and ductility, and their behavior on grain boundaries are discussed and compared to literature. Loading Cu with helium bubbles is shown here to increase strength but decrease ductility.

42 ENGINEERING↗

Finite Element Analysis of Active and Sensory Thermopiezoelectric Composite Materials

Analytical formulations are developed to account for the coupled mechanical, electrical, and thermal response of piezoelectric composite materials. The coupled response is captured at the material level through the thermopiezoelectric constitutive equations and leads to the inherent capability to model both the sensory and active responses of piezoelectric materials. A layerwise laminate theory is incorporated to provide more accurate analysis of the displacements, strains, stresses, electric fields, and thermal fields through-the-thickness. Thermal effects which arise from coefficient of thermal expansion mismatch, pyroelectric effects, and temperature dependent material properties are explicitly accounted for in the formulation. Corresponding finite element formulations are developed for piezoelectric beam, plate, and shell elements to provide a more generalized capability for the analysis of arbitrary piezoelectric composite structures. The accuracy of the current formulation is verified with comparisons from published experimental data and other analytical models. Additional numerical studies are also conducted to demonstrate additional capabilities of the formulation to represent the sensory and active behaviors. A future plan of experimental studies is provided to characterize the high temperature dynamic response of piezoelectric composite materials.

Lee, Ho-Jun↗

Fully Implicit Ablation and Thermal Response Program for Spacecraft Heatshield Analysis

A fully implicit ablation and thermal response program has been developed for the simulation of one-dimensional transient transport of thermal energy in a multilayer stack of isotropic materials and structure which can ablate from a front surface and decompose in-depth. Equations and numerical procedures for solution are described. Solutions are compared with those of Aerotherm Charring Material Thermal Response and Ablation Program, and with the arcjet data. The code is numerically more stable, and solves much wider range of problems compared with the existing explicit code. Applications of the code for the analysis of aeroshell heatshields of Stardust, Mars 2001, and Mars Microprobe using the advanced Light Weight Ceramic Ablators developed at the NASA Ames Research Center are presented and discussed in detail.

Chen, Y. K.↗

Fractal analysis of collision cascades in pulsed-ion-beam-irradiated solids [Collision cascade densities in ion pulsed ion irradiated solids { a fractal approach]

The buildup of radiation damage in ion-irradiated crystals often depends on the spatial distribution of atomic displacements within collision cascades. Although collision cascades have previously been described as fractals, the correlation of their fractal parameters with experimental observations of radiation damage buildup remains elusive. Here, we use a pulsed-ion-beam method to study defect interaction dynamics in 3C-SiC irradiated at 100 °C with ions of different masses. These data, together with results of previous studies of SiC and Si, are analyzed with a model of radiation damage formation which accounts for the fractal nature of collision cascades. Our emphasis is on the extraction of the effective defect diffusion length from pulsed beam measurements. Results show that, for both Si and SiC, collision cascades are mass fractals with fractal dimensions in the range of ~1–2, depending on ion mass, energy, and the depth from the sample surface. Within our fractal model, the effective defect diffusion length is ~10 nm for SiC and ~20 nm for Si, and it decreases with increasing cascade density. These results demonstrate a general method by which the fractal nature of collision cascades can be used to explain experimental observations and predict material’s response to radiation.

36 MATERIALS SCIENCE↗

Outer planet probe entry thermal protection. II - Heat shielding requirements

Solutions are presented for the material thermal response for heat shields of blunt probes entering Saturn and Uranus. Both monolithic and sandwich concepts were considered having exposed charring ablative or reflective materials. The solutions show that (1) Teflon heat shields are sized by mass loss considerations, other materials (unless entering the Uranus cold-dense atmosphere) by heat soak considerations, (2) steeper entries require less heat shield mass, (3) sizing requirements vary little about the bodies for heat soak dominated materials, and (4) carbon-phenolic appears superior overall, but silica is superior for the steeper entries and the high helium content atmospheres.

Nicolet, W. E.↗

X-ray tomography system to investigate granular materials during mechanical loading

We integrate a small and portable medical x-ray device with mechanical testing equipment to enable in situ, non-invasive measurements of a granular material's response to mechanical loading. We employ an orthopedic C-arm as the x-ray source and detector to image samples mounted in the materials tester. We discuss the design of a custom rotation stage, which allows for sample rotation and tomographic reconstruction under applied compressive stress. We then discuss the calibration of the system for 3D computed tomography, as well as the subsequent image reconstruction process. Using this system to reconstruct packings of 3D-printed particles, we resolve packing features with 0.52 mm resolution in a (60 mm){sup 3} field of view. By analyzing the performance bounds of the system, we demonstrate that the reconstructions exhibit only moderate noise.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

PMT F7 Silver Standard Material Properties Characterization

PMT F7 epoxy resin was characterized to capture the material's thermochemical and thermo-mechanical properties. DSC testing was performed and the data was used to develop a cure kinetics model which predicts the material cure response and specific heat capacity. TMA and DMA testing were performed and the data was used to develop thermo-mechanical models which predict the material CTE, cure shrinkage, and modulus evolution with cure. Convergent Manufacturing Technologies US determined test parameters, analyzed data, and performed model fitting. NASA completed tests and provided data to Convergent Manufacturing Technologies US.

Epoxy↗

Exploration of Two-Dimensional Materials for Remote Sensing Applications

Two-dimensional materials were explored through collaboration with Steve Howell and Catalyn Spataru, led by James Bartz during FY15 and FY16 at Sandia National Laboratories. Because of their two-dimensional nature, these materials may offer properties exceeding those of bulk materials. This work involved Density Functional Theory simulations and optical methods, instrumentation development, materials growth and materials characterization. Through simulation the wide variety of two dimensional materials was down-selected for fabrication and testing. Out of the two dimensional semiconductors studied, black phosphorus bilayers showed the strongest spectral absorption tuning with applied electric field. Laser scanning confocal microscopy, spectroscopy and atomic force microscopy allowed for identification of micron scale samples. A technique involving conductive tip atomic force microscopy and back-side illumination was developed simple assembly and characterization of material spectral response.

36 MATERIALS SCIENCE↗

The Role of Unit-Cell Topology in Modulating the Compaction Response of Additively Manufactured Cellular Materials using Simulations and Validation Experiments

Additive manufacturing has enabled a transformational ability to create cellular structures (or foams) with tailored topology. Compared to their monolithic polymer counterparts, cellular structures are potentially suitable for systems requiring materials with high specific energy-absorbing capability to provide enhanced damping. In this work, we demonstrate the utility of controlling unit-cell topology with the intent of obtaining a desired stress–strain response and energy density. Using mesoscale simulations that resolve the unit-cell sub-structures, we validate the role of unit-cell topology in selectively activating a buckling mode and thereby modulating the characteristic stress–strain response. Simulations incorporate a linear viscoelastic constitutive model and a hyperelastic model for simulating large deformation of the polymer under both tension and compression. Simulated results for nine different cellular structures are compared with experimental data to gain insights into three different modes of buckling and the corresponding stress–strain response.

36 MATERIALS SCIENCE↗