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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Mechanical Behavior of Additively Manufactured Molybdenum and Fabrication of Microtextured Composites

Refractory metals are a class of high-melting-temperature materials suitable for use in extreme environment applications. Interestingly, during additive manufacturing many pure refractory metals exhibit a switch from (001) to (111) build direction fiber preference with increasing surface energy density. Here we exploit this solidification physics to fabricate material with “mesoscale composite” engineered structures consisting of features with contrasting (001) and (111) build direction microtextures. Separately, elevated temperature tensile testing of EBM fabricated material with a randomized distribution of mixed (001)/(111)-fiber grains is shown to exhibit excellent properties. These results are utilized to build a crystal plasticity model for evaluating the local inelastic response of the composite mesoscale structures. Analysis of printed microstructures and microstructure-scale simulations indicate that both macro-scale and localized material behavior may be tailored. This strategy can be potentially used to synthesize materials with optimized performance for high-temperature applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Compatibilization Strategy and Mechanism for Co-stabilizing Commingled Plastics and Pyrolyzed Rubber in Asphalt

Hot mix asphalt mixture is considered the ideal approach to reuse waste plastics in high-value applications because of its very high amount of usage in highway construction. However, the differences in polarity and density between polymers and asphalt lead to polymer coalescence and therefore the poor storage stability of modified asphalt. These challenges are exalted when recycling commingled plastics. This study introduced an innovative compatibilization strategy and mechanism for co-stabilizing commingled plastics and pyrolyzed rubber in asphalt. Commingled plastics were first grafted with maleic anhydride for surface activation, followed by reactive kneading with pyrolyzed rubber and crosslinking agent to form an integrated thermoplastic elastomer (ITPE) for asphalt modification. The mechanical, thermal, and interfacial behaviors of the ITPE were evaluated through tensile testing, thermogravimetric analysis, and scanning electron microscopy. The storage stability and rheological properties of the modified binder blends were evaluated through the cigar tube test and dynamic shear rheometer testing. Results demonstrated a successful formation of imide bonds in the ITPE, which can improve the strength, ductility, and thermal stability of rubber–plastic composites. Appropriate utilization of crosslinking agents can improve both rutting and fatigue resistance of ITPE-modified asphalt with good storage stability because of the co-existence of rigid plastic and soft rubbery regimes and the formation of a crosslink network. Furthermore, excessive content of crosslinker led to severe phase separation and reduced storage stability of modified binder blends. Extra crosslinker tended to float in asphalt because of its low density and caused an excessive formation of the crosslink network in the top section of the asphalt.

asphalt binder modifiers↗
NASA NTRSDate not supplied

Method Development for Experimental Characterization of Dynamic Strength of Aluminum Structures

Space Flight Hardware (SFH) experiences intense vibratory loading during flight, which only lasts a few minutes. When determining the appropriate size of these components to withstand such loading without becoming damaged (plastically deforming or breaking), standard design practice is to assume that the peak dynamic loads are applied statically. In doing so, the resulting stress is compared against a material strength parameter obtained from a quasi-static experiment. Since the near-peak stresses are only experienced over a small fraction of time in reality, this approach leads to design conservatism that unnecessarily increases structural mass as well as the associated inefficiency and financial cost. In an effort to modernize engineering design standards to appropriately consider the higher practical strength of dynamically loaded structures, this overarching research project seeks to develop an experimental test procedure for quantifying the dynamic strength of metallic alloys as a function of excitation frequency. In the ideal case, the characterization test would include an in-situ method for monitoring the onset and progression of plastic deformation of the test specimen undergoing vibratory loading. These new tests are designed to be high intensity (forcing amplitude), short term (60 seconds at full amplitude), and cyclic in nature (sinusoidal excitation via attached stinger to an otherwise cantilevered beam). In addition, the initial metallic alloy under investigation is 6061 aluminum, due to its wide use and applicability for SFH. Thus far, the most promising monitoring method under development with live-capacity is to track hysteresis behavior of the beam from power dissipation trends, calculated via force (from transducer on excitation stinger) and velocity (measurements from Laser Doppler Vibrometer) data and work to distinguish between elastic and plastic features. As a key component of this ongoing method development, any pseudo-live indication of plasticity can be corroborated against the outcome of a pre-post assessment of damage via macroscopic evaluation of beam geometry (i.e. assessing any permanent change in the beam’s tip deflection). Support for experimental design decisions as well as dynamic strength data from tests with excitation frequencies of 10, 40, and 55 Hz will be discussed. This work contributes to the foundation for a new type of vibration-based characterization experiments and generates initial data on the functional strength of 6061 aluminum under the conditions considered. Keywords: vibrations, plastic deformation, aluminum

vibrations↗
DOE OSTI2025

Development of a thermal creep model for aluminum alloy 6061 cladding in U-10Mo monolithic fuel plates

Plate-type fuel elements consisting of a high-density, low-enriched uranium (LEU) U–10Mo-based fuel foil encapsulated in an aluminum alloy (AA) cladding are fabricated using the hot isostatic pressing (HIP) technique. During the HIP process, the fuel plate system is heated to 560 °C, then cooled to room temperature. This heat cycle significantly affects the mechanical properties of the aluminum cladding, and experimental investigations have shown that, post-HIP bonding, the mechanical properties of the aluminum cladding transition from those of AA 6061-T6 to something closer to the O temper. More specifically, the ultimate strength of the cladding decreases while its ductility increases, making it challenging to capture the changes in mechanical behavior and material properties. Understanding the residual stresses generated during the HIP process is critical for assessing the fuel plate’s integrity under various temperature, pressure, and irradiation. To simulate the HIP bonding process, the elastic, plastic, and thermal properties of the cladding are assumed to be similar to those of AA 6061-O temper. However, the primary challenge lies in the lack of available data for the creep model of the AA 6061 cladding during this transient process of HIP. The present study focuses on developing a computational model that predicts the creep behavior of the aluminum cladding in the fuel plates during the HIP process, as cladding creep significantly influences the residual stresses generated in U-10Mo fuel plates during HIP fabrication. Furthermore, as HIP bonding occurs at high temperatures that are nearing the melting point of aluminum, the present work considered a temperature-dependent Arrhenius-type creep model. In particular, a hyperbolic sine creep model is employed to estimate the creep properties of the as-fabricated aluminum cladding. In conclusion, the residual stresses predicted in the U-10Mo fuel when using the newly calibrated creep model closely align with the experimental measurements, validating the model’s accuracy.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2022

Understanding the Elastic, Plastic, and Damage Features in Fracturing of Self-reinforced Thermoplastic Composites via Non-destructive Digital Imaging Correlation

This work demonstrated the utilization of non-destructive Digital Imaging Correlation (DIC) method to characterize the elastic, plastic, and damage features during the Mode I intra-laminar fracturing process of self-reinforced thermoplastic composites by using a self-reinforced polypropylene (PP) composite as an example. The DIC results clearly showed the development of huge plastic zone (PZ) and non-negligible Fracture Process Zone (FPZ) in front of the notch tip during the fracturing process, and the geometries and sizes of the foregoing zones at the peak load were further quantified. Such an interesting fracturing behavior of self-reinforced thermoplastic composites is way different from brittle materials (e.g., glass, acrylic, etc.), ductile materials (e.g., aluminum, steel, etc.), and even quasi-brittle materials (e.g., concrete, nanoparticle-reinforced composites, tough ceramics, wood, cement, carbon/glass fiber-reinforced polymers, etc.). Thus, understanding the elastic, plastic, and damage features is the first step before better characterizing the material fracture properties of self-reinforced thermoplastic composites through new analytical methods and computational modeling. These efforts are of utmost importance for wide applications of self-reinforced thermoplastic composites in various engineering fields in the future.

Lightweight Composites, Self-reinforced Thermoplas↗
NASA NTRS1992

Unified Viscoplastic Behavior of Metal Matrix Composites

The need for unified constitutive models was recognized more than a decade ago in the results of phenomenological tests on monolithic metals that exhibited strong creep-plasticity interaction. Recently, metallic alloys have been combined to form high-temperature ductile/ductile composite materials, raising the natural question of whether these metallic composites exhibit the same phenomenological features as their monolithic constituents. This question is addressed in the context of a limited, yet definite (to illustrate creep/plasticity interaction) set of experimental data on the model metal matrix composite (MMC) system W/Kanthal. Furthermore, it is demonstrated that a unified viscoplastic representation, extended for unidirectional composites and correlated to W/Kanthal, can accurately predict the observed longitudinal composite creep/plasticity interaction response and strain rate dependency. Finally, the predicted influence of fiber orientation on the creep response of W/Kanthal is illustrated.

Arnold, S. M.↗
NASA NTRS1991

Flow and fracture behavior of NiAl in relation to the brittle-to-ductile transition temperature

NiAl has only three independent slip systems operating at low and intermediate temperatures whereas five independent deformation mechanisms are required to satisfy the von Mises criterion for general plasticity in polycrystalline materials. Yet, it is generally recognized that polycrystalline NiAl can be deformed extensively in compression at room temperature and that limited tensile ductility can be obtained in extruded materials. In order to determine whether these results are in conflict with the von Mises criterion, tension and compression tests were conducted on powder-extruded, binary NiAl between 300 and 1300 K. The results indicate that below the brittle-to-ductile transition temperature (BDTT) the failure mechanism in NiAl involves the initiation and propagation of cracks at the grain boundaries which is consistent with the von Mises analysis. Furthermore, evaluation of the flow behavior of NiAl indicates that the transition from brittle to ductile behavior with increasing temperature coincides with the onset of recovery mechanisms such as dislocation climb. The increase in ductility above the BDTT is therefore attributed to the climb of the 001 line type dislocations which in combination with dislocation glide enable grain boundary compatibility to be maintained at the higher temperatures.

Noebe, R. D.↗
DOE OSTI2025

Understanding the limitations and potential of micro tensile testing of tungsten and needs for crystal plasticity modelling

Tungsten is the leading plasma facing material candidate due to its exceptional properties. Understanding the response to neutron irradiation is crucial for the lifetime evaluation of tungsten. The limited space in nuclear reactors and the high levels of radioactivity of the specimens after irradiation are significant barriers to accurately measuring the mechanical properties after neutron irradiation. Testing of micro tensile specimens is one approach to reduce the total amount of irradiated material needed for a set of mechanical testing experiments. However, micro samples are not necessarily measuring the bulk material properties, as size effects produce higher measured mechanical properties than is observed in engineering size counterparts. Determining the minimal sample size for reliable bulk property measurement, combined with modeling efforts, is essential. We conducted room temperature tensile tests on tungsten micro tensile specimens fabricated with focused ion beam, plasma focused ion beam and femto-second laser ablation system to dimension of 2×2×7?µm³, 7×7×18?µm³, and 80×100×233?µm³ (width×thickness×gauge-length), respectively. Elevated tensile testing was performed up to 475°C on 5×5×18?µm³ specimens fabricated with focused ion beam. The smallest specimens exhibited a high degree of ductility and strength, whereas the largest specimens demonstrated behavior akin to bulk tungsten. To investigate the effects introduced by the micro specimen fabrication processes and to obtain the necessary bulk dislocation density for the crystal plasticity model, we employed X-ray diffraction depth profiling. This measurement was performed using different X-ray sources with varying penetration depths. Finally, the potential and limitations of micro mechanical tests for tungsten will be discussed.

36 - MATERIALS SCIENCE↗
DOE OSTI2023

A Review of the Mechanical Properties of Materials Used in Nb 3 Sn Magnets for Particle Accelerators

Superconducting magnets experience significant thermo-mechanical loads throughout their life cycle. These are introduced by the electro-magnetic forces during powering, but also by the prestress applied in many magnet designs. Further to this, the large thermal excursion that components of different materials experience can generate significant internal forces. The loads are also experienced by the superconducting coils, whose critical current can decrease as a consequence of the applied strain. It is then crucial to predict the overall mechanical behavior and conservatively design a magnet, avoiding failure of the mechanical components and of the superconducting coils. Finite Element Analysis (FEA) is generally used to perform these tasks, but its results rely heavily on the material properties and models used. This is in particular true for the coil composite, which is simplified to allow reasonable model sizes in full magnet models. Here we present the state-of-art knowledge of the mechanical properties of the materials mostly used in superconducting magnet construction. We review elastic and plastic properties at room and cryogenic temperature, thermal contraction, and summarize the state-of-art failure criteria for these materials. Finally, the paper summarizes the present understanding of the mechanical behavior and limits of Nb3Sn coils. For the first time, an orthotropic failure criteria is proposed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Solutionization via Severe Plastic Deformation: Effect on Natural Aging in an Al-Mg-Si-(Mn) Alloy

Shear Assisted Processing and Extrusion (ShAPE), a severe plastic deformation technique that is fast and scalable, was used to produce thin-wall tubing from alloy 6082 (Al-0.8Mg-0.9Si-0.7Mn) with in-situ solutionization during processing quickly followed by quenching. Quench medium and input material heat treatment were varied and natural aging behavior (T1 heat treatment) was evaluated using tensile testing. As-cast input material was found to have higher strength early in post-ShAPE natural aging and homogenized input material was found to have strengthening during natural aging. Compared to air quenching, water quenching gave greater strength both early in and after natural aging. These observations along with microscopy suggest that: 1. air quenching was too slow; 2. as-cast material was not fully solutionized but plastic deformation broke up the coarse intermetallic particles, which provided strengthening; and 3. homogenized material was solutionized well, which led to good natural aging behavior.

Milligan, Brian K.↗
DOE OSTI2022

Characterization of the structure and chemistry of the solid–electrolyte interface by cryo-EM leads to high-performance solid-state Li-metal batteries

Solid-state lithium-metal (Li 0 ) batteries are gaining traction for electric vehicle applications because they replace flammable liquid electrolytes with a safer, solid-form electrolyte that also offers higher energy density and better resistance against Li dendrite formation. Solid polymer electrolytes (SPEs) are highly promising candidates because of their tunable mechanical properties and easy manufacturability; however, their electrochemical instability against lithium metal (Li 0 ), mediocre conductivity, and poorly understood Li 0 /SPE interphases have prevented extensive application in real batteries. In particular, the origin of the low Coulombic efficiency (CE) associated with SPEs remains elusive, as the debate continues as to whether it originates from unfavored interfacial reactions or lithium dendritic growth and dead lithium formation. In this work, we use state-of-the-art cryo-electromicroscopy (cryoEM) imaging and spectroscopic techniques to characterize the structure and chemistry of the interface between Li 0 and a polyacrylate-based SPE. Contradicting the conventional knowledge, we find that no protective interphase forms, owing to the sustained reactions between deposited Li dendrites and polyacrylic backbones and succinonitrile plasticizer. Due to the reaction induced volume change, large amounts of cracks form inside the Li dendrites with a stress corrosion-cracking behavior, indicating that Li0cannot be passivated in this SPE system. Based on this observation, we then introduce additive engineering leveraging on the knowledge of liquid electrolytes, and demonstrate that the Li 0 surface can be effectively protected against corrosion using fluoroethylene carbonate (FEC), leading to densely packed Li 0 domes with conformal and stable solid-electrolyte interphases (SEIs) films. Owing to the high room temperature ionic conductivity of 1.01 mS/cm -1 , the high transference number of 0.57 and the stabilized lithium electrolyte interface, this improved new SPE delivers an excellent lithium plating/stripping CE of 99% and 1800 hours of stable cycling in Li||Li symmetric cells (0.2 mA/cm -2 , 1mAh/cm -2 ). Furthermore, this improved cathodic stability along with the high anodic stability enables record high cycle life of >2000 cycles for Li||LiFePO 4 and >400 cycles for Li||LiCoO 2 full cells.

25 ENERGY STORAGE↗
NASA NTRS1991

Probabilistic analysis of structures involving random stress-strain behavior

The present methodology for analysis of structures with random stress strain behavior characterizes the uniaxial stress-strain curve in terms of (1) elastic modulus, (2) engineering stress at initial yield, (3) initial plastic-hardening slope, (4) engineering stress at point of ultimate load, and (5) engineering strain at point of ultimate load. The methodology is incorporated into the Numerical Evaluation of Stochastic Structures Under Stress code for probabilistic structural analysis. The illustrative problem of a thick cylinder under internal pressure, where both the internal pressure and the stress-strain curve are random, is addressed by means of the code. The response value is the cumulative distribution function of the equivalent plastic strain at the inner radius.

Millwater, H. R.↗
NASA NTRS1993

Use of photostress and strain gages to analyze behavior of weldments

Tensile and pure bending tests were conducted on specimens having welded joints made from 2219-T87 aluminum alloy and 2319 filler. Data were collected using photoelastic coatings and strain gages. Stress-strain relationships and contraction ratios were determined at several points in a grid covering the weld material and heat affected zone. Material behavior was nonlinear and nonuniform at all points in the grid and contraction ratios did not conform to those predicted by Chakrabarty's plasticity theory. Yielding in joints made using four new welding procedures was examined. None of the new procedures produced more uniform yielding in the joint.

Gambrell, S. C., Jr.↗
NASA NTRS2000

Creep and Toughness of Cryomilled NiAl Containing Cr

NiAl-AlN + Cr composites were produced by blending cryomilled NiAl powder with approx. 10 vol % Cr flakes. In comparison to the as-consolidated matrices, hot isostatically pressed Cr-modified materials did not demonstrate any significant improvement in toughness. Hot extruded NiAl-AlN+10.5Cr, however, possessed a toughness twice that determine for the base NiAl-AlN alloy. Measurement of the 1200 to 1400 K plastic flow properties revealed that the strength of the composites was completely controlled by the properties of the NiAl-AlN matrices. This behavior could be successfully modeled by the Rule-of-Mixtures, where load is shed from the weak Cr to the strong matrix.

Whittenberger, J. Daniel↗
NASA NTRS1996

The cerebellum: a neuronal learning machine?

Comparison of two seemingly quite different behaviors yields a surprisingly consistent picture of the role of the cerebellum in motor learning. Behavioral and physiological data about classical conditioning of the eyelid response and motor learning in the vestibulo-ocular reflex suggests that (i) plasticity is distributed between the cerebellar cortex and the deep cerebellar nuclei; (ii) the cerebellar cortex plays a special role in learning the timing of movement; and (iii) the cerebellar cortex guides learning in the deep nuclei, which may allow learning to be transferred from the cortex to the deep nuclei. Because many of the similarities in the data from the two systems typify general features of cerebellar organization, the cerebellar mechanisms of learning in these two systems may represent principles that apply to many motor systems.

Non-NASA Center↗
NASA NTRS2009

Modeling Bird Migration under Climate Change: A Mechanistic Approach

How will migrating birds respond to changes in the environment under climate change? What are the implications for migratory success under the various accelerated climate change scenarios as forecast by the Intergovernmental Panel on Climate Change? How will reductions or increased variability in the number or quality of wetland stop-over sites affect migratory bird species? The answers to these questions have important ramifications for conservation biology and wildlife management. Here, we describe the use of continental scale simulation modeling to explore how spatio-temporal changes along migratory flyways affect en-route migration success. We use an individually based, biophysical, mechanistic, bird migration model to simulate the movement of shorebirds in North America as a tool to study how such factors as drought and wetland loss may impact migratory success and modify migration patterns. Our model is driven by remote sensing and climate data and incorporates important landscape variables. The energy budget components of the model include resting, foraging, and flight, but presently predation is ignored. Results/Conclusions We illustrate our model by studying the spring migration of sandpipers through the Great Plains to their Arctic breeding grounds. Why many species of shorebirds have shown significant declines remains a puzzle. Shorebirds are sensitive to stop-over quality and spacing because of their need for frequent refueling stops and their opportunistic feeding patterns. We predict bird "hydrographs that is, stop-over frequency with latitude, that are in agreement with the literature. Mean stop-over durations predicted from our model for nominal cases also are consistent with the limited, but available data. For the shorebird species simulated, our model predicts that shorebirds exhibit significant plasticity and are able to shift their migration patterns in response to changing drought conditions. However, the question remains as to whether this behavior can be maintained over increasing and sustained environmental change. Also, the problem is much more complex than described by the current processes captured in our model. We have taken some important and interesting steps, and our model does demonstrate how local scale information about individual stop-over sites can be linked into the migratory flyway as a whole. We are incorporating additional, species specific, mechanistic processes to better reflect different climate change scenarios

Smith, James A.↗
DOE OSTI2024

Evaluating Pressure‐dependent Discharge Behavior of Foil Versus In situ Plated Lithium Metal Anodes in Solid‐State Batteries

Abstract Anode‐free manufacturing of solid‐state batteries (SSBs) shows promise to maximize energy density by eliminating excess lithium (Li) and simplifying battery production. However, high reversibility during discharge (stripping of Li) is necessary for long‐lifetime SSBs with a limited Li reservoir. Further, the plastic flow of Li changes depending on the Li thickness, leading to possible differences in discharge performance under stack pressure. This work investigates the pressure‐dependent discharge performance of anode‐free manufactured SSBs with in situ plated Li and compares the performance to that of conventional thick Li foil cells. Distinct stripping behavior is observed at low pressures (0–1 MPa), where Li diffusivity and initial interfacial contact may control accessible capacity, compared to high pressures (3–10 MPa) where mechanical deformation of Li likely governs stripping behavior. Analysis of impedance spectra collected during stripping shows that additional stack pressure delays the formation of deep, as opposed to lateral, voids in the Li anode. These results provide insights to guide the transition from thick Li foil anodes to anode‐free manufactured SSBs.

Haslam, Catherine G.↗
DOE OSTI2026

Selective depolymerization of polyolefin copolymer via high-entropy alloy catalyzed pyrolysis in a double-layered ultrafast heating reactor

Chemical recycling of polyolefin copolymers (PCPs) is essential for mitigating plastic pollution, yet achieving selective depolymerization into C 2 –C 3 monomers at high productivity remains challenging. Here, we introduce a double-layered ultrafast heating reactor (DUHR) that integrates Joule heating with a high-entropy alloy (HEA) catalyst composed of near-equimolar Co, Cu, Fe, Mn, and Ni. We achieve highly selective depolymerization of PCP into ethylene and propylene, yielding a 70% non-condensable fraction. Significant aromatic fractions form via radical-driven pathways—a behavior distinct from conventional externally heated pyrolyzers—highlighting DUHR's ability to generate reactive species and modulate reaction pathways. Furthermore, these findings demonstrate an effective strategy for chemical recycling of real-world plastic waste for polyolefin circularity and sustainable resource recovery.

Chemical recycling↗