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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Grain-Size-Independent Plastic Flow at Ultrahigh Pressures and Strain Rates

A basic tenet of material science is that the flow stress of a metal increases as its grain size decreases, an effect described by the Hall-Petch relation. This relation is used extensively in material design to optimize the hardness, durability, survivability, and ductility of structural metals. This work reports experimental results in a new regime of high pressures and strain rates that challenge this basic tenet of mechanical metallurgy. We report measurements of the plastic flow of the model body-centered-cubic metal tantalum made under conditions of high pressure (> 100 GPa) and strain rate (~10 7 s –1 ) achieved by using the Omega laser. Under these unique plastic deformation (“flow”) conditions, the effect of grain size is found to be negligible for grain sizes > 0.25 μm sizes. A multiscale model of the plastic flow suggests that pressure and strain rate hardening dominate over the grain-size effects. Theoretical estimates, based on grain compatibility and geometrically necessary dislocations, corroborate this conclusion.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Size-Tuned Plastic Flow Localization in Irradiated Materials at the Submicron Scale

Three-dimensional discrete dislocation dynamics (3D-DDD) simulations reveal that, with reduction of sample size in the submicron regime, the mechanism of plastic flow localization in irradiated materials transitions from irradiation-controlled to an intrinsic dislocation source controlled. Furthermore, the spatial correlation of plastic deformation decreases due to weaker dislocation interactions and less frequent cross slip as the system size decreases, thus manifesting itself in thinner dislocation channels. A simple model of discrete dislocation source activation coupled with cross slip channel widening is developed to reproduce and physically explain this transition. In order to quantify the phenomenon of plastic flow localization, we introduce a “deformation localization index,” with implications to the design of radiation-resistant materials.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

SU-C-213-05: Evaluation of a Composite Copper-Plastic Material for a 3D Printed Radiation Therapy Bolus

Purpose: To evaluate a novel 3D printed bolus fabricated from a copper-plastic composite as a thin flexible, custom fitting device that can replicate doses achieved with conventional bolus techniques. Methods: Two models of bolus were created on a 3D printer using a composite copper-PLA/PHA. Firstly, boluses were constructed at thicknesses of 0.4, 0.6 and 0.8 mm. Relative dose measurements were performed under the bolus with an Attix Chamber as well as with radiochromic film. Results were compared to superficial Attix Chamber measurements in a water equivalent material to determine the dosimetric water equivalence of the copper-PLA/PHA plastic. Secondly, CT images of a RANDO phantom were used to create a custom fitting bolus across the anterolateral scalp. Surface dose with the bolus placed on the RANDO phantom was measured with radiochromic film at tangential angles with 6, 10, 10 flattening filter free (FFF) and 18 MV photon beams. Results: Mean surface doses for 6, 10, 10FFF and 18 MV were measured as a percent of Dmax for the flat bolus devices of each thickness. The 0.4 mm thickness bolus was determined to be near equivalent to 2.5 mm depth in water for all four energies. Surface doses ranged from 59–63% without bolus and 85–90% with the custom 0.4 mm copper-plastic bolus relative to the prescribed dose for an oblique tangential beam arrangement on the RANDO phantom. Conclusion: Sub-millimeter thickness, 3D printed composite copper-PLA/PHA bolus can provide a build-up effect equivalent to conventional bolus. At this thickness, the 3D printed bolus allows a level of flexure that may provide more patient comfort than current 3D printing materials used in bolus fabrication while still retaining the CT based custom patient shape. Funding provided by an intra-department grant of the University of Minnesota Department of Radiation Oncology.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Nanoscale stacking fault–assisted room temperature plasticity in flash-sintered TiO 2

Ceramic materials have been widely used for structural applications. However, most ceramics have rather limited plasticity at low temperatures and fracture well before the onset of plastic yielding. The brittle nature of ceramics arises from the lack of dislocation activity and the need for high stress to nucleate dislocations. Here, we have investigated the deformability of TiO 2 prepared by a flash-sintering technique. Our in situ studies show that the flash-sintered TiO 2 can be compressed to ~10% strain under room temperature without noticeable crack formation. The room temperature plasticity in flash-sintered TiO 2 is attributed to the formation of nanoscale stacking faults and nanotwins, which may be assisted by the high-density preexisting defects and oxygen vacancies introduced by the flash-sintering process. Distinct deformation behaviors have been observed in flash-sintered TiO 2 deformed at different testing temperatures, ranging from room temperature to 600°C. Potential mechanisms that may render ductile ceramic materials are discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Gradient nanostructured steel with superior tensile plasticity

Nanostructured metallic materials with abundant high-angle grain boundaries exhibit high strength and good radiation resistance. While the nanoscale grains induce high strength, they also degrade tensile ductility. We show that a gradient nanostructured ferritic steel exhibits simultaneous improvement in yield strength by 36% and uniform elongation by 50% compared to the homogenously structured counterpart. In situ tension studies coupled with electron backscattered diffraction analyses reveal intricate coordinated deformation mechanisms in the gradient structures. The outermost nanolaminate grains sustain a substantial plastic strain via a profound deformation mechanism involving prominent grain reorientation. This synergistic plastic co-deformation process alters the rupture mode in the post-necking regime, thus delaying the onset of fracture. The present discovery highlights the intrinsic plasticity of nanolaminate grains and their significance in simultaneous improvement of strength and tensile ductility of structural metallic materials.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Mechanochemically accelerated deconstruction of chemically recyclable plastics

Plastics redesign for circularity has primarily focused on monomer chemistries enabling faster deconstruction rates concomitant with high monomer yields. Yet, during deconstruction, polymer chains interact with their reaction medium, which remains underexplored in polymer reactivity. Here, we show that, when plastics are deconstructed in reaction media that promote swelling, initial rates are accelerated by over sixfold beyond those in small-molecule analogs. This unexpected acceleration is primarily tied to mechanochemical activation of strained polymer chains; however, changes in the activity of water under polymer confinement and bond activation in solvent-separated ion pairs are also important. Together, deconstruction times can be shortened by seven times by codesigning plastics and their deconstruction processes.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of Plasticizer Content and Ceramic Addition on Electrochemical Properties of Cross-Linked Polymer Electrolyte

The development of a safe electrolyte is the key to improving energy density for next generation lithium batteries. In this work, UV-crosslinked poly(ethylene oxide) (PEO) -based polymer and composite electrolytes are systematically investigated on their ionic conductivity, mechanical and electrochemical properties. The polymer electrolytes are plasticized with non-flammable linear short-chain PEO. In the composite electrolytes, a doped lithium aluminum titanium phosphate (LATP) ceramic, LICGC™, is used as the ceramic filler. It is found that the addition of the plasticizer leads to a tradeoff between ion transport and mechanical properties. In contrast, the addition of ceramic fillers improves both the ionic conductivity and mechanical properties. The sample with 20 wt% of LICGC™ shows a conductivity of ~0.6 mS cm –1 at 50 °C. This sample also demonstrates much longer cycle life than the neat polymer electrolyte in Li platting/stripping test with a capacity of 1 mAh cm –2 . Further, a full cell made with this composite electrolyte against Li metal anode and high voltage LiNi 0.6 Mn 0.2 Co 0.2 O 2 cathode shows 94% capacity retention after 30 cycles, compared to 58% capacity retention with the neat polymer electrolyte. These results demonstrate that a hybrid of polymer/ceramic/non-flammable plasticizer is a promising path to high energy density, high voltage lithium batteries.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Compressive strength of the plastic-bonded explosive surrogate idoxuridine under quasistatic and dynamic compression

Inert simulant materials, or “mocks”, are often used as surrogates for plastic-bonded explosives (PBX) in non-detonative tests in order to mitigate hazards. Mocks should reproduce as many non-detonative properties of the explosive as possible, including structural behavior in a variety of thermal and mechanical environments. Recently, the molecular crystal idoxuridine (IDOX) has been identified as an ideal mock for the main component in the explosive polymer-matrix composite PBX 9501, and has performed favorably under quasistatic loading conditions. Here, in order to assess robustness over a range of mechanical environments, plastic-bonded IDOX was compression tested from 0.001/s to 2000/s strain rates and compared to PBX 9501 historical data. Plastic-bonded IDOX showed good agreement to PBX 9501 across these strain rates, justifying continued development and production as a mock.

Burch, Alexandra C.↗
DOE OSTI2020

Understanding plasticity in irradiated alloys through TEM in situ compression pillar tests

Depth-sensing transmission electron microscopic (TEM) in situ mechanical testing has become widely utilized for understanding deformation in irradiated materials. Until now, compression pillars have primarily been used to study the elastic properties and yield of irradiated materials. In this study, we utilize TEM in situ compression pillars to investigate plastic deformation in two ion-irradiated alloys: Fe–9% Cr oxide dispersion strengthened (ODS) alloy and nanocrystalline Cu–24% Ta. We develop an algorithm to automate the extraction of instantaneous pillar dimensions from TEM videos, which we use to calculate true stress–strain curves and strain hardening exponents. True stress–strain curves reveal intermitted plastic flow in all specimen conditions. In the Fe–9% Cr ODS, intermitted plastic flow is linked to strain bursts observed in TEM videos. Low strain hardening or strain softening is observed in all specimen conditions. TEM videos link the strain softening in irradiated Fe–9% Cr ODS to dislocation cross-slip, and in Cu–24% Ta to grain boundary sliding.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Heterosynaptic plasticity in memristive and memcapacitive lipid bilayers: A snapshot review

Synaptic plasticity refers to activity-dependent synaptic strengthening or weakening between neurons. It is usually associated with homosynaptic plasticity, which refers to a synaptic junction controlled by interactions between specific neurons. Heterosynaptic plasticity, on the other hand, lacks this specificity. It involves much larger populations of synapses and neurons and can be associated with changes in synaptic strength due to nonlocal alterations in the ambient electrochemical environment. Here, this paper presents specific examples demonstrating how variations in the ambient electrochemical environment of lipid membranes can impact the nonlinear dynamical behaviors of memristive and memcapacitive systems in droplet interface bilayers (DIBs). Examples include the use of pH as a modulatory factor that alters the voltage-dependent memristive behavior of alamethicin ion channels in DIB lipid bilayers, and the discovery of long-term potentiation (LTP) in a lipid bilayer-only system after application of electrical stimulation protocols.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Plastic Strain Recovery in Nanocrystalline Materials

Understanding the mechanisms of deformation of nanocrystalline (nc) materials is critical to the design of micro and nano devices and to develop materials with superior fracture strength and wear resistance for applications in new energy technologies. In this project we focused on understanding the following plastic deformation processes described in detail in the following sections: 1. Plastic strain recovery, 2. Effect of microstructural variability on the yield stress of nc metals, and 3. The role of partial and extended full dislocations in plastic deformation of nc metals.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Active Well Counting Using New PSD Plastic Detectors

This report presents results and analysis from a series of proof-of-concept measurements to assess the suitability of segmented detectors constructed from Eljen EJ-299-34 PSD-plastic scintillator with pulse-shape discrimination capability for the purposes of quantifying uranium via active neutron coincidence counting. Present quantification of bulk uranium materials for international safeguards and domestic materials control and accounting relies on active neutron coincidence counting systems, such as the Active Well Coincidence Counter (AWCC) and the Uranium Neutron Coincidence Collar (UNCL), that use moderated He-3 proportional counters along with necessarily low-intensity 241Am(Li) neutron sources. Scintillation-based fast-neutron detectors are a potentially superior technology to the existing AWCC and UNCL designs due to their spectroscopic capability and their inherently short neutron coincidence times that largely eliminate random coincidences and enable interrogation by stronger sources. One of the past impediments to the investigation and adoption of scintillation counters for the purpose of quantifying bulk uranium was the commercial availability of scintillators having the necessary neutron-gamma pulse-shape discrimination properties only as flammable liquids. Recently, Eljen EJ-299-34 PSD-plastic scintillator became commercially available. The present work is the first assessment of an array of PSD-plastic detectors for the purposes of quantifying bulk uranium. The detector panel used in the present work was originally built as the focal plane for a fast-neutron imager, but it was repurposed for the present investigation by construction of a stand to support the inner well of an AWCC immediately in front of the detector panel. The detector panel and data acquisition of this system are particularly well suited for performing active-well fast-neutron counting of LEU and HEU samples because the active detector volume is solid, the 241Am(Li) interrogating neutrons are largely below the detector threshold, and the segmented construction of the detector modules allow for separation of true neutron-neutron coincidences from inter-detector scattering using the kinematics of neutron scattering. The results from a series of measurements of a suite of uranium standards are presented, and compared to measurements of the same standards and source configurations using the AWCC. Using these results, the performance of the segmented detectors reconfigured as a well counter is predicted and outperforms the AWCC.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Demonstration of finite element simulations in MOOSE using crystallographic models of irradiation hardening and plastic deformation

This report describes the implementation of a crystal plasticity framework (VPSC) for irradiation hardening and plastic deformation in the finite element code, MOOSE. Constitutive models for irradiation hardening and the crystal plasticity framework are described in a previous report [1]. Here we describe these models briefly and then describe an algorithm for interfacing VPSC with finite elements. Example applications of tensile deformation of a dog bone specimen and a 3D pre-irradiated bar specimen performed using MOOSE are demonstrated.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2018

Dynamic elastic-plastic response of a 2-DOF mass-spring system.

The objective of the work presented here arose from abnormal, drop scenarios and specifically the question of how the accelerations and accumulation of plastic strains of internal components could be a ected by the material properties of the external structure. In some scenarios, the impact loads can induce cyclic motion of the internal components. Therefore, a second objective was to explore di erences that could be expected when simulations are conducted using isotropic hardening vs. kinematic hardening plasticity models. The simplest model that can be used to investigate the objectives above is a two-degree-offreedom mass/spring model where the springs exhibit elastic-plastic behavior. The purpose of this memo is to develop such model and present a few results that address the objectives.

42 ENGINEERING↗
DOE OSTI2018

Measurement of Neutrino Absolute Deep Inelastic Scattering Cross Section in Iron, Lead, Carbon, and Plastic Using MINERvA Detector at $E_{\nu} = 6$ \GeV

A deep inelastic sample is selected from the nuclear charged current inclusive analysis, by requiring reconstructed $Q^{2} \geq 1.0$ (GeV/c)$^{2}$ and $W \geq 2.0$ GeV/c$^{2}$. The neutrino energy range of $5 < E_{\nu} < 50$ previously applied to this analysis in the Low Energy (LE) analysis is removed and the energy range cut is imposed on the muon energy from $2 < E_{\mu} < 50$ GeV. Machine learning vertexing is used to improve the track-based vertexing resulting in higher purity and efficiency of the sample. A local sideband method is utilized to remove the plastic background for the events reconstructed in the target. After plastic backgrounds and non-DIS backgrounds are subtracted, the reconstructed neutrino energy and Bjorken-x are unsmeared to their true quantities via Bayesian unfolding. The unfolded distributions of carbon, iron, lead, and plastic are efficiency corrected and then divided by the flux and the number of nucleons in the target to produce the absolute cr oss section as a function of $E_{\nu}$ and differential cross section as function of $x_{bj}$. The results of the analysis show good agreement between data and MC for $E_{\nu}$ and $x_{bj}$ (see Figures \ref{fig:xsecEnuC} through \ref{fig:xsecXCH}). None of the distributions displayed significant differences with the theoretical models underlying MINERvAs MC.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Evaluation of High Temperature Plastics as a Ceramic Replacement

This report describes the 2015-2017 fiscal year research efforts to evaluate high temperature plastics as replacement materials for ceramics in electrical contact assemblies. The main objective of this work was to assess the feasibility of replacing existing high-price ceramic inserts with a polymeric material. Current ceramic parts are expensive due to machining costs and can suffer brittle failure. Therefore, replacing the ceramic with a more cost-effective material — in this case a plastic — is highly desirable. Not only are plastics easier to process, but they can also eliminate final tooling and are less brittle than ceramics. This effort used a three-phase approach: selection of appropriate materials determined by a comprehensive literature review, performance of an initial thermal stability screening, understanding of aging behavior under normal and off-normal conditions, and evaluation of performance at elevated temperatures. Two polymers were determined to meet the desired criteria: polybenzimidazole, and Vespel® SP-1 polyimide. Polymer derived ceramics may also be useful but will require further development of molding capabilities that were beyond the scope of this program.

36 MATERIALS SCIENCE↗
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 OSTI2019

Failure Formulations in Modular Plasticity Models

Computational prediction of ductile failure remains a challenging and important problem as demonstrated by the recent Sandia Fracture Challenges. In addition to emphasizing the complexity of such problems, the variety of solution strategies also highlighted the number of possible approaches to this problem. A common engineering approach for such efforts is to use a failure model in conjunction with element deletion. In the second Sandia Fracture Challenge, for instance, nine of the fourteen teams used some form of element deletion. For such schemes, a critical decision pertains to the selection of the appropriate failure model; of which many may be found in the literature (see the review of Corona and Reedlunn). The variety may also be observed in the aforementioned second Sandia Fracture Challenge in which at least eight different failure criteria are listed for the nine element deletion based approaches. The selection of the appropriate failure model is a difficult challenge depending on the material being considered and such criteria can variously depend on stress state (i.e. triaxiality, Lode angle) and loading conditions (i.e. strain rate, temperature). Separate implementations of each criteria with different plasticity models can be a repetitive and cumbersome process which may limit available models for an engineering analyst. To mitigate this issue, an effort was pursued to flexibly implement failure models in which different failure models could be specified and utilized within the same elastic-plastic constitutive routine by simply changing the input syntax. Similarly, the same models are implemented across a suite of elastic-plastic formulations enabling consistent definitions. As will be discussed later, a specific "modular failure" model is also implemented which allows for the selection or specification of different dependencies depending on the current need. At this stage, this effort is limited to defining failure models; progression/damage evolution in the constitutive model is not treated and left to future efforts.

42 ENGINEERING↗