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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 1,261 records · Page 70
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Enhanced Hot Tensile Ductility of Mg-3Al-1Zn Alloy Thin-Walled Tubes Processed Via a Combined Severe Plastic Deformation

In the current study, combined parallel tubular channel angular pressing (PTCAP) and tube backward extrusion (TBE), as a recently developed severe plastic deformation (SPD) method, were applied at 300 °C on a commercial Mg-3Al-1Zn alloy tubes to achieve an ultrafine grained structure. Then, the microstructure, hardness, tensile properties, and fractography evaluations were done at room temperature on the SPD-processed samples. Also, to study the hot tensile ductility of the SPD-processed samples, tensile testing was performed at an elevated temperature of 400 °C, and then, the fractured surface of the tensile samples was studied. It was observed that a bimodal microstructure, with large gains surrounded by many tiny ones, was created in the sample processed by PTCAP followed by TBE. This microstructure led to reach higher hardness and higher strength at room temperature and also led to reach very high elongation to failure (~ 181%) at 400 °C. Also, the value of elongation to failure for this sample was ~ 14.1% at room temperature. The fractographic SEM images showed the occurrence of predominately ductile fracture in the samples pulled at 400 °C. This was mostly due to the nucleation of microvoids and their subsequent growth and coalescence with each other.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Experimental and Numerical Investigations of Cyclic Plastic Deformation of Al-Mg Alloy

In this work, low-cycle fatigue (LCF) tests are performed on as-received and solution-treated Al-Mg alloy (AA 5754). Solution heat treatment of the as-received alloy is performed at 530 °C for 2 h and then quenched in water at room temperature. The low-cycle fatigue response of the as-received and solution-treated alloy is evaluated at five different strain amplitudes from 0.2 to 0.6%. The strain rate of 0.5 × 10{sup −3} s{sup −1} is kept constant in all the LCF tests. The LCF behavior of AA 5754 is modeled by finite element method (FEM) using Chaboche kinematic hardening cyclic plasticity model. Hardening behavior or fatigue life of as-received and solution-treated alloy is successfully simulated using this model. The results obtained by FEM simulations are compared with those obtained by LCF experiments. Microstructural studies are also performed for as-received and solution-treated alloy. The fracture surfaces obtained from LCF tests are analyzed by scanning electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Drawing Direction Effect on Microstructure and Mechanical Properties of Twinning-Induced Plasticity Steel During Wire Drawing

The effect of drawing direction on microstructure and mechanical properties in twinning-induced plasticity (TWIP) steel during wire drawing has been investigated to improve drawability for wire rod applications. The steel wires subjected to unidirectional (UD) and reverse-directional (RD) wire drawing were analyzed. The yield and tensile strength processed by the RD were slightly higher than those by the UD, whereas the ductility and drawability have inverse features, which is totally different from the results of plain carbon steel and Al wire. Although final shear strain of wires deformed by the RD is lower than that by the UD, the RD wires had a more complex stress history and a higher <111> texture component at the surface area, which encouraged twinning rate, resulting in fast exhaustion of ductility, finally earlier fracture of wires. In contrast to the materials deformed by mainly slip mechanism, the RD process cannot improve the ductility and drawability in TWIP steel due to the stress state dependency of twinning mechanism. Also, based on the different strengthening behaviors between pearlitic and TWIP steels during UD and RD, it is induced that microstructure and applied stress state simultaneously control the mechanical properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A New Approach for Consolidation of Pure Magnesium Powder Using an Integrated Severe Plastic Deformation Route

In this paper, a new approach using a novel severe plastic deformation route is presented for consolidation and processing of a high-density and ultrafine-grained pure magnesium. Pure magnesium particles were successfully consolidated at 400 °C into a sufficiently dense bulk material using a new combined method including cyclic extrusion compression, equal channel angular pressing (ECAP) and conventional extrusion. The grain refinement, consolidation behavior and mechanical properties were deeply investigated. Results showed that the as-consolidated material had a fine grain structure with excellent tensile strength and ductility compared to as-cast and as-ECAPed specimens. Vickers microhardness increased from 38.75 to 52.58 during the process. Porosity also reduced considerably from 12.55 to 1.2% during the process which led to a dense bulk material. Results indicate that the introduced method is a promising and effective process for producing strong bulk materials from metal powders.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Deformation Behavior and Microstructural Evolution of Reeled Pipeline Steels during Cyclic Plastic Deformation

API X60 steel used for reeled pipeline was subjected to different amounts of cyclic plastic deformation (CPD) by multiple tension–compression tests in order to study the deformation behavior and microstructural evolution during each stage of reel-lay installation process. It was found that the yield strength was significantly reduced by about 110 MPa during the first CPD cycle due to the Bauschinger effect. However, the yield strength was little affected by the subsequent CPD cycles, and the yield strength difference between tension and compression tended to reach a steady-state value of 23 MPa after multiple CPD cycles. With the increase in CPD cycles, the proportion of low-angle grain boundaries declined from 50.9 to 35.7%, and the CPD contributed to the formation of immovable dislocation walls and cells due to the dislocation rearrangement, causing the stable yield strength. The CPD process with strain level of 3% had no prominent effect on the tensile strength and elongation, because the change in microstructures was not enough to alter the work hardening completely after multiple CPD cycles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A Nanoindentation Study of the Plastic Deformation and Fracture Mechanisms in Single-Crystalline CaFe 2 As 2

In this paper, the plastic deformation and fracture mechanisms in single-crystalline CaFe 2 As 2 has been studied using nanoindentation and density functional theory simulations. CaFe 2 As 2 single crystals were grown in a Sn-flux, resulting in homogeneous and nearly defect-free crystals. Nanoindentation along the [001] direction produces strain bursts, radial cracking, and lateral cracking. Ideal cleavage simulations along the [001] and [100] directions using density functional theory calculations revealed that cleavage along the [001] direction requires a much lower stress than cleavage along the [100] direction. This strong anisotropy of cleavage strength implies that CaFe 2 As 2 has an atomic-scale layered structure, which typically exhibits lateral cracking during nanoindentation. This special layered structure results from weak atomic bonding between the (001) Ca and Fe 2 As 2 layers.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Multi-fidelity Uncertainty Quantification for Homogenization Problems in Structure-Property Relationships from Crystal Plasticity Finite Elements

Crystal plasticity finite element method (CPFEM) has been an integrated computational materials engineering (ICME) workhorse to study materials behaviors and structure-property relationships for the last few decades. These relations are mappings from the microstructure space to the materials properties space. Due to the stochastic and random nature of microstructures, there is always some uncertainty associated with materials properties, for example, in homogenized stress-strain curves. For critical applications with strong reliability needs, it is often desirable to quantify the microstructure-induced uncertainty in the context of structure-property relationships. However, this uncertainty quantification (UQ) problem often incurs a large computational cost because many statistically equivalent representative volume elements (SERVEs) are needed. In this article, we apply a multi-level Monte Carlo (MLMC) method to CPFEM to study the uncertainty in stress-strain curves, given an ensemble of SERVEs at multiple mesh resolutions. By using the information at coarse meshes, we show that it is possible to approximate the response at fine meshes with a much reduced computational cost. We focus on problems where the model output is multi-dimensional, which requires us to track multiple quantities of interest (QoIs) at the same time. In conclusion, our numerical results show that MLMC can accelerate UQ tasks around 2.23x, compared to the classical Monte Carlo (MC) method, which is widely known as ensemble average in the CPFEM literature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Process-Structure-Property Modeling for Severe Plastic Deformation Processes Using Orientation Imaging Microscopy and Data-Driven Techniques

Machining is a severe plastic deformation process, wherein the workpiece material is subjected to high deformation rates and temperatures. During metal machining, the dynamic recrystallization mechanism causes grain refinement into the sub-micron range. In this study, we investigate the microstructure evolution of oxygen-free high conductivity copper (OFHC Cu) subject to a machining process where the cutting speed and rake angle are controlled to manipulate the process strain, strain rate, and temperatures. Microstructures of the deformed chips are quantified using orientation imaging microscopy and novel statistical descriptors that capture the morphology and local lattice misorientations generated during the several mechanistic stages of the dynamic recrystallization process. Mechanical properties of the resulting chips are quantified using spherical nanoindentation protocols. A multiple output Gaussian process regression model is used to simultaneously model the structure-property evolution, which differs from more common approaches that establish such relationships sequentially. This modeling strategy is particularly attractive since it can flexibly provide both structure and property uncertainty estimates. In addition, the statistical modeling framework allows for the inclusion of multi-fidelity data. The statistical metrics utilized serve as efficient microstructure descriptors, which retain the physics of the observed structures without having to introduce ad hoc microstructure feature definitions.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Hugoniot Measurements on a Slurry of Finely Divided Tungsten and Plastic [Book Chapter]

A previous paper reported hugoniot measurements on a two-phase material consisting of a matrix and an embedded material (silica- phenolic) using the LLNL electric gun facility. The results showed a good bit of scatter in the measurements. This was attributed to the grossly heterogeneous nature of the material. Measurements have since been made on a slurry of finely divided tungsten powder in a plastic, greatly reducing the scale of the inhomogeneity. The results show greatly reduced scatter, as expected from the above interpretation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of ternary alloy additions on the microstructure of highly immiscible Cu alloys subjected to severe plastic deformation: An evaluation of the effective temperature model

Phase evolution in dilute, strongly immiscible Cu-Mo, Cu-Mo-Ni, and Cu-Mo-Ag alloys during severe plastic deformation at low-temperature has been experimentally investigated. For the Cu95Mo05 alloy, Mo nanoparticles are formed, ~10 nm in diameter, as part of a steady state microstructure, with less than ~1 at.% Mo dissolved in the matrix. Addition of 10 or 20 at.% Ni to this binary alloy results in a significant increase in the Mo solubility, whereas comparable additions of Ag has a corresponding little effect. The steady state microstructures of alloys during ball milling of elemental powders are very similar to those during HPT processing of initially homogeneous solutions. The results are discussed in terms of an effective temperature model. Model MD simulations are presented to help relate the predictions of the effective temperature model to atomistic mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Phase evolution in two-phase alloys during severe plastic deformation

Herein, phase evolution in FCC metals with strongly interacting alloy components during severe plastic deformation is investigated using molecular dynamics simulations. Specifically, we study the alloy microstructure in steady state, nucleation and growth of precipitates in supersaturated alloys, and the decomposition of precipitates in undersaturated alloys. The results are compared to a modified effective temperature model, providing a physical understanding for the atomic processes underlying the model and a perspective on its strengths and weaknesses. Key observations in this work are nucleation and growth of precipitates during SPD at a temperature of 100 K; Gibbs-Thomson-like behavior relating solubility to precipitate size under steady-state shearing; a direct relationship between the effective temperature and the shear modulus; and the importance of cluster agglomeration during precipitate growth. The study also reveals that the mechanisms of forced chemical mixing depends on precipitate size, adding complications for effective temperature models describing inhomogeneous systems. The simulations are shown to provide good semiquantitative agreement with experimental findings reported in the literature.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Temperature-dependent mechanical properties and crystal plasticity parameters for additively manufactured Haynes-214 alloy: Experiments and numerical modeling

Our experimental mechanical testing data demonstrated that the additively manufactured (AM) laser powder bed fusion (L-PBF) Haynes-214 alloy exhibits non-linear mechanical properties as the temperature rises from ambient to 870 °C. Crystal plasticity (CP) simulations provide an effective approach to gaining deeper insights into microstructure-property linkages under thermomechanical loading. This method can reduce the need for costly high-temperature mechanical testing while accounting for the effects of crystallographic texture and grain morphology on the mechanical behavior of AM materials. However, calibrating a CP model is time-consuming because individual simulations are computationally expensive and hundreds (or more) of iterations over parameter sets may be required. To address this issue, we have designed a machine learning-differential evolution (ML-DE) CP framework that can accurately interpolate the tensile properties of AM L-PBF Haynes-214 alloy across a wide temperature range from ambient to 870 °C, with minimal reliance on experimental data. The framework uses electron backscatter diffraction (EBSD) measurements to generate statistically equivalent microstructural volume elements to serve as inputs to the CP modeling framework. Stress–strain curves were generated from 1000 CP simulations, which serve as the training data set for the three ML regression algorithms explored: linear, extra-trees, and multi-layer perceptron. These three regression models were independently evaluated to compare their efficiency and identify the most suitable algorithm for the given problem. Results revealed that the extra-trees ML regressor outperforms the other models in both qualitative and quantitative aspects with an R 2 of 0.98. Subsequently, the differential evolution optimization approach is employed to calibrate the ML-based CP material parameters with experimental results obtained at various temperatures. Finally, temperature-dependent CP material parameters are formulated. The effectiveness and efficiency of the designed framework are validated through comparison with experimental results, demonstrating a high degree of agreement. These calibrated parametric constitutive equations enable further use of the CP model to study the deformation behavior of this alloy under a wide range of thermo-mechanical loading conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Catalytic Conversion of Model Compounds of Plastic Pyrolysis Oil over ZSM-5

Mechanistic investigation of the catalytic conversion of model compounds for plastic pyrolysis oil (1-octene, octadiene, octane, and toluene) over ZSM-5 in a fixed-bed reactor was studied. 1-Octene breaks down into smaller olefins, which undergo further cracking, oligomerization, cyclization, and hydrogen transfer to eventually produce benzene, toluene, xylene (BTX), coke, and hydrogen. The effect of contact time on 1-octene conversion was further investigated and compared with thermodynamics analyses to elucidate the reaction network. Under the reaction conditions (500 oC, 1 atm), octadiene undergoes thermal coking, significantly contributing to reactor fouling. The products from octane cracking are similar to the products from 1-octene conversion whereas toluene undergoes disproportionation, dealkylation and coking. The analysis of spent catalyst showed long-chain hydrocarbons created by oligomerization reactions filled the pores and covered the surface of the catalyst. As a result, when mesoporous ZSM-5 is used instead of conventional, product selectivity is maintained for 70 hours in time-on-stream experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Effect of reaction media on hydrogenolysis of polyethylene plastic waste: Polymer-surface interactions in small alkane/polymer blends

The polymer reaction media and its properties can be altered by recycling a fraction of liquid products or adding alkane solvents. Less clear is whether this strategy affects hydrogenolysis. Herein, we investigated the effect of short-chain alkanes C n consisting of n carbons (n=8, 16, and 32) on the upcycling of high-density polyethylene (HDPE) plastic waste to lubricant-range products over Ru/TiO 2 catalysts by multiscale simulations and experiments. First, we trained a force field for polymer/surface interactions on a Ru 22 nanoparticle (NP) supported on TiO 2 . Using replica exchange molecular dynamics simulations, we studied the effect of small hydrocarbons on the adsorption of a surrogate polymer, C 142 , on the catalyst. We found segregation of long chains (C 142 ) at the catalyst surface due to the enthalpy gained by adsorbing more C-C bonds of the long chains, compensating for entropic losses upon adsorption. Short-chain molecules decrease the adsorbed carbons of long chains on the Ru NP due to blocking Ru active sites. Compared to the bulk chains, competitive adsorption results in a broader, heavy-tailed distribution of end-to-end distance of adsorbed chains. Our experiments demonstrated that catalyst activity declines significantly beyond simple dilution due to changes in polymer adsorption, and tuning the reaction media by creating suitable blends impacts hydrogenolysis. Density distributions for a 50:50%wt mixture of PP and PE show that PE chains are segregated at the surface, so they are prone to C-C bond breaking much faster than PP chains. H/D exchange experiments show preferential deuteration of PE, while CH 3 groups of PP remain undeuterated. Furthermore, this may be explained by the preferential sorption of PE over PP, leading to specific distribution in the polymer blend.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Modelling dislocation-graphene interactions in a BCC Fe matrix by molecular dynamics simulations and gradient plasticity theory

We report graphene nanosheets (GNS) can enhance the strength and ductility of metal-based composites as they can obstruct the propagation of dislocations. The present article employs Molecular Dynamics (MD) simulations to investigate dislocation-GNS interaction mechanisms and possible influencing factors, including the number of GNS layers, the thickness of the metallic amorphous layer and the C - C bond strength. The results indicated that the shear strength of the metal/GNS interface and the bending stiffness of GNS determined the ability of GNS to block dislocation transmission. A physically based phenomenological parameter that can capture such dislocation-GNS interactions is the mechanical interface energy that has been put forth within gradient plasticity. By fitting the theoretical expressions to the simulation data, it was possible to obtain estimates for the mechanical interface energy for the GNS. It was found that increasing the GNS layers and adding an amorphous layer resulted in a strengthening in the stress–strain response and increased the value of this interfacial parameter. This indicates that the mechanical interfacial energy can be a unified measure for capturing and tuning the strength of various interfaces such as grain boundaries, GNS, amorphous-crystalline interface and bimetal interfaces.

36 MATERIALS SCIENCE↗
DOE OSTI2015

A developmentally plastic adult mouse kidney cell line spontaneously generates multiple adult kidney structures

Despite exciting new possibilities for regenerative therapy posed by the ability to induce pluripotent stem cells, recapitulation of three-dimensional kidneys for repair or replacement has not been possible. ARID3a-deficient mouse tissues generated multipotent, developmentally plastic cells. Therefore, we assessed the adult mouse ARID3a−/− kidney cell line, KKPS5, which expresses renal progenitor surface markers as an alternative cell source for modeling kidney development. Remarkably, these cells spontaneously developed into multicellular nephron-like structures in vitro, and engrafted into immunocompromised medaka mesonephros, where they formed mouse nephron structures. These data implicate KKPS5 cells as a new model system for studying kidney development. - Highlights: • An ARID3a-deficient mouse kidney cell line expresses multiple progenitor markers. • This cell line spontaneously forms multiple nephron-like structures in vitro. • This cell line formed mouse kidney structures in immunocompromised medaka fish kidneys. • Our data identify a novel model system for studying kidney development.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Converting plastic waste pyrolysis ash into flash graphene

Pyrolysis of plastic waste (PW), a commercial method of recycling, is currently economically challenging and produces up to 20% by mass valueless pyrolysis ash (PA) as a byproduct. Here, direct, facile upcycling of PW-derived PA into high purity turbostratic flash graphene (tFG) is demonstrated. The tFG displays excellent dispersibility, yielding a concentration of 2.84 mg/mL in aqueous surfactant solution. The tFG was used to fabricate tFG-PVA nanocomposites, and low doses of tFG (0.1%–1%) improve failure strain by 15%–30% when compared to the samples of neat PVA. Furthermore, the addition of tFG to PVA films showed decreased hydrophilic interactions, increasing the water contact angle by 235% and adsorbing 500% less water than neat PVA. The tFG was also added to Portland cement paste as well as concrete, and exhibited 43% and 25% increases in compressive strength, respectively. The tFG is used directly in both composite applications, requiring no purification or chemical functionalization, unlike many other products used in nanocomposites.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Plastic waste upgrade to olefins via mild slurry microwave pyrolysis over solid acids

Chemical upcycling technologies are emerging as the most viable to combat plastic waste accumulation. Among them, catalytic pyrolysis is very promising as it is feedstock agnostic. However, the high energy demand associated with pyrolysis can lead to significant carbon dioxide production. In this work, we demonstrate that coupling microwave heating with suitable solid acid promoters in a slurry reactor coupled with a distillation unit can overcome the energy-related challenge of conventional pyrolysis, by operating at modest temperatures (350–375 °C), enhancing transport, and furnishing high yields of olefins (~88 %) in seconds, with medium-sized olefins (>75 %) composing a significant fraction. Reduced thermal gradients minimize coke formation, further improving the performance. Techno-economic analysis and life cycle assessment indicate the potential of the technology.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗