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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Failure Analysis and Recovery of a 50 MM Highly Elastic Intermetallic NiTi Ball Bearing for an ISS Application

The ISS Distillation Assembly centrifuge is the pathfinder application for 50mm bore, deep-groove ball bearings made from the highly elastic intermetallic material 60NiTi. Superior corrosion and shock resistance are required to withstand the acidic wastewater exposure and heavy spacecraft launch related loads that challenge conventional steel bearings. During early ground testing one bearing unexpectedly and catastrophically failed after operating for only 200 hours of run time. A second bearing running on the same shaft was completely unaffected. A thorough investigation into the root cause of the failure determined that an excessively tight press-fit of the bearing outer race coupled with NiTis relatively low elastic modulus were key contributing factors. The proposed failure mode was successfully duplicated by experiment. To further corroborate the root cause theory, a successful bearing life test using improved installation practices (selective fitting) was conducted. The results show that NiTi bearings are suitable for space applications provided that care is taken to accommodate their unique material characteristics.

failure analyses↗
NASA NTRS2018

Ni-Ti Next Generation Bearings for Space Applications

NASA applications challenge traditional bearing materials. The rigors of launch often include heavy shock loads and exposure to corrosive environments (e.g., salt spray). Unfortunately, ball and roller bearings made from hardened steels are vulnerable to Brinell denting and rust which can limit performance and life. Ceramic materials can eliminate corrosion concerns but their high stiffness and extreme hardness actually makes denting problems worse. In this presentation, an emerging superelastic alloy, NiTi, is introduced for rolling element bearing applications. Through a decade of RD, NiTi alloy bearings have been put through a comprehensive series of life and performance tests. Hardness, corrosion, strength, stiffness, and rolling contact fatigue tests have been conducted and reported. Ball bearings ranging in size from 12 to 50mm bore have been successfully engineered and operated over a wide range of speeds and test conditions including being submerged in water. The combination of high hardness, moderate elastic modulus, low density, and intrinsic corrosion immunity provide new possibilities for mechanisms that operate under extreme conditions. Recent preliminary tests indicate that bearings can be made from NiTi alloys that are easily lubricated by conventional oils and greases and exhibit acceptable rolling contact fatigue resistance. This presentation introduces the NiTi materials systems and shows how NASA is using it to alleviate several specific problems encountered in advanced space applications.

bearings↗
NASA NTRS2018

Polyurethane Microparticles for Stimuli Response and Reduced Oxidative Degradation in Highly Porous Shape Memory Polymers

Shape memory polymers (SMPs) have been found to be promising biomaterials for a variety of medical applications; however, the clinical translation of such technology is dependent on tailorable properties such as gravimetric changes in degradation environments. For SMPs synthesized from amino-alcohols, oxidation resulting in rapid mass loss may be problematic in terms of loss of material functionality as well as toxicity and cytocompatibility concerns. Control of gravimetric changes was achieved through the incorporation of small molecule antioxidants, either directly into the polymer matrix or included in microparticles to form a SMP composite material. Direct incorporation of small molecule antioxidants, such as phenolic alcohols, was found to alter shape memory attributes and increase elastic modulus at the expense of the strain to failure. Such changes could not ensure retention of the antioxidants and therefore did not increase oxidative stability. However, the inclusion of antioxidants in microparticles was found to produce materials with similar thermomechanical and shape memory properties while increasing oxidative resistance compared to controls. The microparticle composite SMPs also act as a platform for environmental sensing, such as pH-dependent fluorescence shifts and payload release, as demonstrated by fluorescent dyes and the release of antioxidants. The use of polyurethane-urea microparticles in porous SMPs is demonstrated to increase biostability of the materials, by approximately 25%, and ultimately extend their lifespan for use in aneurysm occlusion as determined through calculated in vivo degradation rates corresponding to a porcine aneurysm environment.

Weems, A. C.↗
NASA NTRS2018

Characterizing Material Scalability for Ultralight Lattice Design

Stiff yet ultra-light lattice structures constructed using digital materials have many practical applications as the building block for aircraft and other structures. By furthering our understanding of how material configuration affects the structural properties of an ultralight lattice, we can intelligently design these structures based on their intended function. Here we compare the behavior of ultralight lattice structures when fabricated by different materials. The individual unit cells of the lattice structures are referred to as voxels. The stiffness, elastic modulus, and yield strength of the specimens in compression and tension are determined through mechanical testing. Specimens are tested both as single voxel as well as 4x4x4 voxel constructions on an Instron 5982 Universal Testing System until failure. Each voxel is manufactured in bulk through injection molding, with a unit cell pitch of 76.2 mm. Individual voxels are fastened with machine screws and nuts to create assemblies. Four separate materials are used as voxel compositions in this experiment. These include a homogeneous polymer referred to as Ultem 1000, a glass-fiber reinforced polymer referred to as Ultem 2200, a polymer with chopped carbon fibers as 30% of its fill, and homogenous polypropylene. This work compares mechanical behavior, as well as the convergence behavior of the lattice as the size of the lattice assembly increases for various materials. The goal of this study is to characterize the behavior of homogenous lattices such that heterogenous lattices can be designed with different material voxels to achieve target material properties for ultralight space applications.

Sajjadi, Afsheen↗
NASA NTRS2018

Simulation of Stochastic Mud-Crack Damage Formation in an Environmental Barrier Coating

The integrated Finite Element Analysis–Micromechanics Analysis Code/Ceramics Analysis and Reliability Evaluation of Structures (FEAMAC/CARES) program was used to simulate the formation of mudflat-cracks from thermomechanical loading on a multi-layered Environmental Barrier Coating (EBC) system deposited on a ceramic substrate. FEAMAC/CARES combines MAC/GMC multiscale composite micromechanics code with CARES/Life probabilistic multiaxial failure criteria code and Abaqusfinite element analysis. In this work, step function elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio finite elements enabled the depiction of crack boundaries and formation of mudflat patterned damage. Demonstrated examples include finite element models of button–sized disk–shaped 3-D specimen, and a 2-D model of through-the-thickness cross-section. All models were subjected to a progressive cool down from 1300oC to room temperature. Mudflat crack damage in the coating system resulted from the buildup of residual tensile stresses between the individual material constituents from thermal expansion mismatch. A 2-parameter Weibull distribution characterized the coating layer stochastic strength response and the effect of the Weibull modulus on the formation of damage was studied here.

residual tensile stress↗
NASA NTRS2018

Weibull-Based Stochastic Simulation of Mud-Crack Damage Formation in an Environmental Barrier Coating

The integrated Finite Element Analysis Micromechanics Analysis Code/Ceramics Analysis and Reliability Evaluation of Structures (FEAMAC/CARES) program was used to simulate the formation of mudflat-cracks from thermomechanical loading on a multi-layered Environmental Barrier Coating (EBC) system deposited on a ceramic substrate. FEAMAC/CARES combines MAC/GMC (Micromechanics Analysis Code/Generalized Method of Cells) multiscale composite micromechanics code with CARES/Life probabilistic multiaxial failure criteria code and Abaqusfinite element analysis. In this work, step function elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio finite elements enabled the depiction of crack boundaries and formation of mudflat patterned damage. Demonstrated examples include finite element models of button-sized disk-shaped 3-D specimen, and a 2-D model of through-the-thickness cross-section. All models were subjected to a progressive cool down from 1300 degrees Centigrade to room temperature. Mudflat crack damage in the coating system resulted from the buildup of residual tensile stresses between the individual material constituents from thermal expansion mismatch. A 2-parameter Weibull distribution characterized the coating layer stochastic strength response and the effect of the Weibull modulus on the formation of damage was studied here.

Residual Tensile Stress↗
NASA NTRS2020

Lot-to-lot Variability of BN Grades for Space Electric Propulsion Applications

Historically, several grades of hot pressed hexagonal boron nitride have been used for space electric propulsion applications. This study investigates the material properties of a selection of commercially available boron nitride grades including HP, M26, M, BNXX, and Shapal Hi-M. This work complements data which was presented at JANNAF 2018. The grades selected for this study are of interest because their available billet size is sufficient for space electric propulsion. This research investigates a range of material properties, tailored and focused on enhancing performance, reliability, and economics of electric propulsion thrusters. This work builds upon previous efforts by studying lot-to-lot variability of some of the properties of interest. Coefficient of friction, moisture absorption, moisture sensitivity, hot press directionality, flexural strength, compression strength, elastic modulus, thermal conductivity, thermal emissivity, thermal expansion, density, X-ray diffraction phase, microstructure, and chemical composition were all investigated across two lots of materials to help guide the selection of advanced ceramics. Variability between lots is the critical concern of the study.

Mackey, Jonathan A.↗
NASA NTRS2020

Stochastic Simulation of Mudcrack Damage Formation in an Environmental Barrier Coating

The FEAMAC/CARES program, which integrates finite element analysis (FEA) with the MAC/GMC (Micromechanics Analysis Code with Generalized Method of Cells) and the CARES/Life (Ceramics Analysis and Reliability Evaluation of Structures / Life Prediction) programs, was used to simulate the formation of mudcracks during the cooling of a multilayered environmental barrier coating (EBC) deposited on a silicon carbide substrate. FEAMAC/CARES combines the MAC/GMC multiscale micromechanics analysis capability (primarily developed for composite materials) with the CARES/Life probabilistic multiaxial failure criteria (developed for brittle ceramic materials) and Abaqus (Dassault Systèmes) FEA. In this report, elastic modulus reduction of randomly damaged finite elements was used to represent discrete cracking events. The use of many small-sized low-aspect-ratio elements enabled the formation of crack boundaries, leading to development of mudcrack-patterned damage. Finite element models of a disk-shaped three-dimensional specimen and a twodimensional model of a through-the-thickness cross section subjected to progressive cooling from 1,300 °C to an ambient temperature of 23 °C were made. Mudcrack damage in the coating resulted from the buildup of residual tensile stresses between the individual material constituents because of thermal expansion mismatches between coating layers and the substrate. A two-parameter Weibull distribution characterized the coating layer stochastic strength response and allowed the effect of the Weibull modulus on the formation of damage and crack segmentation lengths to be studied. The spontaneous initiation of cracking and crack coalescence resulted in progressively smaller mudcrack cells as cooling progressed, consistent with a fractal-behaved fracture pattern. Other failure modes such as delamination, and possibly spallation, could also be reproduced. The physical basis assumed and the heuristic approach employed, which involves a simple stochastic cellular automaton methodology to approximate the crack growth process, are described. The results ultimately show that a selforganizing mudcrack formation can derive from a Weibull distribution that is used to describe the stochastic strength response of the bulk brittle ceramic material layers of an EBC.

Nemeth, Noel N.↗
NASA NTRS2020

Fatigue Failures at Defective Grains in a Single Crystal Nickel-Base Superalloy

Single crystal nickel-base superalloys used as turbine engine blades can have much higher creep and fatigue resistance than many polycrystalline superalloys due to the absence of weak grain boundaries as well as the ability to orient the blades in the primary loading direction on to the low elastic modulus [001] orientation, which significantly lowers the stresses imposed on the blades. However, grain defects can occur in these crystals, impairing these advantages. In the present study, fatigue tests of a single crystal superalloy uncovered unexpected defective grains in the test specimens, which initiated premature fatigue failures. The characteristics of these defective grains and the associated failures were evaluated and related to the observed fatigue lives.

superalloy↗
NASA NTRS2023

Recrystallization of A Shot Peened Single Crystal Nickel-Base Superalloy

Single crystal nickel-base superalloys used as turbine engine airfoils can have much higher creep and thermal fatigue resistance required for blades and vanes than polycrystalline superalloys due to the absence of weak grain boundaries, as well as the low elastic modulus in the [001] single crystal growth direction (Refs. 1 and 2). This has allowed an increase in the turbine rim inlet temperatures for improved performance and efficiency. However, these advantages in performance require constraints on acceptable levels of single crystal defects, such as macroscopic grain boundaries at low angles to the primary grain (i.e., low angle boundaries or LAB), higher angle boundaries, small new grains nucleated at the blade surface (a.k.a. freckles), larger new grains, and also the single crystal blades’ orientation, typically degrees off of the [001] direction and the orientation of a transverse [010] direction with respect to blade geometry. Therefore, single crystal turbine airfoils, which are frequently used with as-cast surfaces, are grain etched and inspected before and after heat treatments to ensure these aspects conform to acceptability limits.

single crystal↗
NASA NTRSDate not supplied

Using Digital Image Correlation for Quantifying Load Induced in Elastomers at Cryogenic Temperatures

Elastomers have glass transition temperatures (TG) that are well below room temperature. Below this temperature, elastomers can suddenly exhibit significantly different mechanical properties than those exhibited at warmer temperatures. A unique test was developed to measure the induced load generated by elastomers that have been gripped on both ends and cooled to cryogenic temperatures. The test simulates a space flight critical component that will result in loss of vehicle if the elastomer separates from the gripped end. Digital image correlation (DIC) was used to measure the strain on the material surface and the displacement of the grips during testing. Two cameras were mounted on an isolated tripod to capture images through optical glass fitted on the thermal chamber. DIC measurements were used to measure the elastic modulus, coefficient of thermal expansion, and the loads at the gripped ends, above and below the TG. There was nearly no load developed while the temperature was above the TG but loads rapidly increased two orders of magnitude as the temperature dropped below the TG.

Matlock Mennu↗
NASA NTRS2025

Radiation-Resistant Ti/BN Coatings: Insights From 171 Days Exposure to Space Radiation and Atomic Oxygen in Low Orbit

Atmospheric Plasma Spray (APS) and Vacuum Plasma Spray (VPS) techniques were used to develop Ti/2 vol.% hBN coatings, for extreme space environments and tested aboard the International Space Station as part of the MISSE-17 (Materials International Space Station Experiments) program. The coatings were exposed to atomic oxygen, space radiation, and low-orbit thermal cycling. VPS coatings showed a 56% increase in microhardness, a 26% rise in elastic modulus, minimal porosity and crack density changes compared to APS coatings. The change in mechanical properties is attributed to the formation of TiO, TiO₂ and TiN from nitrogen retention, alongside radiation-induced dislocations, which enhanced surface hardening. The oxidation of titanium led to the formation of TiO and TiO₂, while boron nitride was retained and underwent transmutation in VPS coatings. XPS and EDS analyses confirmed the enhanced space-environment resistance of VPS coatings, making them ideal for long-term spacecraft protection in lunar and Martian conditions.

Abhijith Kunneparambil Sukumaran↗
DOE OSTI2024

Determining the Crosslinking and Degradation Reaction Kinetics in Photovoltaic Encapsulants Using Accelerated Aging: Preprint

Degradation of photovoltaic (PV) module encapsulant mechanical characteristics that lead to embrittlement and delamination remains a cause of failure in solar installations. A multiscale reliability model based on detailed molecular degradation reaction kinetics was previously published, connecting the encapsulant mechanical properties (elastic modulus, yield strength, and adhesion energy) to the degraded molecular structure and interfacial bond density to adjacent solar cell and glass substrates. The model, developed primarily for poly(ethylene-co-vinyl acetate) (EVA) encapsulants, remains to be experimentally validated. Determining the degradation and crosslinking kinetics of alternative encapsulants, such as polyolefin elastomer (POE) and EVA/POE/EVA composites (EPE), can further generalize the model. Importantly, the activation energy for crosslinking of fully cured PV encapsulant products from temperature or UV is presently unknown or unavailable. In this work, we subject EVA, POE, and EPE encapsulants to a set of accelerated aging conditions, varying the temperature, UV intensity, and relative humidity. We use DSC, FTIR, and Soxhlet extraction (gel content) to characterize the encapsulants' changing molecular structure. This allows for determination of the photochemical degradation and crosslinking kinetics of the encapsulants. Preliminary results show an increase in gel content (crosslinking) and a decrease in crystallinity of EVA, POE, and EPE encapsulants under hot-aerobic (90 deg C, 22% RH) and hot-anaerobic (90oC, sealed in N2 air) accelerated aging, even in the absence of UV and crosslinking initiating agents. For a least squares regression with an assumed first-order crosslinking kinetics, the crosslinking rate parameters were computed for the three encapsulants under hot-aerobic and hot-anaerobic aging conditions. FTIR analysis showed insignificant encapsulant degradation for hot-aerobic and hot-anaerobic aging, demonstrating the critical role of UV and moisture in accelerating degradation. Aging conditions with UV exposure and elevated humidity are presently in progress.

adhesion↗
DOE OSTI2024

Physical characterization of High Entropy Alloys through Differential Scanning Calorimetry and Nanoindentation

In recent years several accelerator facilities have been limiting their beam power output not due to constraint of the accelerators but by concerns on the survivability of their targets, which in turn has led to R&D efforts into new, more resistant materials. One of these novel materials are High Entropy Alloys, the main focus of the internship project. This paper details the activities performed during the CCI 10-week internship by the authors, as well as to discuss the results obtained from said internship. The project consisted of the physical characterization of 12 batches of High Entropy Alloys (HEAs); the methods used to analyze the materials were Nanoindentation, which allows to determine the elastic modulus of the material and its hardness, and Differential Scanning Calorimetry (DSC), allowing the determination of specific heat.

Pacheco Uribe, Rene↗
DOE OSTI2024

Effects of N-Doping on Silicon Carbide

Silicon carbide (SiC) is a widely preferred material within many industries due to its favorable properties, most notably its low electrical resistivity at high temperatures, excellent thermal conductivity, and sturdy mechanical properties. Doping, particularly n-type doping, is shown to extremely reduce electrical resistivity, but due to structural changes within the lattice caused by interaction with thermal neutrons, it is possible that other attributes of SiC may also be affected. In addition to review of past literature and data, four-point probe testing, scanning electron microscopy, nanoindentation, strength tests, differential scanning calorimetry and laser flash analysis were used to investigate the effects of n-doping 3C ß-phase SiC. According to temperature dependent measurements, electric resistivity and thermal conductivity both declined as dopant levels increases. Dopant levels are shown to have a significant effect on the mechanical performance of SiC, with the highest dopant levels (4 x 1018 cm-3) providing a 40% decrease in elastic modulus from 420 GPa to 258 GPa and a 30% decrease in hardness from 40 GPa to 27.7 GPa. These values are still above average and doped SiC may prove valuable for nuclear applications.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Novel Preprocessing Techniques for Enhancing Flowability of Miscanthus

Purpose-grown energy crops possess significant potential as promising feedstocks for biofuel and biochemical production. However, similar to other biomass feedstocks, their utilization has been hindered by handling and feeding challenges such as clogging and segregation, which prevent biorefineries from operating at full capacity. These challenges arise primarily due to particle attributes including irregular shape, high flexibility, and high compressibility, leading to interlocking, high compaction, and significant friction under stress consolidation. To enhance operational reliability, it is crucial to focus on preprocessing techniques to address these issues, alongside accurately characterizing the mechanical and physical properties and flow performance of these feedstocks. This study investigates novel preprocessing techniques, including pelletization and torrefaction, to fundamentally alter these particle attributes and improve flowability. Miscanthus, an herbaceous energy crop, was the primary focus of this study. Samples were processed using a Forest Concepts Crumbler rotary shear system and an oscillating multi-stack screen bed to achieve two nominal (baseline) particle sizes: 6mm and 2mm. The study evaluated the efficiency and energy consumption of size reduction, revealing that while 2mm particles required more energy, they exhibited better flowability and higher yield strength compared to 6mm particles. Shear and compression tests assessed the material's shear strength, internal friction, and elastic modulus, while wedge-shaped hopper tests measured the critical arching distance and mass flow rate. The results provide valuable insights into the mechanical properties and processing efficiency of Miscanthus, contributing to the development of a preprocessing framework that enhances energy efficiency and material flowability in bioenergy production. However, further preprocessing and development are required to optimize this framework fully.

09 - BIOMASS FUELS↗
DOE OSTI2024

Material property characterization of 3D printed polypropylene wood plastic composites

Abstract Wood flour (WF) at 10 wt.% and 20 wt.% loadings was used as a reinforcing filler to enhance the applicability of polypropylene (PP) for 3D printing. After performing printability tests of PP wood plastic composites (WPCs), the mechanical properties of both injection‐molded and 3D‐printed PP WPC specimens were explored. Test specimens were prepared from 3D printed hexagons for analyzing the mechanical properties. Adding WF to neat PP increased the storage modulus and the glass transition temperature while decreasing the degree of crystallinity and the coefficient of thermal expansion, while enhancing the printability of neat PP. The tensile strength, tensile modulus of elasticity, flexural strength, and flexural modulus of elasticity of injection‐molded neat PP improved by up to 21%, 59%, 30%, and 56%, respectively, with 20 wt.% WF. However, the impact strength of injection‐molded neat PP decreased by 85%, with 20 wt.% WF. After 3D printing, the tensile strength and tensile modulus of elasticity of printed neat PP increased by up to 84% and 60%, respectively, with 20 wt.% WF. The flexural strength and flexural modulus of elasticity of neat printed PP remained unchanged compared to those of PP filled with 20 wt.% WF, while the impact strength decreased by 87%. Highlights WF was used as a reinforcement in polypropylene designed for 3D printing A pilot‐scale, pellet‐fed 3D printer was used to print hollow hexagons, and then test specimens were fabricated from these hexagons for mechanical properties The tensile and flexural properties of 3D printed neat polypropylene improved, while the impact strength decreased after adding 20 wt.% WF to the neat PP.

Hwang, Sungjun↗
NASA NTRS1945

The Elastic Constants for Wrought Aluminum Alloys

There are several constants which have been devised as numerical representations of the behavior of metals under the action of loadings which stress the metal within the range of elastic action. Some of these constants, such as Young's modulus of elasticity in tension and compression, shearing modulus of elasticity, and Poisson's ratio, are regularly used in engineering calculations. Precise tests and experience indicate that these elastic constants are practically unaffected by many of the factors which influence the other mechanical properties of materials and that a few careful determinations under properly controlled conditions are more useful and reliable than many determinations made under less favorable conditions. It is the purpose of this paper to outline the methods employed by the Aluminum Research Laboratories for the determination of some of these elastic constants, to list the values that have been determined for some of the wrought aluminum alloys, and to indicate the variations in the values that may be expected for some of the commercial products of these alloys.

ALUMINUM ALLOYS, WROUGHT-ELASTICITY↗