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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

3D printing of void-free glass monoliths: rheological and geometric considerations

Direct ink writing (DIW) is a versatile additive manufacturing technique capable of printing 3D architectures from a broad range of materials. The key advantage of DIW is the ability to spatially control both the architecture and the composition of the printed part, which enables the production of components with previously unachievable combinations of functionalities. One emergent application space for DIW has been in additively manufactured glass optics, where a “green body” is patterned layer-by-layer by extruding a silica-based slurry through a microfluidic nozzle and then thermally consolidated to transparent glass. A critical aspect of the process is ensuring that the printed part is completely free of voids that can occur in the interstitial spaces between the extruded filaments. This outcome is governed by the interplay between ink rheology and strains imposed by the printing process and geometric packing of the filaments. Here, we explore the strain- and rate-dependent deformation events in the DIW process to determine conditions that enable the printing of void-free monoliths without sacrificing shape fidelity. We focus on yield stress fluids consisting of fumed silica nanoparticles dispersed in organic solvents at varied volume fractions to control the rheological properties. We investigate the printability of these ink materials as a function of print process variables and devise the appropriate dimensionless parameters that capture the geometry-dependent and rate-dependent effects on the deformation of the extruded ink. Lastly, we use these scaling arguments to construct a phase diagram for void-free monolith printability.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Surface Control of Cold Hibernated Elastic Memory Self-Deployable Structure

A new class of simple, reliable, lightweight, low packaging volume and cost, self-deployable structures has been developed for use in space and commercial applications. This technology called 'cold hibernated elastic memory' (CHEM) utilizes shape memory polymers (SMP)in open cellular (foam) structure or sandwich structures made of shape memory polymer foam cores and polymeric composite skins. Some of many potential CHEM space applications require a high precision deployment and surface accuracy during operation. However, a CHEM structure could be slightly distorted by the thermo-mechanical processing as well as by thermal space environment Therefore, the sensor system is desirable to monitor and correct the potential surface imperfection. During these studies, the surface control of CHEM smart structures was demonstrated using a Macro-Fiber Composite (MFC) actuator developed by the NASA LaRC and US Army ARL. The test results indicate that the MFC actuator performed well before and after processing cycles. It reduced some residue compressive strain that in turn corrected very small shape distortion after each processing cycle. The integrated precision strain gages were detecting only a small flat shape imperfection indicating a good recoverability of original shape of the CHEM test structure.

glass transition temperature Tg↗
DOE OSTI2022

Atomistic simulations of nanoindentation on nanoglasses: Effects of grain size and gradient microstructure on the mechanical properties

The use of nanoglass (NG) microstructures has been shown as an effective strategy to improve the ductility of rather brittle metallic glass alloys. To evaluate the effects of grain size and gradient design on the mechanical properties of NGs, we perform molecular dynamics simulations of nanoindentation on Cu 64 Zr 36 NGs. We consider samples with uniform 3 and 7 nm grain sizes as well as gradient microstructures with gradient grain sizes varying from 3 to 7 nm. Here, the results show that the deformation mechanism in NGs with small grain sizes is dominated by the activation and evolution of multiple shear transformation zones. Increasing grain sizes enhances the elastic modulus and hardness at the cost of reduced abrasion resistance. Though the average grain size at the indentation surface plays a crucial role in the deformation behavior of gradient NG models, their strain localization and plastic deformation states are affected by the grain sizes far from the indenter. Desired combinations of mechanical properties can be realized by different NG microstructure designs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Room Temperature Quasi-static Characterization and Constitutive Model Parametrization of Flexible Polyurethane Foams of Different Densities Loaded in Different Orientations

This report describes the efforts to characterize and model General Plastics TF6070 and EF4000 flexible polyurethane foams under room temperature, large deformation quasi-static cyclic mechanical loading conditions. Densities from three to fifteen pound per cubic foot (PCF) are examined, which correspond to relative densities of approximately 4 to 20%. These foams are open cell structured and flexible at room temperature with a glass transition transition less than -30°C, and they fully recover their original shape when unloaded (at room temperature). Uniaxial compression tests were conducted with accompanying lateral image series for Digital Image Correlation (DIC) analysis with the goal of extracting transverse strain responses. Due to difficulties with DIC analysis at large strains, lateral strains were instead extracted for each test via edge tracking. The experimental results exhibit a nonlinear elastic response and anisotropic material behavior (particularly for the lower densities). Some hysteresis is observed that is different between the first and subsequent cycles of deformation indicating both a small degree of permanent damage (reduced stiffness during reloading) and viscoelasticity. These inelastic mechanisms are not considered in the modeling and calibration in this report. This work considers only the rate independent, room temperature foam behavior. Individual foam densities were calibrated for loading in two directions, parallel and perpendicular to the foam bubble rise direction, since the mechanical behavior is different in these two directions. The Flex Foam constitutive model was used for all parameterizations despite the fact that the model is isotropic. A review of the constitutive model is given as well as necessary data reduction procedures to parameterize it for each foam density and orientation are discussed. Finally, two different parameterizations are developed that take the undeformed foam density as an input that span all densities considered. These two parameterized models represent foams loaded in the rise and transverse directions respectively. We summarize the assumptions and limitations of the parameterizations provided in this report to guide analysis choices with them. All parameterizations presented herein have the following traits, room temperature, rate independent, damage-free, and non-dissipative . Isotropy (even if they are representing anisotropic data). Supplied Sierra Solid Mechanics Flex Foam Model Inputs are in units: pounds, inches, Celsius, and seconds

36 MATERIALS SCIENCE↗
NASA NTRS1985

Characterization of solid particle erosion resistance of ductile metals based on their properties

This paper presents experimental results pertaining to spherical glass bead and angular crushed glass particle impingement. A concept of energy absorption to explain the failure of material is proposed and is correlated with the erosion characteristics of several pure metals. Analyses of extensive erosion data indicate that the properties - surface energy, specific melting energy, strain energy, melting point, bulk modulus, hardness, atomic volume - and the product of the parameters - linear coefficient of thermal expansion x bulk modulus x temperature rise required for melting, and ultimate resilience x hardness - exhibit the best correlations. The properties of surface energy and atomic volume are suggested for the first time for correlation purposes and are found to correlate well with erosion rates at different angles of impingement. It further appears that both energy and thermal properties contribute to the total erosion.

Rao, P. V.↗
NASA NTRS1991

Structural characterization of high temperature composites

Glass, ceramic, and carbon matrix composite materials have emerged in recent years with potential properties and temperature resistance which make them attractive for high temperature applications such as gas turbine engines. At the outset of this study, only flexural tests were available to evaluate brittle matrix composites at temperatures in the 600 to 1000 C range. The results are described of an ongoing effort to develop appropriate tensile, compression, and shear test methods for high temperature use. A tensile test for unidirectional composites was developed and used to evaluate the properties and behavior of ceramic fiber reinforced glass and glass-ceramic matrix composites in air at temperatures up to 1000 C. The results indicate generally efficient fiber reinforcement and tolerance to matrix cracking similar to polymer matrix composites. Limiting properties in these materials may be an inherently very low transverse strain to failure, and high temperature embrittlement due to fiber/matrix interface oxidation.

Mandell, J. F.↗
NASA NTRS1998

Development of In-Fiber Reflective Bragg Gratings as Shear Stress Monitors in Aerodynamic Facilities

Bragg gratings centered at nominal wavelengths of 1290 nm and 1300 run were inscribed in a 9/125 microns germano-silicate optical fiber, using continuous wave frequency doubled Ar+ laser radiation at 244 nm. Such gratings have been used extensively as temperature and strain monitors in smart structures. They have, however, never been used for measuring aerodynamic shear stresses. As a test of their sensitivity as shear stress monitors, a Bragg fiber attached to a metal plate was subjected to laminar flows in a glass pipe. An easily measurable large flow-induced wavelength shift (Delta Lambda(sub B)) was observed in the Bragg reflected wavelength. Thereafter, the grating was calibrated by making one time, simultaneous measurements of Delta Lambda(sub B) and the coefficient of skin friction (C(sub f)) with a skin friction balance, as a function of flow rates in a subsonic wind tunnel. Onset of fan-induced transition in the tunnel flow provided a unique flow rate for correlating Delta Lambda(sub B) and (C(sub f) values needed for computing effective modulus of rigidity (N(sub eff)) of the fiber attached to the metal plate. This value Of N(sub eff) is expected to remain constant throughout the elastic stress range expected during the Bragg grating aerodynamic tests. It has been used for calculating the value of Cf at various tunnel speeds, on the basis of measured values of Bragg wavelength shifts at those speeds.

Parmar, Devendra S.↗
NASA NTRS1991

Combined effect of matrix cracking and stress-free edge on delamination

The effect of the stress-free edge on the growth of local delaminations initiating from a matrix crack in (O sub 2/90 sub 4) sub s and (+/- 45.90 sub 4) sub s glass epoxy laminates is investigated using 3D finite element analysis. The presence of high interlaminar normal stresses at the intersection (corner) of the matrix crack with the stress-free edge, suggests that a mode I delamination may initiate at the corners. The strain energy release rates (G) were calculated by modeling a uniform through-width delamination and two inclined delaminations at 10.6 deg and 45 deg to the matrix crack. All components of G have high values near the free edges. The mode I component of G is high at small delamination length and becomes zero for a delamination length of one-ply thickness. The total G values near the free edge agreed well with previously derived closed form solution. The quasi-3D solutions agreed well with the 3D interior solutions.

Salpekar, Satish A.↗
DOE OSTI2024

Static and Dynamic Thermomechanical Properties of Phase-Separated Epoxy Networks with Tuned Microstructures

Here, polymerization-induced phase separation is a useful method for the construction of heterogeneous epoxy networks with properties exceeding their homogeneous counterparts. In this work, we examine the static and dynamic thermomechanical properties of phase-separated epoxy networks salient to their application as encapsulants. Three heterogeneous epoxy-amine networks with nano-, meso-, and macro-phase-separated morphologies comprised of hard and soft domains are compared to a rigid, unstructured network. The glass transition profiles of the heterogeneous networks are complex, spanning many decades in the frequency domain. The nanophase-separated morphology leads to higher coefficient of thermal expansion, yet surprisingly is characterized by reduced residual stress. Under both quasi-static and dynamic compression (strain rates of order 10 –3 and 10 3 s –1 , respectively), the nanophase-separated network also exhibits higher modulus and strength. In split-Hopkinson bar experiments, the energy dissipation characteristics of the epoxy networks were nearly identical. Curiously, however, the Hugoniot response of the macro-phase-separated network determined by ballistic shockwave analysis indicates a remarkable ability of this material to mitigate shockwave propagation in comparison to many homogeneous and heterogeneous polymer materials. Collectively, this work reveals several previously unreported phenomena with respect to structure–property relationships in phase-separated epoxy networks, illustrating the potential value of systematically tuned microstructures for optimization of application-specific physical properties.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Dynamics of solid lubrication as observed by optical microscopy

A bench metallograph was converted into a micro contact imager by the addition of a tribometer employing a steel ball in sliding contact with a glass disk. The sliding contact was viewed in real time by means of projection microscope optics. The dynamics of abrasive particles and of solid lubricant particles within the contact were observed in detail. The contact was characterized by a constantly changing pattern of elastic strain with the passage of surface discontinuities and solid particles. Abrasive particles fragmented upon entering the contact, embedded in one surface and scratched the other; in contrast, the solid lubricant particles flowed plastically into thin films. The rheological behavior of the lubricating solids gave every appearance of a paste-like consistency within the Hertzian contact.

Sliney, H. E.↗
NASA NTRS1976

Dynamics of solid lubrication as observed by optical microscopy

A bench metallograph was converted into a 'micro contact imager' by the addition of a tribometer employing a steel ball in sliding contact with a glass disk. The sliding contact was viewed in real time by means of projection microscope optics. The dynamics of abrasive particles and of solid lubricant particles within the contact were observed in detail. The contact was characterized by a constantly changing pattern of elastic strain with the passage of surface discontinuities and solid particles. Abrasive particles fragmented upon entering the contact, embedded in one surface and scratched the other; in contrast, the solid lubricant particles flowed plastically into thin films. The rheological behavior of the lubricating solids gave every appearance of a paste-like consistency within the Hertzian contact.

Sliney, H. E.↗
NASA NTRS1985

Fatigue of graphite/epoxy buffer strip panels with center cracks

The effects of fatigue loading on the behavior of graphite/epoxy panels with either S-Glass or Kevlar-49 buffer strips is studied. Buffer strip panels are fatigued and tested in tension to measure their residual strength with crack-like damage. Panels are made with 45/0/-45/90 sub 2s layup with either S-Glass or Kevlar-49 buffer strip material. The buffer strips are parallel to the loading direction and made by replacing narrow strips of the 0-degree graphite plies with strips of either 0-degree S-Glass/epoxy or Kevlar-49/epoxy on a one-for-one basis. The panels are subjected to a fatigue loading spectrum MINITWIST, the shortened version of the standardized load program for the wing lower surface of a transport aircraft. Two levels of maximum strain are used in the spectrum with three durations of the fatigue spectrum. One group of panels is preloaded prior to the application of the fatigue cycling. The preload consists of statistically loading the spectrum in tension until the crack-tip damage zone reaches the ajacent buffer strips. After fatigue loading, all specimens are statistically loaded in tension to failure to determine their residual strengths.

Bigelow, C. A.↗
NASA NTRS1990

Combined effect of matrix cracking and stress-free edge on delamination

The effect of the stress-free edge on the growth of local delaminations initiating from a matrix crack in (0 sub 2/90 sub 4) sub s and (+ or - 45.90 sub 4) sub s glass epoxy laminates is investigated using 3-D finite element analysis. The presence of high interlaminar normal stresses at the intersection (corner) of the matrix crack with the stress-free edge, suggests that a mode I delamination may initiate at the corners. The strain energy release rates (G) were calculated by modeling a uniform through-width delamination and two inclined delaminations at 10.6 deg and 45 deg to the matrix crack. All components of G have high values near the free edges. The mode I component of G is high at small delamination length and becomes zero for a delamination length of one-ply thickness. The total G values near the free edge agreed well with previously derived closed form solution. The quasi-3D solutions agreed well with the 3-D interior solutions.

Salpekar, S. A.↗
DOE OSTI2021

Nanomechanical testing of freestanding polymer films: in situ tensile testing and Tg measurement

Abstract A method for small-scale testing and imaging of freestanding, microtomed polymer films using a push-to-pull device is presented. Central to this method was the development of a sample preparation technique which utilized solvents at cryogenic temperatures to transfer and deposit delicate thin films onto the microfabricated push-to-pull devices. The preparation of focused ion beam (FIB)-milled tensile specimens enabled quantitative in situ TEM tensile testing, but artifacts associated with ion and electron beam irradiation motivated the development of a FIB-free specimen preparation method. The FIB-free method was enabled by the design and fabrication of oversized strain-locking push-to-pull devices. An adaptation for push-to-pull devices to be compatible with an instrumented nanoindenter expanded the testing capabilities to include in situ heating. These innovations provided quantitative mechanical testing, postmortem TEM imaging, and the ability to measure the glass transition temperature, via dynamic mechanical analysis, of freestanding polymer films. Results for each of these mentioned characterization methods are presented and discussed in terms of polymer nanomechanics. Graphic Abstract

36 MATERIALS SCIENCE↗
NASA NTRS1983

Shock-wave properties and high-pressure equations of state of geophysically important materials

Shock wave (Hugoniot), shock temperature, and release data are presented for several geophysically important, refractory materials. A sensitive multichannel optical pyrometer was developed to measure shock temperatures (2500 to 5600 K at pressures from 48 to 117 GPa) in anorthite (CaAl2Si2O8) glass. Shock temperatures of 3750 to 6000 K at pressures from 140 to 182 GPa were measured in calcium oxide (CaO). Temperature data were used to constrain the energetics of the B1-B2 phase transition at 70 GPa in CaO, and to construct a finite strain equation of state for CaO consistent with previous Hugoniot data. The CaO equation of state was used with equation of state parameters of other oxides to construct a theoretical mixed oxide Hugoniot of anorthite, which is in agreement with new Hugoniot data above about 50 GPa, determined using experimental techniques developed. The mixed oxide model, however, overestimates the shock temperatures, and does not accurately predict measured release paths.

Boslough, M. B.↗
NASA NTRS2001

Ultrasonic Assessment of Impact-Induced Damage and Microcracking in Polymer Matrix Composites

The main objective of this NASA FAR project is to conduct ultrasonic assessment of impact-induced damage and microcracking in polymer matrix composites at various temperatures. It is believed that the proposed study of impact damage assessment on polymer matrix composites will benefit several NASA missions and current interests, such as ballistic impact testing of composite fan containment and high strain rate deformation modeling of polymer matrix composites. Impact-induced damage mechanisms in GLARE and ARALL fiber-metal laminates subject to instrumented drop-weight impacts at various temperatures were studied. GLARE and ARALL are hybrid composites made of alternating layers of aluminum and glass (for GLARE) and aramid- (for ARALL) fiber-reinforced epoxy. Damage in pure aluminum panels impacted by foreign objects was mainly characterized by large plastic deformation surrounding a deep penetration dent. On the other hand, plastic deformation in fiber-metal laminates was often not as severe although the penetration dent was still produced. The more stiff fiber-reinforced epoxy layers provided better bending rigidity; thus, enhancing impact damage tolerance. Severe cracking, however, occurred due to the use of these more brittle fiber-reinforced epoxy layers. Fracture patterns, e.g., crack length and delamination size, were greatly affected by the lay-up configuration rather than by the number of layers, which implies that thickness effect was not significant for the panels tested in this study. Immersion ultrasound techniques were then used to assess damages generated by instrumented drop-weight impacts onto these fiber-metal laminate panels as well as 6061-T6 aluminum/cast acrylic sandwich plates adhered by epoxy. Depending on several parameters, such as impact velocity, mass, temperature, laminate configuration, sandwich construction, etc., various types of impact damage were observed, including plastic deformation, radiating cracks emanating from the impact site, ring cracks surrounding the impact site, partial and full delamination, and combinations of these damages.

Liaw, Benjamin↗
NASA NTRS2003

Ultrasonic Assessment of Impact-Induced Damage and Microcracking in Polymer Matrix Composites

The main objective of this NASA Faculty Awards for Research (FAR) project is to conduct ultrasonic assessment of impact-induced damage and microcracking in fiber-metal laminated (FML) composites at various temperatures. It is believed that the proposed study of impact damage assessment on FML composites will benefit several NASA's missions and current interests, such as ballistic impact testing of composite fan containment and high strain rate deformation modeling of polymer matrix composites. Impact-induced damage mechanisms in GLARE and ARALL fiber-metal laminates subject to instrumented drop-weight impacts at various temperatures were studied. GLARE and ARALL are hybrid composites made of alternating layers of aluminum and glass- (for GLARE) and aramid- (for ARALL) fiber reinforced epoxy. Damage in pure aluminum panels impacted by foreign objects was mainly characterized by large plastic deformation surrounding a deep penetration dent. On the other hand, plastic deformation in fiber-metal laminates was often not as severe although the penetration dent was still produced. The more stiff fiber-reinforced epoxy layers provided better bending rigidity; thus, enhancing impact damage tolerance. Severe cracking, however, occurred due to the use of these more brittle fiber-reinforced epoxy layers. Fracture patterns, e.g., crack length and delamination size, were greatly affected by the lay-up configuration rather than by the number of layers, which implies that thickness effect was not significant for the panels tested in this study. Immersion ultrasound techniques were then used to assess damages generated by instrumented drop-weight impacts onto these fiber-metal laminate panels as well as 2024-T3 aluminum/cast acrylic sandwich plates adhered by epoxy. Depending on several parameters, such as impact velocity, mass, temperature, laminate configuration, sandwich construction, etc., various types of impact damage were observed, including plastic deformation, radiating cracks emanating from the impact site, ring cracks surrounding the impact site, partial and full delamination, and combinations of these damages.

Gyekanyesi, John↗
DOE OSTI2020

Quantitative Proteome Profiling Reveals Cellobiose-Dependent Protein Processing and Export Pathways for the Lignocellulolytic Response in Neurospora crassa

Filamentous fungi are intensively used for producing industrial enzymes, including lignocellulases. Employing insoluble cellulose to induce the production of lignocellulases causes some drawbacks, e.g., a complex fermentation operation, which can be overcome by using soluble inducers such as cellobiose. Here, a triple β-glucosidase mutant of Neurospora crassa, which prevents rapid turnover of cellobiose and thus allows the disaccharide to induce lignocellulases, was applied to profile the proteome responses to cellobiose and cellulose (Avicel). Our results revealed a shared proteomic response to cellobiose and Avicel, whose elements included lignocellulases and cellulolytic product transporters. While the cellulolytic proteins showed a correlated increase in protein and mRNA levels, only a moderate correlation was observed on a proteomic scale between protein and mRNA levels (R 2 = 0.31). Ribosome biogenesis and rRNA processing were significantly overrepresented in the protein set with increased protein but unchanged mRNA abundances in response to Avicel. Ribosome biogenesis, as well as protein processing and protein export, was also enriched in the protein set that showed increased abundance in response to cellobiose. NCU05895, a homolog of yeast CWH43, is potentially involved in transferring a glycosylphosphatidylinositol (GPI) anchor to nascent proteins. This protein showed increased abundance but no significant change in mRNA levels. Disruption of CWH43 resulted in a significant decrease in cellulase activities and secreted protein levels in cultures grown on Avicel, suggesting a positive regulatory role for CWH43 in cellulase production. The findings should have an impact on a systems engineering approach for strain improvement for the production of lignocellulases.

59 BASIC BIOLOGICAL SCIENCES↗