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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 1,423 records · Page 79
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Iosipescu shear characterization of polymeric and metal matrix composites

The paper outlines the results of an experimental/analytical investigation of deformation and stress fields in the test section of graphite/epoxy and boron/aluminum Iosipescu specimens using high-resolution moire interferometry and finite-element analysis. Very good correlation between experiment and analysis is demonstrated for the graphite/epoxy specimens. This, in turn, justifies the use of correction factors employed in the previous investigations to eliminate differences in the initial shear moduli obtained from 0-deg and 90-deg Iosipescu specimens. The significant discrepancies observed in the case of boron/aluminum specimens are attributed to localized yielding at the notch tips caused by the clamping action, the associated in-plane bending effects and changing boundary conditions due to slippage in the grips.

Pindera, M.-J.↗
NASA NTRS1968

Propulsive re-entry aerodynamics Interim report, 1 Jun. 1967 - 1 Jun. 1968

This report discusses the progress accomplished during the first year of a two-year contract to study Propulsive Re-Entry Aerodynamics. Analytical methods were developed during the first year to predict the flow field in the immediate vicinity of a planetary entry system composed of an aeroshell with a single retrorocket which exhausts into a subsonic or supersonic counterflowing planetary atmosphere. In the second year a digital computer program will be developed for the analytical solutions, and the analytical model will be tested by performing an experimental test program and comparing the experimental results with the analytical predictions. The analytical investigation considers the flow field due to a single supersonic retrorocket exhausting from an aeroshell into oncoming subsonic, transonic, or supersonic streams in the large thrusting coefficient regime, 0.5 < C(sub T) = T/q(sub ∞) A(sub m) < 15, which is the range of thrusting coefficients encountered during the terminal landing phase for planetary landing on Mars or Venus. Analyses are provided for all the geometrical features of the flow field such as the location of the terminal shock, jet boundary, and the profile for the interface between the jet and atmospheric gases. In addition, analyses are developed which describe the growth of the mixing layers along the interface and at the edge of the jet boundary and dead-air region and the reattachment of the shear layer to the aeroshell or the recompression of the shear layer in wake type flow. A comprehensive discussion of the experimental wind tunnel test program to be accomplished in Phase II is presented.

Philip O Jarvinen↗
DOE OSTI2020

In situ indentation and high cycle tapping deformation responses in a nanolaminate crystalline/amorphous metal composite

The incorporation of nanostructured and amorphous metals into modern applications is reliant on the understanding of deformation and failure modes in constrained conditions. To study this, a 105 nm crystalline Cu/160 nm amorphous Cu 45 Zr 55 (at.%) multilayer structure was fabricated with the two crystalline layers sputter deposited between the top-middle-bottom amorphous layers and prepared to electron transparency. The multilayer was then in situ indented either under a single load to a depth of ~ 100 nm (max load of ~ 100 μN) or held at 20 μN and then repeatedly indented with an additional 5 μN up to 20,000 cycles in a transmission electron microscope to compare the deformation responses in the nanolaminate. For the single indentation test, the multilayer showed serrated load-displacement behavior upon initial indentation inductive of shear banding. Additionally, at an indentation depth of ~ 32 nm, the multilayer exhibited perfect plastic behavior and no strain hardening. Both indented and fatigue-indented films revealed diffraction contrast changes with deformation. Subsequent Automated Crystal Orientation Mapping (ACOM) measurements confirmed and quantified global texture changes in the crystalline layers with specifically identified grains revealing rotation. Using a finite element model, the in-plane displacement vectors under the indent mapped conditions where ACOM determined grain rotation was observed, indicating the stress flow induced grain rotation. Furthermore, the single indented Cu layers also exhibited evidence of deformation induced grain growth, which was not evident in the fatigue-indented Cu based multilayer. Finally, the single indented multilayer retained a significant plastic crater in the upper most amorphous layer that directly contacted the indenter; a negligible crater impression in the same region was observed in the fatigued tested multilayer. These differences are explained by the different loading methods, applied load, and deformation mechanisms experienced in the multilayers.

36 MATERIALS SCIENCE↗
NASA NTRS2020

Aerospace Threaded Fastener Strength With Joint Shims

Bolted joints with a nonload-carrying member, like a shim or spacer, and loaded in shear introduce bending moment into the bolt that reduces the bolt shear load-carrying capability. Various design criteria are available that attempt to account for the additional bending and provide reduced allowable bolt loads. The actual shear load-carrying capability of a typical aerospace fastener with various thickness shims was determined by test using both aluminum and steel joint members. The results are compared against existing design criteria, which are shown to be adequate for their intended purposes.

threaded fastener, bolt, strength criteria, shim, ↗
DOE OSTI2017

Electron Acceleration at Pulsar Wind Termination Shocks

We study the acceleration of electrons and positrons at an electromagnetically modified, ultrarelativistic shock in the context of pulsar wind nebulae. We simulate the outflow produced by an obliquely rotating pulsar in proximity of its termination shock with a two-fluid code that uses a magnetic shear wave to mimic the properties of the wind. We integrate electron trajectories in the test-particle limit in the resulting background electromagnetic fields to analyze the injection mechanism. We find that the shock-precursor structure energizes and reflects a sizable fraction of particles, which becomes available for further acceleration. We investigate the subsequent first-order Fermi process sustained by small-scale magnetic fluctuations with a Monte Carlo code. We find that the acceleration proceeds in two distinct regimes: when the gyroradius r{sub g} exceeds the wavelength of the shear λ, the process is remarkably similar to first-order Fermi acceleration at relativistic, parallel shocks. This regime corresponds to a low-density wind that allows the propagation of superluminal waves. When r{sub g}<λ, which corresponds to the scenario of driven reconnection, the spectrum is softer.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS2011

Flexible Ablators: Applications and Arcjet Testing

Flexible ablators were conceived in 2009 to meet the technology pull for large, human Mars Exploration Class, 23 m diameter hypersonic inflatable aerodynamic decelerators. As described elsewhere, they have been recently undergoing initial technical readiness (TRL) advancement by NASA. The performance limits of flexible ablators in terms of maximum heat rates, pressure and shear remain to be defined. Further, it is hoped that this emerging technology will vastly expand the capability of future NASA missions involving atmospheric entry systems. This paper considers four topics of relevance to flexible ablators: (1) Their potential applications to near/far term human and robotic missions (2) Brief consideration of the balance between heat shield diameter, flexible ablator performance limits, entry vehicle controllability and aft-body shear layer impingement of interest to designers of very large entry vehicles, (3) The approach for developing bonding processes of flexible ablators for use on rigid entry bodies and (4) Design of large arcjet test articles that will enable the testing of flexible ablators in flight-like, combined environments (heat flux, pressure, shear and structural tensile loading). Based on a review of thermal protection system performance requirements for future entry vehicles, it is concluded that flexible ablators have broad applications to conventional, rigid entry body systems and are enabling to large deployable (both inflatable and mechanical) heat shields. Because of the game-changing nature of flexible ablators, it appears that NASA's Office of the Chief Technologist (OCT) will fund a focused, 3-year TRL advancement of the new materials capable of performance in heat fluxes in the range of 200-600 W/sq. cm. This support will enable the manufacture and use of the large-scale arcjet test designs that will be a key element of this OCT funded activity.

Thermal Protection↗
NASA NTRS2011

Sensor for Direct Measurement of the Boundary Shear Stress in Fluid Flow

The formation of scour patterns at bridge piers is driven by the forces at the boundary of the water flow. In most experimental scour studies, indirect processes have been applied to estimate the shear and normal stress using measured velocity profiles. The estimations are based on theoretical models and associated assumptions. However, the turbulence flow fields and boundary layer in the pier-scour region are very complex. In addition, available turbulence models cannot account accurately for the bed roughness effect. Direct measurement of the boundary shear and normal stress and their fluctuations are attractive alternatives. However, this approach is a challenging one especially for high spatial resolution and high fidelity measurements. The authors designed and fabricated a prototype miniature shear stress sensor including an EDM machined floating plate and a high-resolution laser optical encoder. Tests were performed both in air as well as operation in water with controlled flow. The sensor sensitivity, stability and signal-to-noise level were measured and evaluated. The detailed test results and a discussion of future work will be presented in this paper.

shear stress↗
DOE OSTI2023

Sidewall Breach During Lithium-Ion Battery Thermal Runaway Triggered by Cell-to-Cell Propagation Visualized Using High-Speed X-Ray Imaging

With the rapid deployment of Li-ion batteries (LiBs) in a range of applications, it is crucial to ensure their safe operation. Therefore, it is necessary to investigate the rapid thermal runaway failure that LiBs can undergo if improperly operated or subjected to abuse scenarios so that hazardous events can be avoided or mitigated. Sidewall breaches or ruptures of LiBs during thermal runaway are considered the most hazardous failure scenario, resulting in hot abrasive flare from the casing of the cell that can impinge on neighbouring cells and lead to the propagation of thermal runaway throughout a battery pack. Yet, the process leading up to the sidewall breach is not well understood due to the extreme difficulty in visualizing such a failure in commercially relevant cells. With the application of a newly developed chamber for remote-controlled abuse testing of batteries coupled with simultaneous X-ray imaging, we demonstrate here for the first time an in-situ visualization of a sidewall breach. By further applying spatiotemporal mapping techniques, the internal thermal runaway events leading up to the sidewall breach can be analyzed in detail. Subsequently, the speed of the electrode layer delamination could be calculated to a speed of 0.6 m/s. These new insights bring more clarity regarding this phenomenon, that in turn can help battery designers improve battery safety.

battery safety↗
NASA NTRS1989

Evaluation of the split cantilever beam for Mode 3 delamination testing

A test rig for testing a thick split cantilever beam for scissoring delamination (mode 3) fracture toughness was developed. A 3-D finite element analysis was conducted on the test specimen to determine the strain energy release rate, G, distribution along the delamination front. The virtual crack closure technique was used to calculate the G components resulting from interlaminar tension, GI, interlaminar sliding shear, GII, and interlaminar tearing shear, GIII. The finite element analysis showed that at the delamination front no GI component existed, but a GII component was present in addition to a GIII component. Furthermore, near the free edges, the GII component was significantly higher than the GIII component. The GII/GIII ratio was found to increase with delamination length but was insensitive to the beam depth. The presence of GII at the delamination front was verified experimentally by examination of the failure surfaces. At the center of the beam, where the failure was in mode 3, there was significant fiber bridging. However, at the edges of the beam where the failure was in mode 3, there was no fiber bridging and mode 2 shear hackles were observed. Therefore, it was concluded that the split cantilever beam configuration does not represent a pure mode 3 test. The experimental work showed that the mode 2 fracture toughness, GIIc, must be less than the mode 3 fracture toughness, GIIIc. Therefore, a conservative approach to characterizing mode 3 delamination is to equate GIIIc to GIIc.

Martin, Roderick H.↗
NASA NTRS1991

Evaluation of the split cantilever beam for mode III delamination testing

A test rig for testing a thick split cantilever beam for scissoring delamination (mode 3) fracture toughness was developed. A 3-D finite element analysis was conducted on the test specimen to determine the strain energy release rate, G, distribution along the delamination front. The virtual crack closure technique was used to calculate the G components resulting from interlaminar tension, GI, interlaminar sliding shear, GII, and interlaminar tearing shear, GIII. The finite element analysis showed that at the delamination front no GI component existed, but a GII component was present in addition to a GIII component. Furthermore, near the free edges, the GII component was significantly higher than the GIII component. The GII/GIII ratio was found to increase with delamination length but was insensitive to the beam depth. The presence of GII at the delamination front was verified experimentally by examination of the failure surfaces. At the center of the beam, where the failure was in mode 3, there was significant fiber bridging. However, at the edges of the beam where the failure was in mode 3, there was no fiber bridging and mode 2 shear hackles were observed. Therefore, it was concluded that the split cantilever beam configuration does not represent a pure mode 3 test. The experimental work showed that the mode 2 fracture toughness, GIIc, must be less than the mode 3 fracture toughness, GIIIc. Therefore, a conservative approach to characterizing mode 3 delamination is to equate GIIIc to GIIc.

Martin, Roderick, H.↗
DOE OSTI2021

A Computational Study of the Shear Behavior of Reinforced Concrete Beams Affected from Alkali–Silica Reactivity Damage

In this study, an investigation of the shear behavior of full-scale reinforced concrete (RC) beams affected from alkali–silica reactivity damage is presented. A detailed finite element model (FEM) was developed and validated with data obtained from the experiments using several metrics, including a force–deformation curve, rebar strains, and crack maps and width. The validated FEM was used in a parametric study to investigate the potential impact of alkali–silica reactivity (ASR) degradation on the shear capacity of the beam. Degradations of concrete mechanical properties were correlated with ASR expansion using material test data and implemented in the FEM for different expansions. The finite element (FE) analysis provided a better understanding of the failure mechanism of ASR-affected RC beam and degradation in the capacity as a function of the ASR expansion. The parametric study using the FEM showed 6%, 19%, and 25% reduction in the shear capacity of the beam, respectively, affected from 0.2%, 0.4%, and 0.6% of ASR-induced expansion.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Numerical simulation of systems of shear bands in ductile metal with inclusions

We develop a method for numerical simulations of high strain-rate loading of mesoscale samples of ductile metal with inclusions. Because of its small-scale inhomogeneity, the composite material is prone to localized shear deformation (adiabatic shear bands). This method employs the Generalized Method of Cells of Paley and Aboudi [Mech. Materials, vol. 14, pp. 127–139, 1992] to ensure that the micro mechanical behavior of the metal and inclusions is reflected properly in the behavior of the composite at the mesoscale. To find the effective plastic strain rate when shear bands are present, we extend and apply the analytic and numerical analysis of shear bands of Glimm, Plohr, and Sharp [Mech. Materials, vol. 24, pp. 31–41, 1996]. Our tests of the method focus on the stress/strain response in uniaxial-strain flow, both compressive and tensile, of depleted uranium metal containing silicon carbide inclusions. We use the Preston-Tonks-Wallace viscoplasticity model [J. Appl. Phys., vol. 93, pp. 211–220, 2003], which applies to the high strain-rate regime of an isotropic viscoplastic solid. In results, we verify the elevated temperature and thermal softening at shear bands in our simulations of pure DU and DU/SiC composites. We also note that in composites, due the asymmetry caused by the inclusions, shear band form at different times in different subcells. In particular, in the subcells near inclusions, shear band form much earlier than they do in pure DU.

36 MATERIALS SCIENCE↗
NASA NTRS1981

JT9D performance deterioration results from a simulated aerodynamic load test

The results of testing to identify the effects of simulated aerodynamic flight loads on JT9D engine performance are presented. The test results were also used to refine previous analytical studies on the impact of aerodynamic flight loads on performance losses. To accomplish these objectives, a JT9D-7AH engine was assembled with average production clearances and new seals as well as extensive instrumentation to monitor engine performance, case temperatures, and blade tip clearance changes. A special loading device was designed and constructed to permit application of known moments and shear forces to the engine by the use of cables placed around the flight inlet. The test was conducted in the Pratt & Whitney Aircraft X-Ray Test Facility to permit the use of X-ray techniques in conjunction with laser blade tip proximity probes to monitor important engine clearance changes. Upon completion of the test program, the test engine was disassembled, and the condition of gas path parts and final clearances were documented. The test results indicate that the engine lost 1.1 percent in thrust specific fuel consumption (TSFC), as measured under sea level static conditions, due to increased operating clearances caused by simulated flight loads. This compares with 0.9 percent predicted by the analytical model and previous study efforts.

Stakolich, E. G.↗
NASA NTRS1981

JT9D performance deterioration results from a simulated aerodynamic load test

This paper presents the results of testing to identify the effects of simulated aerodynamic flight loads on JT9D engine performance. The test results were also used to refine previous analytical studies on the impact of aerodynamic flight loads on performance losses. To accomplish these objectives, a JT9D-7AH engine was assembled with average production clearances and new seals as well as extensive instrumentation to monitor engine performance, case temperatures, and blade tip clearance changes. A special loading device was designed and constructed to permit application of known moments and shear forces to the engine by the use of cables placed around the flight inlet. The test was conducted in the Pratt and Whitney Aircraft X-Ray Test Facility to permit the use of X-ray techniques in conjunction with laser blade tip proximity probes to monitor important engine clearance changes. Upon completion of the test program, the test engine was disassembled, and the condition of gas path parts and final clearances were documented. The test results indicate that the engine lost 1.1 percent in thrust specific fuel consumption (TSFC), as measured under sea level static conditions, due to increased operating clearances caused by simulated flight loads. This compares with 0.9 percent predicted by the analytical model and previous study efforts.

Stakolich, E. G.↗
NASA NTRS1987

Mechanical response of unidirectional boron/aluminum under combined loading

Three test methods were employed to characterize the response of unidirectional Boron/Aluminum metal matrix composite material under monotonic and cyclic loading conditions, namely, losipescu shear, off-axis tension and compression. The characterization of the elastic and plastic response includes the elastic material properties, yielding and subsequent hardening of the unidirectional composite under different stress ratios in the material principal coordinate system. Yield loci generated for different stress ratios are compared for the three different test methods, taking into account residual stresses and specimen geometry. Subsequently, the yield locus for in-plane shear is compared with the prediction of an analytical, micromechanical model. The influence of the scatter in the experimental data on the predicted yield surface is also analyzed. Lastly, the experimental material strengths in tension and compression are correlated with the maximum stress and the Tsai-Wu failure criterion.

Becker, Wolfgang↗
DOE OSTI2025

Subvoxel Control of Fiber Orientation via Multidirectional Shearing in 3D Printing

Anisotropy, the characteristic of materials exhibiting different properties based on their direction, is widespread in nature. Conventional manufacturing techniques often fall short in recreating such complex anisotropy. While 3D printing allows for precise fiber deposition in anisotropic composites, previous studies have only achieved bulk reorientation of fibers at the voxel level in two dimensions. This limits the replication of localized 3D anisotropies found in natural materials. To address this, a novel 3D printing technique is presented that enables subvoxel control of fiber orientation in all three directions using multidirectional shearing via nozzle rotation and inclination. The fiber orientation control in these experimental tests is driven by a numerical model, enabling a fully digital approach to program microstructures within a strand. This programmability is demonstrated through mechanical and thermal tests, illustrating a localized and controllable response to external stimuli. Achieving such complex anisotropy holds potential across several fields, including wearables and biomedical implants, lightweight composite structures, and energy storage technologies such as batteries and supercapacitors.

3D printing↗
DOE OSTI2018

Microstructure and Mechanical Properties of Cast Al-5Zn-2Mg Alloy Subjected to Equal-Channel Angular Pressing

In the present work, cast Al-5Zn-2Mg alloy was processed through equal-channel angular pressing (ECAP) in route B{sub C} up to four number of passes. Microstructure and mechanical properties were investigated on processed and unprocessed materials. In cast condition, the material was composed of dendritic structure. After homogenization treatment, large-sized grains were observed. After ECAP processing, significant grain refinement was observed. After ECAP processing, high-density dislocations and high degree of misorientation between the grains were observed. In cast material, rod-shaped precipitates were observed, while, after ECAP processing, spherical-shaped precipitates were observed. ECAP processing leads to a noticeable improvement in the mechanical properties of the material. After four passes, 122% improvement in the microhardness and 135% improvement in the ultimate tensile strength of the material were observed. After three passes, a slight decrease in the mechanical properties was observed. This is attributed to the dissolution of the metastable η′ phase, annihilation of dislocations, dynamic recrystallization and texturing during ECAP processing. Brittle fracture mode was observed in tensile testing cast and homogenized samples. After ECAP processing, fracture mode was changed into shear fracture mode.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Grain boundary slip – twin transmission in titanium

Here, using a combination of mechanical testing, scanning electron microscopy, and a unified crystal plasticity framework for discrete intragranular shear localization, we investigate intense, localized slip bands on prismatic planes and {10$\bar{1}$2} $\langle$$\bar{1}$011$\rangle$ tensile twins, and their transmission across the grain boundaries (GBs) in commercially pure titanium. The analyses show that the orientation and curvature of the GB influence the local stress fields at the GBs, and consequently, the slip/twin transmission across the boundary. In addition to host grain properties, neighboring grain properties, such as active slip systems and instances of heterogeneity like slip bands and twins, heavily affect the deformation mechanisms in each grain. Finally, the applicability of geometric factors to predict the transmission in the experimentally observed co-located pairs is discussed. The local stress field calculated by the discrete slip and twin band model is shown to be capable of determining whether a transmission has occurred in an observed co-located pair, and also the direction of the transmission.

36 MATERIALS SCIENCE↗