Results for “lateral strain” — Page 13

NASA NTRS1974

Investigation of space shuttle orbiter subsonic stability and control characteristics in the NAAL low speed wind tunnel (0A62b), volume 1

Experimental aerodynamic investigations were conducted on a sting-mounted 0.0405 scale representation of the 140A/B space shuttle orbiter in a 7.75 ft by 11 ft low speed wind tunnel during the time period from November 14, 1973, to December 6, 1973, with the primary test objectives being to establish basic longitudinal stability characteristics in and out of ground effect, as well as lateral-directional stability characteristics in free air. Two dual podded nacelle configurations were also tested, one with three dual podded nacelles on the lower wing surface, and the other with a single dual nacelle on the lower centerline with dual nacelle pylons mounted above each wing. Stability and control characteristics were investigated at nominal elevon, rudder, aileron, and body flap deflections. Pressure bugs were used to determine pressures on the vertical tail at spanwise stations, and aerodynamic force and moment data were measured in the stability axis system by an internally mounted, six component strain gage balance.

Mennell, R.↗

NASA NTRS2004

Development of a Strain Energy Deployable Boom for the Space Technology 5 Mission

The Space Technology 5 (ST5) mission is one of a series of technology demonstration missions for the New Millennium Program. This mission will fly three fully functional 25 kilogram micro class spacecraft in formation through the Earth s magnetosphere; the primary science instrument is a very sensitive magnetometer. The constraints of a 25 kg "Micosat" resulted in a spin stabilized, octagonal spacecraft that is 30 cm tall by 50 cm diameter and has state of the art solar cells on all eight sides. A non-magnetic boom was needed to place the magnetometer as far from the spacecraft and its residual magnetic fields as possible. The ST-5 spacecraft is designed to be spun up and released from its deployer with the boom and magnetometer stowed for later release. The deployer is the topic of another paper, This paper describes the development efforts and resulting self-deploying magnetometer boom.

Meyers, Stew↗

NASA NTRS2004

Development of a Strain Energy Deployable Boom for the Space Technology 5 Mission

The Space Technology 5 (ST5) mission is one of a series of technology demonstration missions for the New Millennium Program. This mission will fly three fully functional 25-kilogram micro-class spacecraft in formation through the Earth's magnetosphere; the primary science instrument is a very sensitive magnetometer. The constraints of a 25-kg Micosat resulted in a spin stabilized, octagonal spacecraft that is 30 cm tall by 50 cm diameter and has state-of-the-art solar cells on all eight sides. A non-magnetic boom was needed to place the magnetometer as far from the spacecraft and its residual magnetic fields as possible. The ST-5 spacecraft is designed to be spun up and released from its deployer with the boom and magnetometer stowed for later release. The deployer is the topic of another paper. This paper describes the development efforts and resulting self-deploying magnetometer boom.

Meyers, Stew↗

NASA NTRS2002

Development of a Generic Creep-Fatigue Life Prediction Model

The objective of this research proposal is to further compile creep-fatigue data of steel alloys and superalloys used in military aircraft engines and/or rocket engines and to develop a statistical multivariate equation. The newly derived model will be a probabilistic fit to all the data compiled from various sources. Attempts will be made to procure the creep-fatigue data from NASA Glenn Research Center and other sources to further develop life prediction models for specific alloy groups. In a previous effort [1-3], a bank of creep-fatigue data has been compiled and tabulated under a range of known test parameters. These test parameters are called independent variables, namely; total strain range, strain rate, hold time, and temperature. The present research attempts to use these variables to develop a multivariate equation, which will be a probabilistic equation fitting a large database. The data predicted by the new model will be analyzed using the normal distribution fits, the closer the predicted lives are with the experimental lives (normal line 1 to 1 fit) the better the prediction. This will be evaluated in terms of a coefficient of correlation, R 2 as well. A multivariate equation developed earlier [3] has the following form, where S, R, T, and H have specific meaning discussed later.

Goswami, Tarun↗

NASA NTRS1984

Tectonic lineaments in the cenozoic volcanics of southern Guatemala: Evidence for a broad continental plate boundary zone

The northern Caribbean plate boundary has been undergoing left lateral strike slip motion since middle Tertiary time. The western part of the boundary occurs in a complex tectonic zone in the continental crust of Guatemala and southernmost Mexico, along the Chixoy-Polochic, Motogua and possibly Jocotan-Chamelecon faults. Prominent lineaments visible in radar imagery in the Neogene volcanic belt of southern Guatemala and western El Salvador were mapped and interpreted to suggest southwest extensions of this already broad plate boundary zone. Because these extensions can be traced beneath Quaternary volcanic cover, it is thought that this newly mapped fault zone is active and is accommodating some of the strain related to motion between the North American and Caribbean plates. Onshore exposures of the Motoqua-Polochic fault systems are characterized by abundant, tectonically emplaced ultramafic rocks. A similar mode of emplacement for these off shore ultramafics, is suggested.

Baltuck, M.↗

DOE OSTI2022

Graphene Nanopattern for Single-Crystal Film Growth, Defect Reduction and Layer Transfer

Thin film heterostructures are key building blocks for advanced electronic and optoelectronic devices. For this, direct heteroepitaxy has been pursued for decades, although it has been challenging to reduce crystal defects stemming from lattice mismatches and thermal mismatches between materials. The layer transfer method has been proposed as an alternative approach, wherein dissimilar materials are separately grown and then hetero-integrated. However, the applicability of layer transfer techniques is limited by several technical challenges, such as controllability, throughput, and damage to the substrate. Remote epitaxy, which is a recently developed method to produce single-crystalline membranes, is a promising approach but cannot be applied to elemental materials such as Si and Ge. In this work, we report graphene nanopattern as a universal template for the growth of single-crystal thin films that can be exfoliated as a freestanding form. This is realized by the chemical inertness of graphene, which allows selective nucleation at the exposed region, followed by lateral overgrowth onto graphene to form a planarized thin film. By employing graphene nanopattern, both group IV and III-V materials are utilized as the substrate as well as the epilayer. The epilayer can be exfoliated at the graphene interface because partially covered graphene effectively weakens the interface, which is corroborated by theoretical analyses of spalling theory. We reveal that graphene nanopattern not only works as a weakened interface for exfoliation, but also allows for dislocation reduction in heteroepitaxial films. This is because of the flexibility and the dangling-bond-free nature of graphene, which provides an additional path for strain relaxation. Therefore, these results represent a meaningful step toward production of high-quality single-crystal membranes that can be hetero-integrated.

Kim, Hyunseok↗

DOE OSTI2022

Graphene Nanopattern for Single-Crystal Film Growth, Defect Reduction and Layer Transfer

Thin film heterostructures are key building blocks for advanced electronic and optoelectronic devices. For this, direct heteroepitaxy has been pursued for decades, although it has been challenging to reduce crystal defects stemming from lattice mismatches and thermal mismatches between materials. The layer transfer method has been proposed as an alternative approach, wherein dissimilar materials are separately grown and then hetero-integrated. However, the applicability of layer transfer techniques is limited by several technical challenges, such as controllability, throughput, and damage to the substrate. Remote epitaxy, which is a recently developed method to produce single-crystalline membranes, is a promising approach but cannot be applied to elemental materials such as Si and Ge. In this work, we report graphene nanopattern as a universal template for the growth of single-crystal thin films that can be exfoliated as a freestanding form. This is realized by the chemical inertness of graphene, which allows selective nucleation at the exposed region, followed by lateral overgrowth onto graphene to form a planarized thin film. By employing graphene nanopattern, both group IV and III-V materials are utilized as the substrate as well as the epilayer. The epilayer can be exfoliated at the graphene interface because partially covered graphene effectively weakens the interface, which is corroborated by theoretical analyses of spalling theory. We reveal that graphene nanopattern not only works as a weakened interface for exfoliation, but also allows for dislocation reduction in heteroepitaxial films. This is because of the flexibility and the dangling-bond-free nature of graphene, which provides an additional path for strain relaxation. Therefore, these results represent a meaningful step toward production of high-quality single-crystal membranes that can be hetero-integrated.

Kim, Hyunseok↗

DOE OSTI2024

Testing and Characterization to Develop a Mechanistic Explanation for Unsaturated Drift of Fiber Optic Sensors during High-Dose Irradiation

The primary limitation for any optical fiber-based sensor for nuclear reactor applications is radiation-induced attenuation (RIA) of the transmitted and/or reflected signals. Based on several recent studies, RIA is tolerable for some fused silica optical fibers with the proper choice of sensing wavelength and fiber dopants. For extreme temperature applications (> 1000°C), sapphire optical fibers have been proposed; however, recent optical transmission measurements performed on bulk sapphire samples showed prohibitively large RIA. For some sensors, radiation-induced dimensional changes in the fiber materials can also cause significant drift. Moreover, the drift that was observed in numerous experiments performed in the High Flux Isotope Reactor (HFIR), the Advanced Test Reactor, the Massachusetts Institute of Technology Reactor, and other international facilities far exceeded what would be expected based on compaction of fused silica glass. Clearly, additional work is needed to better understand the origins of both RIA and radiation-induced drift in both silica and sapphire optical fiber-based sensors before these sensors can be reliably deployed for nuclear applications. This work evaluated the underlying mechanisms that may be responsible for RIA and drift in silica and sapphire materials. First, detailed characterization was performed on bulk fused silica glass samples that were previously irradiated to different neutron fluences at different temperatures to better understand the structural changes that drive radiation-induced drift in the absence of coating effects that are discussed later. Results show that the non-monotonic compaction that occurs with increasing neutron fluence continues up to fast neutron fluences approaching 10 22 n/cm 2 , which has important implications for physics-based models that may be used to compensate for the sensor drift. Initial Raman spectroscopy and synchrotron x-ray diffraction provide insights into the nature of the structural changes. Next, detailed characterizations were performed on silica fibers with various coatings that were subjected to several different thermal treatments. The hypothesis is that the coatings convert to carbon-rich materials that compact under irradiation, putting a large compressive strain on the fiber. Out-of-pile testing confirms that both polyimide and acrylate fiber coatings convert to glassy carbon (GC) materials when heated under inert conditions, and the degree of order (i.e., graphitization) increases with increasing temperature. The results provide increasingly strong evidence that the combination of polymeric coatings and inert (or vacuum) conditions render fiber optic sensors susceptible to significant radiation-induced drift that would not otherwise exist in uncoated fibers. Finally, transmission electron microscopy was performed on bulk sapphire samples that were irradiated to two neutron fluences at different temperatures to gain insights into the potential mechanisms driving the prohibitive RIA at higher neutron fluences and temperatures. Contrary to previous hypotheses, results show that scattering from radiation-induced voids cannot explain the observed RIA. Similarly, models for scattering losses from dislocation loops also do not agree with the experimental results. Instead, fitting to the experimental data shows that increased absorption from aluminum vacancy centers is the most likely explanation for the the prohibitively large RIA that was observed at high irradiation temperature and dose. In addition, the voids that formed in these single-crystal samples were found to align along the basal plane (a-axis) as opposed to that seen in previous observations of c-axis alignment in polycrystalline samples, which could have important implications for anisotropic swelling and other phenomena that could affect sensor performance at high neutron fluence.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2024

Testing and Characterization to Develop a Mechanistic Explanation for Unsaturated Drift of Fiber Optic Sensors during High-Dose Irradiation

The primary limitation for any optical fiber-based sensor for nuclear reactor applications is radiation-induced attenuation (RIA) of the transmitted and/or reflected signals. Based on several recent studies, RIA is tolerable for some fused silica optical fibers with the proper choice of sensing wavelength and fiber dopants. For extreme temperature applications (> 1000°C), sapphire optical fibers have been proposed; however, recent optical transmission measurements performed on bulk sapphire samples showed prohibitively large RIA. For some sensors, radiation-induced dimensional changes in the fiber materials can also cause significant drift. Moreover, the drift that was observed in numerous experiments performed in the High Flux Isotope Reactor (HFIR), the Advanced Test Reactor, the Massachusetts Institute of Technology Reactor, and other international facilities far exceeded what would be expected based on compaction of fused silica glass. Clearly, additional work is needed to better understand the origins of both RIA and radiation-induced drift in both silica and sapphire optical fiber-based sensors before these sensors can be reliably deployed for nuclear applications. This work evaluated the underlying mechanisms that may be responsible for RIA and drift in silica and sapphire materials. First, detailed characterization was performed on bulk fused silica glass samples that were previously irradiated to different neutron fluences at different temperatures to better understand the structural changes that drive radiation-induced drift in the absence of coating effects that are discussed later. Results show that the non-monotonic compaction that occurs with increasing neutron fluence continues up to fast neutron fluences approaching 10 22 n/cm 2 , which has important implications for physics-based models that may be used to compensate for the sensor drift. Initial Raman spectroscopy and synchrotron x-ray diffraction provide insights into the nature of the structural changes. Next, detailed characterizations were performed on silica fibers with various coatings that were subjected to several different thermal treatments. The hypothesis is that the coatings convert to carbon-rich materials that compact under irradiation, putting a large compressive strain on the fiber. Out-of-pile testing confirms that both polyimide and acrylate fiber coatings convert to glassy carbon (GC) materials when heated under inert conditions, and the degree of order (i.e., graphitization) increases with increasing temperature. The results provide increasingly strong evidence that the combination of polymeric coatings and inert (or vacuum) conditions render fiber optic sensors susceptible to significant radiation-induced drift that would not otherwise exist in uncoated fibers. Finally, transmission electron microscopy was performed on bulk sapphire samples that were irradiated to two neutron fluences at different temperatures to gain insights into the potential mechanisms driving the prohibitive RIA at higher neutron fluences and temperatures. Contrary to previous hypotheses, results show that scattering from radiation-induced voids cannot explain the observed RIA. Similarly, models for scattering losses from dislocation loops also do not agree with the experimental results. Instead, fitting to the experimental data shows that increased absorption from aluminum vacancy centers is the most likely explanation for the the prohibitively large RIA that was observed at high irradiation temperature and dose. In addition, the voids that formed in these single-crystal samples were found to align along the basal plane (a-axis) as opposed to that seen in previous observations of c-axis alignment in polycrystalline samples, which could have important implications for anisotropic swelling and other phenomena that could affect sensor performance at high neutron fluence.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1992

Effect of low-speed impact damage and damage location on behavior of composite panels

The effect of low speed impact damage on the compression and tension strength of thin and moderately thick composite specimens was investigated. Impact speed ranged from 50 to 550 ft./sec., with corresponding impact energies from 0.25 to 30.7 ft. x lb. Impact locations were near the center of the specimen or near a lateral unloaded edge. In this study, thin specimens with only 90 degree and + or - 45 degree plies that were impacted away from the unloaded edge suffered less reduction in load carrying capability because of impact damage than of the same specimens impacted near the unloaded edge. Failure loads of thicker compression loaded specimens with a similar stacking sequence were independent of impact location. Failure loads of thin tension loaded specimens with 0 degree plies was independent of impact location, whereas failure loads of thicker compression loaded specimens with 0 degree plies were dependent upon impact location. A finite element analysis indicated that high axial strains occurred near the unloaded edges of the postbuckled panels. Thus, impacts near the unloaded edge would significantly affect the behavior of the postbuckled panel.

Jegley, Dawn C.↗

DOE OSTI2023

Impact of inoculation practices on microbiota assembly and community stability in a fabricated ecosystem

Studying plant-microbe-soil interactions is challenging due to their high complexity and variability in natural ecosystems. While fabricated ecosystems provide opportunities to recapitulate aspects of these systems in reduced complexity and controlled environments, inoculation can be a significant source of variation. To tackle this, we evaluated how different bacteria inoculation practices and plant harvesting time points affect the reproducibility of a microbial synthetic community (SynCom) in association with the model grass Brachypodium distachyon. We tested three microbial inoculation practices: seed inoculation, transplant inoculation, and seedling inoculation; and two harvesting points: early (14-day-old plants) and late (21 days post-inoculation). We grew our plants and bacterial strains in sterile devices (EcoFABs) and characterized the microbial community from root, rhizosphere, and sand using 16S ribosomal RNA gene sequencing. The results showed that inoculation practices significantly affected the rhizosphere microbial community only when harvesting at an early time point but not at the late stage. As the SynCom showed a persistent association with B. distachyon at 21 days post-inoculation regardless of inoculation practices, we assessed the reproducibility of each inoculation method and found that transplant inoculation showed the highest reproducibility. Moreover, plant biomass was not adversely affected by transplant inoculation treatment. We concluded that bacteria inoculation while transplanting coupled with a later harvesting time point gives the most reproducible microbial community in the EcoFAB-B. distachyon-SynCom fabricated ecosystem and recommend this method as a standardized protocol for use with fabricated ecosystem experimental systems.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1975

On the oscillation of the laterally heterogeneous earth, 1

The perturbative effects, as cause by lateral inhomogeneities in the earth structure and by Coriolis force, contaminate the originally toroidal and spheroidal earth's oscillations, making them of mixed type. For this reason, in order to make the computation of the perturbations more uniform and homogeneous, it was suggested that the earth's free oscillations be expanded into a series in terms of generalized harmonics familiar from the theory of angular momentum in quantum mechanics. Making use of Gibbsian symbolism and of some operators from the theory of angular momentum, explicit expressions were deduced for the perturbative terms in the differential equation of the earth's free oscillations. Decomposition of the strain tensor in terms of canonical vectors was also obtained.

Musen, P.↗

DOE OSTI2023

HFTS-1 (Final Report)

Despite the long history of hydraulic fracturing, the optimal number of fracturing stages during multi-stage fracture stimulation in horizontal wells can be a complex subject. In addition to the increased expense of multistage fracturing in horizontal wells, increasing the number of fracturing stages does not always correlate with a commensurate increase in production. The problem is the application of a uniform fracture stimulation design to all stages with no consideration for geological variations along the wellbore. The result is an inefficient use and costly waste of energy and water. Optimization of the fracturing process requires an understanding of the cause-and-effect relationship between fracturing parameters and local geological properties at a given location along the wellbore. Realizing that the generalized rock mechanics theories and hypotheses are not truly applicable to fractured and laminated shales, quantifiable impacts of a shale’s geomechanical and depositional features are a prerequisite for design and implementation of optimized hydraulic fractures. The overarching goal of this project is to understand and define the relationships of shale geology and fracture dynamics using detailed field data that includes coring of the fracture domain. Finally, resource recovery from shale formations is estimated to be less than fifteen percent. Research proposed in this project will establish the foundations for investigating enhanced recovery techniques for increased resource recovery in existing fracture treated wells. Natural gas as an EOR fluid is in the initial stages of being used broadly in the oil and gas industry and as such, many aspects of the process need to be researched and addressed prior to widespread acceptance. In addition, re-fracturing techniques, particularly using cemented liners also need to be further investigated. This project explores several of these EOR techniques in greater detail, not just at the theoretical level, but through actual field test sites. This report delves into the research program, identified tasks, several studies, observations, results, and conclusions under the Hydraulic Fracturing Test Site (HFTS) project. This test project is subdivided into three distinct phases and each phase is discussed in detail under separate sections. The original test site for Phase 1 as well as the Phase 2 site are in Midland Basin in Texas and operated by Laredo Petroleum. In the first two phases, the program targeted the Wolfcamp formation in Midland Basin. Phase 3 of the study targeted the EagleFord play in South Texas with Devon Energy as the operator. Significant conclusions from this study include: 1) lateral and vertical fracture growth mapping as well as proppant transport behavior, 2) Use of field gas and its applicability for huff n puff EOR injection in the Midland Basin, 3) Development and validation of proppant log, both at core scale as well as in-fill well implementation by analyzing drilling mud return samples, 4) Applicability of liner refracturing including best practices for enhanced unit level productivity. This report will detail all these studies as well as technical results and conclusions from said studies. These include general subsurface characterization work, completion designs as implemented, studies looking at fracture geometry, high resolution microseismic study, advanced crosswell strain mapping studies including drainage characterization, core characterization results, proppant analysis (core and observation wells), geochemistry, etc. to name a few.

02 PETROLEUM↗

NASA NTRS2004

Tethers as Debris: Simulating Impacts of Kevlar Tethers on Shuttle Tiles

In a previous paper I examined the effects of impacts of polymer tethers on aluminum plates using the SPHC hydrodynamic code. In this paper I apply tether models to a new target - models of Space Shuttle tiles developed during the STS 107 accident investigation. In this three-dimensional simulation, a short tether fragment strikes a single tile supported on an aluminum backing plate. A tile of the LI-900 material is modeled. Penetration and damage to the tile and the backwall are characterized for three normal impact velocities. The tether is modeled as a bundle of eight 1-mm strands, with the bundle having dimensions 2-mm x 4-mm x 20-cm. The bulk material properties used are those of Kevlar(TradeMark) 49, for which a Mie-Gruneisen multiphase equation of state (eos) is used. In addition, the strength model is applied in a linear sense, such that tensile loads along the strand length are supported, but there is no strength in the lateral directions. Tile models include the various layers making up the tile structure. The outermost layer is a relatively dense borosilicate glass, known as RCG, 0.5-mm thick. The RCG layer is present on the top and four sides of the tile. Below this coating is the bulk of the tile, 1.8- in thick, made of LI-900, a product consisting of rigidized fiberous silica with a density of 9 lWft3. Below the main insulating layer is a bottom layer of the same material that has been treated to increase its density by approximately 69% to improve its strength. This densified layer is bonded to a Strain Isolation Pad (SIP), modeled as a refractory felt fabric. The SIP is bonded to an aluminum 2024 wall 0.1-in thick. The tile and backwall materials use a Me-Gruneisen multiphase eos, with the exception of the SIP felt, which uses a fabric equation of state. Fabrics must be crushed to the full bulk material density before bulk material properties and a Mie-Gruneisen eos are applied. Tether fragment impact speeds of 3,7, and 10 km/s are simulated, with impact velocities normal to the tile face. Damage results are presented in tabular format.

Evans, Steven W.↗

NASA NTRS2001

Proliferation, differentiation and apoptosis in connexin43-null osteoblasts

Osteoblasts are highly coupled by gap junctions formed primarily by connexin43 (Cx43). We have shown that interference with Cx43 expression or function disrupts transcriptional regulation of osteoblast genes, and that deletion of Cx43 in the mouse causes skeletal malformations, delayed mineralization, and osteoblast dysfunction. Here, we studied the mechanisms by which genetic deficiency of Cx43 alters osteoblast development. While cell proliferation rates were similar in osteoblastic cells derived from calvaria of Cx43-null and wild type mice, camptothecin-induced apoptosis was 3-fold higher in mutant compared to wild type osteoblasts. When grown in mineralizing medium, Cx43-null cells were able to produce mineralized matrix but it took one week longer to reach the same mineralization levels as in normal cells. Likewise, expression of alkaline phosphatase activity per cell--a marker of osteoblast differentiation--was maximal only 2 weeks later in Cx43-null relative to wild-type cells. These observations suggest that Cx43 is important for a normal and timely development of the osteoblastic phenotype. Delayed differentiation and increase programmed cell death may explain the skeletal phenotype of Cx43-null mice.

NASA Discipline Cell Biology↗

DOE OSTI2023

Interactions with microbial consortia have variable effects in organic carbon and production of exometabolites among genotypes of Populus trichocarpa

Abstract Poplar is a short‐rotation woody crop frequently studied for its significance as a sustainable bioenergy source. The successful establishment of a poplar plantation partially depends on its rhizosphere—a dynamic zone governed by complex interactions between plant roots and a plethora of commensal, mutualistic, symbiotic, or pathogenic microbes that shape plant fitness. In an exploratory endeavor, we investigated the effects of a consortium consisting of ectomycorrhizal fungi and a beneficial Pseudomonas sp. strain GM41 on plant growth (including height, stem girth, leaf, and root growth) and as well as growth rate over time, across four Populus trichocarpa genotypes. Additionally, we compared the level of total organic carbon and plant exometabolite profiles across different poplar genotypes in the presence of the microbial consortium. These data revealed no significant difference in plant growth parameters between the treatments and the control across four different poplar genotypes at 7 weeks post‐inoculation. However, total organic carbon and exometabolite profiles were significantly different between the genotypes and the treatments. These findings suggest that this microbial consortium has the potential to trigger early signaling responses in poplar, influencing its metabolism in ways crucial for later developmental processes and stress tolerance.

59 BASIC BIOLOGICAL SCIENCES↗

NASA NTRS1992

Effect of low-speed impact damage and damage location on behavior of composite panels

An investigation of the effects of low-speed impact damage on the compression and tension strength of thin (less than .05 inches thick) and moderately thick (between .12 and .17 inches thick) composite specimens was conducted. Impact speeds ranged from 50 to 550 ft/sec (impact energies from .25 to 30.7 ft-lb) and impact locations were near or away from a lateral unloaded edge. In this study, thin tension-loaded or compression-loaded specimens with only 90 deg and +/- 40 deg plies which were impacted away from the unloaded edge suffered less reduction in maximum load-carrying capability due to impact damage than the same specimens impacted near the unloaded edge. Unlike the thin laminates, failure loads of thicker compression-loaded specimens with a similar stacking sequence were independent of impact location. Failure loads of thin tension-loaded specimens with 0 deg plies were independent of impact location while failure loads of thicker compression-loaded specimens with 0 deg plies were dependent upon impact location. A finite-element analysis of strain distributions across the panel width indicated that high axial strains occur near the unloaded edges of postbuckled panels, indicating that impacts near the unloaded edge would significantly effect the behavior of postbuckled panels.

Jegley, Dawn↗

NASA NTRS2001

Large-Scale Flow Structure in Turbulent Nonpremixed Flames under Normal- And Low-Gravity Conditions

It is well known that buoyancy has a major influence on the flow structure of turbulent nonpremixed jet flames. Buoyancy acts by inducing baroclinic torques, which generate large-scale vortical structures that can significantly modify the flow field. Furthermore, some suggest that buoyancy can substantially influence the large-scale structure of even nominally momentum-dominated flames, since the low velocity flow outside of the flame will be more susceptible to buoyancy effects. Even subtle buoyancy effects may be important because changes in the large-scale structure affects the local entrainment and fluctuating strain rate, and hence the structure of the flame. Previous studies that have compared the structure of normal- and micro-gravity nonpremixed jet flames note that flames in microgravity are longer and wider than in normal-gravity. This trend was observed for jet flames ranging from laminar to turbulent regimes. Furthermore, imaging of the flames has shown possible evidence of helical instabilities and disturbances starting from the base of the flame in microgravity. In contrast, these characteristics were not observed in normal-gravity. The objective of the present study is to further advance our knowledge of the effects of weak levels of buoyancy on the structure of transitional and turbulent nonpremixed jet flames. In later studies we will utilize the drop tower facilities at NASA Glenn Research Center (GRC), but the preliminary work described in this paper was conducted using the 1.25-second drop tower located at the University of Texas at Austin. A more detailed description of these experiments can be found in Idicheria et al.

Clemens, N. T.↗