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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Influence of Material Distribution on Impact Resistance of Hybrid Composites

Impact events occur in a wide variety of circumstances. A typical example is a bullet impacting a target made of composite material. These impact events produce time-varying loads on a structure that can result in damage. As a first step to understanding the damage resistance issue in composite laminates, an accurate prediction of the transient response during an impact event is necessary. The analysis of dynamic loadings on laminated composite plates has undergone considerable development recently. Rayleigh-Ritz energy method was used to determine the impact response of laminated plates. The impact response of composite plates using shear deformation plate theory was analyzed. In recent work a closed-form solution was obtained for a rectangular plate with four edges simply supported subjected to a center impact load using classical plate theory. The problem was further investigated and the analysis results compared of both classical plate theory and shear deformation theory, and found that classical plate theory predicts very accurate results for the range of small deformations considered. In this study, the influence of cross sectional material distribution on the comparative impact responses of hybrid metal laminates subjected to low and medium velocity impacts is investigated. A simple linear model to evaluate the magnitude of the impact load is proposed first, and it establishes a relation between the impact velocity and the impact force. Then a closed-form solution for impact problem is presented. The results were compared with the finite element analysis results. For an 11 layer-hybrid laminate, the impact response as a function of material distribution in cross-section is presented. With equal areal weight, the effect of the number of laminate layers on the impact resistance is also investigated. Finally, the significance of the presented results is discussed.

Abatan, Ayu↗
NASA NTRS2001

Development of Tough, Strong, and Pest-Resistant MoSi2-(Beta)Si3N4 Composites for High-Temperature Structural Applications

A new MoSi2-base composite was developed that contains in-situ reinforcement of whisker-type beta-Si3N4 grains in a MoSi2 matrix. The advantages of this in-situ reinforced MoSi2-Si3N4 are lower density, higher fracture toughness and better strength than typical MoSi2 alloys, combined with excellent environmental and pest resistance. The average fracture toughness of the in-situ reinforced material determined by one technique was 12.2 MPa.m(exp 1/2) compared to 4.9 to 5.5 MPa.m(exp 1/2) for similar materials with the exception that the beta-Si3N4 had a blocky morphology as opposed to the whisker-like morphology typical of the in-situ toughened material. This MoSi2-(beta)Si3N4 was also resistant to pesting at intermediate temperatures (400 to 600 C) even when precracked or under applied load; conditions that would quickly reduce typical MoSi2 alloys to oxidized powder.

Hebsur, M. G.↗
NASA NTRS2001

The Effect of Hydrogen Annealing on the Oxidation Resistance of Four EPM Single Crystal Superalloys

Four single crystal EPM (enabling propulsion materials) developmental airfoil superalloys were hydrogen annealed at 1300 C for up to 100 hours to remove sulfur and improve oxidation resistance. Although the 1100 and 1150 C cyclic oxidation resistance was remarkably improved by annealing for 24 or 100 hours, the behavior was still considerably inferior to that of commercially available single crystal superalloys, especially those that are either Y-doped or hydrogen annealed. Excessive degradation in the developmental alloys appeared to be correlated with low Cr contents and, to a lesser extent, high Co and Re contents.

Smialek, James L.↗
NASA NTRS2002

Surface Enhancement Improves Crack Resistance

The low plasticity burnishing (LPB) process produces a deep layer of surface compression in a quick and affordable manner to produce metal surfaces free of scratches, nicks, and gouges. The process, designed for easy inclusion in the manufacturing environment, can be performed with conventional Computer Numerical Control machine tools. This allows parts to be processed during manufacturing, rather than as a post process in a separate facility. A smooth, free-rolling spherical ball suspended in a fluid allows for single-point contact. The ball comes into mechanical contact only with the surface to be burnished, and can be moved in any direction. LPB can be applied to all types of carbon and alloy steel, stainless steel, cast iron, aluminum, titanium, and nickel- based super alloys. In addition to improving a surface's resistance to fatigue and damage, treatment stops the growth of shallow cracks. The LPB process is used on the leading edges of turbine blades to improve resistance to foreign object damage and crack growth. This means significant savings for aircraft owners, since maintenance requirements to inspect for fatigue damage, replace parts, and remove corrosion damage increase the cost of operation.

Source record↗
NASA NTRS1984

Flame Resistant Foam

Solimide manufactured by Imi-Tech Corporation, is a lightweight fire resistant material produced under a manufacturing process that allows it to be uniformly foamed. Can be produced in a variety of densities and structural configurations and remains resilient under exposure to temperatures ranging from minus 300 to plus 500 degrees Fahrenheit. Is resistant to open flame and generates virtually no smoke or toxic by-products. Used in aircraft for its superior damping characteristics, lighter weight and fire barrier properties, it's also applicable to ships and surface transportation systems such as transit cars, trains, buses and automobiles.

Source record↗
NASA NTRS2002

High Strength and Wear Resistant Aluminum Alloy for High Temperature Applications

In this paper, a new high strength and wear resistant aluminum cast alloy invented by NASA-MSFC for high temperature applications will be presented. Developed to meet U.S. automotive legislation requiring low-exhaust emission, the novel NASA 398 aluminum-silicon alloy offers dramatic improvement in tensile and fatigue strengths at elevated temperatures (500 F-800 F), enabling new pistons to utilize less material, which can lead to reducing part weight and cost as well as improving performance. NASA 398 alloy also offers greater wear resistance, surface hardness, dimensional stability, and lower thermal expansion compared to conventional aluminum alloys for several commercial and automotive applications. The new alloy can be produced economically using permanent steel molds from conventional gravity casting or sand casting. The technology was developed to stimulate the development of commercial aluminum casting products from NASA-developed technology by offering companies the opportunity to license this technology.

Lee, Jonathan A.↗
NASA NTRS2003

Impact Resistance of Lightweight Hybrid Structures for Gas Turbine Engine Fan Containment Applications

The ballistic impact resistance of hybrid composite sandwich structures was evaluated with the ultimate goal of developing new materials or structures for potential gas turbine engine fan containment applications. The sandwich structures investigated consisted of GLARE-5 laminates as face sheets with lightweight cellular metallic materials such as honeycomb, foam, and lattice block as a core material. The impact resistance of these hybrid sandwich structures was compared to GLARE-5 laminates and 2024-T3 Al sheet, which were tested as a function of areal weight (material thickness). The GLARE-5 laminates exhibited comparable impact properties to that of 2024-T3 Al at low areal weights, even though there were significant differences in the static tensile properties of these materials. The GLARE-5, however, did have a greater ballistic limit than straight aluminum sheet at higher areal weights. Furthermore, there is up to a 25% advantage in ballistic limit for the GLARE-5/foam sandwich structures compared to straight 2024-T3 Al. But no advantage in ballistic limit was observed between any of the hybrid sandwich structures and thicker versions of GLARE-5. Recommendations for future work are provided, based on these preliminary data.

Hebsur, Mohan G.↗
NASA NTRS2003

Erosion Resistant Coatings for Polymer Matrix Composites in Propulsion Applications

Polymer Matrix Composites (PMCs) offer lightweight and frequently low cost alternatives to other materials in many applications. High temperature PMCs are currently used in limited propulsion applications replacing metals. Yet in most cases, PMC propulsion applications are not in the direct engine flow path since particulate erosion degrades PMC component performance and therefore restricts their use in gas turbine engines. This paper compares two erosion resistant coatings (SANRES and SANPRES) on PMCs that are useful for both low and high temperature propulsion applications. Collaborating over a multi-year period, researchers at NASA Glenn Research Center, Allison Advanced Developed Company, and Rolls-Royce Corporation have optimized these coatings in terms of adhesion, surface roughness, and erosion resistance. Results are described for vigorous hot gas/particulate erosion rig and engine testing of uncoated and coated PMC fan bypass vanes from the AE 3007 regional jet gas turbine engine. Moreover, the structural durability of these coatings is described in long-term high cycle fatigue tests. Overall, both coatings performed well in all tests and will be considered for applications in both commercial and defense propulsion applications.

Sutter, James K.↗
NASA NTRS2003

Creep Resistance of Disk Alloy CH98 with Tungsten and Niobium Additions

Gas turbine engines for future subsonic transports will likely have higher pressure ratios which will require nickel-base superalloy disks with temperature capability up to 1400 F, an increase of about 200 F over current engines. Several advanced disk alloys are being developed to fill this need. One of these, CH98, is a promising candidate for gas turbine engines and is being studied in NASA's AST Program. Additions of the refractory elements tungsten and niobium have been shown to improve tensile and creep properties while maintaining good high temperature fatigue crack growth resistance. Further improvements in creep and crack growth resistance can be achieved with a coarse grain microstructure. The purpose of the present study is aimed at providing a detailed assessment of 0.2 percent creep rates for coarse grain CH98 with tungsten and niobium additions over a range of temperatures and stresses of interest to disk applications.

Gayda, John↗
NASA NTRS2003

Tantalum Addition to Zirconium Diboride for Improved Oxidation Resistance

Ultrahigh temperature ceramics have performed unreliably due to material flaws and attachment design. These deficiencies are brought to the fore by the low fracture toughness and thermal shock resistance of UHTCs. If these deficiencies are overcome, we are still faced with poor oxidation resistance as a limitation on UHTC applicability to reusable launch vehicles. We have been addressing the deficiencies of UHTCs with our focus on composite constructions and functional grading to address the mechanical issues, and on composition modification to address the oxidation issue. The approaches and progress toward the latter are reported.

Levine, Stanley R.↗
NASA NTRS2003

Oxidation-Reduction Resistance of Advanced Copper Alloys

Resistance to oxidation and blanching is a key issue for advanced copper alloys under development for NASA's next generation of reusable launch vehicles. Candidate alloys, including dispersion-strengthened Cu-Cr-Nb, solution-strengthened Cu-Ag-Zr, and ODS Cu-Al2O3, are being evaluated for oxidation resistance by static TGA exposures in low-p(O2) and cyclic oxidation in air, and by cyclic oxidation-reduction exposures (using air for oxidation and CO/CO2 or H2/Ar for reduction) to simulate expected service environments. The test protocol and results are presented.

Greenbauer-Seng, L.↗
NASA NTRS2004

Ground Reaction Force and Mechanical Differences Between the Interim Resistive Exercise Device (iRED) and Smith Machine While Performing a Squat

Musculoskeletal unloading in microgravity has been shown to induce losses in bone mineral density, muscle cross-sectional area, and muscle strength. Currently, an Interim Resistive Exercise Device (iRED) is being flown on board the ISS to help counteract these losses. Free weight training has shown successful positive musculoskeletal adaptations. In biomechanical research, ground reaction forces (GRF) trajectories are used to define differences between exercise devices. The purpose of this evaluation is to quantify the differences in GRF between the iRED and free weight exercise performed on a Smith machine during a squat. Due to the differences in resistance properties, inertial loading and load application to the body between the two devices, we hypothesize that subjects using iRED will produce GRF that are significantly different from the Smith machine. There will be differences in bar/harness range of motion and the time when peak GRF occurred in the ROMbar. Three male subjects performed three sets of ten squats on the iRED and on the Smith Machine on two separate days at a 2-second cadence. Statistically significant differences were found between the two devices in all measured GRF variables. Average Fz and Fx during the Smith machine squat were significantly higher than iRED. Average Fy (16.82 plus or minus.23; p less than .043) was significantly lower during the Smith machine squat. The mean descent/ascent ratio of the magnitude of the resultant force vector of all three axes for the Smith machine and iRED was 0.95 and 0.72, respectively. Also, the point at which maximum Fz occurred in the range of motion (Dzpeak) was at different locations with the two devices.

Amonette, William E.↗
NASA NTRS2002

Estrogen has opposing effects on vascular reactivity in obese, insulin-resistant male Zucker rats

We hypothesized that estradiol treatment would improve vascular dysfunction commonly associated with obesity, hyperlipidemia, and insulin resistance. A sham operation or 17beta-estradiol pellet implantation was performed in male lean and obese Zucker rats. Maximal vasoconstriction (VC) to phenylephrine (PE) and potassium chloride was exaggerated in control obese rats compared with lean rats, but estradiol significantly attenuated VC in the obese rats. Estradiol reduced the PE EC50 in all groups. This effect was cyclooxygenase independent, because preincubation with indomethacin reduced VC response to PE similarly in a subset of control and estrogen-treated lean rats. Endothelium-independent vasodilation (VD) to sodium nitroprusside was similar among groups, but endothelium-dependent VD to ACh was significantly impaired in obese compared with lean rats. Estradiol improved VD in lean and obese rats by decreasing EC50 but impaired function by decreasing maximal VD. The shift in EC50 corresponded to an upregulation in nitric oxide synthase III protein expression in the aorta of the estrogen-treated obese rats. In summary, estrogen treatment improves vascular function in male insulin-resistant, obese rats, partially via an upregulation of nitric oxide synthase III protein expression. These effects are counteracted by adverse factors, such as hyperlipidemia and, potentially, a release of an endothelium-derived contractile agent.

Non-NASA Center↗
NASA NTRS1994

Altered baroreflex control of forearm vascular resistance during simulated microgravity

Reflex peripheral vasoconstriction induced by activation of cardiopulmonary baroreceptors in response to reduced central venous pressure (CVP) is a basic mechanism for elevating systemic vascular resistance and defending arterial blood pressure during orthostatically-induced reductions in cardiac filling and output. The sensitivity of the cardiopulmonary baroreflex response [defined as the slope of the relationship between changes in forearm vascular resistance (FVR) and CVP] and the resultant vasoconstriction are closely and inversely associated with the amount of circulating blood volume. Thus, a high-gain FVR response will be elicited by a hypovolemic state. Exposure to microgravity during spaceflight results in reduced plasma volume. It is therefore reasonable to expect that the FVR response to cardiopulmonary baroreceptor unloading would be accentuated following adaptation to microgravity. Such data could provide better insight about the physiological mechanisms underlying alterations in blood pressure control following spaceflight. We therefore exposed eleven men to 6 degrees head-down bedrest for 7 days and measured specific hemodynamic responses to low levels of the lower body negative pressure to determine if there are alterations in cardiopulmonary baroreceptor stimulus-FVR reflex response relationship during prolonged exposure to an analog of microgravity.

NASA Program Space Physiology and Countermeasures↗
NASA NTRS2000

Ionizing-radiation resistance in the desiccation-tolerant cyanobacterium Chroococcidiopsis

The effect of X-ray irradiation on cell survival, induction, and repair of DNA damage was studied by using 10 Chroococcidiopsis strains isolated from desert and hypersaline environments. After exposure to 2.5 kGy, the percentages of survival for the strains ranged from 80 to 35%. In the four most resistant strains, the levels of survival were reduced by 1 or 2 orders of magnitude after irradiation with 5 kGy; viable cells were recovered after exposure to 15 kGy but not after exposure to 20 kGy. The severe DNA damage evident after exposure to 2.5 kGy was repaired within 3 h, and the severe DNA damage evident after exposure to 5 kGy was repaired within 24 h. The increase in trichloroacetic acid-precipitable radioactivity in the culture supernatant after irradiation with 2.5 kGy might have been due to cell lysis and/or an excision process involved in DNA repair. The radiation resistance of Chroococcidiopsis strains may reflect the ability of these cyanobacteria to survive prolonged desiccation through efficient repair of the DNA damage that accumulates during dehydration.

Non-NASA Center↗
NASA NTRS2000

Resistance of extraocular motoneuron terminals to effects of amyotrophic lateral sclerosis sera

In sporadic ALS (s-ALS), axon terminals contain increased intracellular calcium. Passively transferred sera from patients with s-ALS increase intracellular calcium in spinal motoneuron terminals in vivo and enhance spontaneous transmitter release, a calcium-dependent process. In this study, passive transfer of s-ALS sera increased spontaneous release from spinal but not extraocular motoneuron terminals, suggesting that the resistance to physiologic abnormalities induced by s-ALS sera in mice parallels the resistance of extraocular motoneurons to dysfunction and degeneration in ALS.

NASA Program Biomedical Research and Countermeasur↗
NASA NTRS2004

Results of the International Space Station Interim Resistance Exercise Device Man-in-the-Loop Test

The Interim Resistance Exercise Device (iRED), developed for the International Space Station (ISS), was evaluated using human subjects for a Man-In-The-Loop Test (MILT). Thirty-two human subjects exercised using the iRED in a test that was conducted over a 63-working-day period. The subjects performed the same exercises will be used on board ISS, and the iRED operating constraints that are to be used on ISS were followed. In addition, eight of the subjects were astronauts who volunteered to be in the evaluation in order to become familiar with the iRED and provide a critique of the device. The MILT was scheduled to last for 57,000 exercise repetitions on the iRED. This number of repetitions was agreed to as a number typical of that expected during a 3-person, 17-week ISS Increment. One of the canisters of the iRED failed at the 49,683- repetition mark (87.1% of targeted goal). The remaining canister was operated using the plan for operations if one canister fails during flight (contingency operations). This canister remained functional past the 57,000-repetition mark. This report details the results of the iRED MILT, and lists specific recommendations regarding both operation of the iRED and future resistance exercise device development.

Moore, A. D., Jr.↗
NASA NTRS1995

Resistance exercise-induced fluid shifts: change in active muscle size and plasma volume

The purpose of this study was to test the hypothesis that the reduction in plasma volume (PV) induced by resistance exercise reflects fluid loss to the extravascular space and subsequently selective increase in cross-sectional area (CSA) of active but not inactive skeletal muscle. We compared changes in active and inactive muscle CSA and PV after barbell squat exercise. Magnetic resonance imaging (MRI) was used to quantify muscle involvement in exercise and to determine CSA of muscle groups or individual muscles [vasti (VS), adductor (Add), hamstring (Ham), and rectus femoris (RF)]. Muscle involvement in exercise was determined using exercise-induced contrast shift in spin-spin relaxation time (T2)-weighted MR images immediately postexercise. Alterations in muscle size were based on the mean CSA of individual slices. Hematocrit, hemoglobin, and Evans blue dye were used to estimate changes in PV. Muscle CSA and PV data were obtained preexercise and immediately postexercise and 15 and 45 min thereafter. A hierarchy of muscle involvement in exercise was found such that VS > Add > Ham > RF, with the Ham and RF showing essentially no involvement. CSA of the VS and Add muscle groups were increased 10 and 5%, respectively, immediately after exercise in each thigh with no changes in Ham and RF CSA. PV was decreased 22% immediately following exercise. The absolute loss of PV was correlated (r2 = 0.75) with absolute increase in muscle CSA immediately postexercise, supporting the notion that increased muscle size after resistance exercise reflects primarily fluid movement from the vascular space into active but not inactive muscle.

NASA Discipline Cardiopulmonary↗