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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

High temperature, short term tensile strength of C6000/PMR-15 composites

Tensile tests were conducted on 0 unidirectionally reinforced Celion 6000 graphite fibers in PMR-15 polyimide matrix. Tensile strengths for coupons subjected to short and long term uniform temperatures were obtained. Thick coupons, heated on one side to produce significant transient through thickness temperature gradients, were tested and compared to the strength of specimens with uniform temperature distributions. All coupons were radiantly heated and reached maximum test temperatures within 15 sec. Tensile loads were applied to the coupons after 15 sec of elevated temperature exposure. Loading rates were selected so that specimen failures occurred within a maximum of 45 sec after reaching the test temperature. Results indicate that significant tensile strength remains beyond the material post cure temperature.

Digiovanni, P. R.↗
NASA NTRS1988

Tensile behavior of tungsten and tungsten-alloy wires from 1300 to 1600 K

The tensile behavior of a 200-micrometer-diameter tungsten lamp (218CS-W), tungsten + 1.0 atomic percent (a/o) thoria (ST300-W), and tungsten + 0.4 a/o hafnium carbide (WHfC) wires was determined over the temperature range 1300 t0 1600 K at strain rates of 3.3 X 10 to the -2 to 3.3 X 10 to the -5/sec. Although most tests were conducted on as-drawn materials, one series of tests was undertaken on ST300-W wires in four different conditions: as-drawn and vacuum-annealed at 1535 K for 1 hr, with and without electroplating. Whereas heat treatment had no effect on tensile properties, electropolishing significantly increased both the proportional limit and ductility, but not the ultimate tensile strength. Comparison of the behavior of the three alloys indicates that the HfC-dispersed material possesses superior tensile properties. Theoretical calculations indicate that the strength/ductility advantage of WHfC is due to the resistance to recrystallization imparted by the dispersoid.

Hee, Man Yun↗
NASA NTRS1990

Tensile and compressive failure modes of laminated composites loaded by fatigue with different mean stress

Laminated composite materials tend to fail differently under tensile or compressive load. Under tension, the material accumulates cracks and fiber fractures, while under compression, the material delaminates and buckles. Tensile-compressive fatigue may cause either of these failure modes depending on the specific damage occurring in the laminate. This damage depends on the stress ratio of the fatigue loading. Analysis of the fatigue behavior of the composite laminate under tension-tension, compression-compression, and tension-compression had led to the development of a fatigue envelope presentation of the failure behavior. This envelope indicates the specific failure mode for any stress ratio and number of loading cycles. The construction of the fatigue envelope is based on the applied stress-cycles to failure (S-N) curves of both tensile-tensile and compressive-compressive fatigue. Test results are presented to verify the theoretical analysis.

Rotem, Assa↗
NASA NTRS1992

A preliminary characterization of the tensile and fatigue behavior of tungsten-fiber/Waspaloy-matrix composite

A microstructural study and a preliminary characterization of the room temperature tensile and fatigue behavior of a continuous, tungsten fiber, Waspaloy-matrix composite was conducted. A heat treatment was chosen that would allow visibility of planar slip if it occurred during deformation, but would not allow growth of the reaction zone. Tensile and fatigue tests showed that the failed specimens contained transverse cracks in the fibers. The cracks that occurred in the tensile specimen were observed at the fracture surface and up to approximately 4.0 mm below the fracture surface. The crack spacing remained constant along the entire length of the cracked fibers. Conversely, the cracks that occurred in the fatigue specimen were only observed in the vicinity of the fracture surface. In instances where two fiber cracks occurred in the same plane, the matrix often necked between the two cracked fibers. Large groups of slip bands were generated in the matrix near the fiber cracks. Slip bands in the matrix of the tensile specimen were also observed in areas where there were no fiber cracks, at distances greater than 4 mm from the fracture surface. This suggests that the matrix plastically flows before fiber cracking occurs.

Corner, Ralph E.↗
NASA NTRS1992

The effect of microalloying additions on the tensile properties of polycrystalline NiAl

The presently evaluated 0.1 at. pct Fe and Ga additions to NiAl, while beneficial in the case of monocrystalline NiAl ductility, does not improve ductility in the polycrystalline case; it also has little effect on tensile properties. A similar microalloying addition of Zr, by contrast, significantly depressed the tensile ductility of NiAl, and nearly doubled the brittle-to-ductile transition temperature (BDTT). The dependence of tensile properties on temperature was in all cases similar; tensile elongations remained low and constant until the BDTT was reached, and then dramatically increased.

Noebe, R. D.↗
NASA NTRS1944

Tensile Tests of Round-head, Flat-head, and Brazier-head Rivets

An investigation was conducted to determine the tensile strength of round-head (AN43C), flat-head(AN442), and brazier-head (AN4556) aluminum-alloy rivets because of the scarcity of information on the tensile strength of rivets. The results of the investigation are presented as curves that show the variation of the ratio of the tensile strength of the rivet to the tensile strength of the rivet crank with the ratio of the sheet thickness to the rivet diameter for the different types of rivet.

Schuette, Evan H↗
NASA NTRS1994

Improved Flat Specimens For Tensile And Fatigue Testing Of Composites

Improved shape proposed for flat, reduced-gauge-section specimens for tensile and fatigue testing of advanced composite materials at ambient and high temperatures. Typical specimen consists of flat bar 15.2 centimeters long, 1.27 centimeters wide, and 0.318 centimeters thick, with full-width tab regions at ends, 3.81-centimeters-long gauge section of reduced width in middle, and two transition regions where width tapers between tab and gauge widths along 6.35-centimeters-radius circular arc tangent to edge of gauge section. Specimen gripped by squeezing between tabs in tab regions, and tensile test load applied via tab grips. Configuration reduces undesired concentrations of stresses in transition and tab regions, forcing tensile failure to occur in gauge section and ensuring more-consistent results in tensile tests.

Worthem, Dennis W.↗
NASA NTRS1993

Tensile and stress-rupture behavior of hafnium carbide dispersed molybdenum and tungsten base alloy wires

The tensile strain rate sensitivity and the stress-rupture strength of Mo-base and W-base alloy wires, 380 microns in diameter, were determined over the temperature range from 1200 K to 1600 K. Three molybdenum alloy wires; Mo + 1.1w/o hafnium carbide (MoHfC), Mo + 25w/o W + 1.1w/o hafnium carbide (MoHfC+25W) and Mo + 45w/o W + 1.1w/o hafnium carbide (MoHfC+45W), and a W + 0.4w/o hafnium carbide (WHfC) tungsten alloy wire were evaluated. The tensile strength of all wires studied was found to have a positive strain rate sensitivity. The strain rate dependency increased with increasing temperature and is associated with grain broadening of the initial fibrous structures. The hafnium carbide dispersed W-base and Mo-base alloys have superior tensile and stress-rupture properties than those without HfC. On a density compensated basis the MoHfC wires exhibit superior tensile and stress-rupture strengths to the WHfC wires up to approximately 1400 K. Addition of tungsten in the Mo-alloy wires was found to increase the long-term stress rupture strength at temperatures above 1400 K. Theoretical calculations indicate that the strength and ductility advantage of the HfC dispersed alloy wires is due to the resistance to recrystallization imparted by the dispersoid.

Yun, Hee Mann↗
NASA NTRS1995

Elevated temperature tensile and creep behavior of a SiC fiber-reinforced titanium metal matrix composite

In this research program, the tensile properties and creep behavior in air of (0)(sub 4), (0/90)(sub s) and (90)(sub 4) SCS-9/Beta 21S composite layups with 0.24 volume fraction fiber were evaluated. Monotonic tensile tests at 23, 482, 650 and 815 C yielded the temperature dependence of the elastic modulus, proportional limit, ultimate tensile strength and total strain at failure. At 650 C, the UTS of the (0)(sub 4) and (0/90)(sub s) layups decreases by almost 50 percent from the room temperature values, indicating that operating temperatures should be less than 650 C to take advantage of the specific tensile properties of these composites.

Thurston, Rita J.↗
NASA NTRS1994

A new derivation of the tensile strength of cometary nuclei: Application to comet Shoemaker-Levy 9

The splitting of comets as exemplified by comet Shoemaker-Levy 9, when it passed near Jupiter, is a common phenomenon. Multiple splitting is also not an uncommon occurrence. It is clear that the comet nucleus is fragile, i.e., its tensile strength is small compared with that of solid materials. We show that aggregates of sub-micron interstellar dust particles presumed to consist of a silicate core, an inner mantle of complex organic refractory molecules, and an outer mantle dominated by H2O ice (Greenberg, 1982) provide the basis for a quantitative derivation of the tensile strength of comet SL9 using molecular interactions at the contact interfaces. In fact, using a mean particle size representing interstellar dust as it would appear in its final presolar state one derives a tensile strength which describes remarkably well the multiple splitting phenomenon. This derivation of the tensile strength of a particle aggregate resulting from molecular interactions is quite general and can be applied to physical situations involving any sorts of aggregates as well as those representing comet nuclei.

Greenberg, J. Mayo↗
NASA NTRS1995

Tensile Behavior of Al2o3/feal + B and Al2o3/fecraly Composites

The feasibility of Al2O3/FeAl + B and Al2O3/FeCrAlY composites for high-temperature applications was assessed. The major emphasis was on tensile behavior of both the monolithics and composites from 298 to 1100 K. However, the study also included determining the chemical compatibility of the composites, measuring the interfacial shear strengths, and investigating the effect of processing on the strength of the single-crystal Al2O3 fibers. The interfacial shear strengths were low for Al203/FeAl + B and moderate to high for Al203/FeCrAlY. The difference in interfacial bond strengths between the two systems affected the tensile behavior of the composites. The strength of the Al203 fiber was significantly degraded after composite processing for both composite systems and resulted in poor composite tensile properties. The ultimate tensile strength (UTS) values of the composites could generally be predicted with either rule of mixtures (ROM) calculations or existing models when using the strength of the etched-out fiber. The Al2O3/FeAl + B composite system was determined to be unfeasible due to poor interfacial shear strengths and a large mismatch in coefficient of thermal expansion (CTE). Development of the Al2O3/FeCrAlY system would require an effective diffusion barrier to minimize the fiber strength degradation during processing and elevated temperature service.

Draper, S. L.↗
NASA NTRS2000

Effect of Air and Vacuum Storage on the Tensile Properties of X-Ray Exposed Aluminized-FEP

Metallized Teflon(Registered Trademark) FEP (fluorinated ethylene propylene), a common spacecraft thermal control material, from the exterior layer of the Hubble Space Telescope (HST) has become embrittled and suffers from extensive cracking. Teflon samples retrieved during Hubble servicing missions and from the Long Duration Exposure Facility (LDEF) indicate that there may be continued degradation in tensile properties over time. An investigation has been conducted to evaluate the effect of air and vacuum storage on the mechanical properties of x-ray exposed FEP. Aluminized-FEP (Al-FEP) tensile samples were irradiated with 15.3 kV Cu x-rays and stored in air or under vacuum for various time periods. Tensile data indicate that samples stored in air display larger decreases in tensile properties than for samples stored under vacuum. Air-stored samples developed a hazy appearance, which corresponded to a roughening of the aluminized surface. Optical property changes were also characterized. These findings indicate that air exposure plays a role in the degradation of irradiated FEP, therefore proper sample handling and storage is necessary with materials retrieved from space.

deGroh, Kim K.↗
NASA NTRS2002

Tensile Strength of Carbon Nanotubes Under Realistic Temperature and Strain Rate

Strain rate and temperature dependence of the tensile strength of single-wall carbon nanotubes has been investigated with molecular dynamics simulations. The tensile failure or yield strain is found to be strongly dependent on the temperature and strain rate. A transition state theory based predictive model is developed for the tensile failure of nanotubes. Based on the parameters fitted from high-strain rate and temperature dependent molecular dynamics simulations, the model predicts that a defect free micrometer long single-wall nanotube at 300 K, stretched with a strain rate of 1%/hour, fails at about 9 plus or minus 1% tensile strain. This is in good agreement with recent experimental findings.

Wei, Chen-Yu↗
NASA NTRS2002

Tensile Properties of Hydrogels and of Snake Skin

Stimulus-responsive or 'smart' gels are of potential interest as sensors and actuators, in industrial separations, and as permeable delivery systems. In most applications, a certain degree of mechanical strength and toughness will be required, yet the large-strain behavior of gels has not been widely reported. Some exceptions include work on gelatin and other food gels, some characterization of soft gels applicable for in-vitro cell growth studies, and toughness determinations on commercial contact lens materials. In general, it can be anticipated that the gel stiffness will increase with increasing degree of crosslinking, but the tensile strength may go through a maximum. Gel properties can be tailored by varying not only the degree of crosslinking, but also the polymer concentration and the nature of the polymer backbone (e.g. its stiffness or solubility). Polypeptides provide an especially interesting case, where secondary structure affects trends in moduli and conformational transitions may accompany phase changes. A few papers on the tensile properties of responsive gels have begun to appear. The responsive hydrogel chosen for the present study, crosslinked hydroxypropylcellulose, shrinks over a rather narrow temperature range near 44 C. Some vertebrate skin is also subject to substantial strain. Among reptiles, the morphologies of the skin and scales show wide variations. Bauer et al. described the mechanical properties and histology of gecko skin; longitudinal tensile properties of snake skin were examined by Jayne with reference to locomotion. The present measurements focus on adaptations related to feeding, including the response of the skin to circumferential tension. Tensile properties will be related to interspecific and regional variation in skin structure and folding.

Hinkley, Jeffrey A.↗
NASA NTRS2003

Influence Of Holes On The In-Plane Tensile Strength And Fatigue Durability Of A NICALON(Trademark)/Si-N-C Ceramic Matrix Composite

Effects of different sizes of holes as well as different percentages of open areas on the in-plane tensile strength and fatigue durability of the SiC/Si-N-C composite were investigated in this study. Test specimens with no holes, four different diameters of holes (1.0 to 3.2 mm), and four different open areas (20 to 35%) were machined. All mechanical testing was performed in air at a temperature of 910 C. Fatigue tests were conducted with a load ratio, R = 0.05, and a frequency of 0.33 Hz. In general, both the in-plane tensile strength of the composite and its fatigue durability decreased with an increase in the size of the hole and percentage of the open area. Reductions in the in-plane tensile strength and cyclic fatigue life of the composite were described by empirical equations with the diameter of the hole and the percent open area as the independent variables. The validity of these two empirical equations was verified with additional tensile and fatigue test data generated on the composite specimens.

Kalluri, Sreeramesh↗
NASA NTRS2007

In-Plane Cracking Behavior and Ultimate Strength for 2D Woven and Braided Melt-Infiltrated SiC/SiC Composites Tensile Loaded in Off-Axis Fiber Directions

The tensile mechanical properties of ceramic matrix composites (CMC) in directions off the primary axes of the reinforcing fibers are important for architectural design of CMC components that are subjected to multi-axial stress states. In this study, 2D-woven melt-infiltrated (MI) SiC/SiC composite panels with balanced fiber content in the 0 degree and 90 degree directions were tensile loaded in-plane in the 0 degree direction and at 45 degree to this direction. In addition, a 2D triaxially-braided MI composite panel with balanced fiber content in the plus or minus 67 degree bias directions and reduced fiber content in the axial direction was tensile loaded perpendicular to the axial direction tows (i.e., 23 degrees from the bias fibers). Stress-strain behavior, acoustic emission, and optical microscopy were used to quantify stress-dependent matrix cracking and ultimate strength in the panels. It was observed that both off-axis loaded panels displayed higher composite onset stresses for through-thickness matrix cracking than the 2D-woven 0/90 panels loaded in the primary 0 degree direction. These improvements for off-axis cracking strength can in part be attributed to higher effective fiber fractions in the loading direction, which in turn reduces internal stresses on critical matrix flaws for a given composite stress. Also for the 0/90 panel loaded in the 45 degree direction, an improved distribution of matrix flaws existed due to the absence of fiber tows perpendicular to the loading direction. In addition, for the +67/0/-67 braided panel, the axial tows perpendicular to the loading direction were not only low in volume fraction, but were also were well separated from one another. Both off-axis oriented panels also showed relatively good ultimate tensile strength when compared to other off-axis oriented composites in the literature, both on an absolute strength basis as well as when normalized by the average fiber strength within the composites. Initial implications are discussed for constituent and architecture design to improve the directional cracking of SiC/SiC CMC components with MI matrices.

Morscher, Gregory N.↗
NASA NTRS2014

Use of Slow Strain Rate Tensile Testing to Assess the Ability of Several Superalloys to Resist Environmentally-Assisted Intergranular Cracking

Intergranular fatigue crack initiation and growth due to environmental degradation, especially at notched features, can often limit the fatigue life of disk superalloys at high temperatures. For clear comparisons, the effects of alloy composition on cracking in air needs to be understood and compared separately from variables associated with notches and cracks such as effective stress concentration, plastic flow, stress relaxation, and stress redistribution. The objective of this study was to attempt using simple tensile tests of specimens with uniform gage sections to compare the effects of varied alloy composition on environment-assisted cracking of several powder metal and cast and wrought superalloys including ME3, LSHR, Udimet 720(TradeMark) ATI 718Plus(Registered TradeMark) alloy, Haynes 282(Trademark), and Inconel 740(TradeMark) Slow and fast strain-rate tensile tests were found to be a useful tool to compare propensities for intergranular surface crack initiation and growth. The effects of composition and heat treatment on tensile fracture strain and associated failure modes were compared. Environment interactions were determined to often limit ductility, by promoting intergranular surface cracking. The response of various superalloys and heat treatments to slow strain rate tensile testing varied substantially, showing that composition and microstructure can significantly influence environmental resistance to cracking.

fatigue(materials)↗
NASA NTRS2014

Slow Strain Rate Tensile Testing to Assess the Ability of Superalloys to Resist Environment-Assisted Intergranular Cracking

Intergranular fatigue crack initiation and growth due to environmental degradation, especially at notched features, can often limit the fatigue life of disk superalloys at high temperatures. For clear comparisons, the effects of alloy composition on cracking in air needs to be understood and compared separately from variables associated with notches and cracks such as effective stress concentration, plastic flow, stress relaxation, and stress redistribution. The objective of this study was to attempt using simple tensile tests of specimens with uniform gage sections to compare the effects of varied alloy composition on environment-assisted cracking of several powder metal and cast and wrought superalloys including ME3, LSHR, Udimet 720, ATI 718Plus alloy, Haynes 282, and Inconel 740. Slow and fast strain-rate tensile tests were found to be a useful tool to compare propensities for intergranular surface crack initiation and growth. The effects of composition and heat treatment on tensile fracture strain and associated failure modes were compared. Environment interactions were determined to often limit ductility, by promoting intergranular surface cracking. The response of various superalloys and heat treatments to slow strain rate tensile testing varied substantially, showing that composition and microstructure can significantly influence environmental resistance to cracking.

Heat resistant alloys↗