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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Large fracture toughness boron-epoxy composites

The high tensile strengths of strong interfacial bonding may be combined with the large fracture toughness of weak interfacial bonding in brittle fiber/brittle matrix composites by intermittently coating the filaments before layup so as to have random alternate weak and strong regions. Appropriate coating materials enable Cook-Gordon Mode I interfacial debonding to take place, which produces very long pull-out lengths with an associated large contribution to toughness. Unidirectional boron-epoxy composites have been so made which have toughnesses greater than 200 kJ/sq m while retaining rule of mixtures tensile strengths. Similar trends have been observed for crossply layups.

Atkins, A. G.↗
NASA NTRS1982

Thermal degradation of the tensile properties of undirectionally reinforced FP-AI203/EZ 33 magnesium composites

The effects of isothermal and cyclic exposure on the room temperature axial and transverse tensile strength and dynamic flexural modulus of 35 volume percent and 55 volume percent FP-Al2O3/EZ 33 magnesium composites were studied. The composite specimens were continuously heated in a sand bath maintained at 350 C for up to 150 hours or thermally cycled between 50 and 250 C or 50 and 350 C for up to 3000 cycles. Each thermal cycle lasted for a total of six minutes with a hold time of two minutes at the maximum temperature. Results indicate to significant loss in the room temperature axial tensile strength and dynamic flexural modulus of composites thermally cycled between 50 and 250 C or of composites isothermally heated at 350 C for up to 150 hours from the strength and modulus data for the untreated, as fabricated composites. In contrast, thermal cycling between 50 and 350 C caused considerable loss in both room temperature strength and modulus. Fractographic analysis and measurement of composite transverse strength and matrix hardness of thermally cycled and isothermally heated composites indicated matrix softening and fiber/matrix debonding due to void growth at the interface and matrix cracking as the likely causes of the strength and modulus loss behavior.

Bhatt, R. T.↗
NASA NTRS1983

Thermal degradation of the tensile properties of undirectionally reinforced FP-Al2O3/EZ 33 magnesium composites

The effects of isothermal and cyclic exposure on the room temperature axial and transverse tensile strength and dynamic flexural modulus of 35 volume percent and 55 volume percent FP-Al203/EZ 33 magnesium composites were studied. The composite specimens were continuously heated in a sand bath maintained at 350 C for up to 150 hours or thermally cycled between 50 and 250 C or 50 and 350 C for up to 3000 cycles. Each thermal cycle lasted for a total of six minutes with a hold time of two minutes at the maximum temperature. Results indicate no significant loss in the room temperature axial tensile strength and dynamic flexural modulus of composites thermally cycled between 50 and 250 C or of composites isothermally heated at 350 C for up to 150 hours from the strength and modulus data for the untreated, as-fabricated composites. In contrast, thermal cycling between 50 and 350 C caused considerable loss in both room temperature strength and modulus. Fractographic analysis and measurement of composite transverse strength and matrix hardness of thermally cycled and isothermally heated composites indicated matrix softening and fiber/matrix debonding due to void growth at the interface and matrix cracking as the likely causes of the strength and modulus loss behavior. Previously announced in STAR as N82-21260

Bhatt, R.T.↗
NASA NTRS1983

Epoxy hydantoins as matrix resins

Tensile strength and fracture toughness of castings of the hydantoin resins cured with methylenedianiline are significantly higher than MY 720 control castings. Water absorption of an ethyl, amyl hydantoin formulation is 2.1 percent at equilibrium and Tg's are about 160 C, approximately 15 deg below the final cure temperature. Two series of urethane and ester-extended hydantoin epoxy resins were synthesized to determine the effect of crosslink density and functional groups on properties. Castings cured with methylenedianiline or with hexahydrophthalic anhydride were made from these compounds and evaluated. The glass transition temperatures, tensile strengths and moduli, and fracture toughness values were all much lower than that of the simple hydantoin epoxy resins. Using a methylene bishydantoin epoxy with a more rigid structure gave brittle, low-energy fractures, while a more flexible, ethoxy-extended hydantoin epoxy resin gave a very low Tg.

Weiss, J.↗
NASA NTRS1973

Development of polyphenylquinoxaline graphite composites

The potential of polyphenylquinoxaline (PPQ)/graphite composites to serve as structural material at 316 C (600 F)has been demonstrated using a block copolymer, BlCo(13), PPQ derivative. Initially, thirteen polyphenylquinoxalines were evaluated. From this work, four candidate polymers were selected for preliminary evaluation as matrices for HMS graphite fiber reinforced composites. The preliminary composite evaluation enabled selection of one of the four polymers for advanced composite preparation and testing. Using an experimentally established cure schedule for each of the four polymers, preliminary laminates of 50% resin volume content, prepared without postcure, were tested for flexure strength and modulus, interlaminar shear strength (short beam), and tensile strength and modulus at ambient temperature. A block copolymer (Bl Co 13) derived from one mole p-bis (phenylglyoxalyl) benzene, one fourth mole 3,3'-diaminobenzidine and three-fourths mole 3,3', 4,4'-tetraminobenzophenone was selected for extensive study. Tensile, flexural, and interlaminar shear values were obtained after aging and testing postcured BlCo(13) laminates at 316 C (600 F). The potential of PPQ/graphite laminates to serve as short term structural materials at temperatures up to 371 C (700 F) was demonstrated through weight loss experiments.

Hoggatt, J. T.↗
NASA NTRS1980

Quantitative ultrasonic evaluation of engineering properties in metals, composites, and ceramics

Ultrasonic techniques that have demonstrated potential for material characterization are reviewed. These techniques rely on physical acoustic properties of materials and the interaction of elastic stress waves with morphological factors in the ultrasonic regime. The speed of wave propagation and energy loss by interaction with material microstructure and geometrical factors underlie ultrasonic determination of material properties. Two categories of ultrasonic measurements are discussed: those related to material strengths (e.g., elastic moduli, tensile strength, and fracture toughness) and those related to morphology and material conditions that govern strength and performance (e.g., microstructure, void content, residual stress, fatigue damage). It is shown that large-scale industrial application of ultrasonic NDE will depend on advancement in such areas as theory development, instrumentation, system automation, standardization, and coordination with design.

Vary, A.↗
NASA NTRS1982

Effects of cobalt on structure, microchemistry and properties of a wrought nickel-base superalloy

The effect of cobalt on the basic mechanical properties and microstructure of wrought nickel-base superalloys has been investigated experimentally by systematically replacing cobalt by nickel in Udimet 700 (17 wt% Co) commonly used in gas turbine (jet engine) applications. It is shown that the room temperature tensile yield strength and tensile strength only slightly decrease in fine-grained (disk) alloys and are basically unaffected in coarse-grained (blading) alloys as cobalt is removed. Creep and stress rupture resistances at 760 C are found to be unaffected by cobalt level in the blading alloys and decrease sharply only when the cobalt level is reduced below 8 vol% in the disk alloys. The effect of cobalt is explained in terms of gamma prime strengthening kinetics.

Jarrett, R. N.↗
NASA NTRS1984

ACEE Composite Structures Technology: Review of selected NASA research on composite materials and structures

The NASA Aircraft Energy Efficiency (ACEE) Composite Primary Aircraft Structures Program was designed to develop technology for advanced composites in commercial aircraft. Research on composite materials, aircraft structures, and aircraft design is presented herein. The following parameters of composite materials were addressed: residual strength, damage tolerance, toughness, tensile strength, impact resistance, buckling, and noise transmission within composite materials structures.

Source record↗
NASA NTRS1988

Halogenation Enhances Carbon-Fiber/Epoxy Composites

Interlaminar shear strength increased by inexpensive treatment. New surface treatment for carbon fibers enhances interlaminar shear strength, ILSS, without altering tensile strength significantly. Exposure of polyacrylonitrile-based T-300, or equivalent, fibers to bromine vapor at room temperature improves ILSS of epoxy composites made from these fibers by 30 percent. Enhanced ILSS obtained from halogenation of carbon fibers beneficial in many aerospace and terrestrial applications.

Jaworske, Donald A.↗
NASA NTRS1991

High resolution electron microscopy study of a high Cu variant of Weldalite (tm) 049 and a high strength Al-Cu-Ag-Mg-Zr alloy

Weldalite (trademark) 049 is an Al-Cu-Li-Ag-Mg alloy that is strengthened in artificially aged tempers primarily by very thin plate-like precipitates lying on the set of (111) matrix planes. This precipitate might be expected to be the T(sub 1) phase, Al2CuLi, which has been observed in Al-Cu-Li alloys. However, in several ways this precipitate is similar to the omega phase which also appears as the set of (111) planes plates and is found in Al-Cu-Ag-Mg alloys. The study was undertaken to identify the set of (111) planes precipitate or precipitates in Weldalite (trademark) 049 in the T8 (stretched and artificially aged) temper, and to determine whether T(sub 1), omega, or some other phase is primarily responsible for the high strength (i.e., 700 MPa tensile strength) in this Al-Cu-Li-Ag-Mg alloy.

Herring, R. A.↗
NASA NTRS2011

Low Velocity Impact Damage to Carbon/Epoxy Laminates

Impact damage tends to be more detrimental to a laminate's compression strength as compared to tensile strength. Proper use of Non Destructive Evaluation (NDE) Techniques can remove conservatism (weight) from many structures. Test largest components economically feasible as coupons. If damage tolerance is a driver, then consider different resin systems. Do not use a single knockdown factor to account for damage.

Nettles, Alan T.↗
NASA NTRS1995

Mechanical properties testing and results for thermal barrier coatings

Thermal Barrier Coatings (TBC's) provide a significant challenge in the evaluation of their mechanical properties in ways that provide data that is not specimen dependent. The paper reviews various developments of the principal author over the past several years for both plasma sprayed and physical vapor deposited (PVD) materials, as well as new data on the fatigue behavior of one material system. The test methods that have been employed address tensile and compressive modulus and ultimate strength, tensile and compressive fatigue strength, and interfacial strength. This testing is now underway. Property testing is especially difficult for TBC's owing to the limitation on fabrication thickness of the coating. Bending tests are not used as these tests do not provide sufficiently uniform states of strain for property evaluations. Test specimens with uniform states of axial stress have been devised for each material system. The results show that the material property results between various experimenters and experimental methods are not yet consistent. However, the results provide critical design data at a suitable level of accuracy for life prediction. The paper will review both tensile and compressive mechanical testing of uniaxial specimens showing property dependencies on material density and temperatures for both material systems. Successful test results for both tensile and compressive fatigue loadings will be given. The test data shows that the fatigue strength of the TBC's is highly stress dependent in both loading conditions and is likely to depend on stress range and not mean stress. The fatigue strength of the plasma sprayed TBC's appears to increase with elevated temperatures in a range of temperatures below the creep activation temperature for the materials. The plasma sprayed TBC materials have been confirmed to have cyclic hysteresis at all temperature levels down to room temperature. Limited failure analysis data for various specimens suggest that the failure modes are driven by normal geometric discontinuities in the TBC's.

Cruse, T. A.↗
NASA NTRS1999

Comparison of the Tensile, Creep, and Rupture Strength Properties of Stoichiometric SiC Fibers

Tensile strength, creep strength, and rupture strength properties were measured for the following types of polymer-derived stoichiometric SiC fibers: Hi-Nicalon Type S from Nippon Carbon, Tyranno SA from Ube, and Sylramic from Dow Corning. Also included in this study were an earlier version of the SA fiber plus two recent developmental versions of the Sylramic fiber. The tensile strength measurements were made at room temperature on as-received fibers and on fibers after high-temperature inert exposure. The creep-rupture property data were obtained at 1400 deg C in air as well as, argon. Some fiber types showed strong effects of environment on their strength properties. These results are compared and discussed in terms of underlying mechanisms and implications for ceramic composites.

Yun, H. M.↗
NASA NTRS2003

Cryogenic Properties of Aluminum-Beryllium and Beryllium Materials

Ultimate tensile strength, yield strength, and elongation were obtained for the aluminum- beryllium alloy, AlBeMetl62 (38%Al-62%Be), at cryogenic (-195.5 C (-32O F) and (- 252.8 C) (-423 F)) temperatures, and for an optical grade beryllium, O-30H (99%Be), at -252.8 C. AlBeMet162 material was purchased to the requirements of SAE- AMs7912, "Aluminum-Beryllium Alloy, Extrusions". O-30H material was purchased to the requirements of Brush Wellman Inc. specification O-30H Optical Grade Beryllium. The ultimate tensile and yield strengths for extruded AlBeMet162 material increased with decreasing temperature, and the percent elongation decreased with decreasing temperature. Design properties for the ultimate tensile strength, yield strength, and percent elongation for extruded AlBeMetl62 were generated. It was not possible to distinguish a difference in the room and cryogenic ultimate strength for the hot isostatically pressed (HIP'ed) O-30H material. The O-30H elongation decreased with decreasing temperature.

Gamwell, Wayne R.↗
NASA NTRS2003

Cryogenic Properties of Aluminum Beryllium and Beryllium Materials

Ultimate tensile strength, yield strength, and elongation were obtained for the aluminum-beryllium alloy, AlBeMetl62 (38%Al-62%Be), at cryogenic (-195.5 C (-320 F) and (-252.8 C) (-423 F)) temperatures, and for an optical grade beryllium, O-30H (99%Be), at -252.8 C. AlBeMetl62 material was purchased to the requirements of SAE-AMS7912, "Aluminum-Beryllium Alloy, Extrusions." O-30H material was purchased to the requirements of Brush Wellman Inc. specification O-30H Optical Grade Beryllium. The ultimate tensile and yield strengths for extruded AlBeMetl62 material increased with decreasing temperature, and the percent elongation decreased with decreasing temperature. Design properties for the ultimate tensile strength, yield strength, and percent elongation for extruded AlBeMetl62 were generated. It was not possible to distinguish a difference in the room and cryogenic ultimate strength for the hot isostatically pressed (HIP'ed) O-30H material. The O30H elongation decreased with decreasing temperature.

Gamwell, Wayne R.↗