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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Some important aspects in testing high-modulus fiber composite tubes in axial tension.

Tubular specimens were potted in metal grips to determine the feasibility of this gripping method in applying multiaxial loads. Strain gage rosettes were used to assess grip transitional strains, through thickness strain variation, and strain variations along the tube length and circumference. The investigation was limited to loading graphite/epoxy and glass/epoxy tubes in axial tension. Results include modifications made to the grips to reduce transitional strains, illustrations of the tube failure modes, and some material properties. The gripping concept shows promise as a satisfactory technique for applying multiaxial loads to high-strength, high-modulus fiber composite tubes.

Sullivan, T. L.↗
NASA NTRS1971

Determining and analyzing the strength and impact resistance of high modulus glass

An error was noticed recently in the computer program used to reduce the laboratory sonic measurements to tabulated values of Young's modulus of the bulk samples of experimental glasses. Correction of this error gave revised values for the last fifty experimental glasses prepared in this laboratory. This corrected data, when examined as input material for the calculation of Young's modulus of bulk glasses from composition by the C. J. Phillips procedure, resulted in new values for the contribution per mol of several oxides. The new value for the zinc oxide molal factor is especially significant since it is slightly greater than the factor for beryllia for the types of glasses melted in the UARL research program. This discovery provides a new tool in the search for nontoxic, i.e. without beryllia, high modulus glass fibers particularly when coupled with recent measurements that showed zinc oxide contributes significantly to increased impact strength. New glass compositions prepared in this period and the latest impact strength values measured are also included.

Bacon, J. F.↗
NASA NTRS1972

Some important aspects in testing high-modulus fiber composite tubes designed for multiaxial loading

Tubular specimens were potted in metal grips to determine the feasibility of this gripping method in applying multiaxial loads. Strain gage rosettes were used to assess grip transitional strains, through thickness strain variation and strain variations along the tube length and circumference. The investigation was limited to loading 0 deg, + or - 45 deg, and 90 deg graphite/epoxy and glass/epoxy tubes in axial tension. Results include modifications made to the grips to reduce transitional strains, illustrations of the tube failure modes, and some material properties. The gripping concept shows promise as a satisfactory technique for applying multiaxial loads to high strength, high modulus fiber composite tubes.

Sullivan, T. L.↗
NASA NTRS1972

Some important aspects in testing high-modulus fiber composite tubes designed for multiaxial loading.

Tubular specimens were potted in metal grips to determine the feasibility of this gripping method in applying multiaxial loads. Strain gage rosettes were used to assess grip transitional strains, through thickness strain variation and strain variations along the tube length and circumference. The investigation was limited to loading 0, 45, plus or minus 45, and 90 deg graphite/epoxy and glass/epoxy tubes in axial tension. Results include modifications made to the grips to reduce transitional strains, illustrations of the tube failure modes, and some material properties. The gripping concept shows promise as a satisfactory technique for applying multiaxial loads to high-strength, high-modulus fiber composite tubes.

Sullivan, T. L.↗
NASA NTRS1974

Non-toxic invert analog glass compositions of high modulus

Glass compositions having a Young's modulus of at least 15 million psi are described. They and a specific modulus of at least 110 million inches consist essentially of, in mols, 15 to 40% SiO2, 6 to 15% Li2O, 24 to 45% of at least two bivalent oxides selected from the group consisting of Ca, NzO, MgO and CuO; 13 to 39% of at least two trivalent oxides selected from the group consisting of Al2O3, Fe2O3, B2O3, La2O3, and Y2O3 and up to 15% of one or more tetravelent oxides selected from the group consisting of ZrO2, TiO2 and CeO2. The high modulus, low density glass compositions contain no toxic elements. The composition, glass density, Young's modulus, and specific modulus for 28 representative glasses are presented. The fiber modulus of five glasses are given.

Bacon, J. F.↗
NASA NTRS1990

Friction and wear of TPS fibers: A study of the adhesion and friction of high modulus fibers

The adhesional and frictional forces between filaments in a woven fabric or felt, strongly influenced the processability of the fiber and the mechanical durability of the final product. Even though the contact loads between fibers are low, the area of contact is extremely small giving rise to very high stresses; principally shear stresses. One consequence of these strong adhesional and frictional forces is the resistance of fibers to slide past each other during weaving or when processed into nonwoven mats or felts. Furthermore, the interfiber frictional forces may cause surface damage and thereby reduce the fiber strength. Once formed into fabrics, flexural handling and manipulation of the material again causes individual filaments to rub against each other resulting in modulus, brittle fibers such as those used in thermal protection systems (TPS). The adhesion and friction of organic fibers, notably polyethylene terephthalate (PET) fibers, have been extensively studied, but there has been very little work reported on high modulus inorganic fibers. An extensive study was made of the adhesion and friction of flame drawn silica fibers in order to develop experimental techniques and a scientific basis for data interpretation. Subsequently, these methods were applied to fibers of interest in TPS materials.

Bascom, Willard D.↗
NASA NTRS2003

Analyses of Failure Mechanisms in Woven Graphite/Polyimide Composites with Medium and High Modulus Graphite Fibers Subjected to In-Plane Shear

The application of the Iosipescu shear test for the room and high temperature failure analyses of the woven graphite/polyimide composites with the medium (T-650) and igh (M40J and M60J) modulus graphite fibers is discussed. The M40J/PMR-II-50 and M60J/PMR-II-50 composites were tested as supplied and after thermal conditioning. The effect of temperature and conditioning on the initiation of intralaminar damage and the shear strength of the composites was established.

Kumosa, M.↗
NASA NTRS2003

Mechanical Behaviour of Woven Graphite/Polyimide Composites with Medium and High Modulus Graphite Fibers Subjected to Biaxial Shear Dominated Loads

A major limitation of woven fiber/polymer matrix composite systems is the inability of these materials to resist intralaminar and interlaminar damage initiation and propagation under shear-dominated biaxial loading conditions. There are numerous shear test methods for woven fabric composites, each with its own advantages and disadvantages. Two techniques, which show much potential, are the Iosipescu shear and +/- 45 deg tensile tests. In this paper, the application of these two tests for the room and high temperature failure analyses of woven graphite/polyimide composites is briefly evaluated. In particular, visco-elastic micro, meso, and macro-stress distributions in a woven eight harness satin (8HS) T650/PMR-15 composite subjected to these two tests are presented and their effect on the failure process of the composite is evaluated. Subsequently, the application of the Iosipescu tests to the failure analysis of woven composites with medium (T650) and high (M40J and M60J) modulus graphite fibers and PMR-15 and PMR-II-50 polyimide resins is discussed. The composites were tested as-supplied and after thermal conditioning. The effect of temperature and thermal conditioning on the initiation of intralaminar damage and the shear strength of the composites was established.

Kumose, M.↗
NASA NTRS1982

Residual stress in high modulus carbon fibers

The modulus and residual strain in carbon fibers are measured by successively electrochemically milling away the fiber surface. Electrochemical etching is found to remove the carbon fiber surface very uniformly, in contrast to air and wet oxidation. The precision of fiber diameter measurements is improved by using a laser diffraction technique instead of optical methods. More precise diameter measurements reveal that past correlations of diameter and fiber modulus are largely measurement artifact. The moduli of most carbon fibers decrease after the outer layers of the fibers are removed. Owing to experimental difficulties, the moduli and strengths of the fibers at their centers are not determined, and moduli are estimated on the basis of microstructure. The calculated residual stresses are found to be insensitive to these moduli estimates as well as the exact form of regression equation used to describe the moduli and residual strain distributions. Axial compressive residual stresses are found to be very high for some higher modulus carbon fibers. It is pointed out that the compressive stress makes the fibers insensitive to surface flaws when loaded in tension but it may initiate failure by buckling when loaded in compression.

Chen, K. J.↗
NASA NTRS1971

The kinetics of crystallization of molten binary and ternary oxide systems and their application to the origination of high modulus glass fibers

Emphasis on the consideration of glass formation on a kinetic process made it possible to think of glass compositions different from those normally employed in the manufacture of glass fibers. Approximately 450 new glass compositions were prepared and three dozen of these compositions have values for Young's modulus measured on bulk specimens greater than nineteen million pounds per square inch. Of the new glasses about a hundred could be drawn into fibers by mechanical methods at high speeds. The fiber which has a Young's modulus measured on the fiber of 18.6 million pounds per square inch and has been prepared in quantity as a monofilament (to date more than 150 million lineal feet of 0.2 to 0.4 mil fiber have been produced). This fiber has also been successfully incorporated both in epoxy and polyimide matrices. The epoxy resin composite has shown a modulus forty percent better than that achievable using the most common grade of competitive glass fiber, and twenty percent better than that obtainable with the best available grade of competitive glass fiber. Other glass fibers of even higher modulus have been developed.

Bacon, J. F.↗
NASA NTRS2004

In-Plane Shear Testing of Medium and High Modulus Woven Graphite Fiber Reinforced/Polyimide Composites

Iosipescu shear tests were performed at room temperature and at 316 C (600 F) o woven composites with either M40J or M60J graphite fibers and PMR-II-50 polyimide resin matrix. The composites were tested as supplied and after thermo-cycling, with the thermo-cycled composites being tested under dry and wet conditions. Acoustic emission (AE) was monitored during the room and high temperature Iosipescu experiments. The shear stresses at the maximum loads and the shear stresses at the significant onset of AE were determined for the composites as function of temperature and conditioning. The combined effects of thermo-cycling and moisture on the strength and stiffness properties of the composites were evaluated. It was determined that the room and high temperature shear stresses at the maximum loads were unaffected by conditioning. However, at room temperature the significant onset of AE was affected by conditioning; the thermal conditioned wet specimens showed the highest shear stress at the onset of AE followed by thermal-conditioned and then as received specimens. Also, at igh temperature the significant onset of AE occurred in some specimens after the maximum load due to the viscoelastoplastic nature of the matrix material.

Gentz, M.↗
DOE OSTI2024

Additive manufacturing of sandwich panels with continuous fiber reinforced high modulus composite facings

Abstract An improved approach consisting of a combination of fiber placement and fused filament fabrication is introduced for the additive manufacture (AM) of structural grade sandwich beams. Here, sandwich beams are additively manufactured using in‐situ deposition and consolidation of continuous fiber unidirectional facings made from a commingled yarn system of e‐glass fiber (~50% vol.) and amorphous PET, and a hexagonal honeycomb core structure made from PETG. Both facings and the sandwich core are manufactured on a single machine, in one sequence (skin‐core‐skin), employing the benefit of matrix compatibility to create autohesion at the interfaces. Flexural and transverse shear rigidity are determined experimentally and compared with analytical predictions and show correlation to within 3%. Flexural strength and core shear strength are also measured. Post‐mortem examinations show that core fracture and core facing debond were the dominant failure mode in flexure. Single cantilever beam tests were performed to evaluate core facing debond toughness. Subsequently, surface preheat using infrared heaters was utilized to increase autohesion between core and facing. The results show debond toughness was increased 4 times using infrared heating. This research effort presents a manufacturing approach that has the potential for the AM of stiff, well bonded, structural grade sandwich beams, in an integrated sequence, employing in‐situ consolidation to the facings, without the need for the use of intermediate adhesives for skin‐to‐core bonding. Highlights An improved additive manufacturing technique for making sandwich panels is developed. Sandwich panel facings have fiber volume fractions of approximately 50%. Surface preheat improves core‐to‐facing debond toughness by a factor of 4. Top and bottom facings are consolidated during manufacture leading to better properties. Experimental results are compared to analytical predictions and show good correlation.

17 WIND ENERGY↗