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At least 667 records · Page 37

All sources NASA NTRS DOE OSTI

NASA NTRS1971

Design properties of randomly reinforced fiber/resin composites

The pseudoisotropic laminate analogy is used in conjunction with fiber composite micro and macromechanics to predict the thermal and mechanical properties of planar randomly reinforced fiber composites (PRRFC). Theoretical results are presented for boron/epoxy, Thornel-50/epoxy, and S-glass/epoxy PRRFC. The results show that the thermal and elastic properties depend on both constituent materials and the fiber volume ratio. The strength depends also on the type of applied stress.

Chamis, C. C.↗

NASA NTRS1972

Design properties of randomly reinforced fiber/resin composites.

The pseudoisotropic laminate analogy is used in conjunction with fiber composite micro and macromechanics to predict the thermal and mechanical properties of planar randomly reinforced fiber composites (PRRFC). Theoretical results are presented for boron/epoxy, Thornel-50/epoxy, and S-glass/epoxy PRRFC. The results show that the thermal and elastic properties depend on both constituent materials and the fiber volume ratio (FVR). The strength depends also on the type of applied stress.

Chamis, C. C.↗

NASA NTRS2004

Tensile Properties of Polymeric Matrix Composites Subjected to Cryogenic Environments

Polymer matrix composites (PMC s) have seen limited use as structural materials in cryogenic environments. One reason for the limited use of PMC s in cryogenic structures is a design philosophy that typically requires a large, validated database of material properties in order to ensure a reliable and defect free structure. It is the intent of this paper to provide an initial set of mechanical properties developed from experimental data of an advanced PMC (IM7/PETI-5) exposed to cryogenic temperatures and mechanical loading. The application of this data is to assist in the materials down-select and design of cryogenic fuel tanks for future reusable space vehicles. The details of the material system, test program, and experimental methods will be outlined. Tension modulus and strength were measured at room temperature, -196 C, and -269 C on five different laminates. These properties were also tested after aging at -186 C with and without loading applied. Microcracking was observed in one laminate.

Whitley, Karen S.↗

NASA NTRS1982

Environmental exposure effects on composite materials for commercial aircraft

The data base for composite materials' properties as they are affected by the environments encountered in operating conditions, both in flight and at ground terminals is expanded. Absorbed moisture degrades the mechanical properties of graphite/epoxy laminates at elevated temperatures. Since airplane components are frequently exposed to atmospheric moisture, rain, and accumulated water, quantitative data are required to evaluate the amount of fluids absorbed under various environmental conditions and the subsequent effects on material properties. In addition, accelerated laboratory test techniques are developed are reliably capable of predicting long term behavior. An accelerated environmental exposure testing procedure is developed, and experimental results are correlated and compared with analytical results to establish the level of confidence for predicting composite material properties.

Gibbons, M. N.↗

NASA NTRS1989

Optimum interface properties for metal matrix composites

Due to the thermal expansion coefficient mismatch (CTE) between the fiber and the matrix, high residual sresses exist in metal matrix composite systems upon cool down from processing temperature to room temperature. An interface material can be placed between the fiber and the matrix to reduce the high tensile residual stresses in the matrix. A computer program was written to minimize the residual stress in the matrix subject to the interface material properties. The decision variables are the interface modulus, thickness and thermal expansion coefficient. The properties of the interface material are optimized such that the average distortion energy in the matrix and the interface is minimized. As a result, the only active variable is the thermal expansion coefficient. The optimum modulus of the interface is always the minimum allowable value and the interface thickness is always the maximum allowable value, independent of the fiber/matrix system. The optimum interface thermal expansion coefficient is always between the values of the fiber and the matrix. Using this analysis, a survey of materials was conducted for use as fiber coatings in some specific composite systems.

Ghosn, Louis J.↗

NASA NTRS1981

Composite structural materials

Physical properties of fiber reinforced composites; structural concepts and analysis; manufacturing; reliability; and life prediction are subjects of research conducted to determine the long term integrity of composite aircraft structures under conditions pertinent to service use. Progress is reported in (1) characterizing homogeneity in composite materials; (2) developing methods for analyzing composite materials; (3) studying fatigue in composite materials; (4) determining the temperature and moisture effects on the mechanical properties of laminates; (5) numerically analyzing moisture effects; (6) numerically analyzing the micromechanics of composite fracture; (7) constructing the 727 elevator attachment rib; (8) developing the L-1011 engine drag strut (CAPCOMP 2 program); (9) analyzing mechanical joints in composites; (10) developing computer software; and (11) processing science and technology, with emphasis on the sailplane project.

Ansell, G. S.↗

NASA NTRS1991

The effect of matrix mechanical properties on (0)8 unidirectional SiC/Ti composite fatigue resistance

The relationship between constituent and MMC properties in fatigue loading is investigated with low-cycle fatigue-resistance testing of an alloy Ti-15-3 matrix reinforced with SiC SCS-6 fibers. The fabrication of the composite is described, and specimens are generated that are weak and ductile (WD), strong and moderately ductile (SM), or strong and brittle (SB). Strain is measured during MMC fatigue tests at a constant load amplitude with a load-controlled waveform and during matrix-alloy fatigue tests at a constant strain amplitude using a strain-controlled waveform. The fatigue resistance of the (0)8 SiC/Ti-15-3 composite is found to be slightly influenced by matrix mechanical properties, and the composite- and matrix-alloy fatigue lives are not correlated. This finding is suggested to relate to the different crack-initiation and -growth processes in MMCs and matrix alloys.

Gabb, T. P.↗

NASA NTRS1989

Effects of thermal cycling on composite materials for space structures

The effects of thermal cycling on the thermal and mechanical properties of composite materials that are candidates for space structures are briefly described. The results from a thermal analysis of the orbiting Space Station Freedom is used to define a typical thermal environment and the parameters that cause changes in the thermal history. The interactions of this environment with composite materials are shown and described. The effects of this interaction on the integrity as well as the properties of GR/thermoset, Gr/thermoplastic, Gr/metal and Gr/glass composite materials are discussed. Emphasis is placed on the effects of the interaction that are critical to precision spacecraft. Finally, ground test methodology are briefly discussed.

Tompkins, Stephen S.↗

NASA NTRS2005

Modeling and Testing of the Viscoelastic Properties of a Graphite Nanoplatelet/Epoxy Composite

In order to facilitate the interpretation of experimental data, a micromechanical modeling procedure is developed to predict the viscoelastic properties of a graphite nanoplatelet/epoxy composite as a function of volume fraction and nanoplatelet diameter. The predicted storage and loss moduli for the composite are compared to measured values from the same material using three test methods; Dynamical Mechanical Analysis, nanoindentation, and quasi-static tensile tests. In most cases, the model and experiments indicate that for increasing volume fractions of nanoplatelets, both the storage and loss moduli increase. Also, the results indicate that for nanoplatelet sizes above 15 microns, nanoindentation is capable of measuring properties of individual constituents of a composite system. Comparison of the predicted values to the measured data helps illustrate the relative similarities and differences between the bulk and local measurement techniques.

Odegard, Gregory M.↗

NASA NTRS1982

Modelling of dimensional stability of fiber reinforced composite materials

Various methods of predicting the expansion and diffusion properties of composite laminates are reviewed. The prediction equations for continuous fiber composites can be applied to SMC composites as the effective fiber aspect ratio in the latter is large enough. The effect of hygrothermal expansion on the dimensional stability of composite laminates was demonstrated through the warping of unsymmetric graphite/epoxy laminates. The warping is very sensitive to the size of the panel, and to the moisture content which is in turn sensitive to the relative humidity in the environment. Thus, any long term creep test must be carried out in a humidity-controlled environment. Environmental effects in SMC composites and bulk polyester were studied under seven different environments. The SMC composites chosen are SMC-R25, SMC-R40, and SMC-R65.

Hahn, H. T.↗

NASA NTRS1982

Martian dust mantling and surface composition - Interpretation of thermophysical properties

The goal of the study presented here is to use the diurnal variation of the differences in the brightness temperatures between each of the four surface-sensing IRTM (infrared thermal mapper) wavelength bands to separate the average grain size determined by the thermal inertia into the surface block population and the inertia of the fine component. It is noted that the thermal emissivity of the surface can also be determined and that this in turn can be used to estimate compositional variations. What is more, the atmospheric dust content can be estimated and used to infer sources and sinks of airborne dust. Owing to the number of unknowns, observations at more than one time of day are necessary to determine each of these parameters independently. The data discussed here were obtained by the IRTM, which had five thermal channels centered at 7, 9, 11, 15, and 20 microns and one channel that measured solar reflectance for from 0.3 to 3.0 microns.

Christensen, P. R.↗

NASA NTRS1991

Improved bounds on elastic and transport properties of fiber-reinforced composites - Effect of polydispersivity in fiber radius

Improved rigorous bounds were computed on the effective elastic and transport properties (including the effective axial shear modulus, effective transverse bulk modulus, and effective transverse shear modulus) of a transversely isotropic fiber-reinforced material composed of infinitely-long oriented multisized impenetrable circular cylinders distributed throughout a matrix. Results were used to study the effect of fiber-radius polydispersivity on the elastic and transport properties of such unidirectional composites. It was found that increasing the degree of polydispersivity increases the effective transverse conductivity (or axial shear modulus) and the effective transverse bulk modulus, and slightly decreases the effective transverse shear modulus for cases in which the fibers are more conducting or stiffer than the matrix.

Miller, C. A.↗

NASA NTRS1986

Thermal and flammability characterization of graphite composites

Thermal, mechanical, and flammability properties of graphite composites fabricated with XU71775/H795, a bismaleimide/vinyl-polystyrylpyridine formulation; H795, a bismaleimide; Cycom 6162, a phenolic; and PSP 6022M, a polystyrylpyridine and two types of graphite reinforcement were evaluated and compared with a composite made with an epoxy resin as a matrix. The measured properties included limiting-oxygen index, smoke evolution, thermal degradation products, total-heat release, heat-release rates, mass loss, flame spread, ignition resistance, thermogravimetric analysis, and selected mechanical properties. It was found that the combination of XU71775/H795 with the graphite tape was the optimum design giving the lowest heat release rate.

Kourtides, D. A.↗

DOE OSTI2024

Evaluation of Composite Structural Materials for Heliostat Cost Reduction

Structures manufactured from steel comprise up to 40% of a CSP heliostat's cost. Composite structures represent a potential opportunity to reduce this cost. A reference heliostat structural model has been created with a reflector area of 25m 2 . The design, constructed of low-carbon steel, pro-vides baseline deflection and stiffness under a 21 m/s operating wind speeds. Wind loads on the tracker structure are determined for both operating and stow conditions. An established roster of suitable metal alternative materials is considered including: glass, basalt, and carbon reinforced polymer (GFRP, BFRP, and CFRP respectively). Three heliostat components are investigated: the pylon, torque tube, and the purlin-strut assembly. Composite material properties are substituted for those of steel, and the beams are re-sized to match the original steel components' deflection under given wind loads. Weight and cost changes resulting from this resizing are evaluated. It is found that GFRP and BFRP represent a 3X–6X cost premium for the same operating deflection character-istics as steel across all three investigated component classes; with weight reduction only achieved for the purlin-strut assembly. While CFRP components can achieve approximately 25–75% weight savings depending on the application, this comes with a 9X–14X cost increase over the steel base-line for tube-type structures and roughly 5X cost increase when replacing c-channel structures. This work does not rule out the possibility of cost savings when the heliostat design and kinematics to take advantage of composites' specific properties.

14 SOLAR ENERGY↗

NASA NTRSDate not supplied

Selection, Production, and Properties of Regolith Polymer Composites for Lunar Construction

NASA’s Artemis Program seeks to establish a long-term presence on the Moon to enable scientific exploration and expand the cis-lunar economy by utilizing lunar resources through public-private and international partnerships. Over the next decades, a lunar spaceport will need to be established to provide the services and facilities that are necessary to achieve this goal. Robotic construction technologies using in-situ materials must be developed to build up enabling infrastructure such as launch/landing pads, blast protection, power/communications infrastructure, improved roads, improved operational surfaces, and radiation protection shelters. Kennedy Space Center’s Granular Mechanics and Regolith Operations laboratory at Swamp Works has partnered with SpaceFactory and LERA Consulting Structural Engineers to develop the architectural and structural design of an unpressurized lunar shelter. The shelter, called Lunar Infrastructure Asset (LINA), is designed to support 2.3 m of regolith overburden to protect astronauts and surface assets from radiation, meteoroid impact, thermal gradients/cycling, and to withstand moonquakes. LINA’s structural design criteria and the resulting structure design are detailed in separate papers. A Fused Filament Fabrication (FFF) construction process using regolith polymer composites has been developed and is detailed in a separate publication. This paper presents material formulations and selection rationale for each of the composite components that were examined. Formulations include 70:30, 80:20, and 85:15 wt.% mixture ratios of lunar mare simulant Black Point-1 (BP-1): Polylactic Acid (PLA), 80:20 Lunar Highlands Simulant-1 (LHS-1): PLA and an 80:20 BP-1: PLA formulation with a flow enhancer additive. Test samples were printed in simulated lunar dirty thermal vacuum conditions (-190 °C, 10-3 torr). A series of tests were performed on each formulation to characterize the achieved mixture ratio, mechanical strength properties, off-gassing products during vacuum printing, and porosity and density of printed products. The LHS-1: PLA formulation yielded an advantageous combination of properties and was used in a final test that additively constructed a sub-scaled LINA on regolith simulant in dirty vacuum conditions. The materials and construction process presented in this paper are considered to be at Technology Readiness Level (TRL) 5 with additional testing necessary to characterize long term lunar environmental exposure effects.

lunar infrastructure↗

NASA NTRSDate not supplied

Selection, Production, and Properties of Regolith Polymer Composites for Lunar Construction

NASA’s Artemis Program seeks to establish a long-term presence on the moon to enable scientific discoveries and utilization of lunar resources through public-private partnerships. Over the next decades, a lunar spaceport enabling regular transportation from and to Earth will need to be established to provide the services and facilities that are necessary to achieve this goal. Robotic construction technologies using in-situ materials must be developed to build up enabling infrastructure such as launch/landing pads, blast protection, power/communications towers, improved trafficability pathways and radiation protection shelters. Kennedy Space Center’s Granular Mechanics and Regolith Operations laboratory at Swamp Works has partnered with AI SpaceFactory to develop the architectural and structural design of an unpressurized shelter. The shelter, called Lina, is designed to protect astronauts and surface assets from radiation, meteoroid impact, moon quakes and thermal gradients. Lina’s structural design criteria and the resulting structure design are detailed in separate papers. A Fused Filament Fabrication (FFF) construction process using regolith polymer composites has been developed. This paper presents the material formulations and selection rationale for each of the composite components. Formulations include 70:30, 80:20, and 85:15 wt.% mixture ratios of lunar mare simulant Black Point-1 (BP-1): Polylactic Acid (PLA), 80:20 Lunar Highlands Simulant (LHS-1): PLA and an 80:20 BP-1:PLA formulation with a processing aid/compatibilizer additive. Test samples were printed in simulated lunar dirty thermal vacuum conditions (~-180 °C, ~10 -3 torr). The test environment evolved throughout the duration of the print process. A series of tests were performed to characterize the mixture ratios achieved for each formulation, the off-gassing products during vacuum printing, the strength properties, and porosity of printed products. The LHS-1: PLA formulation yielded an advantageous combination of properties and was used in a final test that additively constructed a sub-scaled Lina on regolith simulant in dirty vacuum conditions.

lunar infrastructure↗

NASA NTRS1983

Simplified composite micromechanics equations for hygral, thermal and mechanical properties

A unified set of composite micromechanics equations of simple form is summarized and described. This unified set can be used to predict unidirectional composite (ply) geometric, mechanical, thermal and hygral properties using constituent material (fiber/matrix) properties. This unified set also includes approximate equations for predicting (1) moisture absorption; (2) glass transition temperature of wet resins; and (3) hygrothermal degradation effects. Several numerical examples are worked-out to illustrate ease of use and versatility of these equations. These numerical examples also demonstrate the interrelationship of the various factors (geometric to environmental) and help provide insight into composite behavior at the micromechanistic level.

Chamis, C. C.↗

NASA NTRS1984

Simplified composite micromechanics equations of hygral, thermal, and mechanical properties

Chamis, C. C.↗