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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Testing of containers made of glass-fiber reinforced plastic with the aid of acoustic emission analysis

Acoustic emission analysis as a quasi-nondestructive test method makes it possible to differentiate clearly, in judging the total behavior of fiber-reinforced plastic composites, between critical failure modes (in the case of unidirectional composites fiber fractures) and non-critical failure modes (delamination processes or matrix fractures). A particular advantage is that, for varying pressure demands on the composites, the emitted acoustic pulses can be analyzed with regard to their amplitude distribution. In addition, definite indications as to how the damages occurred can be obtained from the time curves of the emitted acoustic pulses as well as from the particular frequency spectrum. Distinct analogies can be drawn between the various analytical methods with respect to whether the failure modes can be classified as critical or non-critical.

Wolitz, K.↗
NASA NTRS1979

Detecting moisture in composite honeycomb panels

Radiographic inspection technique detects liquids trapped in cells of honeycomb composite panels constructed with porous fiber-reinforced plastic skins. Procedure is of use in industries such as aerospace or automotive engineering where honeycomb composites are being used or studied.

Culp, J. D.↗
NASA NTRS1979

Strength of adhesive-bonded hybrid structures

Structures prepared from materials with different thermal and mechanical properties by means of fiber-strengthened binders can fail in a number of ways. The present lecture is focused on failures through debonding at the metal or at the fiber-reinforced plastic. A method for calculating the stress distribution in adhesive layers as a function of the load is outlined, and its usefulness in providing insight into the behavior of bonds in hybrid structures is noted. Means of eliminating the unfavorable effects of temperature, humidity, creep and relaxation on the bonds in the manufacture of hybrid structures are examined, along with test methods developed for such structures.

Kirschke, L.↗
NASA NTRS1984

Hygrothermal effects on stresses and deformations in a bonded fiber-reinforced plastic/aluminum system

The hygrothermal effect on time dependent mechanical behavior of a model of nonsymmetrical bonded fiber-reinforced plastic (FRP)/aluminum system was investigated analytically. It was found that a linear viscoelastic closed form solution is sufficient for the prediction model deformations for short periods of time and small strains, while a numerical finite-element solution is preferable for determining adhesive stresses and deformational behavior of the model at any time. The thermoelastic numerical solution shows a certain decrease with time of adhesive stresses, which does not seem to affect significantly the global deformations of the model. On the other hand, it was found that the presence of moisture within the polymeric adhesive layer causes significant decrease in adhesive stresses, which affects deformational changes with time, far beyond the level predicted by the static solution.

Yaniv, G.↗
NASA NTRS1985

Electron emission and acoustic emission from the fracture of graphite/epoxy composites

In past studies it has been shown that the fracture of materials leads to the emission of a variety of species, including electrons, ions, neutral molecules, and photons, all encompassed by the term 'fractoemission' (FE). In this paper, electron emission (EE) from the fracture of single graphite fibers and neat epoxy resin is examined. Measurements of EE are also combined with the detection of acoustic emission (AE) during the testing of graphite-epoxy composite specimens with various fiber orientation. The characteristics of these signals are related to known failure mechanisms in fiber-reinforced plastics. This study suggests that by comparing data from AE and FE measurements, one can detect and distinguish the onset of internal and external failure in composites. EE measurements are also shown to be sensitive to the locus of fracture in a composite material.

Dickinson, J. T.↗
NASA NTRS1989

A stable numerical solution method in-plane loading of nonlinear viscoelastic laminated orthotropic materials

In response to the tremendous growth in the development of advanced materials, such as fiber-reinforced plastic (FRP) composite materials, a new numerical method is developed to analyze and predict the time-dependent properties of these materials. Basic concepts in viscoelasticity, laminated composites, and previous viscoelastic numerical methods are presented. A stable numerical method, called the nonlinear differential equation method (NDEM), is developed to calculate the in-plane stresses and strains over any time period for a general laminate constructed from nonlinear viscoelastic orthotropic plies. The method is implemented in an in-plane stress analysis computer program, called VCAP, to demonstrate its usefulness and to verify its accuracy. A number of actual experimental test results performed on Kevlar/epoxy composite laminates are compared to predictions calculated from the numerical method.

Gramoll, K. C.↗
NASA NTRS1992

Damage tolerance of a composite sandwich with interleaved foam core

A composite sandwich panel consisting of carbon fiber-reinforced plastic (CFRP) skins and a syntactic foam core was selected as an appropriate structural concept for the design of wind tunnel compressor blades. Interleaving of the core with tough interlayers was done to prevent core cracking and to improve damage tolerance of the sandwich. Simply supported sandwich beam specimens were subjected to low-velocity drop-weight impacts as well as high velocity ballistic impacts. The performance of the interleaved core sandwich panels was characterized by localized skin damage and minor cracking of the core. Residual compressive strength (RCS) of the skin, which was derived from flexural test, shows the expected trend of decreasing with increasing size of the damage, impact energy, and velocity. In the case of skin damage, RCS values of around 50 percent of the virgin interleaved reference were obtained at the upper impact energy range. Based on the similarity between low-velocity and ballistic-impact effects, it was concluded that impact energy is the main variable controlling damage and residual strength, where as velocity plays a minor role.

Ishai, Ori↗
NASA NTRS1993

A widely adaptable habitat construction system utilizing space resources

This study suggests that the cost of providing accommodations for various manned activities in space may be reduced by the extensive use of resources that are commonly found throughout the solar system. Several concepts are proposed for converting these resources into simple products with many uses. Concrete is already being considered as a possible moonbase material. Manufacturing equipment should be as small and simple as possible, which leads to the idea of molding it into miniature modules that can be produced and assembled in large numbers to create any conceivable shape. Automated equipment could build up complex structures by laying down layer after layer in a process resembling stereolithography. These tiny concrete blocks handle compression loads and provide a barrier to harmful radiation. They are joined by a web of tension members that could be made of wire or fiber-reinforced plastic. The finished structure becomes air-tight with the addition of a flexible liner. Wire can be made from the iron modules found in lunar soil. In addition to its structural role, a relatively simple apparatus can bend and weld it into countless products like chairs and shelving that would otherwise need to be supplied from Earth. Wire woven into a loose blanket could be an effective micrometeoroid shield, tiny wire compression beams could be assembled into larger beams which in turn form larger beams to create very large space-frame structures. A technology developed with lunar materials could be applied to the moons of Mars or the asteroids. To illustrate its usefulness several designs for free-flying habitats are presented. They begin with a minimal self-contained living unit called the Cubicle. It may be multiplied into clusters called Condos. These are shown in a rotating tether configuration that provides a substitute for gravity. The miniature block proposal is compared with an alternate design based on larger triangular components and a tetrahedral geometry. The overall concept may be expanded to envision city-sized self-sufficient environments where humans could confortably live their entire lives. One such proposal is the Hive. It is configured around a unique sunlight collection system that could provide all its energy needs and that could be scaled up to compensate for the reduced solar intensity at greater distances from the sun. Its outer perimeter consists of a cylindrical section mated to two conical end walls that taper inwards toward a small aperture at the center of rotation. Light collected by two huge mirrors of unusual design enters the aperture and is redirected to the inside of the cylinder. The conical end walls are shielded from direct sunlight and are designed to radiate heat into space. They are lined with air ducts that passively recirculate the atmosphere while extracting moisture by condensation. Although there is no immediate demand for spacecraft on this scale, their consideration can influence even the earliest stages of the development process.

Wykes, Harry B.↗
NASA NTRS1995

Long-term hygrothermal effects on damage tolerance of hybrid composite sandwich panels

A sandwich construction, composed of hybrid carbon-glass fiber-reinforced plastic skins and a syntactic foam core, was selected as the design concept for a wind tunnel compressor blade application, where high damage tolerance and durability are of major importance. Beam specimens were prepared from open-edge and encapsulated sandwich panels which had previously been immersed in water at different temperatures for periods of up to about two years in the extreme case. Moisture absorption and strength characteristics, as related to time of exposure to hygrothermal conditions, were evaluated for the sandwich specimens and their constituents (skins and foam). After different exposure periods, low-velocity impact damage was inflicted on most sandwich specimens and damage characteristics were related to impact energy. Eventually, the residual compressive strengths of the damaged (and undamaged) beams were determined flexurally. Test results show that exposure to hygrothermal conditions leads to significant strength reductions for foam specimens and open-edge sandwich panels, compared with reference specimens stored at room temperature. In the case of skin specimens and for beams prepared from encapsulated sanwich panels that had previously been exposed to hygrothermal conditions, moisture absorption was found to improve strength as related to the reference case. The beneficial effect of moisture on skin performance was, however, limited to moisture contents below 1% (at 50 C and lower temperatures). Above this moisture level and at higher temperatures, strength degradation of the skin seems to prevail.

Ishai, Ori↗
NASA NTRS1999

Developments in Nano-Satellite Structural Subsystem Design at NASA-GSFC

The NASA-GSFC Nano-satellite Technology Development Program will enable flying constellations of tens to hundreds of nano-satellites for future NASA Space and Earth Science missions. Advanced technology components must be developed to make these future spacecraft compact, lightweight, low-power, low-cost, and survivable to a radiation environment over a two-year mission lifetime. This paper describes the efforts underway to develop lightweight, low cost, and multi-functional structures, serviceable designs, and robust mechanisms. As designs shrink, the integration of various subsystems becomes a vital necessity. This paper also addresses structurally integrated electrical power, attitude control, and thermal systems. These innovations bring associated fabrication, integration, and test challenges. Candidate structural materials and processes are examined and the merits of each are discussed. Design and fabrication processes include flat stock composite construction, cast aluminum-beryllium alloy, and an injection molded fiber-reinforced plastic. A viable constellation deployment scenario is described as well as a Phase-A Nano-satellite Pathfinder study.

Rossoni, Peter↗
NASA NTRS1993

Evolution of damage and plasticity in titanium-based, fiber-reinforced composites

The inelastic deformation mechanisms were evaluated for a model titanium-based, fiber-reinforced composite: a beta titanium alloy (Ti-15V-3Al-3Cr-3Sn) reinforced with SiC (SCS-6) fibers. The primary emphasis of this article is to illustrate the sequence in which damage and plasticity evolved for this system. The mechanical responses and the results of detailed microstructural evaluations for the 0(8), 90(8), and +/- 45(2s) line oriented laminates are provided. It is shown that the characteristics of the reaction zone around the fiber play a very important role in the way damage and plasticity evolve, particularly in the microyield regime of deformation, and must be included in any realistic constitutive model. Fiber-matrix debonding was a major damage mode for the off-axis systems. The tension test results are also compared with the predictions of a few constitutive models.

Majumdar, B. S.↗
NASA NTRS1989

Metal matrix composites: Testing, analysis, and failure modes; Proceedings of the Symposium, Sparks, NV, Apr. 25, 26, 1988

The present conference discusses the tension and compression testing of MMCs, the measurement of advanced composites' thermal expansion, plasticity theory for fiber-reinforced composites, a deformation analysis of boron/aluminum specimens by moire interferometry, strength prediction methods for MMCs, and the analysis of notched MMCs under tensile loading. Also discussed are techniques for the mechanical and thermal testing of Ti3Al/SCS-6 MMCs, damage initiation and growth in fiber-reinforced MMCs, the shear testing of MMCs, the crack growth and fracture of continuous fiber-reinforced MMCs in view of analytical and experimental results, and MMC fiber-matrix interface failures.

Johnson, W. S.↗
NASA NTRS1985

Plastic and Failure Analysis of Composites

Three-dimensional finite-element computer program called PAFAC (Plastic and Failure Analysis of Composites) developed for elastic/plastic analysis of fiber-reinforced composite materials and structures. PAFAC written in FORTRAN IV for batch execution. Particularly suited for analyzing laminated metal-matrix composites.

Bigelow, C. A.↗
NASA NTRS1991

Elastic/viscoplastic constitutive model for fiber reinforced thermoplastic composites

A constitutive model to describe the elastic/viscoplastic behavior of fiber-reinforced thermoplastic composites under plane stress conditions is presented. Formulations are given for quasi-static plasticity and time-dependent viscoplasticity. Experimental procedures required to generate the necessary material constants are explained, and the experimental data is compared to the predicted behavior.

Gates, T. S.↗
NASA NTRS1983

Residual strength assessment of low velocity impact damage of graphite-epoxy laminates

This report contains the study of Low Velocity Transverse Impact Damage of graphite-epoxy T300/5208 composite laminates. The specimen, 100 mm diameter clamped plates, were impact damaged by a cantilever-type instrumented 1-inch diameter steel ball. Study was limited to impact velocity 6 m/sec. Rectangular strips, 50 mm x 125 mm, were cut from the impact-damage specimens so that the impact damage zone was in the center of the strips. These strips were tested in tension to obtain their residual strength. An energy dissipation model was developed to predict the residual strength from fracture mechanics concepts. Net energy absorbed I(a) was evaluated from coefficient of restitution concepts based on shear dominated theory of fiber-reinforced materials, with the modification that during loading and unloading the shear deformation are respectively elastic-plastic and elastic. Delamination energy I(d) was predicted by assuming that the stiffness of the laminate dropped due to debonding. Fiber-breakage energy, assumed to be equal to the difference of I(a) and I(d), was used to determine the residual strength. Predictions were compared with test results.

Lal, K. M.↗
NASA NTRS1973

Effects of thermal loading on fiber-reinforced composites with constituents of differing thermal expansivities.

Estimates of the magnitudes of elastic stresses and elastoplastic stresses and strains were made for tungsten fiber-reinforced 80Ni + 20Cr matrix composites. Heating or cooling between 80 and 2000 F was assumed. The calculated elastic stresses exceeded representative or estimated strengths of constituents. For composites with less than 0.65 volume fraction of fiber, plastic flow was considered possible, and elastoplastic solutions indicated that stresses would be reduced but with the concomitant occurrence of sufficiently large strain ranges, particularly in the matrix, to pose a possible thermal fatigue problem. Limited experimental studies on tungsten fiber-copper matrix composites heated and cooled a number of times between 80 and 1600 F in a conventional furnace and then heated from 80 to 1652 F in a hot-stage microscope resulted in matrix microfracture for a 70 volume fraction fiber composite and substantial matrix strain for a 40 volue fraction fiber composite.

Hoffman, C. A.↗
NASA NTRS1990

Thermal and mechanical behavior of metal matrix and ceramic matrix composites

The present conference discusses local stresses in metal-matrix composites (MMCs) subjected to thermal and mechanical loads, the computational simulation of high-temperature MMCs' cyclic behavior, an analysis of a ceramic-matrix composite (CMC) flexure specimen, and a plasticity analysis of fibrous composite laminates under thermomechanical loads. Also discussed are a comparison of methods for determining the fiber-matrix interface frictional stresses of CMCs, the monotonic and cyclic behavior of an SiC/calcium aluminosilicate CMC, the mechanical and thermal properties of an SiC particle-reinforced Al alloy MMC, the temperature-dependent tensile and shear response of a graphite-reinforced 6061 Al-alloy MMC, the fiber/matrix interface bonding strength of MMCs, and fatigue crack growth in an Al2O3 short fiber-reinforced Al-2Mg matrix MMC.

Kennedy, John M.↗