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At least 631 records · Page 35

All sources NASA NTRS DOE OSTI

NASA NTRS1992

Combustion synthesis of ceramic-metal composite materials - The TiC-Al2O3-Al system

Combustion synthesis was applied for producing ceramic-metal composites with reduced levels of porosity, by allowing an excess amount of liquid metal, generated by the exothermic reaction during synthesis, to infiltrate the pores. It is shown that this method, when applied to TiC-Al2O3 system, led to a decreased level of porosity in the resulting TiC-Al2O3-Al product, as compared with that of TiC-Al2O3 system. This in situ procedure is more efficient than the two-stage conventional processes (i.e., sintering followed by liquid metal infiltration), although there are limitations with respect to total penetration of the liquid metal and maintaining a stable propagation of the combustion reaction.

Feng, H. J.↗

NASA NTRS1998

Finite Element Modeling of Transient Thermography Inspection of Composite Materials

Several finite element models of defects such as debond and void have been developed for composite panels subjected to transient thermography inspection. Since the exact nature of the heat generated from the flash lamps is unknown, direct comparison between FEA and experimental results is not possible. However, some similarity of the results has been observed. The shape of the time curve that simulates the heat flux from the flash lamps has minimal effect on the temperature profiles. Double the number of flash lamps could increase the contrast of thermal image and define the shape of defect better.

Chu, Tsuchin Philip↗

NASA NTRS2003

Dry Process for Manufacturing Hybridized Boron Fiber/Carbon Fiber Thermoplastic Composite Materials from a Solution Coated Precursor

An apparatus for producing a hybrid boron reinforced polymer matrix composite from precursor tape and a linear array of boron fibers. The boron fibers are applied onto the precursor tapes and the precursor tape processed within a processing component having an impregnation bar assembly. After passing through variable-dimension forming nip-rollers, the precursor tape with the boron fibers becomes a hybrid boron reinforced polymer matrix composite. A driving mechanism is used to pulled the precursor tape through the method and a take-up spool is used to collect the formed hybrid boron reinforced polymer matrix composite.

Harry L Belvin↗

NASA NTRS2003

Microcrack Quantification in Composite Materials by a Neural Network Analysis of Ultrasound Spectral Data

Intra-ply microcracking in unlined composite pressure vessels can be very troublesome to detect and when linked through the thickness can provide leak paths that may hinder mission success. The leaks may lead to loss of pressure/propellant, increased risk of explosion and possible cryo-pumping into air pockets within the laminate. Ultrasonic techniques have been shown capable of detecting the presence of microcracking and in this work they are used to quantify the level of microcracking. Resonance ultrasound methods are utilized with artificial neural networks to build a microcrack prediction/measurement tool. Two networks are presented, one unsupervised to provide a qualitative measure of microcracking and one supervised which provides a quantitative assessment of the level of microcracking. The resonant ultrasound spectroscopic method is made sensitive to microcracking by tuning the input spectrum to the higher frequency (shorter wavelength) components allowing more significant interaction with the defects. This interaction causes the spectral characteristics to shift toward lower amplitudes at the higher frequencies. As the density of the defects increases more interactions occur and more drastic amplitude changes are observed. Preliminary experiments to quantify the level of microcracking induced in graphite/epoxy composite samples through a combination of tensile loading and cryogenic temperatures are presented. Both unsupervised (Kohonen) and supervised (radial basis function) artificial neural networks are presented to determine the measurable effect on the resonance spectrum of the ultrasonic data taken from the samples.

Walker, James L.↗

NASA NTRS1979

Thermal performance modification of composite materials

This paper reports on an investigation of the concept of modifying the thermal performance of filled polymers through a minor compositional change (presently by coating the filler). The fire-safety of construction materials and the instability of solid rockets are used as examples. A theory is developed which shows that vast improvements are possible by controlling thermal conductivity. Experiments are described that show the weight loss and smoke density in the NBS smoke-density chamber of fiberglass-reinforced epoxy panels, and the instability trends of an AP-HTPB propellant fired in an L-Star rocket motor. The feasibility of tailoring thermal behavior to suit each particular need is demonstrated.

Ramohalli, K.↗

NASA NTRS2019

A Multiscale Nonlocal Progressive Damage Model for Composite Materials

In this paper, the advantages of a nonlocal progressive damage formulation are described and demonstrated. An approximation of the nonlocal formulation was implemented coupled with the MAT162 composite damage model as a User defined material model in the LS DYNA environment. A comparison of the local model and the nonlocal model is simulated for an 8-ply laminate under tension is carried for increasing mesh densities. The results show the regularization achieved by nonlocal models by providing mesh independent results.

Kodagali, Karan↗

NASA NTRS1997

Capability of Thermographic Imaging Defined for Detection in High-Temperature Composite Materials

Significant effort and resources are being expended to develop ceramic matrix (CMC), metal matrix (MMC), and polymer matrix (PMC) composites for high-temperature engine components and other parts in advanced aircraft. The objective of this NASA Lewis Research Center study was to evaluate the ability of a thermographic imaging technique for detecting artificially created defects (flat-bottom holes) of various diameters and depths in four composite systems (two CMC's, one MMC, and one PMC) of interest as high-temperature structural materials.

Roth, Don J.↗

NASA NTRS1991

Thermal-vacuum effects on polymer matrix composite materials

Results are presented on the thermal-vacuum response of a variety of fiber reinforced polymers matrix composites that comprised the UTIAS experiment on the LDEF satellite. Theoretical temperature-time predictions for this experiment are in excellent agreement with test data. Results also show quite clearly the effect of outgassing in the dimensional changes of these materials and the corresponding coefficients of thermal expansion. Finally, comparison with ground-based simulation tests are presented as well. Use of these data for design purposes are also given.

Tennyson, R. C.↗

DOE OSTI2022

Revisiting Multi-Material Composite Structures with Homogenized Composite Properties

Composite structures inherently develop residual stresses during their curing process. Driven predominately by mismatched thermal strains between differing materials or ply orientations, but also affected by curing process phenomena like polymer shrinkage, these residual stresses can lead to failure within composite structures. There are several methods varying in complexity that can be used to model the development of residual stresses, all of which are capable of capturing sufficient detail to understand the residual stress state at the ply level. However, explicitly modeling all plies of a layup in a composite structure can be prohibitively expensive based on the number of plies, structure size, and required element size. The computational cost can be reduced through the homogenization of the composite layup without losing much fidelity of the overall response of the structure. The homogenization process reduces the many plies of a laminate to a single lamina that reduces complexity and increases the mesh size where a single element can span multiple plies. This report focuses on verification and validation efforts for a homogenization process using a suite of finite element simulations rather than an analytic solution derived from classical laminate theory. Initial verification using representative element volumes indicated there was minimal error in the homogenization process; however, this compounded to a small, but acceptable error in strip and split ring experimental composite structures. The error does under predict the residual stress state in the strip and split ring and should be accounted for when simulating composite structures with homogenized properties.

36 MATERIALS SCIENCE↗

NASA NTRS1988

Quantitative non-destructive evaluation of porous composite materials based on ultrasonic wave propagation

Two complementary ultrasonic techniques for characterizing porosity in fiber-reinforced composite laminates are evaluated. Five uniaxial graphite-fiber/epoxy-matrix composites having a range of 1 to 8 percent volume fraction of solid glass inclusions to model porosity were investigated. In one technique, signal loss was measured in transmission mode and slope of attenuation, obtained from the first order coefficient of a two-parameter polynomial fit about the center frequency of the useful bandwidth, was used as the ultrasonic parameter to characterize the porosity. The results of these transmission mode measurements displayed a good correlation between the volume fraction of porosity and the slope of attenuation. Integrated polar backscatter was used as a second ultrasonic parameter for the characterization of the porosity in these samples. A single transducer insonified the samples and measured the resulting backscatter at a polar angle of 30 deg with respect to the normal of the sample surface with the azimuthal angles centered at 0 deg with respect to the fiber orientation (i.e., along the fibers). Integrated polar backscatter also displayed good correlation with the volume fraction of porosity.

Miller, James G.↗

NASA NTRS1991

The use of ultrasonic property measurements as the basis for finite element analysis of composite materials

In this work, the use of ultrasonic property measurements as the basis for finite element analysis of full scale composite components is presented. The approach utilizes multiple velocity measurements at oblique angles of incidence and quantitative analysis of radiographic images for the local determination of each of the nine orthotropic moduli in a woven carbon-carbon composite. These values were then used as input into a finite element code (NASTRAN) to analyze the response of the material to load: here, diametric compression. The predicted response was then compared with strain gage results at several locations to validate the approach.

Madaras, E. I.↗

NASA NTRS2005

Modifications of a Composite-Material Combustion Chamber

Two short reports discuss modifications of a small, lightweight combustion chamber that comprises a carbon/carbon composite outer shell and an iridium/ rhenium inner liner. The first report discusses chamber design modifications made as results of hot-fire tests and post-test characterization. The Books & Reports 32 NASA Tech Briefs, June 2005 modifications were intended to serve a variety of purposes, including improving fabrication, reducing thermal-expansion mismatch stresses, increasing strength-to-weight ratios of some components, and improving cooling of some components. The second report discusses (1) the origin of stress in the mismatch between the thermal expansions of the Ir/Re liner and a niobium sleeve and flange attached to the carbon/ carbon shell and (2) a modification intended to relieve the stress. The modification involves the redesign of an inlet connection to incorporate a compressible seal between the Ir/Re liner and the Nb flange. A nickel alloy was selected as the seal material on the basis of its thermal-expansion properties and its ability to withstand the anticipated stresses, including the greatest stresses caused by the high temperatures to be used in brazing during fabrication.

Williams, Brian E.↗

NASA NTRS1975

Space processing of composite materials

Materials and processes for the testing of aluminum-base fiber and particle composites, and of metal foams under extended-time low-g conditions were investigated. A wetting and dispersion technique was developed, based on the theory that under the absence of a gas phase all solids are wetted by liquids. The process is characterized by a high vacuum environment and a high temperature cycle. Successful wetting and dispersion experiments were carried out with sapphire fibers, whiskers and particles, and with fibers of silicon carbide, pyrolytic graphite and tungsten. The developed process and facilities permit the preparation of a precomposite which serves as sample material for flight experiments. Low-g processing consists then merely in the uniform redistribution of the reinforcements during a melting cycle. For the preparation of metal foams, gas generation by means of a thermally decomposing compound was found most adaptable to flight experiments. For flight experiments, the use of compacted mixture of the component materials limits low-g processing to a simple melt cycle.

Steurer, W. H.↗

NASA NTRS1985

A study of the stress wave factor technique for the characterization of composite materials

This study has investigated the potential of the Stress Wave Factor as an NDT technique for thin composite laminates. The conventional SWF and an alternate method for quantifying the SWF were investigated. Agreement between the initial SWF number, ultrasonic C-scan, inplane displacements as obtained by full field moire interferometry, and the failure location have been observed. The SWF number was observed to be the highest when measured along the fiber direction and the lowest when measured across the fibers. The alternate method for quantifying the SWF used square root of the zeroth moment (square root of M sub o) of the frequency spectrum of the received signal as a quantitative parameter. From this study it therefore appears that the stress wave factor has an excellent potential to monitor damage development in thin composite laminates.

Govada, A. K.↗

NASA NTRS1990

Optimum structural design of robotic manipulators with fiber reinforced composite materials

High-speed robotic arms with advanced structural characteristics can be fabricated from optimally tailored fiber reinforced composites. An integrated design methodology is presented for the optimal structural synthesis of composite robotic manipulators. Optimum configurations of ply angles and ply thicknesses are predicted for maximum structural end-effector stiffness and maximum end-effector load carrying capacity, without altering the geometric dimensions of the links. Multiple posture finite element-based static performance criteria are implemented. A new finite element has been developed for the modeling of tubular composite links. Unique features are the inclusion of shear effects and coupling between stretching and flexure. Numerical solutions are obtained via an efficient optimization algorithm. Applications to an existing SCARA-class manipulator illustrate the effectiveness of the method and demonstrate the dramatic influence of the multi-postural design criteria on the optimal design. For a filament wound structure using a high strength carbon fiber in a thermoplastic matrix, the resultant optimum ply configurations have increased the specific stiffness and specific load capacity by factors of 1.5 and 16, respectively, in comparison to identically sized aluminum links.

Saravanos, D. A.↗

NASA NTRS1992

High-toughness graphite/epoxy composite material experiment

This LDEF experiment was designed to measure the effects of near-earth exposure on graphite/epoxy composites over a range of properties. All of the specimens were 8 plies thick, with one of two different cross-ply angles and with one of four different values of bonding fraction between plies. The mechanical properties of interest are toughness, strength, and elastic modulus. Six toughness specimens and nine strength/modulus specimens were manufactured and flown.

Felbeck, David K.↗

DOE OSTI2020

Creation of discrete active site domains via mesoporous silica poly(styrene) composite materials for incompatible acid–base cascade reactions

This work highlights the design and synthesis of bifunctional mesoporous silicate – polymer composite dual acid–base supported cascade catalysts. Compartmentalization of the two incompatible active sites is sought by segregating acid sites on the silica surface, and base sites within polymer chains and/or polymer domains. The ability to isolate and segregate active sites via control of the mesoporous silica pore size and polymer molecular weight is probed with silica samples functionalized by a grafting-to process. Supplemental activator and reducing agent (SARA) atom transfer radical polymerization is used to synthesize random copolymers containing protected primary amines. Thiol–ene ‘click’ chemistry facilitates silica functionalization via a convergent approach, with the ene-functionalized polymer end group and silica-grafted thiols forming SBA/MCM-SH-poly(styrene-co-2-(4-vinylbenzyl)isoindoline-1,3-dione). Polymer deprotection and thiol oxidation produces primary amine/sulfonic acid containing composite catalysts. With the polymer supported Lewis base and silica grafted Brønsted acid, the two-step deacetalization – Knoevenagel condensation cascade is explored to assess the ability of these polymer/silica hybrids to segregate active sites, allowing both acid and base site accessibility. Six composite catalysts are synthesized and tested in individual and cascade reactions with kinetic results demonstrating that lower molecular weight SBA-15-P1 and MCM-41-P1 catalysts outperform (higher turnover frequencies and initial rates) their higher molecular weight analogues, as well as a polymer-free system containing molecular active sites dispersed on the silica surface. Higher molecular weight composite catalysts perform more poorly due to limited chain solubility, mass transfer limitations, and poor catalyst accessibility. In many cases, the polymer chains effectively thread into the mesopores, with higher molecular weight polymers leading to pore blockage and inhibited mass transfer.

36 MATERIALS SCIENCE↗

NASA NTRS1997

Ultrasonic Nondestructive Evaluation Techniques Applied to the Quantitative Characterization of Textile Composite Materials

In this Progress Report, we describe our further development of advanced ultrasonic nondestructive evaluation methods applied to the characterization of anisotropic materials. We present images obtained from experimental measurements of ultrasonic diffraction patterns transmitted through water only and transmitted through water and a thin woven composite. All images of diffraction patterns have been included on the accompanying CD-ROM in the JPEG format and Adobe TM Portable Document Format (PDF), in addition to the inclusion of hardcopies of the images contained in this report. In our previous semi-annual Progress Report (NAG 1-1848, December, 1996), we proposed a simple model to simulate the effect of a thin woven composite on an insonifying ultrasonic pressure field. This initial approach provided an avenue to begin development of a robust measurement method for nondestructive evaluation of anisotropic materials. In this Progress Report, we extend that work by performing experimental measurements on a single layer of a five-harness biaxial woven composite to investigate how a thin, yet architecturally complex, material interacts with the insonifying ultrasonic field. In Section 2 of this Progress Report we describe the experimental arrangement and methods for data acquisition of the ultrasonic diffraction patterns upon transmission through a thin woven composite. We also briefly describe the thin composite specimen investigated. Section 3 details the analysis of the experimental data followed by the experimental results in Section 4. Finally, a discussion of the observations and conclusions is found in Section 5.

Miller, James G.↗