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At least 253 records · Page 14

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.↗

Effects of through-the-thickness stitching on impact and interlaminar fracture properties of textile graphite/epoxy laminates

This study investigated the effects of through-the-thickness stitching on impact damage resistance, impact damage tolerance, and mode I and mode II fracture toughness of textile graphite/epoxy laminates. Uniweave resin-transfer-molded 48 ply graphite/epoxy (AS4/3501-6) laminates were stitched with Kevlar and glass yarns of different linear densities and stitch spacings. Delaminations were implanted during processing to simulate impact damage. Sublaminate buckling tests were performed to determine the effects of stitching on the compressive strength. The results showed outstanding improvements of up to 400 percent in the compression strength over the unstitched laminates. In impact and static indentation tests the onset of damage occurred at the same level, but the extent of damage was less in stitched laminates. Mode I fracture toughness of 24 ply Uniweave unidirectional (AS4/3501-6) stitched laminates was measured by conducting double-cantilever-beam tests. The critical strain energy release rate (G(sub Ic)) was found to be up to 30 times higher than the unstitched laminates. Mode II fracture toughness of the Uniweave laminates was measured by performing end-notched-flexure tests. Two new methods to compute the apparent G(sub IIc) are presented. The apparent G(sub IIc) was found to be at least 5-15 times higher for the stitched laminates.

Sharma, Suresh K.↗

Development of an Ablative 3D Quartz / Cyanate Ester Composite for the Orion Spacecraft Compression Pad

With the successful flight test of the Orion Multipurpose Crew Vehicle last December, NASA is well on its way to sending humans into deep space with the ultimate goal of putting astronauts on Mars in the 2030s. Orion will receive some upgrades for its next launch in 2018 including a newly developed 3D quartz / cyanate ester composite material for the compression pad. Multiple pad locations in the heat shield serve as a part of the mechanism for holding the Crew and Service Modules together during most mission phases prior to separation followed by Earth re-entry of the Crew Module. Thus the compression pad must survive structural and aerothermal loads, and protect the adjascent structure and heat shield materials from over-heating.This paper describes the approach used for developing the new 3D composite, including continuous 3D weaving on an automated loom followed by resin transfer molding. Mechanical, thermal, arc jet ,and stress relaxation testing of the 3D composite are also described.

Feldman, Jay D.↗

Response of Graphite to Dynamic Loading and Hypervelocity Jet Impacts

The compressive strengths of three varieties of high purity graphite, PCEA, NBG-18, and NBG-25, as well as the depth of penetration of small-scale charges into these materials was experimentally determined. These grades are similar in density, ranging from 1.80 – 1.85 g/cc, and nominal apparent porosity, ranging from 18% to 20%, but provide a wide range in maximum grain or particle size from 10s to 1000s of µm. Two very different manufacturing methods are also represented; PCEA is extruded while NBG-18 and NBG-25 are iso-molded. The quasistatic and dynamic strengths of each grade were determined on a load frame and split-Hopkinson pressure bar, respectively. The depth of penetration (DOP) of two small-scale shaped charges, the Teledyne RP-1 and RP-4, was determined against graphite. The global response of the RP-4 impacts was markedly different as the PCEA samples remained intact while all the NBG-25 samples split into 2 or 3 pieces after the jet penetration had completed. However, for all tests, the trusted DOPs fell within 2 cm. Preliminary hydrocode modeling of the penetration events used existing models that were not designed for graphite. The results can be tuned to reasonably reproduce the DOP, but the wound channel geometry is not reproduced well. A model designed for graphite would need to represent graphite’s non-linear and energy dissipation characteristics.

36 MATERIALS SCIENCE↗

Development and Evaluation of Stitched Sandwich Panels

This study explored the feasibility and potential benefits provided by the addition of through-the-thickness reinforcement to sandwich structures. Through-the-thickness stitching is proposed to increase the interlaminar strength and damage tolerance of composite sandwich structures. A low-cost, out-of-autoclave processing method was developed to produce composite sandwich panels with carbon fiber face sheets, a closed-cell foam core, and through-the-thickness Kevlar stitching. The sandwich panels were stitched in a dry preform state, vacuum bagged, and infiltrated using Vacuum Assisted Resin Transfer Molding (VARTM) processing. For comparison purposes, unstitched sandwich panels were produced using the same materials and manufacturing methodology. Test panels were produced initially at the University of Utah and later at NASA Langley Research Center. Four types of mechanical tests were performed: flexural testing, flatwise tensile testing, core shear testing, and edgewise compression testing. Drop-weight impact testing followed by specimen sectioning was performed to characterize the damage resistance of stitched sandwich panels. Compression after impact (CAI) testing was performed to evaluate the damage tolerance of the sandwich panels. Results show significant increases in the flexural stiffness and strength, out-of-plane tensile strength, core shear strength, edgewise compression strength, and compression-after-impact strength of stitched sandwich structures.

Stanley, Larry E.↗

Development and Testing of a Post-Installable Deepwater Monitoring System Using Fiber-Optic Sensors

This paper addresses the design and development of a fiber-optic monitoring system that can be deployed on existing deepwater risers and flowlines; and provides a summary of test article fabrication and the subsequent laboratory testing performed at the National Aeronautics and Space Administration-Johnson Space Center (NASA-JSC). A major challenge of a post-installed instrumentation system is to ensure adequate coupling between the instruments and the riser or flowline of interest. This work investigates the sensor coupling for pipelines that are suspended in a water column (from topside platform to seabed) using a fiber-optic sensor clamp and subsea bonding adhesive. The study involved the design, fabrication, and test of several prototype clamps that contained fiber-optic sensors. A mold was produced by NASA using 3-D printing methods that allowed the casting of polyurethane clamp test articles to accommodate 4-inch and 8-inch diameter pipes. The prototype clamps were installed with a subsea adhesive in a "wet" environment and then tested in the NASA Structures Test Laboratory (STL). The tension, compression, and bending test data showed that the prototype sensor clamps achieved good structural coupling, and could provide high quality strain measurement for active monitoring.

Seaman, Calvin H.↗

Modeling and characterization of through-the-thickness properties of 3D woven composites

The through-the-thickness properties of three-dimensionally (3D) woven carbon/epoxy composites have been studied. The investigation aimed at the evaluation and development of test methodologies for the property characterization in the thickness direction, and the establishment of fiber architectures were studied: layer-to-layer Angle Interlock, through-the-thickness Orthogonal woven preform with surface pile was also designed and manufactured for the fabrication of tensile test coupons with integrated grips. All the preforms were infiltrated by the resin transfer molding technique. The microstructures of the composites were characterized along the warp and fill (weft) directions to determine the degree of yarn undulations, yarn cross-sectional shapes, and microstructural dimensions. These parameters were correlated to the fiber architecture. Specimens were designed and tested for the direct measurement of the through-the-thickness tensile, compressive and shear properties of the composites. Design optimization was conducted through the analysis of the stress fields within the specimen coupled with experimental verification. The experimentally-derived elastic properties in the thickness direction compared well with analytical predictions obtained from a volume averaging model.

Hartranft, Dru↗

Computational micromechanics model based failure criteria for chopped carbon fiber sheet molding compound composites

Chopped carbon fiber sheet molding compound has a great potential in lightweight automotive, marine, and aerospace applications. One of the most challenging tasks is to predict the failure strength of the material due to its anisotropy and heterogeneity, as well as complex stress states in real-world working conditions. In this work, a novel constitutive model of carbon fiber chip is proposed to capture the pre- and post-failure behaviors under different loading modes. On this basis, we propose a new computational micromechanics model, which is calibrated and validated by uniaxial tensile, compressive, and in-plane shear experiments. Furthermore, a set of microstructures representative volume element (RVE) models under complex loading conditions are reconstructed to understand the relationship between the microstructure characteristics and the failure envelopes. Finally, several modified versions of classical failure criteria are proposed for anisotropic materials with consideration of the fiber orientation tensor. The modified Tsai-Wu failure criterion, which shows the best accuracy among all failure criteria, is highlighted in the comparative study.

36 MATERIALS SCIENCE↗

High Temperature Resin Matrix Composites for Aerospace Structures

Accomplishments and the outlook for graphite-polyimide composite structures are briefly outlined. Laminates, skin-stiffened and honeycomb sandwich panels, chopped fiber moldings, and structural components were fabricated with Celion/LARC-160 and Celion/PMR-15 composite materials. Interlaminar shear and flexure strength data obtained on as-fabricated specimens and specimens that were exposed for 125 hours at 589 K indicate that epoxy sized and polyimide sized Celion graphite fibers exhibit essentially the same behavior in a PMR-15 matrix composite. Analyses and tests of graphite-polyimide compression and shear panels indicate that utilization in moderately loaded applications offers the potential for achieving a 30 to 50 percent reduction in structural mass compared to conventional aluminum panels. Data on effects of moisture, temperature, thermal cycling, and shuttle fluids on mechanical properties indicate that both LARC-160 and PMR-15 are suitable matrix materials for a graphite-polyimide aft body flap. No technical road blocks to building a graphite-polyimide composite aft body flap are identified.

Davis, J. G., Jr.↗

Coal-based Bricks & Blocks (CBBs): Process Development to Prototype Fabrication Coupled with Techno-Economic Analysis and Market Survey

Coal-based bricks and blocks (CBBs) were formulated using anthracite and thermoplastic binder. Lab scale test composites were formed by hot-press molding and commercial extrusion for test articles and for a full-scale prototype. Formulations and test matrices followed a systematic experimental design to examine the effects of and interactions among three primary independent variables: a) thermoplastic type, b) weight fractions of binder relative to the total anthracite weight, and c) relative proportions of large versus small (milled) anthracite size fractions. Technical performance metrics include compressive strength, modulus, porosity/permeability and density. These DoE studies establish composition-property relations and identify the best combination for any desired property of interest – in particular, strength. Based on CBB composition and fabrication process, validated against technical performance metrics, a techno-economic analysis was constructed which incorporated a process flow model, engineering design (with scaling), and calculated capital plus operating costs. Based on measured property metrics and estimated process economics and a projected price by TEA (techno-economic analysis), building and construction target markets were identified by a market survey assessment. With known cost, price, performance metrics and competitive advantages for CBBs matched with commercial applications/uses, a technical gap analysis was performed to identify further development required for scale-up and commercialization.

01 COAL, LIGNITE, AND PEAT↗

Cross-stiffened continuous fiber structures

Under NASA's Novel Composites for Wing and Fuselage Applications (NCWFA) program, Contract NAS1-18784, Grumman is evaluating the structural efficiency of graphite/epoxy cross-stiffened panel elements fabricated using innovative textile preforms and cost effective Resin Transfer Molding (RTM) and Resin Film Infusion (RFI) processes. Two three-dimensional woven preform assembly concepts have been defined for application to a representative window belt design typically found in a commercial transport airframe. The 3D woven architecture for each of these concepts is different; one is vertically woven in the plane of the window belt geometry and the other is loom woven in a compressed state similar to an unfolded eggcrate. The feasibility of both designs has been demonstrated in the fabrication of small test element assemblies. These elements and the final window belt assemblies will be structurally tested, and results compared.

Ewen, John R.↗

Development of stitching reinforcement for transport wing panels

The NASA Advanced Composites Technology (ACT) program has the objective of providing the technology required to obtain the full benefit of weight savings and performance improvements offered by composite primary aircraft structures. Achieving the objective is dependent upon developing composite materials and structures which are damage tolerant and economical to manufacture. Researchers are investigating stitching reinforcement combined with resin transfer molding to produce materials meeting the ACT program objective. Research is aimed at materials, processes, and structural concepts for application in both transport wings and fuselages, but the emphasis to date has been on wing panels. Empirical guidelines are being established for stitching reinforcement in structures designed for heavy loads. Results are presented from evaluation tests investigating stitching types, threads, and density (penetrations per square inch). Tension strength, compression strength, and compression after impact data are reported.

Palmer, Raymond J.↗

Test and analysis results for composite transport fuselage and wing structures

Automated tow placement (ATP) and stitching of dry textile composite preforms followed by resin transfer molding (RTM) are being investigated by researchers at NASA LaRC and Douglas Aircraft Company as cost-effective manufacturing processes for obtaining damage tolerant fuselage and wing structures for transport aircraft. The Douglas work is being performed under a NASA contract entitled 'Innovative Composites Aircraft Primary Structures (ICAPS)'. Data are presented in this paper to assess the damage tolerance of ATP and RTM fuselage elements with stitched-on stiffeners from compression tests of impacted three-J-stiffened panels and from stiffener pull-off tests. Data are also presented to assess the damage tolerance of RTM wing elements which had stitched skin and stiffeners from impacted single stiffener and three blade-stiffened compression tests and stiffener pull-off tests.

Deaton, Jerry W.↗

Performance of Subscale Docking Seals Under Simulated Temperature Conditions

A universal docking system is being developed by the National Aeronautics and Space Administration (NASA) to support future space exploration missions to low Earth orbit (LEO), to the moon, and to Mars. The candidate docking seals for the system are a composite design consisting of elastomer seal bulbs molded into the front and rear sides of a metal ring. The test specimens were subscale seals with two different elastomer cross-sections and a 12-in. outside diameter. The seal assemblies were mated in elastomer seal-on-metal plate and elastomer seal-on-elastomer seal configurations. The seals were manufactured from S0383-70 silicone elastomer compound. Nominal and off-nominal joint configurations were examined. Both the compression load required to mate the seals and the leak rate observed were recorded while the assemblies were subjected to representative docking system operating temperatures of -58, 73, and 122 F (-50, 23, and 50 C). Both the loads required to fully compress the seals and their leak rates were directly proportional to the test temperature.

Smith, Ian M.↗

Processing and Properties of Vacuum Assisted Resin Transfer Molded Phenylethynyl Terminated Imide Composites

Polyimide composites are very attractive for applications that require a high strength to weight ratio and thermal stability. Recent work at NASA Langley Research Center (LaRC) has concentrated on developing new polyimide resin systems that can be processed without the use of an autoclave for advanced aerospace applications. Due to their low melt viscosities and long melt stability, certain phenylethynyl terminated imides (PETI) can be processed into composites using high temperature vacuum assisted resin transfer molding (HT-VARTM). VARTM has shown the potential to reduce the manufacturing cost of composite structures. In the current study, two PETI resins, LARC(Trademark) PETI-330 and LARC(Trademark) PETI-9, were infused into carbon fiber preforms at 260 C and cured at temperatures up to 371 C. Photomicrographs of polished cross sections were taken and void contents, determined by acid digestion, were below 4.5%. Mechanical properties including short block compression (SBC), compression after impact (CAI), and open hole compression (OHC) were determined at room temperature, 177 C, and 288 C. Both PETI-9 and PETI-330 composites demonstrated very good retention of mechanical properties at elevated temperatures. SBC and OHC properties after aging for 1000 hours at temperatures up to 288 C were also determined.

Cano, Roberto J.↗

Preparation of cast aluminum alloy-mica particle composites

A method for making aluminum-mica particle composites is presented in which mica particles are stirred in molten aluminum alloys followed by casting in permanent molds. Magnesium is added either as an alloying element or in the form of pieces to the surface of the alloy melts to disperse up to 3 wt% mica powders in the melts and to obtain high recoveries of mica in the castings. The mechanical properties of the aluminum alloy-mica composite decrease with increasing mica content; however, even at 2.2% it has a tensile strength of 14.22 kg/sq mm with 1.1% elongation, a compression strength of 42.61 kg/sq mm, and an impact strength of 0.30 kgm/sq cm. Cryogenic and self-lubricating bearing are mentioned applications.

Deonath, MR.↗

Development of stitched/RTM composite primary structures

The goal of the NASA Advanced Composites Technology (ACT) Program is to provide the technology required to gain the full benefit of weight savings and performance offered by composite primary structures. Achieving the goal is dependent on developing composite materials and structures which are damage tolerant and economical to manufacture. Researchers at NASA Langley and Douglas Aircraft Co. are studying stitching reinforcement combined with resin transfer molding (RTM) to create structures meeting the ACT program goals. The research is aimed at materials, processes, and structural concepts for application in both transport wings and fuselages. Empirical guidelines are being established for stitching reinforcement in primary structures and test data are reported in another paper. New data are presented herein from evaluation tests of thick (96 ply) and thin (16 ply) stitched laminates and from selection tests of RTM composite resins. Tension strength, compression strength, and post impact compression strength data are reported. Elements of a NASA Langley program to expand the science base for stitched/RTM composites are discussed.

Kullerd, Susan M.↗

Damage-Tolerant Composites Made By Stitching Carbon Fabrics

Work conducted at NASA Langley Research Center to investigate stitching combined with resin transfer molding to make composites more tolerant of damage and potentially cost competitive with metals. Composite materials tailored for damage tolerance by stitching layers of dry carbon fabric with closely spaced threads to provide reinforcement through thickness. Epoxy resin then infused into stitched preforms, and epoxy was cured. Various stitching patterns and thread materials evaluated by use of flat plate specimens. Also, blade-stiffened structural elements fabricated and tested. Stitched flat laminates showed outstanding damage tolerance, excellent compression strength in notched specimens, and acceptable fatigue behavior. Development of particular interest to aircraft and automotive industries.

Dow, Marvin B.↗