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At least 631 records · Page 35

All sources NASA NTRS DOE OSTI

NASA NTRS1982

Prediction of composite hygral behavior made simple

A convenient procedure is described to determine the hygral behavior (moisture expansion coefficients and moisture stresses) of angleplied fiber composites using a pocket calculator. The procedure consists of equations and appropriate graphs for various (+ or - theta) ply combinations. These graphs present reduced stiffness and moisture expansion coefficients as functions of (+ or - theta) in order to simplify and expedite the use of the equations. The procedure is applicable to all types of balanced, symmetric fiber composites including interply and intraply hybrids. The versatility and generality of the procedure is illustrated using several step-by-step numerical examples.

Chamis, C. C.↗

NASA NTRS1982

Prediction of composite hygral behavior made simple

Chamis, C. C.↗

NASA NTRS2009

Design and Manufacturing of Tow-Steered Composite Shells Using Fiber Placement

Advanced composite shells that may offer the potential to improve the structural performance of future aircraft fuselage structures were developed under this joint NASA-industry collaborative effort. Two cylindrical shells with tailored, tow-steered layups and continuously varying fiber angle orientations were designed and built at the National Center for Advanced Manufacturing - Louisiana Partnership. The shells were fabricated from unidirectional IM7/8552 graphite-epoxy pre-preg slit tape material fiber-placed on a constant-diameter mandrel. Each shell had the same nominal 8-ply [plus or minus 45/plus or minus Theta]s layup, where the nominal fiber angle in the tow-steered plies varied continuously from 10 degrees along the crown to 45 degrees on each side, then back to 10 degrees on the keel. One shell was fabricated with all 24 tows placed during each pass of the fiber placement machine, resulting in many tow overlaps on the shell surface. The fiber placement machine's individual tow cut/restart capability was also used to manufacture a second shell with tow drops and a more uniform laminate thickness. This paper presents an overview of the detailed design and manufacturing processes for these shells, and discusses issues encountered during their fabrication and post-cure evaluation. Future plans for structural testing and analyses of the shells are also discussed.

Wu, K. Chauncey↗

NASA NTRS1983

Role of fiber/matrix interphase in carbon fiber-epoxy composite impact toughness

Experimental results were obtained which show the effect of the interphase on composite performance. Various finish variants were formulated, based on different chemical and mechanical properties and applied to Celion 6000 carbon fiber. Inerfacial bond strength and failure mechanisms were studied by single-filament critical length determination. Composite properties at room and elevated temperatures, both wet and dry, were measured. Impact toughness was evaluated with a Dynatup drop dart instrumented impact tester. A significant 30 percent increase in maximum penetration load was obtained by 'Interphase-tailoring' without significant loss in both conditioned and unconditioned composite properties.

Ying, L.↗

NASA NTRS2011

Carbon Nanotube Coatings as Used in Strain Sensors for Composite Tanks

The next generation of cryogenic fuel tanks, crew habitats and other components for future spacecraft will focus on the usc of lightweight carbon fiber composite materials. A critical issue in the design and optimization of such tanks and structures will bc in structural health monitoring, however, current strain sensors have limitations. In this study, a novel carbon nanotube thin film was applied to carbon fiber composites for structural monitoring. Applying a load using a 3-point bend test to simulate bowing of a tank wall, induced significant increases in the film's electrical resistance at small deflections. Upon release of the load, the resistance returned to its approximate start value and was reproducible over multiple tests. The results show that a carbon nanotube thin film has great potential for the health monitoring of composite structures.

Trigwell, Steve↗

NASA NTRS1991

Void control in the crystallization of lithium fluoride

The effect of tungsten-coated graphite fibers on the radiant heat transfer characteristics of salt-fiber composites was studied by measuring the onset of melting as a function of applied furnace power. As the fiber concentration was increased from 0 to 5.40 percent fiber by weight, the furnace temperature required to melt the lithium fluoride also increased. Upon cooling, each of the crystalline salt-fiber composites were cut open with a diamond saw to expose the void. Optical photographs of the voids revealed a trend in void location and size, with the largest void, and the least change in the outer dimension of the boule upon cooling, occurring in the sample with the most fiber.

Jaworske, Donald A.↗

NASA NTRS1965

Research on fiber-reinforced composites

Research in materials science - high temperature structural materials, wetting and adherence of nickel alloys to sapphire, boron carbide filaments, and ceramic and graphite fibers

MATERIALS SCIENCE↗

NASA NTRS1980

Burning characteristics and fiber retention of graphite/resin matrix composites

Graphite fiber reinforced resin matrix composites were subjected to controlled burning conditions to determine their burning characteristics and fiber retention properties. Two types of burning equipment were used. Small samples were burned with a natural gas fired torch to study the effects of fiber orientation and structural flaws such as holes and slits that were machined into the laminates. Larger laminate samples were burned in a Heat Release Rate Calorimeter. Unidirectional epoxy/graphite and polyimide/graphite composites and boron powder filled samples of each of the two composite systems were burn tested and exposed to a thermal radiation. The effects of fiber orientation, flaws, and boron filler additives to the resins were evaluated. A high char forming polyimide resin was no more effective in retaining graphite fibers than a low char forming epoxy resin when burning in air.

Bowles, K. J.↗

NASA NTRS1980

Burning characteristics and fiber retention of graphite/resin matrix composites

Graphite fiber reinforced resin matrix composites were subjected to controlled burning conditions to determine their burning characteristics and fiber retention properties. Small samples were burned with a natural gas fired torch to study the effects of fiber orientation and structural flaws such as holes and slits that were machined into the laminates. Larger laminate samples were burned in a modified heat release rate calorimeter. Unidirectional epoxy/graphite and polyimide/graphite composites and boron powder filled samples of each of the two composite systems were burn tested. The composites were exposed to a thermal radiation of 5.3 Btu/sq ft-sec in air. Samples of each of the unfilled composite were decomposed anaerobically in the calorimeter. Weight loss data were recorded for burning and decomposition times up to thirty-five minutes. The effects of fiber orientation, flaws, and boron filler additives to the resins were evaluated. A high char forming polyimide resin was no more effective in retaining graphite fibers than a low char forming epoxy resin when burned in air. Boron powder additions to both the polyimide and the epoxy resins stabilized the chars and effectively controlled the fiber release.

Bowles, K. J.↗

NASA NTRS1995

Design of a unidirectional composite momentum wheel rim

A preliminary study comparing twelve unidirectional-fiber composite systems to five metal materials conventionally used in momentum wheels is presented. Six different fibers are considered in the study: E-Glass, S-Glass, Boron, AS, T300, and Kevlar. Because of the possibility of high momentum requirements, and thus high stresses, only two matrix materials are considered: a high-modulus (HM) and a intermediate-modulus-high-strength (IMHS) matrix. Each of the six fibers are coupled with each of the two matrix materials. In an effort to optimize the composite system, each composite is considered while varying the fiber volume ratio from 0.0 to 0.7 in increments of 0.1. For fiber volume ratios above 0.2, all twelve unidirectional-fiber composite systems meet the study's requirements with higher factors of safety and less mass than the five conventional isotropic (metal) materials. For example, at a fiber volume ratio of 0.6, the Kevlar/IMHS composite system has a safety factor 4.5 times greater than that of a steel (maraging) system and an approximately 10 percent reduction in weight.

Shogrin, Bradley↗

DOE OSTI2025

Improving adhesive bonding of short carbon fiber thermoplastic composites to aluminum alloys with a hybrid laser-plasma surface modification strategy

This study investigates hybrid laser–plasma surface modification strategies for metal–CFRTP (carbon-fiber-reinforced thermoplastic polymer) dissimilar joints to improve their bonding performance, in contrast to existing literature that mostly focuses on either plasma or laser treatment alone. By conducting double cantilever beam (DCB) tests on adhesively-bonded AA5052 and CFRPA66 (carbon-fiber-reinforced polyamide 66) joints, as an example of metal–CFRTP joints, it was found that laser engraving on the metal surface combined with plasma treatment on the CFRTP surface significantly improved the specific fracture energy of the joint by 187% and 31% compared to as-received and plasma-treated-only joints, respectively. However, the hybrid treatment of laser engraving and plasma on the investigated CFRTP surface did not improve the bonding performance of the joints. The underlying mechanisms related to hybrid laser-plasma surface modification strategies were further investigated by examining the surface and cross-sectional morphologies after DCB testing using microscopy. Computational modeling was performed to elucidate the interaction between grooves on the metal substrate and the CFRTP–adhesive interfacial bonding in metal–CFRTP joints. This study provides new insights into developing surface modification methods for achieving strong metal–CFRTP adhesive joints, aimed at lightweighting structural components in automotive, aerospace, and other applications.

Adhesive bonding↗

NASA NTRS1993

Optimal design of composite hip implants using NASA technology

Using an adaptation of NASA software, we have investigated the use of numerical optimization techniques for the shape and material optimization of fiber composite hip implants. The original NASA inhouse codes, were originally developed for the optimization of aerospace structures. The adapted code, which was called OPORIM, couples numerical optimization algorithms with finite element analysis and composite laminate theory to perform design optimization using both shape and material design variables. The external and internal geometry of the implant and the surrounding bone is described with quintic spline curves. This geometric representation is then used to create an equivalent 2-D finite element model of the structure. Using laminate theory and the 3-D geometric information, equivalent stiffnesses are generated for each element of the 2-D finite element model, so that the 3-D stiffness of the structure can be approximated. The geometric information to construct the model of the femur was obtained from a CT scan. A variety of test cases were examined, incorporating several implant constructions and design variable sets. Typically the code was able to produce optimized shape and/or material parameters which substantially reduced stress concentrations in the bone adjacent of the implant. The results indicate that this technology can provide meaningful insight into the design of fiber composite hip implants.

Blake, T. A.↗

NASA NTRS1974

Stress-rupture strength and microstructural stability of W-HF-C wire-reinforced superalloy composites

W-Hf-C superalloy composites were found to be potentially useful for turbine-blade applications on the basis of stress-rupture strength. The 100- and 1000-hour rupture strengths obtained for 70 volume percent fiber composites tested at 1090 C were 420 and 280 MN/sq m. The investigation indicated that with better quality fibers, composites having 100- and 1000-hour rupture strengths of 570 and 370 MN/sq m may be obtained. Metallographic studies indicated sufficient fiber-matrix compatibility for long-term applications at 1090 C for 1000 hours or more.

Petrasek, D. W.↗

DOE OSTI2022

Real-Time Monitoring of Gas-Phase and Dissolved CO 2 Using a Mixed-Matrix Composite Integrated Fiber Optic Sensor for Carbon Storage Application

Novel chemical sensors that improve detection and quantification of CO 2 are critical to ensuring safe and cost-effective monitoring of carbon storage sites. Fiber optic (FO) based chemical sensor systems are promising field-deployable systems for real-time monitoring of CO 2 in geological formations for long-range distributed sensing. Here, a mixed-matrix composite integrated FO sensor system was developed with a purely optical readout that reliably operates as a detector for gas-phase and dissolved CO 2 . A mixed-matrix composite sensor coating consisting of plasmonic nanocrystals and hydrophobic zeolite embedded in a polymer matrix was integrated on the FO sensor. The mixed-matrix composite FO sensor showed excellent reversibility/stability in a high humidity environment and sensitivity to gas-phase CO 2 over a large concentration range. This remarkable sensing performance was enabled by using plasmonic nanocrystals to significantly enhance the sensitivity and a hydrophobic zeolite to effectively mitigate interference from water vapor. The sensor exhibited the ability to sense CO 2 in the presence of other geologically relevant gases, which is of importance for applications in geological formations. A prototype FO sensor configuration which possesses a robust sensing capability for monitoring dissolved CO 2 in natural water was demonstrated. Reproducibility was confirmed over many cycles, both in a laboratory setting and in the field. More importantly, we demonstrated on-line monitoring capabilities with a wireless telemetry system, which transferred the data from the field to a website. The combination of outstanding CO 2 sensing properties and facile coating processability makes this mixed-matrix composite FO sensor a good candidate suitable for practical carbon storage applications.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2021

Analysis of energetics and economics of sub-ambient hybrid post-combustion carbon dioxide capture

Adsorption of CO 2 from post-combustion flue gas is one of the leading candidates for globally impactful carbon capture systems. In this report, work focused on understanding the opportunities and limitations of sub-ambient CO 2 capture processes utilizing a multistage separation process. A hybrid process design using a combination of pressure-driven separation of CO 2 from flue gas (e.g., adsorption- or membrane-based separation) followed by CO 2 -rich product liquefaction to produce high-purity (>99%) CO 2 at pipeline conditions is considered. The operating pressure of the separation unit is a key cost parameter and also an important process variable that regulates the available heat removal necessary to reach the sub-ambient operating conditions. The economic viability of applying pressure swing adsorption (PSA) processes using fiber sorbent contactors with internal heat management was found to be most influenced by the productivity of the adsorption system, with productivities as high as 0.015 mol CO2 /kg sorb -1 sec -1 being required to reduce costs of capture below $60/ton CO 2 captured. This analysis was carried out using a simplified two-bed process, and thus there is opportunity for further cost reduction with exploration of more complex cycle designs. Three exemplar fiber sorbents (MIL-101(Cr), UiO-66, and zeolite 13X) were considered for application in the sub-ambient process of PSA unit. Among the considered sorbents, zeolite 13X fiber composites were found to perform better at ambient temperatures as compared to sub-ambient. MIL-101(Cr) and UiO-66 fiber composites had improved purity, recovery, and productivity at colder temperatures reducing costs of capture as low as $61/ton CO 2 . Future economic improvement could be achieved by reducing the required operating pressure of the PSA unit and pushing the Pareto frontier closer to the final pipeline requirement via a combination of PSA cycle design and material selection.

42 ENGINEERING↗

NASA NTRS1974

Stress-rupture strength and microstructural stability of W-HF-C wire reinforced superalloy composites

W-Hf-C/superalloy composites were found to be potentially useful for turbine blade applications on the basis of stress-rupture strength. The 100-and 1000-hour rupture strengths obtained for 70 volume percent fiber composites tested at 1090 C were 420 and 280 MN/sq m (61,000 and 41,000 psi). The investigation indicated that with better quality fibers, composites having 100- and 1000-hour rupture strengths of 570 and 370 MN/sq m (82,000 and 54,000 psi) may be obtained. Metallographic studies indicated sufficient fiber-matrix compatibility for long time applications at 1090 C for 1000 hours or more.

Petrasek, D. W.↗

NASA NTRS1974

Stress-rupture strength and microstructural stability of tungsten-hafnium-carbon-wire reinforced superalloy composites

Tungsten-hafnium-carbon - superalloy composites were found to be potentially useful for turbine blade applications on the basis of stress-rupture strength. The 100- and 1000-hr rupture strengths calculated for 70 vol. % fiber composites based on test data at 1090C (2000F) were 420 and 280 MN/m2 (61,000 and 41,000 psi, respectively). The investigation indicated that, with better quality fibers, composites having 100- and 1000-hr rupture strengths of 570 and 370 MN/m2 (82,000 and 54,000 psi, respectively), may be obtained. Metallographic studies indicated sufficient fiber-matrix compatibility for 1000 hr or more at 1090C (2000F).

Petrasek, D. W.↗

NASA NTRS1984

ICAN: Integrated composites analyzer

The ICAN computer program performs all the essential aspects of mechanics/analysis/design of multilayered fiber composites. Modular, open-ended and user friendly, the program can handle a variety of composite systems having one type of fiber and one matrix as constituents as well as intraply and interply hybrid composite systems. It can also simulate isotropic layers by considering a primary composite system with negligible fiber volume content. This feature is specifically useful in modeling thin interply matrix layers. Hygrothermal conditions and various combinations of in-plane and bending loads can also be considered. Usage of this code is illustrated with a sample input and the generated output. Some key features of output are stress concentration factors around a circular hole, locations of probable delamination, a summary of the laminate failure stress analysis, free edge stresses, microstresses and ply stress/strain influence coefficients. These features make ICAN a powerful, cost-effective tool to analyze/design fiber composite structures and components.

Murthy, P. L. N.↗