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At least 325 records · Page 18

All sources NASA NTRS DOE OSTI

NASA NTRS1993

Compressive and shear buckling analysis of metal matrix composite sandwich panels under different thermal environments

Combined inplane compressive and shear buckling analysis was conducted on flat rectangular sandwich panels using the Raleigh-Ritz minimum energy method with a consideration of transverse shear effect of the sandwich core. The sandwich panels were fabricated with titanium honeycomb core and laminated metal matrix composite face sheets. The results show that slightly slender (along unidirectional compressive loading axis) rectangular sandwich panels have the most desirable stiffness-to-weight ratios for aerospace structural applications; the degradation of buckling strength of sandwich panels with rising temperature is faster in shear than in compression; and the fiber orientation of the face sheets for optimum combined-load buckling strength of sandwich panels is a strong function of both loading condition and panel aspect ratio. Under the same specific weight and panel aspect ratio, a sandwich panel with metal matrix composite face sheets has much higher buckling strength than one having monolithic face sheets.

Ko, William L.↗

NASA NTRS1989

In-situ deformation studies of an aluminum metal-matrix composite in a scanning electron microscope

Tensile specimens made of a metal-matrix composite (cast and extruded aluminum alloy-based matrix reinforced with Al2O3 particulate) were tested in situ in a scanning electron microscope equipped with a deformation stage, to directly monitor the crack propagation phenomenon. The in situ SEM observations revealed the presence of microcracks both ahead of and near the crack-tip region. The microcracks were primarily associated with cracks in the alumina particles. The results suggest that a region of intense deformation exists ahead of the crack and corresponds to the region of microcracking. As the crack progresses, a region of plastically deformed material and associated microcracks remains in the wake of the crack.

Manoharan, M.↗

NASA NTRS2003

LS-DYNA Implementation of Polymer Matrix Composite Model Under High Strain Rate Impact

A recently developed constitutive model is implemented into LS-DYNA as a user defined material model (UMAT) to characterize the nonlinear strain rate dependent behavior of polymers. By utilizing this model within a micromechanics technique based on a laminate analogy, an algorithm to analyze the strain rate dependent, nonlinear deformation of a fiber reinforced polymer matrix composite is then developed as a UMAT to simulate the response of these composites under high strain rate impact. The models are designed for shell elements in order to ensure computational efficiency. Experimental and numerical stress-strain curves are compared for two representative polymers and a representative polymer matrix composite, with the analytical model predicting the experimental response reasonably well.

Zheng, Xia-Hua↗

NASA NTRS1980

Improved fiber retention by the use of fillers in graphite fiber/resin matrix composites

A potential problem in the use of graphite fiber reinforced resin matrix composites is the dispersal of graphite fiber during accidental fires. Airborne electrically conductive fibers originating from burning composites could enter and cause shorting in electrical equipment located in surrounding areas. A variety of matrix fillers have been tested for their ability to prevent loss of fiber from graphite fiber/PMR polyimide and graphite fiber/epoxy composites in a fire. The fillers tested included powders of boron, boron carbide (B4C), lime glass, lead glass, and aluminum. Of these fillers, boron was the most effective and prevented any loss of graphite fiber during burning. Mechanical properties of composites containing boron filler were measured and compared to those of composite containing no filler.

Gluyas, R. E.↗

NASA NTRS2000

CEMCAN Software Enhanced for Predicting the Properties of Woven Ceramic Matrix Composites

Major advancements are needed in current high-temperature materials to meet the requirements of future space and aeropropulsion structural components. Ceramic matrix composites (CMC's) are one class of materials that are being evaluated as candidate materials for many high-temperature applications. Past efforts to improve the performance of CMC's focused primarily on improving the properties of the fiber, interfacial coatings, and matrix constituents as individual phases. Design and analysis tools must take into consideration the complex geometries, microstructures, and fabrication processes involved in these composites and must allow the composite properties to be tailored for optimum performance. Major accomplishments during the past year include the development and inclusion of woven CMC micromechanics methodology into the CEMCAN (Ceramic Matrix Composites Analyzer) computer code. The code enables one to calibrate a consistent set of constituent properties as a function of temperature with the aid of experimentally measured data.

Murthy, Pappu L. N.↗

NASA NTRS1995

Organic matrix composite protective coatings for space applications

Successful use of composites in low earth orbit (LEO) depends on their ability to survive long-term exposure to atomic oxygen (AO), ultraviolet radiation, charged particle radiation, thermal cycling, and micrometeoroid and space debris. The AO environment is especially severe for unprotected organic matrix composites surfaces in LEO. Ram facing unprotected graphite/epoxy flown on the 69-month Long Duration Exposure Facility (LDEF) mission lost up to one ply of thickness (5 mils) resulting in decreased mechanical properties. The expected AO fluence of the 30 year Space Station Alpha mission is approximately 20 times that seen on LDEF. This exposure would result in significant material loss of unprotected ram facing organic matrix composites. Several protective coatings for composites were flown on LDEF including anodized aluminum, vacuum deposited coatings, a variety of thermal control coatings, metalized Teflon, and leafing aluminum. Results from the testing and analysis of the coated and uncoated composite specimens flown on LDEF's leading and trailing edges provide the baseline for determining the effectiveness of protectively coated composites in LEO. In addition to LDEF results, results from shuttle flight experiments and ground based testing will be discussed.

Dursch, Harry W.↗

NASA NTRS1991

Mechanical characterization and modeling of non-linear deformation and fracture of a fiber reinforced metal matrix composite

The nonlinear anisotropic mechanical behavior of an aluminum alloy metal matrix composite reinforced with continuous alumina fibers was determined experimentally. The mechanical behavior of the composite were modeled by assuming that the composite has a periodical microstructure. The resulting unit cell problem was solved with the finite element method. Excellent agreement was found between theoretically predicted and measured stress-strain responses for various tensile and shear loadings. The stress-strain responses for transverse and inplane shear were found to be identical and this will provide a simplification of the constitutive equations for the composite. The composite has a very low ductility in transverse tension and a limited ductility in transverse shear that was correlated to high hydrostatic stresses that develop in the matrix. The shape of the initial yield surface was calculated and good agreement was found between the calculated shape and the experimentally determined shape.

Jansson, S.↗

NASA NTRS1991

Relationship between voids and interlaminar shear strength of polymer matrix composites

The effect of voids on the interlaminar shear strength of a polyimide matrix composite system is described. The AS4 graphite/PMR-15 composite was chosen for study because this system can be readily processed by using the standard specified cure cycle to produce void-free composites and because preliminary work in this study had shown that the processing parameters of this resin matrix system can be altered to produce cured composites of varying void contents. Thirty-eight 12-ply unidirectional composite panels were fabricated for this study. A significant range of void contents (0 to 10 percent) was produced. The panels were mapped, ultrasonically inspected, and sectioned into interlaminar shear, flexure, and fiber content specimens. The density of each specimen was measured and interlaminar shear and flexure strength measurements were then made. The fiber content was measured last. The results of these tests were evaluated by using ultrasonic results, photomicrographs, statistical methods, theoretical relationships derived by other investigators, and comparison of the test data with the Integrated Composite Analyzer (ICAN) computer program developed at the Lewis Research Center for predicting composite ply properties. The testing is described in as much detail as possible in order to help others make realistic comparisons.

Bowles, Kenneth J.↗

NASA NTRS1991

Relationship between voids and interlaminar shear strength of polymer matrix composites

The effect of voids on the interlaminar shear strength of a polyimide matrix composite system is described. The AS4 graphite/PMR-15 composite was chosen for study because this system can be readily processed by using the standard specified cure cycle to produce void-free composites and because preliminary work in this study had shown that the processing parameters of this resin matrix system can be altered to produce cured composites of varying void contents. Thirty-eight 12-ply unidirectional composite panels were fabricated for this study. A significant range of void contents (0 to 10 percent) was produced. The panels were mapped, ultrasonically inspected, and sectioned into interlaminar shear, flexure, and fiber content specimens. The density of each specimen was measured and interlaminar shear and flexure strength measurements were then made. The fiber content was measured last. The results of these tests were evaluated by using ultrasonic results, photomicrographs, statistical methods, theoretical relationships derived by other investigations, and comparison of the test data with the Integrated Composite Analyzer (ICAN) computer program developed at the Lewis Research Center for predicting composite ply properties. The testing is described in as much detail as possible in order to help others make realistic comparisons.

Bowles, Kenneth J.↗

NASA NTRS1997

Effect of Cyclic Thermal Loads on Fatigue Reliability in Polymer Matrix Composites

Technological solutions that will ensure the economic viability and environmental compatibility of a future High Speed Civil Transport plane are currently being sought. Lighter structural materials for both airframe primary structures and engine structure components are being investigated. We believe that such objectives can be achieved through the use of high-temperature composites as well as other conventional, lighter weight alloys. One of the prime issues for these structural components is assured long-term behavior with a specified reliability. An investigation was conducted to describe a computational simulation methodology for predicting fatigue life, reliability, and probabilistic long-term behavior of polymer matrix composites. A unified time-, stress-, and load-dependent Multi- Factor Interaction Equation (MFIE) model developed at the NASA Lewis Research Center was used to simulate the long-term behavior of polymer matrix composites.

Chamis, Christos C.↗

NASA NTRS2002

Metal Matrix Composite LOX Turbopump Housing Via Novel Tool-Less Net-Shape Pressure Infiltration Casting Technology

This presentation provides an overview of the effort by Metal Matrix Cast Composites, Inc. to redesign turbopump housing joints using metal matrix composite material and a toolless net-shape pressure infiltration casting technology. Topics covered include: advantage of metal matrix composites for propulsion components, baseline pump design and analysis, advanced toolless pressure infiltration casting process, subscale pump housing, preform splicing and joining for large components, and fullscale pump housing redesign.

Shah, Sandeep↗

NASA NTRS2002

The Role of Ceramics and Ceramic Matrix Composites in NASA's Advanced Space Propulsion Programs

In recent years, NASA has embarked on several new and exciting efforts in the exploration and use of space. The successful accomplishment of many planned missions and projects is dependent upon the development and deployment of previously unproven propulsion systems. Key to many of the propulsion systems is the use of structural ceramics and ceramic matrix composites. In spite of their promise, a number of programmatic and technical hurdles remain before the potential of ceramic materials can be realized. A programmatic environment which focuses on relatively short term hardware demonstration programs precludes traditional longer term material's development efforts. The challenge oftentimes becomes one of engineering ceramics into proposed missions. This is dependent upon a fundamental understanding of processing, degradation and design issues unique to space vehicle design and operations. A review of the general missions and benefits of utilizing ceramics and ceramic matrix composites will be presented. The design parameters and operating conditions will be presented for both specific missions/vehicles and classes of components. Key technical challenges and opportunities are identified along with suggested paths for addressing them.

Eckel, Andrew J.↗

NASA NTRS1990

The Role of Ceramics and Ceramic Matrix Composites in NASA's Advanced Space Propulsion Programs

Eckel, Andrew J.↗

NASA NTRS1997

Strong and Tough Hi-Nicalon Fiber-Reinforced Celsian Matrix Composites

Strong, tough and almost fully dense Hi-Nicalon/BN/SiC fiber reinforced celsian matrix composites have been fabricated by impregnation of the fiber tows with the matrix slurry, winding on a drum, stacking the prepreg tapes in the desired orientation, and hot pressing. The monoclinic celsian phase in the matrix was produced in situ, during hot pressing, from a mixed oxide precursor. The unidirectional composites having approx. 42 volume percent of fibers exhibited graceful failure with extensive fiber pullout in three-point bend tests at room temperature. Values of first matrix cracking stress and strain were 435 +/- 35 MPa and 0.27 +/- 0.01 %, respectively, and ultimate strengths of 900 +/- 60 MPa were observed. The Young's modulus of the composites was 165 +/- 5 GPa.

Bansal, Narottam P.↗

NASA NTRS2000

Novel Vibration Damping of Ceramic Matrix Composite Turbine Blades Developed for RLV Applications

The Reusable Launch Vehicle (RLV) represents the next generation of space transportation for the U.S. space program. The goal for this vehicle is to lower launch costs by an order of magnitude from $10,000/lb to $1,000/lb. Such a large cost reduction will require a highly efficient operation, which naturally will require highly efficient engines. The RS-2200 Linear Aerospike Engine is being considered as the main powerplant for the RLV. Strong, lightweight, temperature-resistant ceramic matrix composite (CMC) materials such as C/SiC are critical to the development of the RS-2200. Preliminary engine designs subject turbopump components to extremely high frequency dynamic excitation, and ceramic matrix composite materials are typically lightly damped, making them vulnerable to high-cycle fatigue. The combination of low damping and high-frequency excitation creates the need for enhanced damping. Thus, the goal of this project has been to develop well-damped C/SiC turbine components for use in the RLV. Foster-Miller and Boeing Rocketdyne have been using an innovative, low-cost process to develop light, strong, highly damped turbopump components for the RS-2200 under NASA s Small Business Innovation Research (SBIR) program. The NASA Glenn Research Center at Lewis Field is managing this work. The process combines three-dimensionally braided fiber reinforcement with a pre-ceramic polymer. The three-dimensional reinforcement significantly improves the structure over conventional two-dimensional laminates, including high through-the-thickness strength and stiffness. Phase I of the project successfully applied the Foster-Miller pre-ceramic polymer infiltration and pyrolysis (PIP) process to the manufacture of dynamic specimens representative of engine components. An important aspect of the program has been the development of the manufacturing process. Results show that the three-dimensionally braided carbon-fiber reinforcement provides good processability and good mechanical stiffness and strength in comparison to materials produced with competing processes as shown in the graphs.

Min, James B.↗

NASA NTRS2014

NASA's Advanced Environmental Barrier Coatings Development for SiC/SiC Ceramic Matrix Composites: Understanding Calcium Magnesium Alumino-Silicate (CMAS) Degradations and Resistance

Environmental barrier coatings (EBCs) and SiCSiC ceramic matrix composites (CMCs) systems will play a crucial role in next generation turbine engines for hot-section component applications because of their ability to significantly increase engine operating temperatures with improved efficiency, reduce engine weight and cooling requirements. The development of prime-reliant environmental barrier coatings is essential to the viability and reliability of the envisioned CMC engine component applications, ensuring integrated EBC-CMC system durability and designs are achievable for successful applications of the game-changing component technologies and lifing methodologies.This paper will emphasize recent NASA environmental barrier coating developments for SiCSiC turbine airfoil components, utilizing advanced coating compositions, state-of-the-art processing methods, and combined mechanical and environment testing and durability evaluations. The coating-CMC degradations in the engine fatigue-creep and operating environments are particularly complex; one of the important coating development aspects is to better understand engine environmental interactions and coating life debits, and we have particularly addressed the effect of Calcium-Magnesium-Alumino-Silicate (CMAS) from road sand or volcano-ash deposits on the durability of the environmental barrier coating systems, and how the temperature capability, stability and cyclic life of the candidate rare earth oxide and silicate coating systems will be impacted in the presence of the CMAS at high temperatures and under simulated heat flux conditions. Advanced environmental barrier coating systems, including HfO2-Si with rare earth dopant based bond coat systems, will be discussed for the performance improvements to achieve better temperature capability and CMAS resistance for future engine operating conditions.

Environmental barrier coatings↗

NASA NTRS1990

A macro-micromechanics analysis of a notched metal matrix composite

A macro-micromechanics analysis was formulated to determine the matrix and fiber behavior near the notch tip in a center-notched metal matrix composite. Results are presented for a boron/aluminum monolayer. The macro-level analysis models the entire notched specimen using a three dimensional finite element program which uses the vanishing-fiber-diameter model to model the elastic-plastic behavior of the matrix and the elastic behavior of the fiber. The micro-behavior is analyzed using a Discrete Fiber-Matrix (DFM) model containing one fabric and the surrounding matrix. The dimensions of the DFM model were determined by the ply thickness and the fiber volume fraction and corresponded to the size of the notch-tip element in the macro-level analysis. The boundary conditions applied to the DFM model were determined from the macro-level analysis. Stress components within the DFM model were calculated and stress distributions are presented along selected planes and surfaces within the DFM model, including the fiber-matrix interface. Yielding in the matrix was examined at the notch tip in both the macro- and micro-level analyses. The DFM model predicted higher stresses (24 percent) in the fiber compared to the global analysis. In the notch-tip element, the interface stresses indicated that a multi-axial criterion may be required to predict interfacial failure. The DFM analysis predicted yielding to initiate in the notch-tip element at a stress level 28 percent lower than predicted by the global analysis.

Bigelow, C. A.↗

NASA NTRS1996

Characterization of SiC Fiber (SCS-6) Reinforced-Reaction-Formed Silicon Carbide Matrix Composites

Silicon carbide fiber (SCS-6) reinforced-reaction-formed silicon carbide matrix composites were fabricated using a reaction-forming process. Silicon-2 at.% niobium alloy was used as an infiltrant instead of pure silicon to reduce the amount of free silicon in the matrix after reaction forming. The matrix primarily consists of silicon carbide with a bimodal grain size distribution. Minority phases dispersed within the matrix are niobium disilicide (NbSi2), carbon, and silicon. Fiber pushout tests on these composites determined a debond stress of approximately 67 MPa and a frictional stress of approximately 60 MPa. A typical four-point flexural strength of the composite is 297 MPa (43.1 KSi). This composite shows tough behavior through fiber pullout.

Singh, M.↗