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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 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Method of thermal strain hysteresis reduction in metal matrix composites

A method is disclosed for treating graphite reinforced metal matrix composites so as to eliminate thermal strain hysteresis and impart dimensional stability through a large thermal cycle. The method is applied to the composite post fabrication and is effective on metal matrix materials using graphite fibers manufactured by both the hot roll bonding and diffusion bonding techniques. The method consists of first heat treating the material in a solution anneal oven followed by a water quench and then subjecting the material to a cryogenic treatment in a cryogenic oven. This heat treatment and cryogenic stress reflief is effective in imparting a dimensional stability and reduced thermal strain hysteresis in the material over a -250.degree. F. to +250.degree. F. thermal cycle.

Dries, Gregory A.↗
NASA NTRS2001

High Strain Rate Behavior of Polymer Matrix Composites Analyzed

Procedures for modeling the high-speed impact of composite materials are needed for designing reliable composite engine cases that are lighter than the metal cases in current use. The types of polymer matrix composites that are likely to be used in such an application have a deformation response that is nonlinear and that varies with strain rate. To characterize and validate material models that could be used in the design of impactresistant engine cases, researchers must obtain material data over a wide variety of strain rates. An experimental program has been carried out through a university grant with the Ohio State University to obtain deformation data for a representative polymer matrix composite for strain rates ranging from quasi-static to high rates of several hundred per second. This information has been used to characterize and validate a constitutive model that was developed at the NASA Glenn Research Center.

Goldberg, Robert K.↗
DOE OSTI2025

Physics-Informed Machine Learning Model for Ceramic Matrix Composite Creep

A physics-informed recurrent neural network (RNN) based surrogate model is developed to emulate the nonlinear, time-dependent constitutive behavior of ceramic matrix composites (CMCs) driven by matrix damage and constituent creep at the microscale. Physics-informed constraints are introduced into the surrogate model through regularization to ground the prediction in physics and improve its predictive capabilities. Training data is generated using the high-fidelity generalized method of cells (HFGMC) approach which calls appropriate creep and damage models for each of the constituents. This coupling permits simulating the nonlinear behavior of CMCs based on constituent response at the microscale along with microstructural features such as fiber and porosity volume fraction and fiber radius. The microscale repeating unit cell is loaded under creep fatigue conditions to replicate the material loading experienced in a turbine engine. Therefore, the RNN-based surrogate model is tasked with predicting, as a function of variable input stress sequence, temperature, and microstructural features, the resulting strain history response while satisfying physical constraints related to creep rate, isochoric inelastic deformation, and strain energy density. The trained surrogate model is shown to effectively match the strain history over quantified distributions of microstructural features and relevant loading regimes and temperatures. Neural network based surrogate models can offer efficient alternatives to running computationally intensive multiscale material models to simulate the nonlinear response of large structural models. Therefore, the presented work provides evidence towards the feasibility of developing, training, and running such models for CMCs with complex microstructures, nonlinear time-dependent material response, and under non-monotonic loading conditions.

ceramic matrix composites↗
NASA NTRS2014

Damage Characterization of EBC-SiCSiC Ceramic Matrix Composites Under Imposed Thermal Gradient Testing

Due to their high temperature capabilities, Ceramic Matrix Composite (CMC) components are being developed for use in hot-section aerospace engine applications. Harsh engine environments have led to the development of Environmental Barrier Coatings (EBCs) for silicon-based CMCs to further increase thermal and environmental capabilities. This study aims at understanding the damage mechanisms associated with these materials under simulated operating conditions. A high heat-flux laser testing rig capable of imposing large through-thickness thermal gradients by means of controlled laser beam heating and back-side air cooling is used. Tests are performed on uncoated composites, as well as CMC substrates that have been coated with state-of-the-art ceramic EBC systems. Results show that the use of the EBCs may help increase temperature capability and creep resistance by reducing the effects of stressed oxidation and environmental degradation. Also, the ability of electrical resistance (ER) and acoustic emission (AE) measurements to monitor material condition and damage state during high temperature testing is shown; suggesting their usefulness as a valuable health monitoring technique. Micromechanics models are used to describe the localized stress state of the composite system, which is utilized along with ER modeling concepts to develop an electromechanical model capable of characterizing material behavior.

protective coatings (nonmetallic)↗
NASA NTRS2013

Multi-Scale CNT-Based Reinforcing Polymer Matrix Composites for Lightweight Structures

Reinforcing critical areas in carbon polymer matrix composites (PMCs), also known as fiber reinforced composites (FRCs), is advantageous for structural durability. Since carbon nanotubes (CNTs) have extremely high tensile strength, they can be used as a functional additive to enhance the mechanical properties of FRCs. However, CNTs are not readily dispersible in the polymer matrix, which leads to lower than theoretically predicted improvement in mechanical, thermal, and electrical properties of CNT composites. The inability to align CNTs in a polymer matrix is also a known issue. The feasibility of incorporating aligned CNTs into an FRC was demonstrated using a novel, yet commercially viable nanofiber approach, termed NRMs (nanofiber-reinforcing mats). The NRM concept of reinforcement allows for a convenient and safe means of incorporating CNTs into FRC structural components specifically where they are needed during the fabrication process. NRMs, fabricated through a novel and scalable process, were incorporated into FRC test panels using layup and vacuum bagging techniques, where alternating layers of the NRM and carbon prepreg were used to form the reinforced FRC structure. Control FRC test panel coupons were also fabricated in the same manner, but comprised of only carbon prepreg. The FRC coupons were machined to size and tested for flexural, tensile, and compression properties. This effort demonstrated that FRC structures can be fabricated using the NRM concept, with an increased average load at break during flexural testing versus that of the control. The NASA applications for the developed technologies are for lightweight structures for in-space and launch vehicles. In addition, the developed technologies would find use in NASA aerospace applications such as rockets, aircraft, aircraft/spacecraft propulsion systems, and supporting facilities. The reinforcing aspect of the technology will allow for more efficient joining of fiber composite parts, thus offering additional weight savings. More robust structures capable of withstanding micrometeoroid and space debris impacts will be possible with the enhanced mechanical properties imparted by the aligned CNTs incorporated into the fiber composite structure, as well as the potential for improved electrical and thermal properties. The materials fabrication approach developed in the present effort is a platform for customer applications where additional reinforcement is required or would be beneficial, especially in FRC structures and component parts. Depending upon the specific customer application, the NRM could be tailored to the specific matrix resin and desired property enhancement.

Eberly, Daniel↗
NASA NTRS1991

Concurrent tailoring of fabrication process and interphase layer to reduce residual stresses in metal matrix composites

A methodology is presented to reduce the residual matrix stresses in continuous fiber metal matrix composites (MMC) by optimizing the fabrication process and interphase layer characteristics. The response of the fabricated MMC was simulated based on nonlinear micromechanics. Application cases include fabrication tailoring, interphase tailoring, and concurrent fabrication-interphase optimization. Two composite systems, silicon carbide/titanium and graphite/copper, are considered. Results illustrate the merits of each approach, indicate that concurrent fabrication/interphase optimization produces significant reductions in the matrix residual stresses and demonstrate the strong coupling between fabrication and interphase tailoring.

Saravanos, D. A.↗
NASA NTRS1993

Assessment of damage in ceramics and ceramic matrix composites using ultrasonic techniques

This paper addresses the application of ultrasonic sensing to damage assessment in ceramics and ceramic matrix composites. It focuses on damage caused by thermal shock or oxidation at elevated temperatures, which often results in elastic anisotropy. This damaged-induced anisotropy is determined by measuring the velocities of ultrasonic waves in different propagation directions. Thermal shock damage is assessed in ceramic samples of reaction bonded silicon nitride (RBSN). Thermal shock treatment from different temperatures up to 1000 C is applied to produce the microcracks. Results indicate that most microcracks produced by thermal shock are located near sample surfaces. Ultrasonic measurements using the surface wave method are found to correlate well with measurements of degradation of mechanical properties obtained independently by other authors using destructive methods. Oxidation damage is assessed in silicon carbide fiber/reaction bonded silicon nitride matrix (SCS-6/RBSN) composites. The oxidation is done by exposing the samples in a flowing oxygen environment at elevated temperatures, up to 1400 C, for 100 hr. The Youngs' modulus in the fiber direction as obtained from ultrasonic measurements decreases significantly at 600 C but retains its original value at temperatures above 1200 C. This agrees well with the results of destructive tests by other authors. On the other hand, the transverse moduli obtained from ultrasonic measurements decrease continually until 1200 C. Measurements on the shear stiffnesses show behavior similar to the transverse moduli. The results of this work show that the damage-induced anisotropy in both ceramics and ceramic matrix composites can be determined successfully by ultrasonic methods. This suggests the possibility of assessing damage severity using ultrasonic techniques.

Chu, Y. C.↗
NASA NTRS2008

Interphase for ceramic matrix composites reinforced by non-oxide ceramic fibers

A ceramic matrix composite material is disclosed having non-oxide ceramic fibers, which are formed in a complex fiber architecture by conventional textile processes; a thin mechanically weak interphase material, which is coated on the fibers; and a non-oxide or oxide ceramic matrix, which is formed within the interstices of the interphase-coated fiber architecture. During composite fabrication or post treatment, the interphase is allowed to debond from the matrix while still adhering to the fibers, thereby providing enhanced oxidative durability and damage tolerance to the fibers and the composite material.

DiCarlo, James A.↗
NASA NTRS1993

Ultrasonic assessment of interfacial oxidation damage in ceramic matrix composites

A new approach to characterizing oxidation damage in ceramic matrix composites using ultrasonic techniques is proposed. In this approach, the elastic constants of the composite are determined nondestructively by measuring the angular dependence of both longitudinal and transverse wave velocities. A micromechanical model for composites with anisotropic constituents is used to find the anisotropic properties of an effective fiber, which is a combination of the fiber and the interface. Interfacial properties are extracted from the properties of this effective fiber by analyzing the difference between effective and actual fiber properties. Unidirectional /0/28 SiC/Si3N4 composites with 30 percent fiber volume fraction and 30 percent matrix porosity are used. The samples are exposed in a flowing oxygen environment at elevated temperatures, up to 1400 C, for 100 hours and then measured by ultrasonic methods at room temperature. The Young's modulus in the fiber direction of the sample oxidized at 600 C decreased significantly but it was unchanged for samples oxidized at temperatures above 1200 C. The transverse moduli obtained from ultrasonic measurements decrease continuously up to 1200 C. The shear stiffnesses show behavior similar to the transverse moduli. The effective elastic moduli of the interfacial carbon coating are determined from the experimental data, and their change due to thermal oxidation is discussed.

Chu, Y. C.↗
NASA NTRS1995

An investigation of theories of failure for ceramic matrix composites

This final report is comprised of the abstract of a masters thesis research grant. The abstract of the thesis, 'An Investigation of Acoustic Emission Techniques for the Discrimination of Damage Mechanisms in Ceramic Matrix Composites', is as follows: In order to further advance the understanding of the mechanical behavior of ceramic matrix composites (CMS's), acoustic emission (AE) techniques were implemented to monitor and identify damage mechanisms in CMC's under tensile loading. In addition to real-time AE monitoring techniques, a data acquisition system was developed and implemented in order to capture AE waveforms resulting from stress-induced damage. Waveforms were inspected for multiple events, separated in distinct events, and then analyzed to determine waveform characteristics in the time and frequency domains. Waveform characteristics included peak amplitude, event duration, MARSE, energy, and dominant and centroidal frequency. In addition to conventional methods for determining a damage discrimination criteria, a study of the distribution and correlation of the waveform characteristics criteria and a study of the distribution and correlation of the waveform characteristics were performed to aid in the determination of a damage discrimination criteria. The damage discrimination criteria was tested for 'uniqueness', i.e., the effectiveness of the criteria to identify and monitor damage independent of the stress-strain relationship. Insitu radiography was used to substantiate the damage accumulation. A simulation test was also performed over the loading history to study the changes in the waveform characteristics of the system response from a constant excitation. This thesis demonstrates the use of waveform analysis to study the AE activity resulting from stress-induced damage in CMC's in conjunction with other nondestructive evaluation techniques to investigate the mechanical behavior of CMC's.

Hemann, John H.↗
DOE OSTI2022

Woven ceramic matrix composite surrogate model based on physics-informed recurrent neural network

A recurrent neural network (RNN) based surrogate model is developed to emulate the nonlinear constitutive behavior of woven ceramic matrix composites (CMCs) driven by matrix damage at multiple length scales. Physics-informed constraints are introduced into the surrogate model through regularization to ground the prediction in physics and improve its predictive capabilities. Training data is generated using the multiscale generalized method of cells (MSGMC) approach coupled with a matrix damage model. This coupling permits simulating the nonlinear behavior of woven CMCs based on constituent response at the micro-, meso-, and macroscales. The multiscale repeating unit cell is loaded under non-monotonic conditions including multiple load / unload cycles and tension / compression. The fiber volume fraction as well as the intra- and intertow void volume fractions are also varied in the generation of training data. Therefore, the RNN-based surrogate model is tasked with predicting, as a function of variable input strain sequence and fiber and void volume fractions, the resulting stress versus strain response while satisfying physical constraints such as positive semi-definiteness of the tangent stiffness matrix and linear elastic unloading. Further, the trained surrogate model effectively matches the stress versus strain response and successfully predicts the tangent modulus throughout the loading regime. Neural network based surrogate models can offer efficient alternatives to running computationally intensive multiscale material models to simulate the nonlinear response of large structural models. Therefore the presented work provides evidence towards the feasibility of developing, training, and running such models for CMCs with complex architectures, nonlinear multiaxial material response, and under non-monotonic loading conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1992

Damage mechanisms in three-dimensional woven reinforced ceramic matrix composites under tensile and flexural loading at room and elevated temperatures

Three-dimensional Nicalon SiC/SiC matrix composites made through a chemical vapor infiltration process were studied under tensile and flexural loading at 23, 1200, and 1550 C in air. In situ damage accumulation monitoring NDE techniques were utilized to identify failure mechanisms in these materials. The effectiveness and durability of a chemical vapor deposition SiC surface coating were also evaluated in severe oxidizing environment. Results show that the failure response was very similar for the 23 and 1200 C specimens, while at 1550 C there were significant changes in both the composite mechanical behavior and the matrix microstructure. Extensive fiber pull-out was observed only in the 1550 C specimen. It is also found that the SiC surface coating can protect the composite up to the critical matrix cracking strength.

Chulya, Abhisak↗
NASA NTRS1996

Stress and Damage in Polymer Matrix Composite Materials Due to Material Degradation at High Temperatures

This report describes analytical methods for calculating stresses and damage caused by degradation of the matrix constituent in polymer matrix composite materials. Laminate geometry, material properties, and matrix degradation states are specified as functions of position and time. Matrix shrinkage and property changes are modeled as functions of the degradation states. The model is incorporated into an existing composite mechanics computer code. Stresses, strains, and deformations at the laminate, ply, and micro levels are calculated, and from these calculations it is determined if there is failure of any kind. The rationale for the model (based on published experimental work) is presented, its integration into the laminate analysis code is outlined, and example results are given, with comparisons to existing material and structural data. The mechanisms behind the changes in properties and in surface cracking during long-term aging of polyimide matrix composites are clarified. High-temperature-material test methods are also evaluated.

McManus, Hugh L.↗
DOE OSTI2021

Multiscale characterization and representation of variability in ceramic matrix composites

Low density, high strength, and high creep and oxidation resistance properties of ceramic matrix composites (CMCs) make them an ideal choice for use in extreme environments in space and military applications. This paper presents a detailed characterization study of structural and manufacturing flaws in Carbon fiber Silicon-Carbide-Nitride matrix (C/SiNC) CMCs at different length-scales. Energy-dispersive spectroscopy (EDS) is used for the chemical characterization of the material’s elemental constituents. High-resolution multiscale graphs obtained from scanning electron microscope (SEM) and confocal laser scanning microscope (LSM) are used to characterize the distribution and morphology of defects at different length scales. This is followed by the classification and quantification of the common manufacturing defects. An image processing algorithm based on the image segmentation process is developed to quantify the variability of various scale-dependent architectural parameters. Finally, a three-dimensional stochastic representative volume element (SRVE) generation algorithm is developed to provide precise representations of material textures at multiple length scales. The developed algorithm accurately accounts for material features and flaws based on a range of multiscale structural and defects characterization results.

36 MATERIALS SCIENCE↗
NASA NTRS2003

Polymer Matrix Composites for Propulsion Systems

The Access-to-Space study identified the requirement for lightweight structures to achieve orbit with a single-stage vehicle. Thus a task was undertaken to examine the use of polymer matrix composites for propulsion components. It was determined that the effort of this task would be to extend previous efforts with polymer matrix composite feedlines and demonstrate the feasibility of manufacturing large diameter feedlines with a complex shape and integral flanges, (i.e. all one piece with a 90 deg bend), and assess their performance under a cryogenic atmosphere.

Nettles, Alan T.↗
DOE OSTI2025

Interface instabilities in hafnium hydride entrained iron metal matrix composites

The chemical interactions in Fe–HfH 2 metal matrix composites (MMCs) are studied across multiple length scales to elucidate the decomposition of the parent phases and corresponding reaction zone physics during direct current sintering. Fe–HfH 2 composites were synthesized with increasing as-mixed hydride contents of Fe–25% HfH 2 , Fe–40% HfH 2 , Fe–55% HfH 2 , and Fe–70% HfH 2 (all in vol. %) to demonstrate the ability to achieve sintered MMCs with target hydride contents. Samples were probed across multiple length scales through a multi-modal workflow employing x-ray diffraction, scanning electron microscopy and segmentation analysis, and synchrotron techniques including hard x-ray fluorescence mapping and nanoprobe x-ray absorption near-edge structure measurements. Under the selected sintering temperature and pressure conditions, hydrogen evolution is seen to evolve through parallel paths: thermal decomposition from during the transformation of HfH 2 to HfH x<2 and through subsequent reaction with the Fe matrix leading to intermetallic phase formation. Specifically, HfFe and HfFe 2 intermetallic formation accelerates the release of hydrogen with a subsequent HfO 2 phase forming at grain boundaries. For this MMC, the consumption or loss of hydrogen can be considerable in compacts with initial hydride loading of 25%–40% HfH 2 approaching 83% hydrogen loss for the lower volume fraction composites. Increasing the volume fraction of HfH 2 to 70% enhanced the retained hydrogen content to 53% and attributed to the reduced interfacial area intrinsic to the increased HfH 2 loading in this MMC.

36 MATERIALS SCIENCE↗
NASA NTRS1991

Ductility of a continuous fiber reinforced aluminum matrix composite

The transverse properties of an aluminum alloy metal matrix composite reinforced by continuous alumina fibers have been investigated. The composite is subjected to both mechanical and cyclic thermal loading. The ductility can vary by an order of magnitude according to the operating conditions. For high mechanical and low thermal loading the ductility is small, for low mechanical and high thermal loading the ductility is an order of magnitude higher. Experiments on a beam in bending confirm that the ductility is strongly dependent on the loading conditions. The observations suggest a means of utilizing the inherent ductility of the matrix.

Jansson, S.↗
NASA NTRS2000

Raman Study of Uncoated and P-bn/sic-coated Hi-nicalon Reinforced Celsian Matrix Composites: Residual Stress in the Fibers - Part 2

Band shifts on Raman spectra were used to assess, at a microscopic scale, the residual strain existing in Hi-Nicalon fibers reinforcing celsian matrix composites. Uncoated as well as p-BN/SiC- and p-B(Si)N/SiC-coated Hi-Nicalon fibers were used as the reinforcements. We unambiguously conclude that the fibers are in a state of compressive residual stress. Quantitative determination of the residual stress was made possible by taking into account the heating induced by laser probing and by using a reference line, of fixed wavenumber. We found fiber compressive residual stress values between 110 and 960 MPa depending on the fiber/matrix coating in the composite. A stress relaxation-like phenomenon was observed at the surface of p-BN/SiC-coated Hi-Nicalon fibers whereas the uncoated or p-B(Si)N/SiC-coated Hi-Nicalon fibers did not show any stress relaxation in the Celsian matrix composites.

Gouadec, Gwenael↗