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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Phase-Field Modeling of Mechanical Damages in Ceramic Matrix Composites

Developed a phase-field model for mechanical damages in CMCs, which incorporates the CMC microstructures, matrix cracking, fiber breakage, and interfacial sliding. Two types of mechanisms, fiber bridging and fiber pull-out, are considered. The obtained simulation results agree with experimental observations and an analytical solution. Simulation results suggest that the performance of CMCs would be enhanced with thicker fibers, longer fibers, and higher fiber density. Opposite trends of interfacial sliding resistances are suggested for the two types of situations. In reality, a mixture of the two situations may exist, and then an intermediate interfacial sliding resistance may be optimal.

Xue, Fei↗
DOE OSTI2023

Evaluation of Additively Manufactured Monolithic SiC and SiC Ceramic Matrix Composites for CSP- Fabrication and Testing of Receiver Design Feature Specimens in a Simulating Lab Test via Laser Heating

Critical to the creation of a multi-component SiC receiver design concept capable of meeting the SETO CST cost goal objectives of <$150/kWth is the optimal utilization of material for solar absorption and heat transfer to transport fluid. This is to maximize the solar-thermal efficiency in the techno-economic analysis of derived use case. As a first step in preparation of sub-component design for on-sun test evaluations we use different proposed SiC absorber element in a customized laser heat flux test to assess an effective heat transfer coefficient characteristic of the design. The test results are analyzed to extract the effective heat transfer coefficient, thus enable optimization of the geometry of receiver components for heat transfer, efficiency attributes and the thermo-structural management of the components. High intensity CO2 laser is used in combination with air flow through the test specimen to assess the effective heat transfer coefficient under heat flux conditions corresponding to high solar concentrations in the range of 1000-2000 suns.

14 SOLAR ENERGY↗
DOE OSTI2024

Evaluation of Additively Manufactured Monolithic SiC and SiC Ceramic Matrix Composites for Concentrating Solar Receiver Applications

Supported by an award from the Solar Technology Office, US Department of Energy, GE Aerospace Research in collaboration with Heliogen Holdings Inc, is engaged in the development of ultra-High Operating Temperature SiC-matrix Solar Thermal Air Receiver (HOTSSTAR). We report the results of our study of the effective heat transfer characteristic of several candidate structure motifs, or feature geometries, made of SiC via additive manufacturing in a simulative laboratory test. The SiC structure motifs studied include different permutations of three-dimensional periodic lattices and defined shapes. The solar-thermal simulating laboratory test setup is constructed using a 4kW CO2 laser system with beam shaping optics to apply radiative heating power on one face of 2”-diameter cylindrical feature specimens representing the structure motifs of interest for receiver element design. Using the test setup, simulative test conditions representative of a concentrated solar flux of up to ~2000 suns could be achieved in the lab tests under varying air flow through the test structure. A numerical analysis scheme is developed to extract an effective or compound heat transfer coefficient representative of the test structure under steady-state heat flow conditions.

14 SOLAR ENERGY↗
DOE OSTI2024

Evaluation of Additively Manufactured Monolithic SiC and SiC-Matrix Ceramic Matrix Composites for Concentrating Solar Receiver Applications - Fabrication and Testing of Receiver Design Feature Specimens in a Simulating Lab Test via Laser Heating

Increasing operating temperatures of solar receivers is paramount to the efficiency of concentrated solar thermal (CST) and solar power (CSP) systems. Owing to its high temperature stability combined with excellent thermal and optical properties, SiC has been the material of choice for application in high-temperature solar receivers. We report the results of our study of the effective heat transfer characteristics of several candidate SiC structure motifs, or feature geometries, which are fabricated via additive manufacturing. The SiC structure motifs studied include different permutations of three-dimensional periodic lattices and defined shapes. A solar-thermal simulating laboratory test setup is constructed using a 4kW CO2 laser system with beam shaping optics to apply concurrent radiative heating power on one face of 2”-diameter cylindrical feature specimens, representing the structure motifs of interest for receiver element design, while flowing through the sample as heat transfer fluid. Using the test setup, simulative test conditions representative of a concentrated solar flux of up to ~2000 suns could be achieved in the lab tests under varying air flow through the test structure. A simple 1D numerical analysis scheme is developed to extract an effective or compound heat transfer coefficient representative of the test structure under steady-state heat flow conditions. The test results and their use to guide the selection and optimization of SiC material and structure motifs for the receiver element design fabrication are discussed.

14 SOLAR ENERGY↗
NASA NTRS1985

A ceramic matrix composite based on polymerization and pyrolysis of ethynylated aromatics

A number of ethynylated aromatic monomers recently have been synthesized which thermally homopolymerize and copolymerize to produce rigid, highly cross-linked polymers with high thermal stability (Tg of about 450 C). On pyrolysis, these polymers lose few volatiles (more than 85 percent char yield) to yield carbon bodies of relatively low porosity. These properties render the ethynylated aromatics of significant interest as matrices for high temperature composites. Incorporation of a SiC particle filler in the matrix improves the rheology of the system and minimizes shrinkage during pyrolysis. Several unidirectional composites have been fabricated combining a graphite or boria-alumina-silica continuous reinforcement with an ethynylated aromatic polymer matrix and SiC filler. Thermogravimetric analysis of composite pyrolysis behavior was used to determine reaction kinetics and to establish a composite fabrication cycle. Composites retained 95 percent of their green weight on pyrolysis. Microstructure of the green and pyrolyzed composites is characterized for materials pyrolyzed at 600 C in vacuum and argon as well as for laminates heated at 1200 C in argon following pyrolysis.

Hurwitz, F. I.↗
NASA NTRS1988

Auger analysis of a fiber/matrix interface in a ceramic matrix composite

Auger electron spectroscopy (AES) depth profiling was used to characterize the fiber/matrix interface of an SiC fiber, reaction bonded Si3N4 matrix composite. Depth profiles of the as received double coated fiber revealed concentration oscillations which disappeared after annealing the fiber in the environment used to fabricate the composite. After the composite was fractured, the Auger depth profiles showed that failure occurred in neither the Beta-SiC fiber body nor in the Si3N4 matrix but, concurrently, at the fiber coating/matrix interface and within the fiber coating itself.

Honecy, Frank S.↗
NASA NTRS1988

Auger analysis of a fiber/matrix interface in a ceramic matrix composite

Auger electron spectroscopy (AES) depth profiling was used to characterize the fiber/matrix interface of an SiC fiber, reaction bonded Si3N4 matrix composite. Depth profiles of the as received double coated fiber revealed concentration oscillations which disappeared after annealing the fiber in the environment used to fabricate the composite. After the composite was fractured, the Auger depth profiles showed that failure occurred in neither the Beta-SiC fiber body nor in the Si3N4 matrix but, concurrently, at the fiber coating/matrix interface and within the fiber coating itself.

Honecy, Frank S.↗
NASA NTRS1989

An investigation of the thermal cycling damage of 25 vol. pct SiCw/alumina ceramic matrix composite

An investigation was made of the thermal cycling damage of a 25 vol pct SiC whisker/alumina (SiCw/Al2O3) composite. Thermal cycling tests were conducted by subjecting a composite specimen to two different fluidized beds. After thermal cycling the composite specimens were subjected to elastic modulus and effective fracture toughness measurements. The thermal cycled specimens were investigated with SEM and TEM studies. It was found that this composite has a relatively high resistance to thermal cycling.

Armstrong, William D.↗
NASA NTRS1989

Effects of loading rate and temperature on dynamic fracture of ceramic matrix composites

A hybrid experimental-numerical procedure was used to determine the dynamic fracture initiation toughnesses and the dynamic stress intensity factors of alumina, TiB2-particulate/SiC-matrix, and SiC(w)/Al2O3-matrix composites at room and elevated temperatures under static and impact loadings. The dynamic fracture initiation toughnesses at room and elevated temperatures were greater than the corresponding static fracture toughness. The crack velocity versus the dynamic stress intensity factor relations showed minor differences due to temperature changes but significant differences due to the change in loading rates.

Yang, K. H.↗
NASA NTRS1991

Thermal shock of fiber reinforced ceramic matrix composites

Monolithic silicon carbide and silicon nitride and a Nicalon fiber reinforced silicon carbide composite were subjected to severe thermal shock conditions via impingement of a hydrogen-oxygen flame. Surface heating rates of 1000 C/sec to 2500 C/sec were generated. The performance of the monolithic reference materials are compared and contrasted to the significantly greater thermal shock resistance of the composite. Ultrasonic and radiographic NDE techniques were used to evaluate the integrity of the composite subsequent to thermal shock. Tensile tests were performed to determine the residual tensile strength and modulus. Physical property changes are discussed as a function of number and severity of thermal shock cycles.

Eckel, Andrew J.↗
NASA NTRS1991

Mechanical behavior of fiber reinforced SiC/RBSN ceramic matrix composites: Theory and experiment

The mechanical behavior of continuous fiber reinforced SiC/RBSN (Reaction Bonded Silicon Nitride) composites with various fiber contents is evaluated. Both catastrophic and noncatastrophic failures are observed in tensile specimens. Damage and failure mechanisms are identified via in-situ monitoring using NDE (nondestructive evaluation) techniques through the loading history. Effects of fiber/matrix interface debonding (splitting) parallel to fibers are discussed. Statistical failure behavior of fibers is also observed, especially when the interface is weak. Micromechanical models incorporating residual stresses to calculate the critical matrix cracking strength, ultimate strength, and work of pull-out are reviewed and used to predict composite response. For selected test problems, experimental measurements are compared to analytical predictions.

Chulya, Abhisak↗
NASA NTRS1990

The effect of weak interface on transverse properties of a ceramic matrix composite

Experimental studies conducted at NASA Lewis on SiC reaction-bonded Si3N4 composite system showed that transverse stiffness and strength were much lower than those predicted from existing analytical models based on good interfacial bonding. It was believed that weakened interfaces were responsible for the decrease in tranverse properties. To support this claim, a two-dimensional FEM analysis was performed for a transverse representative volume element. Specifically, the effect of fiber/matrix displacement compatibility at the interface was studied under both tensile and compressive transverse loadings. Interface debonding was represented using active gap elements connecting the fiber and matrix. The analyses show that the transverse tensile strength and stiffness are best predicted when a debonded interface is assumed for the composite. In fact, the measured properties can be predicted by simply replacing the fibers by voids. Thus, it is found that little or no interfacial bonding exists in the composite, and that an elastic analysis can predict the transverse stiffness and strength.

Shimansky, R. A.↗
NASA NTRS1991

Fracture toughness of fiber-reinforced glass ceramic and ceramic matrix composites

A fracture mechanics investigation of 2D woven Nicalon SiC/SiC and Nicalon SiC/LAS has been undertaken. An energy approach has been adopted to characterize and quantify the fracture properties of these materials. Chevron-notched bend specimens were tested in an edgewise configuration in which the crack propagated perpendicular to the ply direction. R-curves were obtained from repeated loading and unloading of specimens using several methods of data reduction. Values correconding to the plateau regions of the R-curves were taken as steady-state crack-growth resistance. These ranged from 37 to 63 kJ/sq m for 2D-SiC/LAS and 2.6 to 2.8 kJ/sq m for 2D-SiC/SiC composites.

Stull, Kevin R.↗
NASA NTRS1991

Thermal shock fiber-reinforced ceramic matrix composites

Monolithic silicon carbide and silicon nitride and a Nicalon fiber reinforced silicon carbide composite were subjected to severe thermal shock conditions via impingement of a hydrogen-oxygen flame. Surface heating rates of 1000 C/sec to 2500 C/sec were generated. The performance of the monolithic reference materials are compared and contrasted to the significantly greater thermal shock resistance of the composite. Ultrasonic and radiographic NDE techniques were used to evaluate the integrity of the composite subsequent to thermal shock. Tensile tests were performed to determine the residual tensile strength and modulus. Physical property changes are discussed as a function of number and severity of thermal shock cycles.

Eckel, Andrew J.↗
NASA NTRS1991

Micromechanical analysis of the failure process in ceramic matrix composites

An analysis of the effectiveness of fiber reinforcement in brittle matrix composites is presented. The analytical method allows consideration of discrete fiber distribution and examination of the development of crack growth parameters on the microscale. The problem associated with bridging zone development is addressed here; therefore, the bridging zone is considered to be smaller than the main preexisting crack, and the small scale approach is used. The mechanics of the reinforcement is accurately accounted for in the process zone of a growing crack. Closed form solutions characterizing the initial failure process are presented for linear and nonlinear force-fiber pullout displacement relationships. The implicit exact solution for the extended bridging zone is presented as well.

Rubinstein, Asher A.↗
NASA NTRS1991

Mechanical behavior of fiber reinforced SiC/RBSN ceramic matrix composites - Theory and experiment

The mechanical behavior of continuous fiber reinforced SiC/RBSN (Reaction Bonded Silicon Nitride) composites with various fiber contents is evaluated. Both catastrophic and noncatastrophic failures are observed in tensile specimens. Damage and failure mechanisms are identified via in-situ monitoring using NDE (nondestructive evaluation) techniques throughout the loading history. Effects of fiber/matrix interface debonding (splitting) parallel to fibers are discussed. Statistical failure behavior of fibers is also observed, especially when the interface is weak. Micromechanical models incorproating residual stresses to calculate the critical matrix cracking strength, ultimate strength, and work of pull-out are reviewed and used to predict composite response. For selected test problems, experimental measurements are compared to analytical predictions.

Chulya, Abhisak↗
NASA NTRS1991

Reliability analysis of ceramic matrix composite laminates

At a macroscopic level, a composite lamina may be considered as a homogeneous orthotropic solid whose directional strengths are random variables. Incorporation of these random variable strengths into failure models, either interactive or non-interactive, allows for the evaluation of the lamina reliability under a given stress state. Using a non-interactive criterion for demonstration purposes, laminate reliabilities are calculated assuming previously established load sharing rules for the redistribution of load as the failure of laminae occur. The matrix cracking predicted by ACK theory is modeled to allow a loss of stiffness in the fiber direction. The subsequent failure in the fiber direction is controlled by a modified bundle theory. Results using this modified bundle model are compared with previous models which did not permit separate consideration of matrix cracking, as well as to results obtained from experimental data.

Thomas, David J.↗