Modeling the Oxidation Kinetics of Continuous Carbon Fibers in a Ceramic Matrix PDF Download
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Author: Michael C. Halbig
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ISBN:
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Languages : en
Pages : 14
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Book Description
A finite difference model has been developed and was used to study the oxidation kinetics of carbon fibers exposed by the presence of a through-thickness matrix crack in a ceramic matrix composite. Air was the environment of interest so that the model could be compared to experimental testing. The limiting steps of diffusion controlled and reaction controlled kinetics were investigated by changing the value of the simulated temperature which, in turn corresponds to a change in the diffusion coefficient and reaction rate constant. The reaction rates for the oxidation of carbon fibers were compared to theoretical values and oxidation trends predicted by the model were compared to experimental trends.
Author: Michael C. Halbig
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
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Book Description
A finite difference model has been developed and was used to study the oxidation kinetics of carbon fibers exposed by the presence of a through-thickness matrix crack in a ceramic matrix composite. Air was the environment of interest so that the model could be compared to experimental testing. The limiting steps of diffusion controlled and reaction controlled kinetics were investigated by changing the value of the simulated temperature which, in turn corresponds to a change in the diffusion coefficient and reaction rate constant. The reaction rates for the oxidation of carbon fibers were compared to theoretical values and oxidation trends predicted by the model were compared to experimental trends.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 156
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Book Description
Author: Michael C. Halbig
Publisher:
ISBN:
Category :
Languages : en
Pages : 18
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Book Description
Carbon fiber reinforced silicon carbide matrix composites (C/SiC) are a ceramic matrix composite (CMC) material that offers benefits for use in a wide range of high temperature structural applications. However the susceptibility of the carbon fibers to degradation in oxidizing environments has hindered the material's use in certain applications requiring long lives under oxidizing conditions. The susceptibility of carbon fibers to oxidation will be discussed as well as the enhancement (improvement in oxidation resistance) of C/SiC materials. Thermogravimetric analysis of carbon fibers shows susceptibility to oxidation in two distinct kinetic regimes. However, in the thermogravimetric (wt. loss) analysis of unstressed, unenhanced, seal coated C/SiC coupons, the two regimes were not observed due to crack closure and matrix effects, which inhibited the oxidation process. Stressed oxidation (creep rupture) tests put the material under a stress, which is a more realistic condition for many applications. In stressed oxidation tests, the two oxidation kinetics regimes were observed. These tests can provide better insight into how the material will perform in applications involving stress. Stressed oxidation of enhanced materials containing oxidation inhibitors showed significantly improved lives at the specific test conditions considered, although there was susceptibility to oxidation at intermediate temperatures.
Author: United States. National Aeronautics and Space Administration
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ISBN:
Category :
Languages : en
Pages :
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Author:
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ISBN:
Category :
Languages : en
Pages : 22
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Ten different ceramic matrix composite (CMC) materials were subjected to a constant load and temperature in an air environment. Tests conducted under these conditions are often referred to as stressed oxidation or creep rupture tests. The stressed oxidation tests were conducted at a temperature of 1454 deg C at stresses of 69 MPa, 172 MPa and 50% of each material's ultimate tensile strength. The ten materials included such CMCs as C/SiC, SiC/C, SiC/SiC, SiC/SiNC and C/C. The time to failure results of the stressed oxidation tests will be presented. Much of the discussion regarding material degradation under stressed oxidation conditions will focus on C/SiC composites. Thermogravimetric analysis of the oxidation of fully exposed carbon fiber (T300) and of C/SiC coupons will be presented as well as a model that predicts the oxidation patterns and kinetics of carbon fiber tows oxidizing in a nonreactive matrix.
Author: Michael C. Halbig
Publisher:
ISBN:
Category :
Languages : en
Pages : 16
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Book Description
Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 deg C to 1500 deg C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e.; diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics.
Author:
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ISBN:
Category :
Languages : en
Pages : 14
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Book Description
Author: National Aeronautics and Space Adm Nasa
Publisher:
ISBN: 9781724175427
Category :
Languages : en
Pages : 28
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Book Description
Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 C to 1500 C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e. diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics. Halbig, Michael C. and Eckel, Andrew J. and Cawley, James D. Glenn Research Center NASA/TM-1999-208911, NAS 1.15:208911, E-11540, ARL-TR-1692...
Author: Michael C. Halbig
Publisher:
ISBN:
Category : Carbon fibers
Languages : en
Pages : 8
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Book Description
Previous stressed oxidation tests of C/SiC composites at elevated temperatures (350 deg C to 1500 deg C) and sustained stresses (69 MPa and 172 MPa) have led to the development of a finite difference cracked matrix model. The times to failure in the samples suggest oxidation occurred in two kinetic regimes defined by the rate controlling mechanisms (i.e.; diffusion controlled and reaction controlled kinetics). Microstructural analysis revealed preferential oxidation along as-fabricated, matrix microcracks and also suggested two regimes of oxidation kinetics dependent on the oxidation temperature. Based on experimental results, observation, and theory, a finite difference model was developed. The model simulates the diffusion of oxygen into a matrix crack bridged by carbon fibers. The model facilitates the study of the relative importance of temperature, the reaction rate constant, and the diffusion coefficient on the overall oxidation kinetics.
Author: Michael C. Halbig
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Carbon fiber/silicon carbide matrix composites (C/SiC) are promising materials for space applications such as nozzles, thrusters, and bladed disks. However the as-fabricated, cracked nature of the material makes it susceptible to environmental degradation due to fiber oxidation. Theoretical models can be used to gain a better understanding of how certain variables (i.e. temperature, environment, diffusion coefficient and reaction rate constant) are related to a specific process and to supplement or analyze experimental results. Methods for predicting the distribution of local oxygen concentration from the edge to the interior of an open column in a matrix bounded by carbon fiber tows will be discussed. The amounts and distribution of oxygen in a matrix and the gradients in oxygen concentration convey information regarding the oxidation kinetics. The models consider the case of a crack in a ceramic matrix that is bridged by carbon fiber tows. Two analytical solutions and differing finite difference models will be used to predict oxygen concentrations. Results from each prediction method will be presented and compared. The results and their relation towards oxidation kinetics will be discussed. Several geometries for the composite (square and rectangular) are considered in the finite difference models.
