Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 15
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Book Description
The influence of fiber/matrix interface microstructure and interfacial shear strength on the mechanical properties of a fiber-reinforced ceramic composite has been evaluated. The composite consisted of about 30 vol % uniaxially aligned 142 micron diameter SiC fibers (Textron SCS-6) in a reaction- bonded Si3N4 matrix (SiC/RBSN). The interface microstructure was varied by controlling the composite fabrication conditions and by heat treating the composite in an oxidizing environment. Interfacial shear strength was determined by the matrix crack spacing method. The results of microstructural examination indicate that the carbon-rich coating provided with the as-produced SiC fibers was stable in composites fabricated at 1200 C in a nitrogen or in a nitrogen plus 4 percent hydrogen mixture for 40 hr. However this coating degraded in composites fabricated at 1350 C in N2 + 4%H2 for 40 and 72 hr and also in composites heat treated in an oxidizing environment at 600 C for 100 hr after fabrication at 1200 C in a nitrogen. It was determined that degradation occurred by carbon removal which in turn had a strong influence on interfacial shear strength and other mechanical properties. Specifically, as the carbon coating was removed, the composite interfacial shear strength, primary elastic modulus, first matrix cracking stress, and ultimate tensile strength decreased, but the first matrix cracking strain remained nearly the same. Keywords: Ceramic matrix composites; Interfacial shear strength; Mechanical properties.
Author: Ramakrishna T. Bhatt
Publisher:
ISBN:
Category : Additives
Languages : en
Pages : 24
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Book Description
Strong and tough Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride matirix composites (SiC/RBSN) have been fabricated by the fiber lay-up approach. Commercially available uncoated and PBN, PBN/Si-rich PBN, and BN/SiC coated SiC Hi-Nicalon fiber tows were used as reinforcement. The composites contained ~24 vol % of aligned 14 ♯m diameter SiC fibers in a porous RBSN matrix. Both one- and two-dimensional composites were characterized. The effects of interface coating composition, and the nitridation enhancing additive, NiO, on the room temperature physical, tensile, and interfacial shear strenght properties of SiC/RBSN matrix composites were evaluated. Results indicate that all three coated fibers, the thickness of the coating decreased from the outer periphery to the interior of the tows, and that from 10 to 30 percent of the fibers were not covered with the interface coating.
Author: R. T. Bhatt
Publisher:
ISBN:
Category :
Languages : en
Pages : 20
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Book Description
The elevated temperature four-point flexural strength and the room temperature tensile and flexural strength properties after thermal shock were measured for ceramic composites consisting of 30 vol % uniaxially aligned 142 microns diameter SiC fibers in a reaction bonded Si3N4 matrix. The elevated temperature strengths were measured after 15 min of exposure in air at temperatures to 1400 C. The thermal shock treatment was accomplished by heating the composite in air for 15 min at temperatures to 1200 C and then quenching in water at 25 C. The results indicate no significant loss in strength properties either at temperature or after thermal shock when compared with the strength data for composites in the as-fabricated condition. (jes).
Author: R. T. Bhatt
Publisher:
ISBN:
Category :
Languages : en
Pages : 14
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Book Description
The room temperature mechanical and physical properties of silicon carbide fiber-reinforced reaction-bonded silicon nitride composites (SiC/RBSN) have been evaluated. The composites contained similiar to 23 and similiar to 40 volume fraction of aligned 140 micron diameter chemically vapor deposited SiC fibers. Preliminary results for composites tensile and bend strengths and fracture strain indicate that the composites displayed excellent properties when compared with unreinforced RBSN of comparable porosity. Fiber volume fraction showed little influence on matrix first cracking strain did influence the stresses required for matrix first cracking and for ultimate composite fracture strength. It is suggested that by reducing matrix porosity and by increasing the volume fraction of the large diameter SiC fiber, it should be possible to further improve the composite stress at which the matrix first cracks. Keywords: Ceramic powders; Composite fabrication; Microstructure; Density; Axial bend and tensile; Strength; and Integrated shear strength.
Author: National Aeronautics and Space Adm Nasa
Publisher: Independently Published
ISBN: 9781724082459
Category : Science
Languages : en
Pages : 36
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Book Description
Strong and tough Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride matrix composites (SiC/ RBSN) have been fabricated by the fiber lay-up approach. Commercially available uncoated and PBN, PBN/Si-rich PBN, and BN/SiC coated SiC Hi-Nicalon fiber tows were used as reinforcement. The composites contained approximately 24 vol % of aligned 14 micron diameter SiC fibers in a porous RBSN matrix. Both one- and two-dimensional composites were characterized. The effects of interface coating composition, and the nitridation enhancing additive, NiO, on the room temperature physical, tensile, and interfacial shear strength properties of SiC/RBSN matrix composites were evaluated. Results indicate that for all three coated fibers, the thickness of the coatings decreased from the outer periphery to the interior of the tows, and that from 10 to 30 percent of the fibers were not covered with the interface coating. In the uncoated regions, chemical reaction between the NiO additive and the SiC fiber occurs causing degradation of tensile properties of the composites. Among the three interface coating combinations investigated, the BN/SiC coated Hi-Nicalon SiC fiber reinforced RBSN matrix composite showed the least amount of uncoated regions and reasonably uniform interface coating thickness. The matrix cracking stress in SiC/RBSN composites was predicted using a fracture mechanics based crack bridging model. Bhatt, Ramakrishana T. and Hull, David R. and Eldridge, Jeffrey I. and Babuder, Raymond Glenn Research Center NASA/TM-2000-210211, E-12330, NAS 1.15:210211
Author: National Aeronautics and Space Administration (NASA)
Publisher: Createspace Independent Publishing Platform
ISBN: 9781722469405
Category :
Languages : en
Pages : 40
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Book Description
The room temperature mechanical properties of SiC fiber reinforced reaction bonded silicon nitride composites were measured after 100 hrs exposure at temperatures to 1400 C in nitrogen and oxygen environments. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The results indicate that composites heat treated in a nitrogen environment at temperatures to 1400 C showed deformation and fracture behavior equivalent to that of the as-fabricated composites. Also, the composites heat treated in an oxidizing environment beyond 400 C yielded significantly lower tensile strength values. Specifically in the temperature range from 600 to 1000 C, composites retained approx. 40 percent of their as-fabricated strength, and those heat treated in the temperatures from 1200 to 1400 C retained 70 percent. Nonetheless, for all oxygen heat treatment conditions, composite specimens displayed strain capability beyond the matrix fracture stress; a typical behavior of a tough composite. Bhatt, Ramakrishna T. Glenn Research Center RTOP 510-01-0A...
Author: David Belitskus
Publisher: CRC Press
ISBN: 9780824791117
Category : Technology & Engineering
Languages : en
Pages : 376
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Book Description
Examines all important aspects of whisker and fibre reinforced ceramic science and technology, offering a balanced account of developments in the field. The work shows how to improve the strength and stiffness of ceramic composites, at very high temperatures, without brittleness.
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 542
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Book Description
Author:
Publisher:
ISBN:
Category : Aeronautics
Languages : en
Pages : 504
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Book Description
Author: Karl Jakus
Publisher: Elsevier
ISBN: 0080523889
Category : Technology & Engineering
Languages : en
Pages : 569
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Book Description
High Temperature Mechanical Behavior of Ceramic Composites provides an up-to-date comprehensive coverage of the mechanical behavior of ceramic matrix composites at elevated temperatures. Topics include both short-term behavior (strength, fracture toughness and R-curve behavior) and long-term behavior (creep, creep-fatigue, delayed failure and lifetime). Emphasis is on a review of fundamentals and on the mechanics and mechanisms underlying properties. This is the first time that complete information of elevated temperature behavior of ceramic composites has ever been compacted together in a single volume. Of particular importance is that each chapter, written by internationally recognized experts, includes a substantial review component enabling the new material to be put in proper perspective. Shanti Nair is Associate Professor at the Department of Mechanical Engineering at the University of Massachusetts at Amherst. Karl Jakus is Professor at the University of Massachusetts at Amherst.
