Thermal diffusivity imaging of continuous fiber ceramic composite materials and components Page: 3 of 13
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Continuous-fiber ceramic matrix composites (CFCCs) are currently being
developed for various high-temperature applications, including use in advanced
turbine engines. In such composites, the condition of the interfaces between the
fibers and matrix or between laminae in a two-dimensional weave lay-up are critical
to the mechanical and thermal behavior of the component. A nondestructive
evaluation method that could be used to assess the interface condition and/or detect
other "defects" has been developed at Argonne National Laboratory (ANL) and uses
infrared thermal imaging to provide "single-shot" full-field quantitative measurement
of the distribution of thermal diffusivity in large components. By applying digital
filtering, interpolation, and least-squares-estimation techniques for noise reduction,
shorter acquisition and analysis times have been achieved with submillimeter spatial
resolution for materials with a wide range of "thermal thicknesses". The system at
ANL has been used to examine the effects of thermal shock, oxidation treatment,
density variations, and variations in fiber coating in a full array of test specimens. In
addition, actual subscale CFCC components of nonplanar geometries have been
inspected for manufacturing-induced variations in thermal properties.
Advanced ceramics that meet the requirements of tomorrow's technology are
currently being introduced into the manufacturing community. For example, the
titanium alloy with a silicon carbide (SiC)-reinforced ceramic-matrix, Timetal-21S
(Ti-15Mo-3Nb-3A-0.2Si) has reduced the weight of each of the engines of the
Boeing 777 by 360 kg. These materials, in general, have high strength and stability
at high temperatures due to the incorporation of continuous fibers in monolithic
ceramics. CFCCs are being considered as replacements for traditional materials in
numerous applications, including gas turbines, due to their relatively high strength
and toughness at high temperatures (>1250*C), and lower density. Among the
specific materials systems under consideration are SiCt0/SiC and Al2O3(l/Al2O3,
which are desired specifically for their thermal properties (i.e., thermal diffusivity,
thermal conductivity, etc.) and therefore any variations in those properties will
significantly affect their ability to transfer heat properly. Such variations result frof
processing defects, thermal shock, or thermally induced degradation of the
fiber/matrix interface and reduce the advantages for choosing these materials.
Several nondestructive methods for the detection of thermal properties have been
employed in the study of both ceramic and nonceramic materials systems (1]. These
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Ahuja, S.; Ellingson, W.A.; Steckenrider, J.S. & King, S. Thermal diffusivity imaging of continuous fiber ceramic composite materials and components, article, December 31, 1995; Illinois. (digital.library.unt.edu/ark:/67531/metadc678631/m1/3/: accessed December 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.