Assessment of strength-limiting flaws in ceramic heat exchanger components INEL support: Fracture mechanics and nondestructive evaluation technology. Final report, June 1, 1986--May 31, 1993

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An examination of a siliconized SiC material, CS101K, has been performed to determine if linear fracture mechanics concepts can be used to characterize and predict the behavior of this material. Phase II of this project showed that a value that appeared to represent the true fracture toughness could be measured using small specimens with a machined notch, if the notch root radius was less than 75 {mu}m. Methods to produce sharply cracked specimens were then investigated to verify this hypothesis. A new technique, called the {open_quotes}beam support{close_quotes} precracking method, was subsequently developed and used to make sharply cracked SE(B) specimens. ... continued below

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59 p.

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Lloyd, W.R. & Reuter, W.G. June 1, 1993.

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Description

An examination of a siliconized SiC material, CS101K, has been performed to determine if linear fracture mechanics concepts can be used to characterize and predict the behavior of this material. Phase II of this project showed that a value that appeared to represent the true fracture toughness could be measured using small specimens with a machined notch, if the notch root radius was less than 75 {mu}m. Methods to produce sharply cracked specimens were then investigated to verify this hypothesis. A new technique, called the {open_quotes}beam support{close_quotes} precracking method, was subsequently developed and used to make sharply cracked SE(B) specimens. Tests of these specimens showed a slightly rising R-curve-type of behavior, with elevated values of plane strain fracture toughness. Interference of the crack surfaces in the precrack wake was hypothesized as the most likely cause of these phenomena. Subsequent testing with various precrack lengths provided preliminary verification of the hypothesis. Test results show that, for fracture mechanics-based design and assessment, adequate values of fracture toughness can be obtained from EDM-notched specimens, instead of the more costly precracked specimens. These results imply that, for the Si-SiC material tested, caution is warranted when using any of the methods of assessing fracture toughness that use a sharp precrack. It is also reasoned that these results may generally be more applicable to the coarser-grained structural ceramics that exhibit a rougher fracture surface. Based on results of testing EDM-notched bend specimens in 1250{degrees}C air, no degradation of material properties were observed for exposures, under applied stress, up to 900 h. Instead, some increase in fracture toughness was measured for these conditions. These same tests indicated that the threshold stress intensity factor for stress corrosion cracking (static fatigue) in the hot air environment was the same as the fracture toughness.

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59 p.

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OSTI as DE97000108

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  • Other Information: PBD: Jun 1993

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  • Other: DE97000108
  • Report No.: DOE/EE--97000108
  • Grant Number: AC07-76ID01570
  • DOI: 10.2172/385607 | External Link
  • Office of Scientific & Technical Information Report Number: 385607
  • Archival Resource Key: ark:/67531/metadc677580

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  • June 1, 1993

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Lloyd, W.R. & Reuter, W.G. Assessment of strength-limiting flaws in ceramic heat exchanger components INEL support: Fracture mechanics and nondestructive evaluation technology. Final report, June 1, 1986--May 31, 1993, report, June 1, 1993; Idaho Falls, Idaho. (digital.library.unt.edu/ark:/67531/metadc677580/: accessed October 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.