Analysis of a Chevron‐Notch Four‐Point‐Bend Specimen by the Three‐Dimensional Finite‐Element Method

Joch, J.; Zemankova, J.; Kazda, J.

doi:10.1111/j.1151-2916.1988.tb05039.x

Cited by 7 publications

(1 citation statement)

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“…However, analysis of similar-sized specimens has indicated that the use of this slice model equation to determine K Ivb provides a negligible amount of error that is on the order of 5% or less. [21][22][23] The surface crack in flexure fracture toughness (K Isc ) value was determined at room temperature and 1090°C using flexural bars with a polished surface finish and the loading direction (0.635-cm dimension) parallel to the CVD growth direction, in accordance with ASTM C1421 methods. 18 A precrack was formed in the flexure bar using a Knoop indenter in the middle of the 0.635-cm Fig.…”

Section: Base Materials Test Methods and Characterizationmentioning

confidence: 99%

Fracture Toughness and Flexural Strength of Chemically Vapor‐Deposited Silicon Carbide As Determined Using Chevron‐Notched and Surface Crack in Flexure Specimens

Cockeram

2004

Journal of the American Ceramic Society

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Two different techniques used to measure the fracture toughness of silicon carbide (SiC) produced by chemical vapor deposition (CVD) are compared, and the influence of the material growth direction on toughness and flexural strength are evaluated. Fracture toughness values for monolithic CVD SiC are found to be independent of the CVD growth direction and test temperature from ambient to 1100°C with values ranging from 2.8 to 5.5 MPa·m1/2. This isotropic nature is notably different from hot‐pressed α‐SiC and is likely a result of the cubic β‐SiC structure produced by the CVD process and the transgranular fracture mode. The range of fracture toughness results obtained using a chevron‐notched specimen (2.8–4.0 MPa·m1/2) was less than values obtained using a surface crack in flexure method (3.7–5.5 MPa·m1/2), and these differences are statistically significant. These differences can be attributed to difficulties in resolving the true precrack size for the surface crack in the flexure specimen. Flexural strength values for monolithic CVD SiC are found to be isotropic with respect to the CVD growth direction from room temperature to 1090°C, as observed for the fracture toughness values. Flexural strength values measured at 1090°C are significantly higher (69% to 10% higher) than those measured at room temperature, while the modulus measured at 1090°C is less (−25% to −10% lower) than that measured at room temperature. Since the fracture toughness values are independent of temperature between room temperature and 1090°C, the increased flexural strength at elevated temperature is difficult to explain on the basis of classical fracture mechanics and must be influenced by other factors. Surface machining flaws on flexure specimens are shown to produce a 35% to 50% decrease in the flexure strength of monolithic CVD SiC that was quantified using the fracture toughness and flaw‐size data.

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Section: Base Materials Test Methods and Characterizationmentioning

confidence: 99%