Ambient and elevated temperature fracture and cyclic-fatigue properties in a series of Al-containing silicon carbides Page: 65 of 86
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(3) Effect of sample size on Rb(a). Also from Eq.(3.8b), it is clear that the
increased toughness may become sample size dependent if the bridging zone length is
comparable to the crack size. Since some researchers reported a very large bridging
zone length in their tests [33], some concern is warranted: for example, will the
bridging zone length increase with sample size? If so, does it increase linearly with
the structure size? If the bridging zone length is independent of the sample size, then
what is the critical sample size above which the measured toughness can be applied to
structures of different sizes? So far no experiments have been preformed to
investigate these issues.
3.3 CONCLUSIONS
(1) The fracture resistance and stress intensity factors for external loading KApp(a),
internal bridging stresses Kb, and crack initiation Krn, are formulated by linear elastic
fracture mechanics. Linear superposition theorems and the weight function are used to
relate the CODs, stress intensity factors corresponding to their loading origins,
namely, external tractions and the internal bridging stress. The apparent material
resistance from the contribution of external loading is found to be KInKApp(a) H, the
bridging resistance KInKb(a) H, and intrinsic toughness a constant Kn2 H, where H is
Young's modulus E in plane stress condition, and E (I-v2) in plane strain condition,
and v is the Poisson ratio.
(2) Experimental procedures to obtain the fracture resistance and stress intensity
factors are proposed based on above results.
(3) Sample size may affect the measured toughness if the bridging zone length is
comparable to the sample dimensions.55
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Yuan, Rong. Ambient and elevated temperature fracture and cyclic-fatigue properties in a series of Al-containing silicon carbides, thesis or dissertation, August 30, 2004; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc787712/m1/65/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.