Investigation of R-curve Behavior and Its Effect on Strength for Advanced Ceramics
Three kinds of tests, including compact tension (CT) test, SEPB test and indentation flaw resistance test, were carried out on advanced ceramics for gas turbine components in order to investigate R-curve behavior and its effect on strength. Rising R-curve behaviors were observed not only in ceramic matrix composite but also in monolithic ceramics. KRmax value of each sample was nearly equal to its KIC value that was obtained by SEPB method. This was related to the large pre-crack used in SEPB method in which process zone would grow up sufficiently. Indentation flaw resistance of composite was higher than that of monolithic materials. The KIC value obtained by indentation induced flaw (IIF) method increased with increasing the length of flaw introduced by Vickers indentation. This result indicates that the KIC value can be related to the pre-crack length and its process zone length growing with extension crack. Distribution of strength was simulated by Monte Carlo method in both flat and rising R-curve cases using the same flaw distribution. It was found that the Weibull modulus of rising R-curve case was higher than that of flat R-curve case.
KeywordsFracture Toughness Silicon Nitride Compact Tension Weibull Modulus Compact Tension Specimen
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