International Journal of Applied Ceramic Technolog-Sauder, Brusson and Lamon Vol. 7, No. 3, 2010 20 cracks matrix Fig. 11. Schematic diagrams showing the influence of surface roughness-induced clamping stresses OR on the stresses at the crack tip:(a) A=0, OR=0, low stresses on the fiber and(b)A>A>0, or>0, no relaxation of stress concentration at the matrix crack tip a= remote stress applied to a minicomposite). This from fiber interactions, as demonstrated in Calard and ituation is encountered for small epyc epyc se <h(Fig. Lamon 8a).e is the critical thickness such that sliding cannot The value of critical thickness e is not known. It is occur:of of(eq ())and A= Ac(Eq (5). It was governed by the condition observed on test specimens M4, for which ePyC= 30 nm <maximum peak amplitude Rmax. This suggests that oF=元2(o+(A) e>30 nm for the SA3 fiber. When epyc >e, of of, and A<Ac stress relaxation can occur at the crack tip As a consequence, the fibers carry safely much lower Ac=h-e(1-Epyc stresses than previously: W A 2 against Ko> 2o(Fig. 11) situation was observed when epyc>Rmax(Fig. 8b) Thus, from Eq.(9),it appears that e may be A critical situation is encountered when epyc is close smaller than h. But it has not been estimated yet. It to e, so that of may be either> of or of locall requires precise data on Ld, H, and Epyc. The results depending on the peak amplitude variability. The high indicate that &>30 nm for the SA3 fiber. According to OR that operate where A> A may cause fiber failure. data in the literature, it would be <60nm. Anyway, it Thus, failure is governed by the probability of the may be anticipated that for epyc=Romae the noncatas- presence of high peaks in interface cracks and thus by trophic influence of roughness prevails the occurrence of event A>Ae. This may have occurred in minicomposites from batch M2 (epyc= 150 nm), Conclusions either because there were peaks higher than 150 nm (this is possible because grains as large as 400 nm have Differences in the tensile behavior of minicom been observed)or because the coating thickness was sites were correlated with microstructure features in- not uniform and <150 nm locally(for instance be- cluding interface characteristics and fiber cause of fiber packing). Ultimate failure then results roughness. Trends for Hi-NicalonS fiber-reinforceds 5 remote stress applied to a minicomposite). This situation is encountered for small ePyC:ePyCre c oh (Fig. 8a). e c is the critical thickness such that sliding cannot occur: sR f < ss f (Eq. (7)) and A 5 Ac (Eq. (5)). It was observed on test specimens M4, for which ePyC 5 30 nm omaximum peak amplitude Rmax. This suggests that e c 430 nm for the SA3 fiber. When ePyC4e c , ss f < sR f , and AoAc, stress relaxation can occur at the crack tip. As a consequence, the fibers carry safely much lower stresses than previously: s Vf 2 against Ktsb2s (Fig. 11). This situation was observed when ePyC4Rmax (Fig. 8b). A critical situation is encountered when ePyC is close to e c , so that ss f may be either > sR f or < sR f locally, depending on the peak amplitude variability. The high sR that operate where A4Ac may cause fiber failure. Thus, failure is governed by the probability of the presence of high peaks in interface cracks and thus by the occurrence of event A4Ac. This may have occurred in minicomposites from batch M2 (ePyC 5 150 nm), either because there were peaks higher than 150 nm (this is possible because grains as large as 400 nm have been observed6 ) or because the coating thickness was not uniform and o150 nm locally (for instance be￾cause of fiber packing). Ultimate failure then results from fiber interactions, as demonstrated in Calard and Lamon.28 The value of critical thickness e c is not known. It is governed by the condition: sR f ¼ L R 2ðto þ ms RðAcÞÞ ð8Þ With Ac ¼ h  e c ð1  ePyCÞ ð9Þ Thus, from Eq. (9), it appears that e c may be smaller than h. But it has not been estimated yet. It requires precise data on Ld, m, and ePyC. The results indicate that e c 430 nm for the SA3 fiber. According to data in the literature, it would be o60 nm.13 Anyway, it may be anticipated that for ePyC 5 Rmax, the noncatas￾trophic influence of roughness prevails. Conclusions Differences in the tensile behavior of minicompo￾sites were correlated with microstructure features in￾cluding interface characteristics and fiber surface roughness. Trends for Hi-NicalonS fiber-reinforced Fig. 11. Schematic diagrams showing the influence of surface roughness-induced clamping stresses sR on the stresses at the crack tip: (a) A 5 0, sR 5 0, low stresses on the fiber and (b) A4Ac40, sR40, no relaxation of stress concentration at the matrix crack tip. 302 International Journal of Applied Ceramic Technology—Sauder, Brusson and Lamon Vol. 7, No. 3, 2010