CONCLUSIONS The effect of microstructural change on the R-curve behavior was examined for alumina matrix composites reinforced with silicon carbide whiskers, leading to the following conclusions: (1) The increase in the volume fraction of whiskers increases crack closure stresses in both frictional and pull-out bridging processes through the increase in the number of whiskers bridging a crack, and results in the enhancement of rising R-curve behavior at both the first and the second stages. (2) The increase in whisker size increases bridging zone length, whereas it does not cause any change in the maximum bridging stresses. In the present composite system, the decrease in whisker aspect ratio increases the maximum bridging stress as well as the zone length in pull-out bridging process. Therefore, the composite reinforced with whiskers of large size and small aspect ratio has an advantage for realizing the enhancement of rising R-curve behavior. References 1. Yasuda, E., Akatsu, T. and Tanabe, Y. (1991) J.Ceram.Soc.Jpn., 99, 52-58. 2. Nishida, T., Hanaki, Y., Nojima, T. and Pezzotti, G. (1995) J.Am.Ceram.Soc., 78, 3113-3116. 3. Becher, P.F., Hsueh, C.H., Alexander, K.B. and Sun, E.Y. (1996) J.Am.Ceram.Soc., 79, 298-304. 4. Barenblatt, G.I. (1962) Adv.Appl.Mech., 7, 55-129. 5. Samanta, S.C. and Musikant, S. (1985) Ceram.Eng.Sci.Proc., 6, 663-672. 6. Petrovic, J.J., Milewski, J.V., Rohr, D.L. and Gac, F.D. (1985) J.Mater.Sci., 20, 1167-1177. 7. Akatsu, T., Tanabe, Y., Matsuo, Y. and Yasuda, E. (1992) J.Ceram.Soc.Jpn., 100, 1297-1303. 8. Akatsu, T., Tanabe, Y. and Yasuda, E. (1999) J.Mater.Res., 14, 1316-1324.
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