R. Venkatesh/ Materials Science and Engineering 4268(1999)47-54 Evaluating A/r and the residual thermal strain, AxAT Rockwell Science Center for providing the Saphikon at the PRD-166/ SnO2 and Saphikon /SnO2 interfac fibers (Fig. 10a, b)and using Eq(4), it was observed that the A/r value of PRD-166/SnO, interface was about nine times that of the Saphikon/SnO, interface, (Table 7). It References was also found that, in PRD-166/SnO2/glass matrix composites, the compressive radial strain induced due [K.K. Chawla, Ceramic Matrix Composites, Chapman Hall o fiber roughness was about 20 times greater than the London. 1993. tensile thermal radial strain. In Saphikon/SnO,/glass [2R.W.Rice, Ceramic matrix composite toughening mechanisms: An date. in: eramic Science and Engineering Series. Vol. 6 matrix composites, the roughness induced compressive strain was only three times greater than the tensile 3A.G. Evans, J. Am. Cer. Soc. 73(1990)187 thermal strain. This indicates the strong mechanical 4 W.B. Hillig, Annu. Rev. Mater. Sci. 17(1987)341 clamping due to fiber roughness at the fiber/SnO, inter- 5 D B. Marshall, J.E. Ritter, Cer. Bull. 66(1987)309 6K.K. Chawla, Z.R. Xu, R. Venkatesh, J.S. Ha, Interface Engineer face in ASG composites. As fiber roughness increased ing in some oxide/oxide composites, in: 9th International Confer increased shear stress transfer at the interface beyond ence on Composites (ICCM-9), July 12, 1993, Madrid, Spai matrix cracking from fiber to matrix causes a reduction [7 P.E. D Morgan, D B. Marshall,J. Am. Cer. Soc. 78(6)(1995)1553. he debond length. i.e. fibers broke rather than [8 A Maheshwari, KK. Chawla, T.A. Michalske, Mater. Sci. Eng debonded as the matrix crack grew, resulting in a A107(1989)269 9 M. Cinibulk, Cer. Eng. Sci. Proc. 15(5)(1995)72 composite fracture surface in ASG with little or no fiber (10 M. Cinibulk, Cer. Eng. Sci. Proc. 16(5)(1995) pullout on the fracture surface. Similar results have [l K.K. Chawla, A. Choudhary, R. Venkatesh, J.R. Hellmann been obtained by Chawla et al. using atomic force Mater.Char.31(3)(1993)167 microscopy [35 [12 P.E. D. Morgan, R. M. Housley, J. Am. Cer. Soc. 789(1)(1995) 13J.C. Romine, Cer. Eng. Sci. Proc. 8(1987)755. [14 Data Sheet, Saphikon, NH. 4. Conclusion [15 K.M. Prewo, J.J. Brennan, G.K. Layden, Am Cer. Soc. Bull. 65 It has now been realized that fiber surface roughness [16 J.I. Bluhm, Eng. Fracture Mech. 9(1975)593 [17 Wu Shang-Xian, Eng. Fracture Mech. 19(1984)221 and residual stresses in the composite after processing [18] S.N. Patankar, R Venkatesh, KK Chawla, Scripta Metall. Mate play a very important role in governing the strength nd toughness of CMCs As shown in the present work, [9J. Cook, J.E. Gordon, Proc. R. Soc. Lond. A282(1964)508. composites with tensile radial stress at the interface and 20A. G. Evans, M.Y. Ye, J W.Hutchinson, J Am. Cer. Soc. 72(1989) 2300 ery rough fiber surface exhibit very small debond 21]CC. Wu, S.W. Freiman, R.W. Rice, J.J. Mecholsky, J Mater. Sci. length and fail in a brittle manner. Alternatively in 3(1978)2659 composites with tensile radial stress at the interface and [22] R. Venkatesh, k.K. Chawla, J Mater. Sci. Lett. Il(1992) very smooth interface, the fiber/matrix bonding may be 23] T.A. Michalske, J.R. Hellmann, J. Am. Cer. Soc. 71(199 weak enough to compromise the strength of the 224 K.K. Chawla, M. Ferber, Z.R. Xu, R Venkatesh, Mater. Sci Eng A162(1993)35 225] P D. Jero, RJ. Kerans, Scripta Metall. Mater. 24(1991)2315 Another important effect of fiber roughness is abra- [26]RJ Kerans,TAParthasarathy, J.Am. Cer Soc. 74(1991)1585 sion at the fiber/matrix interface. Abrasion is especially w.C. Carter, E.P. Butler, E.R. Fuller Jr, Scripta Metall. Mater important in evaluating cyclic properties of If it occurs abrasion can decrease the interfacial fric [28] T.J. Mackin, P D. Warren, A.G. Evans, Acta Metall. 40(1992) 1251 tional stress and affect the interfacial properties of [29) P D Jero,RJ Kerans, T.A. Parthasarathy, J. Am. Cer. Soc. 7 CMCS. a judicious selection of material systems and (11)(1991)2793 processing can control the interfacial roughness and 30] T.J. Mackin, J. Yang, P D. Warren, J Am. Cer. Soc. 756(12)(1992) thermal stresses that can be utilized in developing tough CMCs B1]TA Parthasarathy, R. Kerans, J. Am. Cer. Soc. 80( 8)(1992) 32 H P. Wang, T.J. Nelson, C L Lim, w.w. Gerberch, J Mater Res 9(2)(1994)498 Acknowledgements 3]P D Jero, T.A. Parthasarathy, Interface properties: their ment with fiber pushout tests. in: R. Naslain(Ed. ) High This work was done at New Mexico Tech. Socorro NM and supported by the US Office of Naval Research [34] B.F. Sorensen, Scripta Metall. Mater. 28(1993)435 (contract no. N00014-89-J-1459). The author would like 35KK. Chawla, Z.R. Xu, A. Hlinak, Y.w. Chung Characteristics to thank Dr K.K. Chawla for his support. Thanks are of three alumina fibers by atomic force opy, in: N P Bansal also due to Dr S. Balsone of Wright-Patterson Air (Ed ) Advances in Ceramic Matrix Composites, Ceramic Trans- actions, vol 38, American Ceramic Society, Columbus, OH, 1993 Force Base and Drs a.h. muir. Jr.. and j. porter of the54 R. Venkatesh Venkatesh / Materials Science and Engineering A Materials Science and Engineering A268 (1999) 47–54 268 (1999) 47–54 Evaluating A/r and the residual thermal strain, DaDT at the PRD-166/SnO2 and Saphikon/SnO2 interfaces, (Fig. 10a,b) and using Eq. (4), it was observed that the A/r value of PRD-166/SnO2 interface was about nine times that of the Saphikon/SnO2 interface, (Table 7). It was also found that, in PRD-166/SnO2/glass matrix composites, the compressive radial strain induced due to fiber roughness was about 20 times greater than the tensile thermal radial strain. In Saphikon/SnO2/glass matrix composites, the roughness induced compressive strain was only three times greater than the tensile thermal strain. This indicates the strong mechanical clamping due to fiber roughness at the fiber/SnO2 inter￾face in ASG composites. As fiber roughness increased, increased shear stress transfer at the interface beyond matrix cracking from fiber to matrix causes a reduction in the debond length, i.e. fibers broke rather than debonded as the matrix crack grew, resulting in a composite fracture surface in ASG with little or no fiber pullout on the fracture surface. Similar results have been obtained by Chawla et al. using atomic force microscopy [35]. 4. Conclusion It has now been realized that fiber surface roughness and residual stresses in the composite after processing play a very important role in governing the strength and toughness of CMCs. As shown in the present work, composites with tensile radial stress at the interface and very rough fiber surface exhibit very small debond length and fail in a brittle manner. Alternatively in composites with tensile radial stress at the interface and very smooth interface, the fiber/matrix bonding may be weak enough to compromise the strength of the composite. Another important effect of fiber roughness is abra￾sion at the fiber/matrix interface. Abrasion is especially important in evaluating cyclic properties of composites. If it occurs, abrasion can decrease the interfacial fric￾tional stress and affect the interfacial properties of CMCs. A judicious selection of material systems and processing can control the interfacial roughness and thermal stresses that can be utilized in developing tough CMCs. Acknowledgements This work was done at New Mexico Tech, Socorro, NM and supported by the US Office of Naval Research (contract no. N00014-89-J-1459). The author would like to thank Dr K.K. Chawla for his support. Thanks are also due to Dr S. Balsone of Wright-Patterson Air Force Base and Drs A.H. Muir, Jr., and J. Porter of the Rockwell Science Center for providing the Saphikon fibers. References [1] K.K. Chawla, Ceramic Matrix Composites, Chapman & Hall, London, 1993. [2] R.W. Rice, Ceramic matrix composite toughening mechanisms: An update, in: Ceramic Science and Engineering Series, Vol. 6, American Ceramic Society, Columbus, OH, p. 589. [3] A.G. Evans, J. Am. Cer. Soc. 73 (1990) 187. [4] W.B. Hillig, Annu. Rev. Mater. Sci. 17 (1987) 341. [5] D.B. Marshall, J.E. Ritter, Cer. Bull. 66 (1987) 309. [6] K.K. Chawla, Z.R. Xu, R. Venkatesh, J.S. Ha, Interface Engineer￾ing in some oxide/oxide composites, in: 9th International Confer￾ence on Composites (ICCM-9), July 12, 1993, Madrid, Spain. [7] P.E.D. Morgan, D.B. Marshall, J. Am. Cer. Soc. 78 (6) (1995) 1553. [8] A. Maheshwari, K.K. Chawla, T.A. Michalske, Mater. Sci. Eng. A107 (1989) 269. [9] M. Cinibulk, Cer. Eng. Sci. Proc. 15 (5) (1995) 721. [10] M. Cinibulk, Cer. Eng. Sci. Proc. 16(5) (1995). [11] K.K. Chawla, A. Choudhary, R. Venkatesh, J.R. Hellmann, Mater. Char. 31 (3) (1993) 167. [12] P.E.D. Morgan, R.M. Housley, J. Am. Cer. Soc. 789 (1) (1995) 263. [13] J.C. Romine, Cer. Eng. Sci. Proc. 8 (1987) 755. [14] Data Sheet, Saphikon, NH. [15] K.M. Prewo, J.J. Brennan, G.K. Layden, Am Cer. Soc. Bull. 65 (1980) 305. [16] J.I. Bluhm, Eng. Fracture Mech. 9 (1975) 593. [17] Wu Shang-Xian, Eng. Fracture Mech. 19 (1984) 221. [18] S.N. Patankar, R. Venkatesh, K.K. Chawla, Scripta Metall. Mater. 25 (1991) 361. [19] J. Cook, J.E. Gordon, Proc. R. Soc. Lond. A282 (1964) 508. [20] A.G. Evans, M.Y. Ye, J.W. Hutchinson, J. Am. Cer. Soc. 72 (1989) 2300. [21] C.C. Wu, S.W. Freiman, R.W. Rice, J.J. Mecholsky, J. Mater. Sci. 13 (1978) 2659. [22] R. Venkatesh, K.K. Chawla, J. Mater. Sci. Lett. 11 (1992) 650. [23] T.A. Michalske, J.R. Hellmann, J. Am. Cer. Soc. 71 (1998) 725. [24] K.K. Chawla, M. Ferber, Z.R. Xu, R. Venkatesh, Mater. Sci. Eng. A162 (1993) 35. [25] P.D. Jero, R.J. Kerans, Scripta Metall. Mater. 24 (1991) 2315. [26] R.J. Kerans, T.A. Parthasarathy, J. Am. Cer. Soc. 74 (1991) 1585. [27] W.C. Carter, E.P. Butler, E.R. Fuller Jr., Scripta Metall. Mater. 25 (1991) 579. [28] T.J. Mackin, P.D. Warren, A.G. Evans, Acta. Metall. 40 (1992) 1251. [29] P.D. Jero, R.J. Kerans, T.A. Parthasarathy, J. Am. Cer. Soc. 74 (11) (1991) 2793. [30] T.J. Mackin, J. Yang, P.D. Warren, J. Am. Cer. Soc. 756 (12) (1992) 3358. [31] T.A. Parthasarathy, R.J. Kerans, J. Am. Cer. Soc. 80 (8) (1992) 2043. [32] H.P. Wang, T.J. Nelson, C.L. Lim, W.W. Gerberch, J. Mater. Res. 9 (2) (1994) 498. [33] P.D. Jero, T.A. Parthasarathy, Interface properties: their measure￾ment with fiber pushout tests, in: R. Naslain (Ed.), High Temper￾ature Ceramic Matrix Composites, Goodhead, Cambridge, 1993, p. 401. [34] B.F. Sorensen, Scripta Metall. Mater. 28 (1993) 435. [35] K.K. Chawla, Z.R. Xu, A. Hlinak, Y.W. Chung, Characteristics of three alumina fibers by atomic force microscopy, in: N.P. Bansal (Ed.), Advances in Ceramic Matrix Composites, Ceramic Trans￾actions, vol. 38, American Ceramic Society, Columbus, OH, 1993, p. 725