E噩≈S Journal of the European Ceramic Society 22(2002)2349-2356 www.elsevier.com/locate/jeurc Tensile fracture behavior of continuous sic fiber-reinforced SiC matrix composites at elevated temperatures and correlation to in Situ constituent properties Shuqi guo*,, Yutaka Kagawa Institute of Industrial Science, The University of Tokyo, 7-22-1, Roppongi, Minato-ku, Tokyo 106-8558, Japan Received 21 March 2001; received in revised form 20 December 2001: accepted 6 January 2002 Abstract The tensile fracture behavior and tensile mechanical properties of polymer infiltration pyrolysis(PIP)-processed two-dimensional plain-woven fabric carbon-coated NicalonM SiC fiber and BN-coated Hi-Nicalon"M SiC fiber-reinforced SiC matrix composites have been investigated. Tensile testing of the composites was carried out in air between 298 and 1400 K. In situ fiber strength and interface shear stress were determined by fracture mirror size and pulled-out fiber length measurements. For the Nicalon/C/Sic. tensile strength remained nearly constant up to 800 K, and while the strength dropped from 140 MPa at 800 K to 41 MPa at 1200 K, with weakest link failure mode. For the Hi-Nicalon/BN/SiC, the tensile strength increased slightly with increase in test tem- perature up to 1200 K; however, a large decrease in the strength was observed at 1400 K. In the case of the Hi-Nicalon/BN/ SiC, the fracture was governed by fiber bundle strength. The temperature dependence of tensile strength and fracture behavior of both omposites was attributed to change of the in situ constituent properties with temperature. C 2002 Elsevier Science Ltd. All rights Keywords: Composites; Fiber strength; Interface shear stress; Mechanical properties; Polymer infiltration pyrolysis; SiC/ SiC 1. Introduction The damage evolution of the composites usually includes two fundamental regimes: (i)at lower stresses Continuous fiber-reinforced ceramic matrix compo- matrix cracking originating from defects in the matrix sites(CFCCs) have become an important class of and followed by interface debonding between the fiber materials for structural applications at elevated tem- and matrix, and (ii) at higher stresses, occurrence of peratures because of their improved flaw tolerance, fiber damage and ultimate failure.6. 7 If matrix cracking large fracture resistance, and noncatastrophic mode of can reach the fully-saturated state prior to composite failure comparing with monolithic ceramic materials. failure, the subsequent deformation and failure are Among CFCCs, SiC fiber-reinforced SiC matrix com- dominated entirely by the fiber flaw population, show- posites have been studied extensively in recent years ing a noncatastrophic failure. 6, 7 However, if the fibers because the Sic fiber shows a potential for applications are sufficiently weak and interface bonding compara- at elevated temperatures. These studies demonstrated tively strong due to interface reaction in an oxidizing that the tensile mechanical behavior and properties of environment at high temperatures, composite failure is the composites strongly depend on the in situ fiber also possible in the regime of matrix cracking, showing strength characteristics, interface properties and matrix a catastrophic fracture similar to the fracture of a cracking stress, as well as the fabrication processes. I-5 monolithic ceramic 8,9 The transition from non- catastrophic to catastrophic fracture depends on in situ constituent properties. Thus, it is important to under 81-0298-51-3613. stand this transition to clarify tensile fracture behavior go. jp(S. Guo). of the composites and to allow correlation with the in Materials Science. I-I Namiki. Tsukuba situ constituent properties. In situ constituent properties of the composites such as fiber strength, interface shear 0955-2219/02/S. see front matter C 2002 Elsevier Science Ltd. All rights reserved. PII:S0955-2219(02)00028-6Tensile fracture behavior of continuous SiC fiber-reinforced SiC matrix composites at elevated temperatures and correlation to in situ constituent properties Shuqi Guo*,1, Yutaka Kagawa Institute of Industrial Science, The University of Tokyo, 7-22-1, Roppongi, Minato-ku, Tokyo 106-8558, Japan Received 21 March 2001; received in revised form 20 December 2001; accepted 6 January 2002 Abstract The tensile fracture behavior and tensile mechanical properties of polymer infiltration pyrolysis (PIP)-processed two-dimensional plain-woven fabric carbon-coated NicalonTM SiC fiber and BN-coated Hi-NicalonTM SiC fiber-reinforced SiC matrix composites have been investigated. Tensile testing of the composites was carried out in air between 298 and 1400 K. In situ fiber strength and interface shear stress were determined by fracture mirror size and pulled-out fiber length measurements. For the Nicalon/C/SiC, tensile strength remained nearly constant up to 800 K, and while the strength dropped from 140 MPa at 800 K to 41 MPa at 1200 K, with weakest link failure mode. For the Hi-Nicalon/BN/SiC, the tensile strength increased slightly with increase in test tem￾perature up to 1200 K; however, a large decrease in the strength was observed at 1400 K. In the case of the Hi-Nicalon/BN/SiC, the fracture was governed by fiber bundle strength. The temperature dependence of tensile strength and fracture behavior of both composites was attributed to change of the in situ constituent properties with temperature. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Composites; Fiber strength; Interface shear stress; Mechanical properties; Polymer infiltration pyrolysis; SiC/SiC 1. Introduction Continuous fiber-reinforced ceramic matrix compo￾sites (CFCCs) have become an important class of materials for structural applications at elevated tem￾peratures because of their improved flaw tolerance, large fracture resistance, and noncatastrophic mode of failure comparing with monolithic ceramic materials. Among CFCCs, SiC fiber-reinforced SiC matrix com￾posites have been studied extensively in recent years because the SiC fiber shows a potential for applications at elevated temperatures. These studies demonstrated that the tensile mechanical behavior and properties of the composites strongly depend on the in situ fiber strength characteristics, interface properties and matrix cracking stress, as well as the fabrication processes.1
5 The damage evolution of the composites usually includes two fundamental regimes: (i) at lower stresses, matrix cracking originating from defects in the matrix and followed by interface debonding between the fiber and matrix, and (ii) at higher stresses, occurrence of fiber damage and ultimate failure.6,7 If matrix cracking can reach the fully-saturated state prior to composite failure, the subsequent deformation and failure are dominated entirely by the fiber flaw population, show￾ing a noncatastrophic failure.6,7 However, if the fibers are sufficiently weak and interface bonding compara￾tively strong due to interface reaction in an oxidizing environment at high temperatures, composite failure is also possible in the regime of matrix cracking, showing a catastrophic fracture similar to the fracture of a monolithic ceramic.8,9 The transition from non￾catastrophic to catastrophic fracture depends on in situ constituent properties. Thus, it is important to under￾stand this transition to clarify tensile fracture behavior of the composites and to allow correlation with the in situ constituent properties. In situ constituent properties of the composites such as fiber strength, interface shear 0955-2219/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(02)00028-6 Journal of the European Ceramic Society 22 (2002) 2349–2356 www.elsevier.com/locate/jeurceramsoc * Corresponding author. Fax: +81-0298-51-3613. E-mail address: guo.shuqi@nims.go.jp (S. Guo). 1 National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan