Availableonlineatwww.sciencedirect.com BCIENCEODIRECT@ COMPOSITES SCIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 64(2004)1311-1319 Stress-dependent matrix cracking in 2D woven SiC-fiber reinforced melt-infiltrated SiC matrix composites Ohio Aerospace Institute, Brookpark, OH, US.A Received 24 February 2003: received in revised form 23 October 2003: accepted 23 October 2003 Available online 23 December 2003 Abstract The matrix cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the two-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated(CVn) with BN, CVI with Sic, slurry infiltrated with Sic particles followed by molten infil- tration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the effective-size of the tows. his resulted in composites with a fiber volume fraction in the load-bearing direction that ranged from 0. 12 to 0. 20. Matrix cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of matrix cracks. It was found that the general matrix crack properties of this system could be fairly well characterized by assuming that no matrix cracks orig- inated in the load-bearing fiber, interphase, chemical vapor infiltrated SiC tow-minicomposites, i.e., all matrix cracks originate in the 90 tow regions or the large unreinforced SiC-Si matrix regions. Also, it was determined that the higher fiber-count tow composites had a much narrower stress range for matrix cracking compared to the standard tow size composites. c 2003 Elsevier Ltd. All Keywords: A Ceramic matrix composites: Stress-strain behavior: B Matrix cracking: D. Acoustic 1. Introduction since matrix cracking results in the desired stress-strain non-linearity, composite toughness, and strength prop- Sic-fiber reinforced, melt-infiltrated(MI) SiC matrix erties [3]. For non-oxide composites, such as the Sic/Sic omposites are leading candidate materials for aircraft system, the presence of matrix cracks enables oxidizing and land-based turbine engine applications such as a environments to diffuse into the interior of the composite combustor liner [1, 2]. However, for such materials to be and cause strength-degradation, especially at intermedi sed, the stress-strain behavior of these materials needs ate temperatures [4, 5]. In addition, for some BN inter to be well characterized for composites with a wide range phase composites, the degree of strength-degradation at of physical characteristics, e.g., thickness, fiber archi- intermediate temperatures is related to the number of tecture, fiber volume fraction, etc. since composite matrix cracks [6]. Therefore, it is essential that a good structures are not necessarily simple shapes but consist of understanding of the stress-dependent matrix crack thickness changes, curvature, and attachment schemes properties of a viable composite system be well-charac depending on the need of the component. In order to terized. For example, this has been done to a large extent nodel the stress-response of these materials a good un- for the Nicalon,C infil- derstanding of their matrix crack properties are required trated(CVI) Sic matrix system [7-101 a considerable amount of has occurred for the Sic fiber-reinforced. bn inter- NASA Glenn Research Center, Ohio Space phase, MI matrix system [11-13]. This development has MS-106-5. Cleveland, OH 44135 USA. Tel: included studying different fiber-types, interphases, and +1216-433-5544. gory. n. morscher(@grc. nasa. gov (G.N. Mor- Nippon Carbon Co., Tokyo, Japa 0266-3538/S- see front matter 2003 Elsevier Ltd. All rights reserved. doi: 10. 1016/j. compscitech 2003 10.02Stress-dependent matrix cracking in 2D woven SiC-fiber reinforced melt-infiltrated SiC matrix composites Gregory N. Morscher * Ohio Aerospace Institute, Brookpark, OH, USA Received 24 February 2003; received in revised form 23 October 2003; accepted 23 October 2003 Available online 23 December 2003 Abstract The matrix cracking of a variety of SiC/SiC composites has been characterized for a wide range of constituent variation. These composites were fabricated by the two-dimensional lay-up of 0/90 five-harness satin fabric consisting of Sylramic fiber tows that were then chemical vapor infiltrated (CVI) with BN, CVI with SiC, slurry infiltrated with SiC particles followed by molten infil￾tration of Si. The composites varied in number of plies, the number of tows per length, thickness, and the effective-size of the tows. This resulted in composites with a fiber volume fraction in the load-bearing direction that ranged from 0.12 to 0.20. Matrix cracking was monitored with modal acoustic emission in order to estimate the stress-dependent distribution of matrix cracks. It was found that the general matrix crack properties of this system could be fairly well characterized by assuming that no matrix cracks orig￾inated in the load-bearing fiber, interphase, chemical vapor infiltrated SiC tow-minicomposites, i.e., all matrix cracks originate in the 90
tow regions or the large unreinforced SiC–Si matrix regions. Also, it was determined that the higher fiber-count tow composites had a much narrower stress range for matrix cracking compared to the standard tow size composites. 2003 Elsevier Ltd. All rights reserved. Keywords: A. Ceramic matrix composites; Stress–strain behavior; B. Matrix cracking; D. Acoustic emission 1. Introduction SiC-fiber reinforced, melt-infiltrated (MI) SiC matrix composites are leading candidate materials for aircraft and land-based turbine engine applications such as a combustor liner [1,2]. However, for such materials to be used, the stress–strain behavior of these materials needs to be well characterized for composites with a wide range of physical characteristics, e.g., thickness, fiber archi￾tecture, fiber volume fraction, etc. since composite structures are not necessarily simple shapes but consist of thickness changes, curvature, and attachment schemes depending on the need of the component. In order to model the stress-response of these materials a good un￾derstanding of their matrix crack properties are required since matrix cracking results in the desired stress–strain non-linearity, composite toughness, and strength prop￾erties [3]. For non-oxide composites, such as the SiC/SiC system, the presence of matrix cracks enables oxidizing environments to diffuse into the interior of the composite and cause strength-degradation, especially at intermedi￾ate temperatures [4,5]. In addition, for some BN inter￾phase composites, the degree of strength-degradation at intermediate temperatures is related to the number of matrix cracks [6]. Therefore, it is essential that a good understanding of the stress-dependent matrix crack properties of a viable composite system be well-charac￾terized. For example, this has been done to a large extent for the NicalonTM, 1 C interphase, chemical vapor infil￾trated (CVI) SiC matrix system [7–10]. A considerable amount of composite development has occurred for the SiC fiber-reinforced, BN inter￾phase, MI matrix system [11–13]. This development has included studying different fiber-types, interphases, and * Present address: NASA Glenn Research Center, Ohio Space Institute, Lewis Field, MS-106-5, Cleveland, OH 44135, USA. Tel.: +1-216-433-5512; fax: +1-216-433-5544. E-mail address: gregory.n.morscher@grc.nasa.gov (G.N. Mor￾scher). 1 Nippon Carbon Co., Tokyo, Japan. 0266-3538/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2003.10.022 Composites Science and Technology 64 (2004) 1311–1319 www.elsevier.com/locate/compscitech COMPOSITES SCIENCE AND TECHNOLOGY