Availableonlineatwww.sciencedirect.com SCIENCEDIRECT° COMPOSITES CIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 66(2006)993-1000 www.elsevier.com/locate/compscitech Tensile creep behavior of notched two-dimensional-C/SiC composite Wu Xiaojun, Qiao Shengru, Hou Juntao, Zhao Qing, Han Dong, Li M Box 547, Department of Materials Science and Engineering of Northwestern Polytechnical Unirersity, 710072 Xian Shaanxi, China Received 15 November 2004: received in revised form 14 August 2005: accepted 16 August 2005 ailable online 4 October 2005 Abstract Tensile creep tests of two-dimensional-C/SiC specimens with double-edge arc notches have been carried out at 1100, 1300 and 1500C vacuum. The matrix cracks on the surface and resonance frequency were examined at different creeping times. At 1100 C, the creep strains of both smooth and notched specimens were concentrated at the transient stage and the steady creep rates were nearly zer whereas steady creep rates of notched specimens and smooth specimens were similar at 1500C. It has been observed that the creep dam- age mainly concentrated at the area near the notches Micro-cracks appeared in the area near the notches and on the cross-points of the woven fiber bundles, and the longitudinal fibers near the notches fractured easily. Both types of curves, namely quantity of micro-cracks vS. time and micro-crack width vs time, were extremely similar as for the creep curves. In general, micro-cracks developed fast during the first 10 h. It has been noticed that within the first 2 h, the micro-cracks near the notches grow faster than those far from the notches, hereas the growth rate of micro-cracks far from notches was faster than those near the notches after 2 h. This phenomenon indicates the stress redistribution during creep. Damage curves at 1300 and 1500 C have similar trend, though the damage and the quantity of micro-cracks at 1500oC are higher than those at 1300oC o 2005 Elsevier Ltd. All rights reserved Keywords: 2D-C/SiC; Notch; Tensile creep: Micro-cracks; Damage 1. Introduction ites. Current work intends to study creep beh notched 2D-C/SiC composites in details The high-temperature creep performance of ID, 2D 2.5D and 3D C/SiC composites has been investigated. 2. Experiments Within the experimental temperature range(<1500C) the creep behavior of C fibers and Sic matrix is not obvi- 2.1. Materials and specimens S. The creep behavior of these composites is mainly caused by damage, such as matrix cracking, fiber fracture, Cross-woven C/SiC composites have been manufac fiber/matrix interfacial debonding, interfacial sliding, etc. tured here. PAN T-300 carbon fibers were woven into The elastic modulus of these composites decreases signifi- cross-woven carbon cloth, and then stacked into pre- cantly because of creep damage. Matrix cracking and inter- form. Each fiber bundle is composed of about 3000 car facial sliding are the main contributors to creep strain bon fibers and each fiber has a diameter of 7 um.The 14. In many applications, the composite component carbon fiber preform was first coated with a layer of unavoidably has rounded notches, but there is little knowl- pyrocarbon with the thickness of 0.2 um by chemical edge about creep behavior of notched 2D-C/SiC compos- vapor deposition (CVD), and then the Sic matrix was deposited by a chemical vapor infiltration(CVI) proces The composite contains 40 vol% fiber and 17 vol% poros- ity, the density is about 2.01 g/cm. The creep specimens ing author. Tel /fax: +02988492084. have the length of 80 mm and thickness of 3 mm, E-lmailaddresscml1072002(@163.com(w.xiaojun). shown in Fig. 1. All the specimens have double-edge 02663538/S. see front matter 2005 Elsevier Ltd. All rights reserved doi:10.1016j.compscitech.2005.08.008Tensile creep behavior of notched two-dimensional-C/SiC composite Wu Xiaojun *, Qiao Shengru, Hou Juntao, Zhao Qing, Han Dong, Li Mei Box 547, Department of Materials Science and Engineering of Northwestern Polytechnical University, 710072 Xian Shaanxi, China Received 15 November 2004; received in revised form 14 August 2005; accepted 16 August 2005 Available online 4 October 2005 Abstract Tensile creep tests of two-dimensional-C/SiC specimens with double-edge arc notches have been carried out at 1100, 1300 and 1500 C in vacuum. The matrix cracks on the surface and resonance frequency were examined at different creeping times. At 1100 C, the creep strains of both smooth and notched specimens were concentrated at the transient stage and the steady creep rates were nearly zero, whereas steady creep rates of notched specimens and smooth specimens were similar at 1500 C. It has been observed that the creep dam￾age mainly concentrated at the area near the notches. Micro-cracks appeared in the area near the notches and on the cross-points of the woven fiber bundles, and the longitudinal fibers near the notches fractured easily. Both types of curves, namely quantity of micro-cracks vs. time and micro-crack width vs. time, were extremely similar as for the creep curves. In general, micro-cracks developed fast during the first 10 h. It has been noticed that within the first 2 h, the micro-cracks near the notches grow faster than those far from the notches, whereas the growth rate of micro-cracks far from notches was faster than those near the notches after 2 h. This phenomenon indicates the stress redistribution during creep. Damage curves at 1300 and 1500 C have similar trend, though the damage and the quantity of micro-cracks at 1500 C are higher than those at 1300 C. 2005 Elsevier Ltd. All rights reserved. Keywords: 2D-C/SiC; Notch; Tensile creep; Micro-cracks; Damage 1. Introduction The high-temperature creep performance of 1D, 2D, 2.5D and 3D C/SiC composites has been investigated. Within the experimental temperature range (<1500 C), the creep behavior of C fibers and SiC matrix is not obvi￾ous. The creep behavior of these composites is mainly caused by damage, such as matrix cracking, fiber fracture, fiber/matrix interfacial debonding, interfacial sliding, etc. The elastic modulus of these composites decreases signifi- cantly because of creep damage. Matrix cracking and inter￾facial sliding are the main contributors to creep strain [1–4]. In many applications, the composite component unavoidably has rounded notches, but there is little knowl￾edge about creep behavior of notched 2D-C/SiC compos￾ites. Current work intends to study creep behavior of notched 2D-C/SiC composites in details. 2. Experiments 2.1. Materials and specimens Cross-woven C/SiC composites have been manufac￾tured here. PAN T-300 carbon fibers were woven into cross-woven carbon cloth, and then stacked into pre￾form. Each fiber bundle is composed of about 3000 car￾bon fibers and each fiber has a diameter of 7 lm. The carbon fiber preform was first coated with a layer of pyrocarbon with the thickness of 0.2 lm by chemical vapor deposition (CVD), and then the SiC matrix was deposited by a chemical vapor infiltration (CVI) process. The composite contains 40 vol% fiber and 17 vol% poros￾ity, the density is about 2.01 g/cm3 . The creep specimens have the length of 80 mm and thickness of 3 mm, as shown in Fig. 1. All the specimens have double-edge 0266-3538/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2005.08.008 * Corresponding author. Tel./fax: +02988492084. E-mail address: cm11072002@163.com (W. Xiaojun). www.elsevier.com/locate/compscitech Composites Science and Technology 66 (2006) 993–1000 COMPOSITES SCIENCE AND TECHNOLOGY