Materials Science and Engineering A 497(2008)235-238 Contents lists available at science direct Materials Science and Engineering A ELSEVIER urnalhomepagewww.elsevier.com/locate/msea Effect of thermal cycling on modulus and tensile strength of 3D needled C/Sic composite in controlled environments Jingjiang Nie, Yongdong Xu*, Junqiang Ma, Litong Zhang, Laifei Cheng, Xiaowei Yin National Key Laboratory of Thermostructure Composite Materials, Northwestem Polytechnical University, Xi'an 710072, China ARTICLE INFO A BSTRACT A needled C/SiC composite was subjected to thermal cycling with a temperature interval om700 to 1200 C, in a pure Ar gas and a simulated air atmosphere. The change of the resonant Received in revised form 1 July 2008 Accepted 7 August 2008 used to determine the reduction in the modulus of the composite Results show that the decreased with increasing thermal cycles. And after thermal cycled in pure Ar and simulated air for 90 cles, the residual tensile strengths were reduced by 46. 2% and 66.5%, being caused by thermo-mismatch Keywords and combining effects of thermo-mismatch and oxidation, respectively O 2008 Elsevier B V. All rights reserved. Resonant frequency 1. Introduction form has been widely applied to fabricate C/sic composite of re-entry vehicles, rocket engine components, advanced braking Carbon fiber reinforced silicon carbide(C/SiC)composites are system, etc. [1-3, 12-14. considered as one of the most potential thermal structural mate In most thermo-structural applications, Sic-matrix compos- rials[1-3. In last decades, a lots of efforts have been achieved ites are subjected to thermal cycling and exposed to oxidizing the development and application of the 2D laminated [4-6. 2.5D atmospheres at elevated temperatures. The thermal cycling or [7-9]and multi-D [10-12](3D, 4D, etc. ) braided C/SiC composites. thermo-oxidation may severely degrade the stiffness and strength in plane but are susceptible to delamination. 2. 5D and multi-D fore, the monitoring of their damage during use is desirable so as composites exhibited improved isotropy, good delamination resis- to provide remedies or changes in service conditions before catas- tance and thick part manufacturing capability, but have a complex trophic failure takes place but those damages especially reduction fabrication process with high cost and are not suited for produ in modulus cannot be observed directly. Fortunately, the changes ing complex parts combining both thick and thin areas [3. 12. To in modulus can be determined by monitoring the changes in modal improve the interlaminar properties, save cost and combine the frequencies [15-17. Srivastava et al. [16]reported that the changes advantages of 2D and multi-D preform types, a novel needled pre- in flexural modulus can be determined by measuring the flexural form, Novoltex, with fibers reinforced in the thickness direction resonant frequency The modulus(e) has a fixed relationship with was developed by SEP (Societe Europeenne de Propulsion, now resonant frequency () as the following equation [17] named as Snecma) at the end of 1970s [ 3, 12]. which was pro- luced from woven fabrics and non-woven webs made of carbon E=0.9465x10-(6)(B)/T eedling process, a thermal treatment was used to convert the car- where L, h and b are the specimen dimensions of length, thick- bon precursor to carbon fibers. To avoid thermal shrinkage during ness and width, M is the specimen mass and t is a correction the thermal treatment, carbon fibers are directly used to fabricate factor. Although lots of efforts on thermal cycling behavior of C/ Sic preforms by needling technique. Now, this needled carbon pre- composites have been carried out, the effect of thermal cycling in oxidizing environment on the modulus and tensile strength is still lack of c In this work, a needled C/SiC composite fabricated by chemi- 4619;fax:+862988494620. cal vapor infiltration(Cvi) was subjected to thermal( E-mail address: ydxu07epgmailco temperature interval ranging from 700 to 1200 C, in a pure Ar gas 5093/s-see front matter o 2008 Elsevier B V. All rights reserved. 0016/msea200808009Materials Science and Engineering A 497 (2008) 235–238 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Effect of thermal cycling on modulus and tensile strength of 3D needled C/SiC composite in controlled environments Jingjiang Nie, Yongdong Xu∗, Junqiang Ma, Litong Zhang, Laifei Cheng, Xiaowei Yin National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, Xi’an 710072, China article info Article history: Received 2 April 2008 Received in revised form 1 July 2008 Accepted 7 August 2008 Keywords: CVI Needled C/SiC composites Thermal cycling Tensile Resonant frequency abstract A needled C/SiC composite was subjected to thermal cycling with a temperature interval ranging from 700 to 1200 ◦C, in a pure Ar gas and a simulated air atmosphere. The change of the resonant frequencies was used to determine the reduction in the modulus of the composite. Results show that the modulus linearly decreased with increasing thermal cycles. And after thermal cycled in pure Ar and simulated air for 90 cycles, the residual tensile strengths were reduced by 46.2% and 66.5%, being caused by thermo-mismatch and combining effects of thermo-mismatch and oxidation, respectively. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Carbon fiber reinforced silicon carbide (C/SiC) composites are considered as one of the most potential thermal structural mate￾rials [1–3]. In last decades, a lots of efforts have been achieved on the development and application of the 2D laminated [4–6], 2.5D [7–9] and multi-D [10–12] (3D, 4D, etc.) braided C/SiC composites. The traditional 2D composites have high mechanical performance in plane but are susceptible to delamination. 2.5D and multi-D composites exhibited improved isotropy, good delamination resis￾tance and thick part manufacturing capability, but have a complex fabrication process with high cost and are not suited for produc￾ing complex parts combining both thick and thin areas [3,12]. To improve the interlaminar properties, save cost and combine the advantages of 2D and multi-D preform types, a novel needled pre￾form, Novoltex®, with fibers reinforced in the thickness direction was developed by SEP (Societe Europeenne de Propulsion, now named as Snecma) at the end of 1970s [3,12], which was pro￾duced from woven fabrics and non-woven webs made of carbon precursor [12] (such as pre-oxidized polyarylonitrile fibers). After needling process, a thermal treatment was used to convert the car￾bon precursor to carbon fibers. To avoid thermal shrinkage during the thermal treatment, carbon fibers are directly used to fabricate preforms by needling technique. Now, this needled carbon pre- ∗ Corresponding author. Tel: +86 29 8849 4619; fax: +86 29 88494620. E-mail address: ydxu07@gmail.com (Y. Xu). form has been widely applied to fabricate C/SiC composites for TPS of re-entry vehicles, rocket engine components, advanced braking system, etc. [1–3,12–14]. In most thermo-structural applications, SiC–matrix compos￾ites are subjected to thermal cycling and exposed to oxidizing atmospheres at elevated temperatures. The thermal cycling or thermo-oxidation may severely degrade the stiffness and strength of composites and in some cases lead to catastrophic failure. There￾fore, the monitoring of their damage during use is desirable so as to provide remedies or changes in service conditions before catas￾trophic failure takes place, but those damages especially reduction in modulus cannot be observed directly. Fortunately, the changes in modulus can be determined by monitoring the changes in modal frequencies [15–17]. Srivastava et al. [16] reported that the changes in flexural modulus can be determined by measuring the flexural resonant frequency. The modulus (E) has a fixed relationship with resonant frequency (f) as the following equation [17]: E = 0.9465 × 10−9 L h 3 M b f 2T (1) where L, h and b are the specimen dimensions of length, thick￾ness and width, M is the specimen mass and T is a correction factor. Although lots of efforts on thermal cycling behavior of C/SiC composites have been carried out, the effect of thermal cycling in oxidizing environment on the modulus and tensile strength is still lack of comprehension. In this work, a needled C/SiC composite fabricated by chemi￾cal vapor infiltration (CVI) was subjected to thermal cycling with a temperature interval ranging from 700 to 1200 ◦C, in a pure Ar gas 0921-5093/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2008.08.009