CARBON47(2009)Io34-1042 availableatwww.sciencedirect.com .. Science Direct ELSEVIER ournalhomepagewww.elsevier.com/locate/carbon Comparison of the mechanical hysteresis of carbon/ceramic- matrix composites with different fiber preforms Hui Mei, Aifei Cheng National Key Laboratory of Thermostructure Composite Materials, School of Materials Science, Northwestem Polytechnical University, Xi'an Shaanxi 710072. PR China ARTICLEINF O ABSTRACT Article history The mechanical hysteresis of four ceramic matrix composites with different carbon fiber preforms, i.e. needled C/SiC, 2D C/SiC, 2.5D C/SiC, and 3D C/SiC, was investigated and com Accepted 8 December 2008 pared during cyclic reloading-unloading tests. An effective coefficient of the fiber volume le online 16 December 2008 fraction in the direction of loading(ECFl) was defined to characterize fiber architectures of the preforms. It is shown that an increase in permanent strain and a decrease in stiff ness with the applied stress were strongly affected by the ECFl The thermal residual stress (TRS) and ultimate tensile strength of the composites are predicted theoretically related to the ECFL, and then validated by experimental results and microstructural observations. he predicted results not only demonstrate good agreement with experimental measure- ments, but also explain why differences in the composite ECFL result in substantial varia- tions in TRS @2008 Elsevier Ltd. All rights reserved. ntroduction lowever, the mechanical hysteresis behaviors and perma nent strain of the above four representative composites were Carbon fiber reinforced silicon carbide matrix composite not yet obtained systematically and compared comprehen (C/Sic) is a type of ceramic matrix composite(CMC)that is sively related to the different fiber architectures. This is very rrently undergoing considerable investigation for applica- important issue to justify proper selections of the fiber pre tion in a wide range of aerospace applications (1, 2 The form architectures for a specified component and to optimize potential components of C/Sic mainly include thermal pro- thermo-mechanical structures for a specified engineering tection system(TPS)and hot structures such as shuttle nose, application case. For example, what fiber architecture in the wing leading edges, rocket thrusters, nozzle extensions, and composite is the best choice to fabricate a shuttle's nose aeroengine convergent/divergent flaps. All the parts are made and what fiber architecture can best withstand air dynamic of several typical fiber preform architectures: needled C/Sic, and thermal flux impact produced in this local place of the 2D C/SiC. 2. 5D C/SiC, and 3D C/Sic. overall surfaces During the last decade, theoretical methodology and In this study, the mechanical hysteresis and the experimental validity for assessing the stress-strain hyster- nent strain of several representative composites with diff sis and the permanent strain of the CMCs during unload/re- ent fiber architectures, i.e. the needled C/sic, 2D C/Sic, 2.5D load tests have been basically and widely reported [3-5], as C/SiC, and 3D C/Sic, during unload/reload cycles were com well as their significant monotonic tensile behaviors 16,7 pletely investigated and then compared systematically. and thermal residual stress(TRS)analysis due to extensive Changes in the hysteresis properties and permanent strain mismatch in coefficients of thermal expansion(CTE)[8, 9]. with increase of the applied stress were discussed with regard Corresponding author: Fax: +86 29 88494620. mailaddress:phdhuimei@yahoo.com(H.Mei) 0008-6223/$- see front matter o 2008 Elsevier Ltd. All rights reserved. do:10.1016/ j carbon200812025Comparison of the mechanical hysteresis of carbon/ceramic￾matrix composites with different fiber preforms Hui Mei* , Laifei Cheng National Key Laboratory of Thermostructure Composite Materials, School of Materials Science, Northwestern Polytechnical University, Xi’an Shaanxi 710072, PR China ARTICLE INFO Article history: Received 18 April 2008 Accepted 8 December 2008 Available online 16 December 2008 ABSTRACT The mechanical hysteresis of four ceramic matrix composites with different carbon fiber preforms, i.e. needled C/SiC, 2D C/SiC, 2.5D C/SiC, and 3D C/SiC, was investigated and com￾pared during cyclic reloading–unloading tests. An effective coefficient of the fiber volume fraction in the direction of loading (ECFL) was defined to characterize fiber architectures of the preforms. It is shown that an increase in permanent strain and a decrease in stiff￾ness with the applied stress were strongly affected by the ECFL. The thermal residual stress (TRS) and ultimate tensile strength of the composites are predicted theoretically related to the ECFL, and then validated by experimental results and microstructural observations. The predicted results not only demonstrate good agreement with experimental measure￾ments, but also explain why differences in the composite ECFL result in substantial varia￾tions in TRS. 2008 Elsevier Ltd. All rights reserved. 1. Introduction Carbon fiber reinforced silicon carbide matrix composite (C/SiC) is a type of ceramic matrix composite (CMC) that is currently undergoing considerable investigation for applica￾tion in a wide range of aerospace applications [1,2]. The potential components of C/SiC mainly include thermal pro￾tection system (TPS) and hot structures such as shuttle nose, wing leading edges, rocket thrusters, nozzle extensions, and aeroengine convergent/divergent flaps. All the parts are made of several typical fiber preform architectures: needled C/SiC, 2D C/SiC, 2.5D C/SiC, and 3D C/SiC. During the last decade, theoretical methodology and experimental validity for assessing the stress–strain hystere￾sis and the permanent strain of the CMCs during unload/re￾load tests have been basically and widely reported [3–5], as well as their significant monotonic tensile behaviors [6,7] and thermal residual stress (TRS) analysis due to extensive mismatch in coefficients of thermal expansion (CTE) [8,9]. However, the mechanical hysteresis behaviors and perma￾nent strain of the above four representative composites were not yet obtained systematically and compared comprehen￾sively related to the different fiber architectures. This is very important issue to justify proper selections of the fiber pre￾form architectures for a specified component and to optimize thermo-mechanical structures for a specified engineering application case. For example, what fiber architecture in the composite is the best choice to fabricate a shuttle’s nose and what fiber architecture can best withstand air dynamic and thermal flux impact produced in this local place of the overall surfaces. In this study, the mechanical hysteresis and the perma￾nent strain of several representative composites with differ￾ent fiber architectures, i.e. the needled C/SiC, 2D C/SiC, 2.5D C/SiC, and 3D C/SiC, during unload/reload cycles were com￾pletely investigated and then compared systematically. Changes in the hysteresis properties and permanent strain with increase of the applied stress were discussed with regard 0008-6223/$ - see front matter 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2008.12.025 * Corresponding author: Fax: +86 29 88494620. E-mail address: phdhuimei@yahoo.com (H. Mei). CARBON 47 (2009) 1034 – 1042 available at www.sc iencedirect.com journal homepage: www.elsevier.com/locate/carbon