COMPOSITES SCIENCE AND TECHNOLOGY ELSEⅤIER Composites Science and Technology 62(2002)499-504 www.elsevier.com/locate/compscitech Thermomechanical properties of carbon fibres at high temperatures(up to 2000C) Cedric Sauder Jacques Lamon *, Rene paille Laboratoire des Composites Thermostructuraux, UMR 580/(CNRS-SNECMA-CEA-Universite Bordeaux 1) 3 allee de la boetie, 33600 Pessac. france Received 17 November 2000: accepted 19 July 2001 Abstract A high-temperature fibre-testing apparatus has been designed. It is dedicated to the determination of various properties at very high temperatures, including electrical conductivity, Youngs modulus, thermal expansion coeficient, strength. Test temperatures as high as 3000C can be applied to carbon fibres. two types of carbon fibres(a PAN-based and a Rayon-based fibre)have been investigated at temperatures up to 2000C. The measured properties are discussed with respect to microstructural features. C 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibres: B. High-temperature properties; B. Thermomechanical properties: Electrical conductivity 1. ntroduction 2. Experimental procedure Carbon fibres represent a large part of the materials The available methods for fibre testing at high tem- ed in aeronautics and aerospace structures, and in the peratures exhibit various limitations. Two methods are reinforcement of composites(C/ brakes, etc. ) They essentially used: in the hot-grip technique, the whole of display a very wide range of thermal, electric and the fibre is exposed to a uniform temperature, whereas in mechanical properties: elastic moduli vary between 30 the cold grip technique only a short part of the fibre is at and 900 GPa, strength can be as high as 6 GPa the test temperature. Youngs modulus and strength data Reliable and accurate data for the mechanical prop-(tensile strength, oR, and statistical parameters) can be erties of carbon fibres and matrices are a prerequisite for measured by using the hot-grip method. The main lim the development of valid models of thermomechanical itation of this method lies in gripping. The use of a cera- behaviour of C/C composites that are based on micro- mic glue excludes tests at temperatures above 1500C mechanics and constituent properties. Very few data are The cold-grip method [3] exhibits several short com available in the literature for the properties of carbon ings. As a result of the presence of a large thermal gra- fibres and matrices at high temperatures [1, 2 dient along fibre, determination of true strain is Mechanical tests on fibres with diameter <7 um or uncertain. Moreover, the method of correcting fibre microcomposites with a diameter A30 um are very dif- elongation measurements is complex and inaccurate, so ficult. Difficulties are enhanced under high-temperature that results are obtained with a large uncertainty. Fur dition herme specimens are required (le The present paper proposes an experimental approach than 10 cm), experimental difficulties are enhanced for measuring the thermomechanical properties of car- bon fibres at temperatures up to 3000C. Temperature 2. Experimental device dependence of properties observed on two types of car bon fibres are discussed with respect to microstructure It is for all of the above reasons that a new for tensile tests at high temperatures was Novelty can be found in the technique of specimen heat sauder@ lcts. -bordeaux.fr (C. Sauder), ing, which takes advantage of the electric conductivity of lamon(@Icts. ul-bordeaux fr (J. Lamon), paler( @Icts. ul-bordeaux fr carbon fibres. An electric current is applied to the fibre. which allows temperature as high as 3000c to be 0266-3538/02/S. see front matter C 2002 Elsevier Science Ltd. All rights reserved. PII:S0266-3538(01)00140-3Thermomechanical properties of carbon fibres at high temperatures (up to 2000
C) Ce´dric Sauder, Jacques Lamon*, Rene´ Pailler Laboratoire des Composites Thermostructuraux, UMR 5801 (CNRS-SNECMA-CEA-Universite´ Bordeaux I), 3 alle´e de La Boe´tie, 33600 Pessac, France Received 17 November 2000; accepted 19 July 2001 Abstract A high-temperature fibre-testing apparatus has been designed. It is dedicated to the determination of various properties at very high temperatures, including electrical conductivity, Young’s modulus, thermal expansion coefficient, strength. Test temperatures as high as 3000
C can be applied to carbon fibres. Two types of carbon fibres (a PAN-based and a Rayon-based fibre) have been investigated at temperatures up to 2000
C. The measured properties are discussed with respect to microstructural features. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon fibres; B. High-temperature properties; B. Thermomechanical properties; Electrical conductivity 1. Introduction Carbon fibres represent a large part of the materials used in aeronautics and aerospace structures, and in the reinforcement of composites (C/C brakes, etc.) They display a very wide range of thermal, electric and mechanical properties: elastic moduli vary between 30 and 900 GPa, strength can be as high as 6 GPa. Reliable and accurate data for the mechanical prop￾erties of carbon fibres and matrices are a prerequisite for the development of valid models of thermomechanical behaviour of C/C composites that are based on micro￾mechanics and constituent properties. Very few data are available in the literature for the properties of carbon fibres and matrices at high temperatures [1,2]. Mechanical tests on fibres with diameter 47 mm or microcomposites with a diameter 30 mm are very dif- ficult. Difficulties are enhanced under high-temperature conditions. The present paper proposes an experimental approach for measuring the thermomechanical properties of car￾bon fibres at temperatures up to 3000
C. Temperature dependence of properties observed on two types of car￾bon fibres are discussed with respect to microstructure. 2. Experimental procedure The available methods for fibre testing at high tem￾peratures exhibit various limitations. Two methods are essentially used: in the hot-grip technique, the whole of the fibre is exposed to a uniform temperature, whereas in the cold grip technique only a short part of the fibre is at the test temperature. Young’s modulus and strength data (tensile strength,
R, and statistical parameters) can be measured by using the hot-grip method. The main lim￾itation of this method lies in gripping. The use of a cera￾mic glue excludes tests at temperatures above 1500
C. The cold-grip method [3] exhibits several short com￾ings. As a result of the presence of a large thermal gra￾dient along fibre, determination of true strain is uncertain. Moreover, the method of correcting fibre elongation measurements is complex and inaccurate, so that results are obtained with a large uncertainty. Fur￾thermore, since long specimens are required (longer than 10 cm), experimental difficulties are enhanced. 2.1. Experimental device It is for all of the above reasons that a new apparatus for tensile tests at high temperatures was designed. Novelty can be found in the technique of specimen heat￾ing, which takes advantage of the electric conductivity of carbon fibres. An electric current is applied to the fibre, which allows temperature as high as 3000
C to be 0266-3538/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0266-3538(01)00140-3 Composites Science and Technology 62 (2002) 499–504 www.elsevier.com/locate/compscitech *Corresponding author. E-mail addresses: sauder@lcts.u-bordeaux.fr (C. Sauder), lamon@lcts.u-bordeaux.fr (J. Lamon), pailer@lcts.u-bordeaux.fr (R. Pailler).