(1998 Published by Elsevier Science Ltd. All rights reserve PII:s0266·3538(97)00150-4 66-353898s1900 MECHANICAL BEHAVIOR AND DAMAGE DEVELOPMENT DURING CYCLIC FATIGUE AT HIGH-TEMPERATURE OF A 2.5D CARBON/SIC COMPOSITE A Almaz,P. Reynaud, D. Rouby, G. Fantozzi& F Abbe ' Groupe d' Etudes de metallurgie Physique ue et de physique des materiaux, UMR CNRS 5510, Institut National des sciences appliquees, 20 av. A. Einstein, 69 62/ Villeurbanne, france h Societe Europeenne de Propulsion, Propulsion d Poudre et Composites. Les Cing Chemins, Le hailan 33 165 St-Medard-en-Jalles Cedex, france Received 29 October 1996; accepted 24 July 1997) Abstract and 2D C/SiC composites. These studies describe the This article describes part of a project to investigate mechanical behavior of these materials (non-linear high-temperature fatigue behavior of a 2. 5D C/SiC mul- behavior under tension, fracture stress independent of bilayer composite. This material is particularly interesting temperature, life- independent of frequency) the origin ince it has been found that damage exists in the as-sup- and mechanisms leading to damage development and plied material owing to the residual stresses produced fracture of the 2.SD C/SiC composite is still poorly understood describes the effect of the number of cycles and the tem- The aim of this work is to describe the damage perature on the composite, and attempts to explain the mechanism for a 2. 5D C/SiC composite, and thus define behavior during testing. The parameters controlling the mechanical laws controlling fracture and cyclic damage development and therefore fatigue life, are fatigue at various temperatures. Moreover, since this believed to be both thermal constraint in the composite, composite contains cracks from processing, it is impor- nd the damage produced. The nature of the damage is tant to determine their effect on fatigue behavior. such thut the material is best considered in lerms Hence, the change in mechanical behavior in relation to damage occuring on the scale of the yarns, rather than at the number of the cycles and the temperature are the smaller fiber level. C 1998 Published by Elsevier described in this paper, and the specific rk of Science Ltd. All rights reserved cracks developed under such loading is identified Keywords: A ceramic-matrix composite, B fatigue, B interface, high-temperature, damage 2 EXPERIMENTAL PROCEDURE 2.1 Material 1 INTRODUCTION Tests were conducted on a long-carbon-fiber silicon- carbide matrix 2, 5D C/SiC composite provided by the This study has concentrated on a multilayer long-fiber- Societe Europeenne de Propulsion (SEP, Bordeaux reinforced ceramic-matrix composite of carbon fibers in France). This composite is composed of cloth made a silicon carbide matrix (2. 5D C/SiC), supplied by the from long woven yarns(see Fig. 7). The preform is Societe Europeenne de Propulsion. This thermo- infiltrated by a pyrocarbon interlayer in order to opti structural composite is intended for use at high-tem- mize the fiber /matrix shear lag, and induce a non-brittle perature under substantial mechanical loads. Hence, it mechanical macroscopi n-ca is important to understand the cyclic fatigue behavior of matrix is deposited by chemical vapor infiltration this material at high-temperature and to study the effect (C.v. I.). The as-received composite exhibits a porosity of environment level below 10% and a density of 2200 kg m . The Previous studies of the tensile mechanical behavior characteristic of this composite is that matrix cracks are under cyclic fatigue at high-temperature have con- created during cooling just after processing, owing to centrated on composites similar, but not identical, the high tensile thermal residual stresses the 2.5D C/SiC. For example the work of Arendts'ane Camus2 on the characterization of the tensile mechan 2.2 Mechanical tests ical behavior at high-temperature of a 2D C/SiC and the The aim of this work is to determine the characteristics ork of Shuler and Iee on cyclic fatigue of [C/SiClo of the 2. 5D C/SiC composite under cyclic tensile/tensileLLSEVIER Compo.srres Suence and Twhno1og.v 58 (1998) 693 699 P‘s 1998 Published by Elsevier Saence Ltd. All rights reserved Printed in Great Britam PII: SO266-3538(97)00150-4 0266.3538:98 $19.00 MECHANICAL BEHAVIOR AND DAMAGE DEVELOPMENT DURING CYCLIC FATIGUE AT HIGH-TEMPERATURE OF A 23D CARBON/Sic COMPOSITE A. Dalmaz,a P. Reynaud,a D. Rouby,” G. Fantozzia & F. Abbeh “Groupe d’Etudes de MCtallurgie Physique et de Physique des Mathiaux, UMR CNRS 5510, Institut National des Sciences AppliquPes, 20 av. A. Einstein, 69 621 Villeurhanne, France hSoeiPtP EuropPenne de Propulsion, Propulsion d Poudre et Composites, Les Cinq Chemins, Le HailIan, 33 165 St-Mhdard-en-Jalles Cedex, France (Received 29 October 1996: accepted 24 July 1997) Abstract This article describes part of a project to investigate the high-temperature fatigue behavior of a 2.50 C/Sic mul￾tilayer composite. This material is particularly interesting since it has been,found that damage exists in the as-sup￾plied material owing to the residual stresses produced during cooling of the composite. This section of work describes the t$ect of the number of cycles and the tem￾perature on the composite, and attempts to explain the behavior during testing. The parameters controlling damage development and therefore fatigue life, are believed to be both thermal constraint in the composite, and the damage produced. The nature of the damage is such that the material is best considered in terms of damage occuring on the scale of the yarns, rather than at the smaller jiber level. 0 1998 Published by Elsevier Science Ltd. All rights reserved and 2D C/Sic composites. These studies describe the mechanical behavior of these materials (non-linear behavior under tension, fracture stress independent of temperature, life-independent of frequency) the origin and mechanisms leading to damage development and fracture of the 2.5D C/Sic composite is still poorly understood. The aim of this work is to describe the damage mechanism for a 2.5D C/Sic composite, and thus define the mechanical laws controlling fracture and cyclic fatigue at various temperatures. Moreover, since this composite contains cracks from processing, it is impor￾tant to determine their effect on fatigue behavior. Hence, the change in mechanical behavior in relation to the number of the cycles and the temperature are described in this paper, and the specific network of cracks developed under such loading is identified. Keyw’ords: A. ceramic-matrix composite, B. fatigue, B. interface, high-temperature, damage 2 EXPERIMENTAL PROCEDURE 2.1 Material 1 INTRODUCTION This study has concentrated on a multilayer long-fiber￾reinforced ceramic-matrix composite of carbon fibers in a silicon-carbide matrix (2.5D C/Sic), supplied by the Soci&i. Europkenne de Propulsion. This thermo￾structural composite is intended for use at high-tem￾perature under substantial mechanical loads. Hence, it is important to understand the cyclic fatigue behavior of this material at high-temperature and to study the effect of environment. Previous studies of the tensile mechanical behavior under cyclic fatigue at high-temperature have con￾centrated on composites similar, but not identical, to the 2.5D C/Sic. For example, the work of Arendts’ and Camus on the characterization of the tensile mechan￾ical behavior at high-temperature of a 2D C/Sic and the work of Shuler’ and Lee4 on cyclic fatigue of [C/SiC]0,90 Tests were conducted on a long-carbon-fiber silicon￾carbide matrix 2.5D C/Sic composite provided by the Soci& Europlenne de Propulsion (SEP, Bordeaux, France). This composite is composed of cloth made from long woven yarns (see Fig. 7). The preform is infiltrated by a pyrocarbon interlayer in order to opti￾mize the fiber/matrix shear lag, and induce a non-brittle mechanical macroscopic behavior. The silicon-carbide matrix is deposited by chemical vapor infiltration (C.V.I.). The as-received composite exhibits a porosity level below 10% and a density of 2200 kgm-‘. The characteristic of this composite is that matrix cracks are created during cooling just after processing, owing to the high tensile thermal residual stresses. 2.2 Mechanical tests The aim of this work is to determine the characteristics of the 2.5D C/Sic composite under cyclic tensile/tensile 693