Availableonlineatwww.sciencedirect.com SCIENCE DIRECT● E噩≈S ELSEVIER Journal of the European Ceramic Society 25(2005)1629-1636 www.elsevier.com/locate/jeurceramsoc Delayed failure of ceramic matrix composites in tension at elevated temperatures Sung R Choi*, Narottam P. Bansal, Michael J. Verrilli Received 22 February 2004; received in revised form 3 May 2004; accepted 23 May 2004 Available online 14 august 2004 Abstract Ultimate tensile strength of five different continuous fiber-reinforced ceramic matrix composites(CMCs), including SiC /BSAS(two dimensional(2D),2 types), SiC/MAS(2D), SiC,/SiC(2D), and C/SiC (2D, 2 types), was determined as a function of test rate at 1 100-1200C in air. All five CMCs exhibited a significant dependency of ultimate tensile strength on test rate such that the ultimate tensile strengt decreased with decreasing test rate. The dependency of ultimate tensile strength on test rate, the applicability of preload technique, and the predictability of life from one loading configuration(constant stress-rate loading) to another(constant stress loading) all suggested that the overall, phenomenological delayed failure of the CMCs would be governed by a power-law type of slow crack growth C2004 Elsevier Ltd. All rights reserved Keywords: Composites; Strength; Stress-rupture testing: Slow crack growth, Lifetime; SiC/SIC 1. Introduction This paper, as a continuation of the previous study describes delayed failure behavior of five different fiber- The successful development and design of continuous reinforced CMCs at 1 100-1200 C in air, including three Sic fiber-reinforced ceramic matrix composites(CMCs)are de pendent on thorough understanding of their basic properties fiber-reinforced CMCs(SiCr/BSAS(2D, 2 types), SiCr/MAS (D)and SiCe/sic(2D woven)) and one carbon fiber- such as deformation, fracture, and delayed failure(slow crack reinforced CMC(C, /SiC(2D woven, 2 types ).Ultimate ten- rowth, fatigue, or damage evolution/accumulation) behav- sile strength of each composite was determined as a function ior. Particularly, complete evaluation and characterization of of test rate in constant stress-rate testing and its rate depen environmental conditions is a prerequisite to ensure acura- dency was analyzed with a power-law type of slow crack life prediction of structural components stand the governing failure mechanism(s)of the composites In a previous study, ultimate tensile strength of three Finally, the results of elevated-temperature constant stress Sic fiber-reinforced CMCs(SiC/CAs, SiCe/MAS-5, and (stress rupture")testing were obtained for SiC:/BSAS and SiCr/SiC)at 1100-1200oC in air was found to be a strong compared with those of constant stress-rate testing to ve function of test rate. This rate dependency of ultimate tensile ify the overall failure mechanism(s)of the composite and to strength, in conjunction with the additional results of both accelerated and stress rupture testing, was found to be at- establish constant stress-rate testing as a means of life pre- diction test methodology for CmCs tributed to a power-law type of slow crack growth or damage evolution/accumulation that described adequately the phe- nomenological time-dependent behavior of the CMCs 2. Experimental procedure Corresponding author. Tel: +1 216 433 8366; fax: +1 216 433 8366 E-mail address: sung. r choi @grc. nasa. gov(SR Choi). Five different CMCs-four SiC fiber-reinforced and one NASA Resident Principle Scientist carbon fiber-reinforced-were used in this study, includ- 0955-2219/S-see front matter c 2004 Elsevier Ltd. All rights reserved doi: 10.1016/j-jeurceramsoc. 2004.05.024Journal of the European Ceramic Society 25 (2005) 1629–1636 Delayed failure of ceramic matrix composites in tension at elevated temperatures Sung R. Choi∗,1, Narottam P. Bansal, Michael J. Verrilli National Aeronautics and Space Administration, John H. Glenn Research Center, Cleveland, OH 44135, USA Received 22 February 2004; received in revised form 3 May 2004; accepted 23 May 2004 Available online 14 August 2004 Abstract Ultimate tensile strength of five different continuous fiber-reinforced ceramic matrix composites (CMCs), including SiCf/BSAS (two dimensional (2D), 2 types), SiCf/MAS (2D), SiCf/SiC (2D), and Cf/SiC (2D, 2 types), was determined as a function of test rate at 1100–1200 ◦C in air. All five CMCs exhibited a significant dependency of ultimate tensile strength on test rate such that the ultimate tensile strength decreased with decreasing test rate. The dependency of ultimate tensile strength on test rate, the applicability of preload technique, and the predictability of life from one loading configuration (constant stress-rate loading) to another (constant stress loading) all suggested that the overall, phenomenological delayed failure of the CMCs would be governed by a power-law type of slow crack growth. © 2004 Elsevier Ltd. All rights reserved. Keywords: Composites; Strength; Stress–rupture testing; Slow crack growth; Lifetime; SiC/SiC 1. Introduction The successful development and design of continuous fiber-reinforced ceramic matrix composites (CMCs) are de￾pendent on thorough understanding of their basic properties such as deformation, fracture, and delayed failure (slow crack growth, fatigue, or damage evolution/accumulation) behav￾ior. Particularly, complete evaluation and characterization of delayed failure behavior of CMCs under specified loading￾environmental conditions is a prerequisite to ensure accurate life prediction of structural components. In a previous study,1 ultimate tensile strength of three SiC fiber-reinforced CMCs (SiCf/CAS, SiCf/MAS-5, and SiCf/SiC) at 1100–1200 ◦C in air was found to be a strong function of test rate. This rate dependency of ultimate tensile strength, in conjunction with the additional results of both accelerated and stress rupture testing, was found to be at￾tributed to a power-law type of slow crack growth or damage evolution/accumulation that described adequately the phe￾nomenological time-dependent behavior of the CMCs. ∗ Corresponding author. Tel.: +1 216 433 8366; fax: +1 216 433 8366. E-mail address: sung.r.choi@grc.nasa.gov (S.R. Choi). 1 NASA Resident Principle Scientist. This paper, as a continuation of the previous study,1 describes delayed failure behavior of five different fiber￾reinforced CMCs at 1100–1200 ◦C in air, including three SiC fiber-reinforced CMCs (SiCf/BSAS (2D, 2 types), SiCf/MAS (1D) and SiCf/SiC (2D woven)) and one carbon fiber￾reinforced CMC (Cf/SiC (2D woven, 2 types)). Ultimate ten￾sile strength of each composite was determined as a function of test rate in constant stress-rate testing and its rate depen￾dency was analyzed with a power-law type of slow crack growth. Preload testing was also carried out to better under￾stand the governing failure mechanism(s) of the composites. Finally, the results of elevated-temperature constant stress (“stress rupture”) testing were obtained for SiCf/BSAS and compared with those of constant stress-rate testing to ver￾ify the overall failure mechanism(s) of the composite and to establish constant stress-rate testing as a means of life pre￾diction test methodology for CMCs. 2. Experimental procedure Five different CMCs—four SiC fiber-reinforced and one carbon fiber-reinforced—were used in this study, includ- 0955-2219/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2004.05.024