Availableonlineatwww.sciencedirect.com e Science Direct COMPOSITES CIENCE AND TECHNOLOGY ELSEVIER Composites Science and Technology 67(2007)1009-1017 www.elsevier.com/locate/compscitech Modeling stress-dependent matrix cracking and stress-strain behavior in 2D woven Sic fiber reinforced CVI SiC composites Gregory N. Morscher a,, Mrityunjay Singh b, J. Douglas Kiser Marc Freedman Ram bhatt Ohio Aerospace Institute, NASA Glenn Research Center, Cleveland, OH, United States b OSS Group, NASA Glenn Research Center, Cleveland, OH, United States Nasa Glenn research center. cleveland. oh United states d Us army. NASA Glenn Research Center. Cleveland. OH. United States 2005: received in revised form 27 April 2006: 14 June 200( Abstract 2D woven Hi-Nicalon and Sylramic-iBN SiC fiber reinforced chemical vapor-infiltrated( Cvn) SiC matrix composites were tested room temperature with modal acoustic emission monitoring in order to determine relationships for stress-dependent matrix cracking The Hi-Nicalon composites varied in the number of plies(1-36), specimen thickness, and constituent content. The Sylramic-iBN com- posites were fabricated with balanced and unbalanced 2D weaves in order to vary the fiber volume fraction in the orthogonal directions Not surprisingly, matrix cracking stresses tended to be but were not always, higher for composites with higher fiber volume fractions in the loading direction. It was demonstrated that simple relationships for stress-dependent matrix cracking could be related to the stress in the load-bearing CVI SiC matrix. For low-density composites, the 90 minicomposites do not share significant loads and matrix cracking matrix cracking was dependent on the unbridged"flaw"size, i.e., the 90 tow size or unbridged transverse crack size Qinicomposites was very similar to single tow minicomposites. For higher-density composites, where significant load is carried by the o% minicomposites o 2006 Elsevier Ltd. All rights reserved Keywords: A. Ceramic-matrix composites; B Matrix cracking: C. Acoustic emission; D. Stress-strain behavior 1. Introduction verse matrix cracks in the woven composite and it is there- fore essential to characterize the stress-strain dependence In the companion paper [l] a relationship for elastic for matrix cracking in order to effectively model stress- modulus was determined for a wide variety of 2D woven strain behavior [2,3]. This pertains not only to stress-strain SiC fiber reinforced SiC matrix composites which varied response for the purpose of modeling stress-redistribution in numbers of plies, constituent content, thickness, density, in a component, but also for the purpose of modeling ele- and number of woven tows in either direction (i.e, balanced vated temperature life properties [4] which depend on the weaves versus unbalanced weaves). A second critical prop- presence of matrix cracks to enable oxidation mechanisms erty for design is the onset of non-linearity in the stress- to cause time-dependent strength-degradation of the strain curve in addition to the stress-strain behavior composite beyond the linear region of the stress-strain curve. Non Recently, the stress-dependent matrix cracking behavior linearity is due to the initiation and propagation of trans- has been quantified for 2D woven Sic fiber reinforced melt-infiltrated (MI) composites reinforced with the high ant Sylramic-iBN fibe ondas padres: Greg nor. Tel:+1216 433 5512: fax: +1 2164335544. cial emphasis was made to vary the 2D woven architecture gory.N Morscher@grc. nasa. gov(G N Morscher). [6, 7] and composites reinforced with the lower modulus 02663538/S. see front matter 2006 Elsevier Ltd. All rights reserved doi:10.1016j.compscitech.2006.06.007Modeling stress-dependent matrix cracking and stress–strain behavior in 2D woven SiC fiber reinforced CVI SiC composites Gregory N. Morscher a,*, Mrityunjay Singh b , J. Douglas Kiser c , Marc Freedman c , Ram Bhatt d a Ohio Aerospace Institute, NASA Glenn Research Center, Cleveland, OH, United States b QSS Group, NASA Glenn Research Center, Cleveland, OH, United States c NASA Glenn Research Center, Cleveland, OH, United States d US Army, NASA Glenn Research Center, Cleveland, OH, United States Received 19 April 2005; received in revised form 27 April 2006; accepted 14 June 2006 Available online 1 September 2006 Abstract 2D woven Hi-Nicalon and Sylramic-iBN SiC fiber reinforced chemical vapor-infiltrated (CVI) SiC matrix composites were tested at room temperature with modal acoustic emission monitoring in order to determine relationships for stress-dependent matrix cracking. The Hi-Nicalon composites varied in the number of plies (1–36), specimen thickness, and constituent content. The Sylramic-iBN com￾posites were fabricated with balanced and unbalanced 2D weaves in order to vary the fiber volume fraction in the orthogonal directions. Not surprisingly, matrix cracking stresses tended to be, but were not always, higher for composites with higher fiber volume fractions in the loading direction. It was demonstrated that simple relationships for stress-dependent matrix cracking could be related to the stress in the load-bearing CVI SiC matrix. For low-density composites, the 90 minicomposites do not share significant loads and matrix cracking was very similar to single tow minicomposites. For higher-density composites, where significant load is carried by the 0 minicomposites, matrix cracking was dependent on the unbridged ‘‘flaw’’ size, i.e., the 90 tow size or unbridged transverse crack size. 2006 Elsevier Ltd. All rights reserved. Keywords: A. Ceramic-matrix composites; B. Matrix cracking; C. Acoustic emission; D. Stress–strain behavior 1. Introduction In the companion paper [1], a relationship for elastic modulus was determined for a wide variety of 2D woven SiC fiber reinforced SiC matrix composites which varied in numbers of plies, constituent content, thickness, density, and number of woven tows in either direction (i.e, balanced weaves versus unbalanced weaves). A second critical prop￾erty for design is the onset of non-linearity in the stress– strain curve in addition to the stress–strain behavior beyond the linear region of the stress–strain curve. Non￾linearity is due to the initiation and propagation of trans￾verse matrix cracks in the woven composite and it is there￾fore essential to characterize the stress–strain dependence for matrix cracking in order to effectively model stress– strain behavior [2,3]. This pertains not only to stress–strain response for the purpose of modeling stress-redistribution in a component, but also for the purpose of modeling ele￾vated temperature life properties [4] which depend on the presence of matrix cracks to enable oxidation mechanisms to cause time-dependent strength-degradation of the composite. Recently, the stress-dependent matrix cracking behavior has been quantified for 2D woven SiC fiber reinforced melt-infiltrated (MI) composites reinforced with the high modulus, creep-resistant Sylramic-iBN fiber type [5]. Spe￾cial emphasis was made to vary the 2D woven architecture [6,7] and composites reinforced with the lower modulus 0266-3538/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2006.06.007 * Corresponding author. Tel.: +1 216 433 5512; fax: +1 216 433 5544. E-mail address: Gregory.N.Morscher@grc.nasa.gov (G.N. Morscher). www.elsevier.com/locate/compscitech Composites Science and Technology 67 (2007) 1009–1017 COMPOSITES SCIENCE AND TECHNOLOGY