opposites Science and Technology 70(2010)435-441 Contents lists available at ScienceDirect Composites Science and technology ELSEVIER journalhomepagewww.elsevier.com/locate/compscitech Correlation of elastic properties of melt infiltrated SiC/Sic composites to in situ properties of constituent phases Y. Gowayed,, G. Ojard R Miller U Santhosh, ]. Ahmad,R. John ersity, 311 W Magnolia Ave, AL 36849-5327, United States Pratt S Whitney, 400 Main Street, M/S 114-43, East Hartford, CT 06108, United States d Research Applications, Inc, 11772 Sorrento valley Rd, Suite 260, San Diego, CA 92121-1085, United States ARTICLE INFO ABSTRACT Article history: The ability to correlate the elastic properties of melt infiltrated Sic Sic composites to properties of con- eceived 14 July 2009 stituent phases using a hybrid Finite Element approach is examined and the influence of material internal Accepted 19 November 2009 vailable online 26 November 2009 esting was carried out in air at room temperature and 1204oC. Through-thickness compres odulus utilizing the stacked disk method was measured at room temperature. In situ moduli uent materials were experimentally evaluated using nano-indentation techniques at room temperature A Ceramic matrix composites A consistent relationship is observed between constituent properties and composite properties for in- A MI SiC/Sic blane normal and shear moduli and Poissons ratio at room temperature. However, experimental data or through-thickness compressive elastic modulus is lower than the calculated value. It is hypothesized B. In situ properties that the existence of voids inside the fiber tows and their collapse under compressive loads is the cause of Elastic properties such discrepancy. Estimates for the change in elastic moduli of constituent phases with temperature were obtained from literature and used to calculate the elastic properties of the composites at 1204C A reasonable correlation between the in-plane elastic moduli of the composite and the in situ elastic properties of constituent phases is observed. 2009 Elsevier Ltd. All rights reserved. 1 Introduction of each of these constituent phases are dependent on the composite manufacturing process limiting the ability to obtain properties of Ceramic matrix composites(CMC) are currently considered for distinctive"stand-alone"phases. Although each stand-alone phase applications in gas turbine engines as well as other high tempera- can be considered isotropic, the composite, as a whole, is aniso- ture applications. Barriers to their successful application include tropic due to the geometry and structure of its constituent phases the lack of knowledge of in situ properties of their constituent The alignment of fibers inside the fabric architecture initiates such phases and the correlation of these properties to as-manufactured anisotropy. The Bn and the Sic-CVI are deposited over the fibers/ omposite properties. The effect of voids and fabric architecture, as fabric further stressing the directional nature of the material prop material internal structure variables, add to complexity of such erties. This deposition leaves closed porosity inside the yarns. The correlation. Overcoming these barriers will provide confidence in composite is then infiltrated with SiC-SC and Si into the open inter- material design tools and help develop design procedures utilizing stices filling most of the remaining space and leaving some voids as the full range of 2D and 3D fabric architectures. open porosity. The large number of constituent phases, combined One of the most promising CMC materials is melt infiltrated ( Mi) with the internal structural features of the composite, outlines a SiC/SiC composites. During their manufacture, woven or braided compound relationship between the properties of constituent fabrics are coated with one or more layers of boron nitride to in- phases and the properties of the composite. rease the composite toughness and provide environmental prote To allow for the development of robust and efficient desig tion to the fibers [1, 2]. The matrix is introduced to the fabric in three tools, a systematic methodology is needed to elucidate the unde consecutive densification steps: (i)chemical vapor infiltration(Cvi) lying mechanisms of contribution of different phases to the com- of Sic, (ii)slurry cast(SC)of SiC, and (iii) melt infiltration( Mi)of a posite properties and consequently aid model development and silicon metal leaving some entrapped voids. Mechanical properties verification. Furthermore, since CMC materials will be primarily used in high temperature applications, the effect of temperature 4 Corres g author.Tel:+13348445496:ax:+13348444068 on each constituent phase needs to be isolated and investigated to understand its contribution to the overall composite behavior. 538/s- see front matter o 2009 Elsevier Ltd. All rights reserved. 0.1016 compscitech200911.016Correlation of elastic properties of melt infiltrated SiC/SiC composites to in situ properties of constituent phases Y. Gowayed b,*, G. Ojard c , R. Miller c , U. Santhosh d , J. Ahmad d , R. John a a Air Force Research Laboratory, AFRL/RXLM, Wright-Patterson AFB, OH 45433, United States bDepartment of Polymer and Fiber Engineering, Auburn University, 311 W Magnolia Ave., AL 36849-5327, United States c Pratt & Whitney, 400 Main Street, M/S 114-43, East Hartford, CT 06108, United States d Research Applications, Inc., 11772 Sorrento Valley Rd, Suite 260, San Diego, CA 92121-1085, United States article info Article history: Received 14 July 2009 Received in revised form 4 November 2009 Accepted 19 November 2009 Available online 26 November 2009 Keywords: A. Ceramic matrix composites A. MI SiC/SiC C. Numerical modeling B. In situ properties C. Elastic properties C. Modeling abstract The ability to correlate the elastic properties of melt infiltrated SiC/SiC composites to properties of con￾stituent phases using a hybrid Finite Element approach is examined and the influence of material internal features, such as the fabric architecture and intra-tow voids, on such correlation is elucidated. Tensile testing was carried out in air at room temperature and 1204 C. Through-thickness compressive elastic modulus utilizing the stacked disk method was measured at room temperature. In situ moduli of constit￾uent materials were experimentally evaluated using nano-indentation techniques at room temperature. A consistent relationship is observed between constituent properties and composite properties for in￾plane normal and shear moduli and Poisson’s ratio at room temperature. However, experimental data for through-thickness compressive elastic modulus is lower than the calculated value. It is hypothesized that the existence of voids inside the fiber tows and their collapse under compressive loads is the cause of such discrepancy. Estimates for the change in elastic moduli of constituent phases with temperature were obtained from literature and used to calculate the elastic properties of the composites at 1204 C. A reasonable correlation between the in-plane elastic moduli of the composite and the in situ elastic properties of constituent phases is observed. 2009 Elsevier Ltd. All rights reserved. 1. Introduction Ceramic matrix composites (CMC) are currently considered for applications in gas turbine engines as well as other high tempera￾ture applications. Barriers to their successful application include the lack of knowledge of in situ properties of their constituent phases and the correlation of these properties to as-manufactured composite properties. The effect of voids and fabric architecture, as material internal structure variables, add to complexity of such correlation. Overcoming these barriers will provide confidence in material design tools and help develop design procedures utilizing the full range of 2D and 3D fabric architectures. One of the most promising CMC materials is melt infiltrated (MI) SiC/SiC composites. During their manufacture, woven or braided fabrics are coated with one or more layers of boron nitride to in￾crease the composite toughness and provide environmental protec￾tion to the fibers [1,2]. The matrix is introduced to the fabric in three consecutive densification steps: (i) chemical vapor infiltration (CVI) of SiC, (ii) slurry cast (SC) of SiC, and (iii) melt infiltration (MI) of a silicon metal leaving some entrapped voids. Mechanical properties of each of these constituent phases are dependent on the composite manufacturing process limiting the ability to obtain properties of distinctive ‘‘stand-alone” phases. Although each stand-alone phase can be considered isotropic, the composite, as a whole, is aniso￾tropic due to the geometry and structure of its constituent phases. The alignment of fibers inside the fabric architecture initiates such anisotropy. The BN and the SiC-CVI are deposited over the fibers/ fabric further stressing the directional nature of the material prop￾erties. This deposition leaves closed porosity inside the yarns. The composite is then infiltrated with SiC-SC and Si into the open inter￾stices filling most of the remaining space and leaving some voids as open porosity. The large number of constituent phases, combined with the internal structural features of the composite, outlines a compound relationship between the properties of constituent phases and the properties of the composite. To allow for the development of robust and efficient design tools, a systematic methodology is needed to elucidate the under￾lying mechanisms of contribution of different phases to the com￾posite properties and consequently aid model development and verification. Furthermore, since CMC materials will be primarily used in high temperature applications, the effect of temperature on each constituent phase needs to be isolated and investigated to understand its contribution to the overall composite behavior. 0266-3538/$ - see front matter 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.compscitech.2009.11.016 * Corresponding author. Tel.: +1 334 844 5496; fax: +1 334 844 4068. E-mail address: gowayya@auburn.edu (Y. Gowayed). Composites Science and Technology 70 (2010) 435–441 Contents lists available at ScienceDirect Composites Science and Technology journal homepage: www.elsevier.com/locate/compscitech