J.Am. Ceram.Soe,88146-153(2005) Dol:10.l11551-2916.2004.00029x Matrix Cracking in 3D Orthogonal Melt-Infiltrated SiC/SiC Composites with Various Z-Fiber Types Ohio Aerospace Institute, Cleveland, OH 44135 Hee mann Y Cleveland State University, Cleveland, OH 44115 James a. dicarlo NASA Glenn Research Center. Cleveland. OH 4413 The occurrence of matrix cracks in melt-infiltrated SiC/Sic cracking behavior in the 0o direction has been well characterized omposites with a three-dimensional (3D)orthogonal architec for different fiber types, constituent volume content, and tow ture was determined at room temperature for specimens tested in ends per cm. 7.8 tension parallel to the y-direction(perpendicular to Z-bundle Three-dimensional (3D) orthogonal(Fig. I(a)) architecture weave direction). The fiber types were Sylramic and Sylramic- SiC/SiC composites are of interest because they offer potential iBN in the X-and Y-directions and lower modulus ZMI, T300 benefits of better reproducibility, improved interlaminar me- and rayon in the Z-direction. Acoustic emission(AE) was used chanical properties, and, for the case of MI composites, po- to monitor the matrix-cracking activity. For y-direction com- tentially higher through-thickness thermal conductivity and posites, the ae data were used to determine the location (+0. 25 better matrix infiltration. It is important to understand how mm) where matrix cracks occurred in the 3D orthogonal archi- he 3D orthogonal architecture affects matrix cracking in these tecture. This enabled the determination of the stress-dependent composites. A thorough study on the accumulation of matrix matrix crack distributions for small but repeatable matrix-rich cracks and the effect of matrix crack accumulation on the unidirectional” and the matrix-poor“ ross-ply”regi ithin stress-strain behavior was performed for a 3D orthogonal com- the architecture Matrix cracking initiated at very low stresses posite with polymer impregnation and pyrolysis Sic matrix (40 MPa) in the"unidirectional""regions for the largest Z- The amount and nature of stress-dependent matrix cracking was direction fiber tow composites. Decreasing the size of the Z-fiber determined, was effectively modeled, and then was used to mod- bundle increased the stress for matrix cracking in the "unidi- rectional"regions. Matrix cracking was analyzed on the basis in 3D architecture MI SiC/SiC composites with various fiber that the source for through-thickness matrix cracks (TTMc) types in the Z-direction is not well understood. originated in the 90 or Z-fiber tows. It was found that matrix Two aspects of 3D orthogonal composites are the focus of cracking in the dimensional cross tional” regions, 一 gions was very similar to two- this study: (I)how the Z-direction tow fiber type and size affect nposites. However, in the"unidirec initiation and progression of stress-dependent matrix cracking in cracking followed a Griffith-type MI SiC/SIC composites and (2)the effect local structure has on relationship, where the stress-distribution for TTMC was matrix cracking in the different regions of the orthogonal ar- versely proportional to the square root of the height of the chitecture. When tested in the direction perpendicular to the Z- Z-fiber tows fiber tows(Y-direction, see Fig. I(b)), there are small but re- eatable matrix-rich unidirectional (UND) composite region with a Z-direction tow perpendicular to the loading direction and a 0/90 cross-ply(XPLY) composite region. With an ad- . Introduction vanced acoustic emission(AE)system, 13 the determination of tion and propagation of multiple matrix cracks in when, where, and how much matrix cracking occurred in these dense ceramic matrix composites when subjected tensile stress is necessary for high strength and osites. However the occurrence of matrix cracks at low stresses, especially for two-dimensional (2D)architectures IL. Experimental Procedure where 90 tows act as matrix flaws, may limit the structura Unload-reload tensile tests were performed on melt-infiltrated capability of some nonoxide composite systems when subjected to oxidizing environments for long times at stresses sufficient Sic matrix composite panels that were fabricated using a 3D orthogonal architecture with two different SiC fiber types in the to cause matrix cracking and hemical vapor-infiltrated(Cvi) SiC fiber-reinforced composites X-and y-direction and three different fiber types in the Z-di- fabricated from the random lay-up of 0/90 fabric, the matrix rection. In general, all the composite architectures were rein- forced in the X-y fiber directions with 10-um diameter Sylramic Sic fibers produced by Dow Corning(Midland, MI and in the Brian Cox- ting editor Z-direction by ZMI (Ube Industries, Tokyo, Japan), T300(Am- co Performance Products, Atlanta, GA), and rayon(ICF In- dustries, New York, NY). After formation into flat X=230 mm Manuscript No. 10551 Received September 23, 2003: approv by y=150 mm preform panels with Z a 2 mm thickness, all the architectures(except for the 3D with rayon Z-fiber)were Author to whom correspondence should be addressed. morschen(a gre. Senior Research Scientists residing at NASA Glenn Research Center. Cleveland, OHMatrix Cracking in 3D Orthogonal Melt-Infiltrated SiC/SiC Composites with Various Z-Fiber Types Gregory N. Morscherw,z Ohio Aerospace Institute, Cleveland, OH 44135 Hee Mann Yunz Cleveland State University, Cleveland, OH 44115 James A. DiCarlo NASA Glenn Research Center, Cleveland, OH 44135 The occurrence of matrix cracks in melt-infiltrated SiC/SiC composites with a three-dimensional (3D) orthogonal architec￾ture was determined at room temperature for specimens tested in tension parallel to the Y-direction (perpendicular to Z-bundle weave direction). The fiber types were Sylramic and Sylramic￾iBN in the X- and Y-directions and lower modulus ZMI, T300, and rayon in the Z-direction. Acoustic emission (AE) was used to monitor the matrix-cracking activity. For Y-direction com￾posites, the AE data were used to determine the location (70.25 mm) where matrix cracks occurred in the 3D orthogonal archi￾tecture. This enabled the determination of the stress-dependent matrix crack distributions for small but repeatable matrix-rich ‘‘unidirectional’’ and the matrix-poor ‘‘cross-ply’’ regions within the architecture. Matrix cracking initiated at very low stresses (B40 MPa) in the ‘‘unidirectional’’ regions for the largest Z￾direction fiber tow composites. Decreasing the size of the Z-fiber bundle increased the stress for matrix cracking in the ‘‘unidi￾rectional’’ regions. Matrix cracking was analyzed on the basis that the source for through-thickness matrix cracks (TTMC) originated in the 901 or Z-fiber tows. It was found that matrix cracking in the ‘‘cross-ply’’ regions was very similar to two￾dimensional cross-woven composites. However, in the ‘‘unidirec￾tional’’ regions, matrix cracking followed a Griffith-type relationship, where the stress-distribution for TTMC was in￾versely proportional to the square root of the height of the Z-fiber tows. I. Introduction THE formation and propagation of multiple matrix cracks in relatively dense ceramic matrix composites when subjected to increasing tensile stress is necessary for high strength and tough composites.1 However, the occurrence of matrix cracks at low stresses, especially for two-dimensional (2D) architectures where 901 tows act as matrix flaws,2,3 may limit the structural capability of some nonoxide composite systems when subjected to oxidizing environments for long times at stresses sufficient to cause matrix cracking.4–6 For 2D melt-infiltrated (MI) and chemical vapor-infiltrated (CVI) SiC fiber-reinforced composites fabricated from the random lay-up of 0/90 fabric, the matrix cracking behavior in the 01 direction has been well characterized for different fiber types, constituent volume content, and tow ends per cm.7,8 Three-dimensional (3D) orthogonal (Fig. 1(a)) architecture SiC/SiC composites are of interest because they offer potential benefits of better reproducibility, improved interlaminar me￾chanical properties,9–11 and, for the case of MI composites, po￾tentially higher through-thickness thermal conductivity and better matrix infiltration.11 It is important to understand how the 3D orthogonal architecture affects matrix cracking in these composites. A thorough study on the accumulation of matrix cracks and the effect of matrix crack accumulation on the stress-strain behavior was performed for a 3D orthogonal com￾posite with polymer impregnation and pyrolysis SiC matrix.9 The amount and nature of stress-dependent matrix cracking was determined, was effectively modeled, and then was used to mod￾el stress-strain behavior. However, matrix-crack accumulation in 3D architecture MI SiC/SiC composites with various fiber types in the Z-direction is not well understood. Two aspects of 3D orthogonal composites are the focus of this study: (1) how the Z-direction tow fiber type and size affect initiation and progression of stress-dependent matrix cracking in MI SiC/SiC composites and (2) the effect local structure has on matrix cracking in the different regions of the orthogonal ar￾chitecture. When tested in the direction perpendicular to the Z- fiber tows (Y-direction, see Fig. 1(b)), there are small but re￾peatable matrix-rich unidirectional (UNI) composite region with a Z-direction tow perpendicular to the loading direction and a 0/90 cross-ply (XPLY) composite region. With an ad￾vanced acoustic emission (AE) system12,13, the determination of when, where, and how much matrix cracking occurred in these different regions was accomplished. II. Experimental Procedure Unload–reload tensile tests were performed on melt-infiltrated SiC matrix composite panels that were fabricated using a 3D orthogonal architecture with two different SiC fiber types in the X- and Y-direction and three different fiber types in the Z-di￾rection. In general, all the composite architecturesy were rein￾forced in the X–Y fiber directions with 10-mm diameter Sylramic SiC fibers produced by Dow Corning (Midland, MI) and in the Z-direction by ZMI (Ube Industries, Tokyo, Japan), T300 (Am￾oco Performance Products, Atlanta, GA), and rayon (ICF In￾dustries, New York, NY). After formation into flat X 5 230 mm by Y 5 150 mm preform panels with Z
2 mm thickness, all the architectures (except for the 3D with rayon Z-fiber) were Journal J. Am. Ceram. Soc., 88 [1] 146–153 (2005) DOI: 10.1111/j.1551-2916.2004.00029.x 146 Brian Cox—contributing editor Research supported by NASA’s Ultra Efficient Engine Technology program. w Author to whom correspondence should be addressed. e-mail: gmorscher@grc. nasa.gov z Senior Research Scientists residing at NASA Glenn Research Center, Cleveland, OH. Manuscript No. 10551. Received September 23, 2003; approved June 17, 2004. y 3D orthogonal preforms woven by Albany International Techniweave, Inc. (Rochester, NY)