Part A: applied scienc and manufacturing ELSEVIER Composites: Part A 30(1999)593-597 Matrix crack evolution in Sic fiber/glass matrix cross-ply laminates Nobuo Takeda", Manami Kiriyama Center for Collaborative Research(CCR). The University of Tokyo, 4-6-1 Komba, Meguro-ku, Tokyo 153, Japan Matrix crack evolution was studied for SiC fiber-reinforced glass-matrix cross-ply laminates. A novel in situ SEM(scanning electron microscope)observation was conducted to measure the fiber/matrix debonding and sliding in 0 plies using specimens with parallel micro- lines printed on the surfaces. Interfacial debondings were found to grow intermittently as the applied stress increased. The debonding length distribution depends on the number of 90 plies as well as the type of damage modes. An analytical model for the matrix crack evolution was proposed using the energy balance calculation based on Kuo and Chou(Kuo ws, Chou Tw. Multiple cracking of unidirectinal and cross-ply ceramic matrix composites. J Am Ceram Soc 1995: 78(3): 745-755), with the modification of including the effects of damage mode interaction as well as Poisson contraction in the debonded regions. The predicted evolution agrees well with the experimental one C1999 Elsevier Science Ltd. All rights reserved Keywords: Glass matrix composites; Matrix crack evolution; Micro-line 1. Introduction sed to measure the overall sequence of matrix cracking, and a novel in situ SEM/micro-line technique was used to Knowledge of matrix crack evolution is important for the quantify the fiber/matrix debonding and sliding behavior in development of fiber-reinforced ceramic matrix composites 0%plies. Then, a modified analytical model based on Kuo CMC)[1]. In particular, it is necessary to study the and Chou [10] was proposed and the theoretical prediction sequence of such microscopic damages up to the final frac- was compared with the experimental results ture to ensure the damage tolerance capability. Many studies some tensile properties of glass or glass-ceramic matrix composite laminates were experimentally obtained [2, 3]. 2. 1. Material The matrix crack growth criterion was studied for SiC/ glass-ceramic unidirectional laminates using fracture SiC (Nicalon", Nippon Carbon) fiber-reinforced borosi- mechanics[4]. The fiber/matrix interfacial properties were licate glass(Pyrex7740, Corning)matrix composites were also studied extensively [5, 6]. A full statistical treatment of fabricated by Nippon Carbon. Fibers coated with approxi- the matrix crack evolution and associated stress-strain mately 70 nm thick carbon layer were used to fabricate behaviors has been conducted recently [7]. The damage laminates by impregnating fiber cross-plies with glass evolution in cross-ply laminates is, however, more complex powder slurry and hot-pressing them at 1100oC for than in unidirectional ones since the matrix cracks occur 10 min. The stacking configuration was [03/90m./03](m both C°and90° plies8-10 1, 2, 3)and the nominal fiber volume fraction Vr was 0.36 Although cross-ply or woven laminates are most impor- The average thickness of a unidirectional ply was 0.2 mm, tant in practical applications of CMC, the microscopic which resulted in the total thickness ranging from 1. 4 mm damage evolution has not been well characterized yet. (m= I)to 1. 8(m= 3) The purpose of the present study is to characterize damage sequences in SiC fiber-reinforced glass-matrix cross-ply 2.2. Replica and in situ SEM/micro-line techniques laminates both experimentally and theoretically from a micro-mechanical viewpoint. A replica technique was 0.4 mm/min using polished specimens of 5 mm in width Corresponding author. Tel /fax: +81-3-3481-4476 e-mail: takeda a and 25 mm in gage length. Tests were stopped intermittently at several loading stages to take replicas of the damage by 1359-835X/99/S- see front matter @1999 Elsevier Science Ltd. All rights reserved P:S1359-835X(98)00155-9Matrix crack evolution in SiC fiber/glass matrix cross-ply laminates Nobuo Takeda*, Manami Kiriyama Center for Collaborative Research (CCR), The University of Tokyo, 4-6-1 Komba, Meguro-ku, Tokyo 153, Japan Abstract Matrix crack evolution was studied for SiC fiber-reinforced glass-matrix cross-ply laminates. A novel in situ SEM (scanning electron microscope) observation was conducted to measure the fiber/matrix debonding and sliding in 08 plies using specimens with parallel micro￾lines printed on the surfaces. Interfacial debondings were found to grow intermittently as the applied stress increased. The debonding length distribution depends on the number of 908 plies as well as the type of damage modes. An analytical model for the matrix crack evolution was proposed using the energy balance calculation based on Kuo and Chou (Kuo WS, Chou TW. Multiple cracking of unidirectinal and cross-ply ceramic matrix composites. J Am Ceram Soc 1995;78(3):745–755), with the modification of including the effects of damage mode interaction as well as Poisson contraction in the debonded regions. The predicted evolution agrees well with the experimental one. q 1999 Elsevier Science Ltd. All rights reserved. Keywords: Glass matrix composites; Matrix crack evolution; Micro-line 1. Introduction Knowledge of matrix crack evolution is important for the development of fiber-reinforced ceramic matrix composites (CMC) [1]. In particular, it is necessary to study the sequence of such microscopic damages up to the final frac￾ture to ensure the damage tolerance capability. Many studies have been devoted to modelling the damage process in unidirectional, cross-ply and woven CMC. For example, some tensile properties of glass or glass–ceramic matrix composite laminates were experimentally obtained [2, 3]. The matrix crack growth criterion was studied for SiC/ glass–ceramic unidirectional laminates using fracture mechanics [4]. The fiber/matrix interfacial properties were also studied extensively [5,6]. A full statistical treatment of the matrix crack evolution and associated stress–strain behaviors has been conducted recently [7]. The damage evolution in cross-ply laminates is, however, more complex than in unidirectional ones since the matrix cracks occur in both 08 and 908 plies [8–10]. Although cross-ply or woven laminates are most impor￾tant in practical applications of CMC, the microscopic damage evolution has not been well characterized yet. The purpose of the present study is to characterize damage sequences in SiC fiber-reinforced glass–matrix cross-ply laminates both experimentally and theoretically from a micro-mechanical viewpoint. A replica technique was used to measure the overall sequence of matrix cracking, and a novel in situ SEM/micro-line technique was used to quantify the fiber/matrix debonding and sliding behavior in 08 plies. Then, a modified analytical model based on Kuo and Chou [10] was proposed and the theoretical prediction was compared with the experimental results. 2. Experiments 2.1. Materials SiC (Nicalone, Nippon Carbon) fiber-reinforced borosi￾licate glass (Pyrexe7740, Corning) matrix composites were fabricated by Nippon Carbon. Fibers coated with approxi￾mately 70 nm thick carbon layer were used to fabricate laminates by impregnating fiber cross-plies with glass powder slurry and hot-pressing them at 11008C for 10 min. The stacking configuration was [03/90m/03] (m ˆ 1, 2, 3) and the nominal fiber volume fraction Vf was 0.36. The average thickness of a unidirectional ply was 0.2 mm, which resulted in the total thickness ranging from 1.4 mm (m ˆ 1) to 1.8 (m ˆ 3). 2.2. Replica and in situ SEM/micro-line techniques Tensile tests were conducted at a cross-head speed of 0.4 mm/min using polished specimens of 5 mm in width and 25 mm in gage length. Tests were stopped intermittently at several loading stages to take replicas of the damage by Composites: Part A 30 (1999) 593–597 1359-835X/99/$ - see front matter q 1999 Elsevier Science Ltd. All rights reserved. PII: S1359-835X(98)00155-9 * Corresponding author. Tel./fax: 181-3-3481-4476; e-mail: takeda@ compmat.rcast.u-tokyo.ac.jp