January 1997 Laminated C-SiC Matrix Composites Produced by Cn 115 FIBER 0.5um 1 um Fig. L. Laminated matrix composite prepared by FCVI showing car Fig 3. The number of laminate layers between individual fibers bon fiber and alternating layers of carbon(dark) and SiC (light). depends on the distance between fibers. Sample L-5 Sample L-l from one laminate layer to an adjacent layer. Typical debonding reduction of reagent depletion during the infiltration process at the fiber-matrix interface(not shown) w observed The term"reagent depletion"refers to the reduction in concen- While these results are encouraging, extensive mechanical test- tration of the reagent as the process gas stream traverses the ing will be required to determine if the laminated matrix does preform. Initially the reagent depletion was very high due to the high surface area of the preform, but since densification isolates an ever-increasing number of tows, the surface area of the pre form gradually reduces. This reduction in surface area, in turn, IV. Discussion reduces reagent depletion and thereby leads to the observed Considerable experimental investigation and/or modeling of increase in layer thickness with time the fracture behavior of laminated matrix composites will likely Several samples were deliberately fractured in order to be reqand layer th o determine optimum material combina- observe, via SEM, the crack path. As shown in Fig. 4, evidence lesses for maximizing mechanical perfor that the laminate layers offer resistance to crack propagation mance ered include identifying the was seen. The crack shown here does To win Jogs occurring materials, the modulus of the matrix compared to that of the ot propagate in a straight preferred relative elastic moduli and strengths for the matrix line, but instead follows a tortuous pat 0.5 Fig. 2. Laminated matrix fills region between layers of cloth Fig 4. Deliberate fracture showing tortuous crack path in the lami- ple L-l-M-3January 1997 Laminated C-SiC Matrix Composites Produced by CVI 115 Fig. 1. Laminated matrix composite prepared by FCVI showing car- Fig. 3. The number of laminate layers between individual fibers bon fiber and alternating layers of carbon (dark) and SiC (light). depends on the distance between fibers. Sample L-5. Sample L-1. from one laminate layer to an adjacent layer. Typical debonding reduction of reagent depletion during the infiltration process. at the fiber–matrix interface (not shown) was also observed. The term “reagent depletion” refers to the reduction in concen- While these results are encouraging, extensive mechanical test￾tration of the reagent as the process gas stream traverses the ing will be required to determine if the laminated matrix does preform. Initially the reagent depletion was very high due to the indeed enhance composite toughness. high surface area of the preform, but since densification isolates an ever-increasing number of tows, the surface area of the pre- IV. Discussion form gradually reduces. This reduction in surface area, in turn, reduces reagent depletion and thereby leads to the observed Considerable experimental investigation and/or modeling of increase in layer thickness with time. the fracture behavior of laminated matrix composites will likely Several samples were deliberately fractured in order to be required in order to determine optimum material combina￾observe, via SEM, the crack path. As shown in Fig. 4, evidence tions and layer thicknesses for maximizing mechanical perfor￾that the laminate layers offer resistance to crack propagation mance. Questions to be answered include identifying the was seen. The crack shown here does not propagate in a straight preferred relative elastic moduli and strengths for the matrix line, but instead follows a tortuous path with jogs occurring materials, the modulus of the matrix compared to that of the Fig. 2. Laminated matrix fills region between layers of cloth. Fig. 4. Deliberate fracture showing tortuous crack path in the lami￾Sample L-3. nated matrix. Sample L-1-M-3