J. Haslam et al. Journal of the European Ceramic Society 20(2000)607-618 slurry was then consolidated by pressure filtration at 5 wiched between two layers of woven, fiber cloth. Sand- MPa to form disc shaped bodies that were fully satu- wiches with up to 27 layers, (14 weaves and 13 frozen rated with water. The saturated bodies were stored in ceramic tapes) were piled up, packed in plastic, evac- sealed plastic bags containing a small paper towel satu- uated, and sealed in plastic. After thawing, the assem- rated with water to help prevent drying. The volume bled layers were vibrated and pressed lightly in between fraction of powder within the saturated, consolidated two steel plates with appropriate spacers to cause the bodies was determined by weight difference method as fluidized powder to flow and intrude the finer layers 52%. 5 At a later time the consolidated powder com- Multi-layer composites in sizes of 40x 100x 3 mm could pact (or a portion cut with a razor blade) was placed be fabricated by this vibration supported single step between two plastic sheets(e. g. a bag) and fluidized with impregnation. The multi-layer cloth composite could an air-powered vibrator into uniform 300 um thick then be dried or frozen for later use. It should be noted esof consolidated particles that the layers of fiber cloth, impregnated with the flui- An illustration of the composite processing steps is dized powder ceramic compact as described were very shown in Fig. 1. Initially, tapes are formed by pressing flexible and could be shaped much like a sheet of un- the fluidized sheets in between two flat steel plates using cross-linked carbon fiber/epoxy prepreg wo spacer bars to fix the thickness. The pressed tape Further processing requires removing the water from were flexible due to the weakly attractive particle poten- the saturated powder matrix by drying in an oven at tial. The tapes, still between the plastic sheets, were fro- 70C, and then sintering the ZrO 2 in a dry HCl gas zen to facilitate composite processing and/or storage environment at temperatures between 1200 and To produce the composite, the frozen tapes were 1300 C20 As reported elsewhere the HCI gas heat removed from between the plastic sheets and sand- treatment did not affect the strength of fiber bundles With the knowledge of the volume of fibers per unit area of cloth the volume fraction of foors within the Vibro Impregnation Process composite was determined by measuring the volume of with Tape Freezing the composite and counting the number of fiber layers sll ach specimen. For composites fabricated for this ly, the average volume fraction of fibers was 0.37±0.02 2.2 Interlaminar shear tests queeze For some design considerations, a desirable property of a woven, layered composite is to have sufficient interlaminar shear strength to resist delamination. This type of failure might be encountered in a bending type pile + pack of loading through the thickness as encountered with a through-thickness temperature gradient. Interlaminar shear strength was determined with 0/90 bar speci mens(3.5x7x20 mm nominal dimensions) diamond cut from larger plates fabricated with 12 or more cloth lay ers. The specimen edges were diamond ground(400 grit) vibrate squeeze to remove a minimum 300 um of damage introduced by the diamond cutting. 3-Point flexural tests were the span was changed for reasons dis- cussed below. The fiber weave orientation wa horizontal with the loading in the vertical direction as layered composite shown in Fig. 2(a). Nylon rods(6.45 mm diameter)were Matrix material Fiberweave 2 Impregnated composite 口 Steel plates o Plastic baa (b) Fig. 2. Schematic of fiber orientation of composite for bending tests. Fig 1. This illustration shows the processing steps used to form the (a)Interlaminar Shear Strength tests.(b)In-plane bend testing composite. flexural strength and elastic modulusslurry was then consolidated by pressure ®ltration at 5 MPa to form disc shaped bodies that were fully satu￾rated with water. The saturated bodies were stored in sealed plastic bags containing a small paper towel satu￾rated with water to help prevent drying. The volume fraction of powder within the saturated, consolidated bodies was determined by weight di€erence method as 52%.15 At a later time, the consolidated powder com￾pact (or a portion cut with a razor blade) was placed between two plastic sheets (e.g. a bag) and ¯uidized with an air-powered vibrator into uniform 300 mm thick `tapes' of consolidated particles. An illustration of the composite processing steps is shown in Fig. 1. Initially, tapes are formed by pressing the ¯uidized sheets in between two ¯at steel plates using two spacer bars to ®x the thickness. The pressed tapes were ¯exible due to the weakly attractive particle poten￾tial. The tapes, still between the plastic sheets, were fro￾zen to facilitate composite processing and/or storage. To produce the composite, the frozen tapes were removed from between the plastic sheets and sand￾wiched between two layers of woven, ®ber cloth. Sand￾wiches with up to 27 layers, (14 weaves and 13 frozen ceramic tapes) were piled up, packed in plastic, evac￾uated, and sealed in plastic. After thawing, the assem￾bled layers were vibrated and pressed lightly in between two steel plates with appropriate spacers to cause the ¯uidized powder to ¯ow and intrude the ®ner layers. Multi-layer composites in sizes of 401003 mm could be fabricated by this vibration supported single step impregnation. The multi-layer cloth composite could then be dried or frozen for later use. It should be noted that the layers of ®ber cloth, impregnated with the ¯ui￾dized powder ceramic compact as described were very ¯exible and could be shaped much like a sheet of un￾cross-linked carbon ®ber/epoxy prepreg. Further processing requires removing the water from the saturated powder matrix by drying in an oven at 70C, and then sintering the ZrO2 in a dry HCl gas environment at temperatures between 1200 and 1300C.20 As reported elsewhere21 the HCI gas heat treatment did not a€ect the strength of ®ber bundles. With the knowledge of the volume of ®bers per unit area of cloth, the volume fraction of ¯oors within the composite was determined by measuring the volume of the composite and counting the number of ®ber layers in each specimen. For composites fabricated for this study, the average volume fraction of ®bers was 0.37‹0.02. 2.2. Interlaminar shear tests For some design considerations, a desirable property of a woven, layered composite is to have sucient interlaminar shear strength to resist delamination. This type of failure might be encountered in a bending type of loading through the thickness as encountered with a through-thickness temperature gradient. Interlaminar shear strength was determined with 0/90 bar speci￾mens (3.5720 mm nominal dimensions) diamond cut from larger plates fabricated with 12 or more cloth lay￾ers. The specimen edges were diamond ground (400 grit) to remove a minimum 300 mm of damage introduced by the diamond cutting. 3-Point ¯exural tests were per￾formed where the span was changed for reasons dis￾cussed below. The ®ber weave orientation was horizontal with the loading in the vertical direction as shown in Fig. 2(a). Nylon rods (6.45 mm diameter) were Fig. 1. This illustration shows the processing steps used to form the composite. Fig. 2. Schematic of ®ber orientation of composite for bending tests. (a) Interlaminar Shear Strength tests. (b) In-plane bend testing for ¯exural strength and elastic modulus. 610 J.J. Haslam et al. / Journal of the European Ceramic Society 20 (2000) 607±618