M. Schmiicker et al /Composites: Part A 34(2003)613-622 In order to achieve higher density and a better homogeneity the green plates were pressed between two aluminium oxide plates. In the final step the green plates were sintered in air at 1300°C. xE 2. 2. Preparation of test se Two series of samples were prepared from the middle of wn In microscopic analysis were taken from series a, whereas the samples corresponding to series b were used to determine the mechanical characteristics, particularly the shear strength. As not all samples from row a were used for microscopy, it could be established that, although the mechanical properties can vary significantly from sample to sample in the direction perpendicular to the winding direction (i.e. form sample 1-12 in Fig. 2), they are reasonably coherent in corresponding samples from a and b This allows the assignment of microscopical and mechan ical data relating adjacent samples. Fig 1. Scanning electron micrograph (overview)of WHlPox all oxide of Nextel 610(3M) alumina fibers and an Al2O3-rich free areas(matrix agglomerations with macropores) from each other alumino-silicate matrix Samples cut from the same plate but from different positions, one from the edge (la)and one The fiber distribution alone, however, does not provide the from the middle(6a)(see Fig. 2), were investigated in order full information on the mesostructure of porous all-oxide clarify whether location dependent differences exist. In ceramics as direct data on interlaminate fiber free areas addition, the effects of green bodies compression were cannot be obtained. A suitable technique to describe the vestigated by comparing a mildly(10%)and a strongly mesostructure of WHIPOX oxide fiber/oxide matrix com- compressed(25%)material posites has recently been developed at DLR [ll]. Fiber fre areas were recorded by means of optical microscopy 2.3. Mechanical testing (transmitted light) utilizing the light conductivity and opacity of fibers and matrix, respectively. Mechanical tests were performed by 3-point bendin sing a 20 mm support distance. Bending bar width and thickness was 10 and 3 mm, respectively. Load deflection 2. Experimental methods curves show a non-brittle fracture behavior [6]. The interlaminar shear strength (ILSS)was calculated accordin 2.1. Processing of WHIPOX CMCs slices WHIPOX CMCs are produced by a continuously work ing winding technique. The fibers first run through a tube furnace where the sizing is burned off. The rovings are then infiltrated with water-based matrix slurry and pre-dried in a continuously working microwave (Agni, Thermal and Materials Technology, Aachen, Germany). The infiltrated yarns are wound onto a plastic mandrel(diameter, 200 mm) Series a>123 4516 in a closed box of constant high air humidity(H2O-saturated air). The winding process i.e. the traverse and rotational speed, is computer controlled, using the PC program Series b> CADWIND(Materials SA; Brussels, Belgium) which llows different fiber orientations and winding patterns. The investigated samples all display winding angles a of 15, i.e. the angle between the fiber rovings and the winding normal is 15 and hence the angle between intersecting fiber Fig. 2. Sketch of sample positions within a WHIPOX plate. Series b specimens were tested mechanically while selected series a specimens were bundles is 30(also see Fig. 10). To obtain fat plates used for microscopic analyzes. For that, an individual series a specimen bar the material is removed from the mandrel and straightened was cut into 20 slices of 1.5 mm thicknessThe fiber distribution alone, however, does not provide the full information on the mesostructure of porous all-oxide ceramics as direct data on interlaminate fiber free areas cannot be obtained. A suitable technique to describe the mesostructure of WHIPOX oxide fiber/oxide matrix com￾posites has recently been developed at DLR [11]. Fiber free areas were recorded by means of optical microscopy (transmitted light) utilizing the light conductivity and opacity of fibers and matrix, respectively. 2. Experimental methods 2.1. Processing of WHIPOX CMCs WHIPOX CMCs are produced by a continuously work￾ing winding technique. The fibers first run through a tube furnace where the sizing is burned off. The rovings are then infiltrated with water-based matrix slurry and pre-dried in a continuously working microwave (Agni, Thermal and Materials Technology, Aachen, Germany). The infiltrated yarns are wound onto a plastic mandrel (diameter, 200 mm) in a closed box of constant high air humidity (H2O-saturated air). The winding process i.e. the traverse and rotational speed, is computer controlled, using the PC program CADWIND (Materials S.A; Brussels, Belgium) which allows different fiber orientations and winding patterns. The investigated samples all display winding angles a of 158, i.e. the angle between the fiber rovings and the winding normal is 158 and hence the angle between intersecting fiber bundles is 308 (also see Fig. 10). To obtain flat plates the material is removed from the mandrel and straightened. In order to achieve higher density and a better homogeneity the green plates were pressed between two aluminium oxide plates. In the final step the green plates were sintered in air at 1300 8C. 2.2. Preparation of test samples Two series of samples were prepared from the middle of each plate, as shown in Fig. 2. The samples used for microscopic analysis were taken from series a, whereas the samples corresponding to series b were used to determine the mechanical characteristics, particularly the shear strength. As not all samples from row a were used for microscopy, it could be established that, although the mechanical properties can vary significantly from sample to sample in the direction perpendicular to the winding direction (i.e. form sample 1–12 in Fig. 2), they are reasonably coherent in corresponding samples from a and b. This allows the assignment of microscopical and mechan￾ical data relating adjacent samples. All WHIPOX materials investigated in this study consist of Nextel 610 (3M) alumina fibers and an Al2O3-rich alumino-silicate matrix. Samples cut from the same plate, but from different positions, one from the edge (1a) and one from the middle (6a) (see Fig. 2), were investigated in order to clarify whether location dependent differences exist. In addition, the effects of green bodies compression were investigated by comparing a mildly (<10%) and a strongly compressed (<25%) material. 2.3. Mechanical testing Mechanical tests were performed by 3-point bending using a 20 mm support distance. Bending bar width and thickness was 10 and 3 mm, respectively. Load deflection curves show a non-brittle fracture behavior [6]. The interlaminar shear strength (ILSS) was calculated according Fig. 1. Scanning electron micrograph (overview) of WHIPOX all oxide CMC. Matrix infiltrated fiber bundles may form laminae separated by fiber free areas (matrix agglomerations with macropores) from each other. Fig. 2. Sketch of sample positions within a WHIPOX plate. Series b specimens were tested mechanically while selected series a specimens were used for microscopic analyzes. For that, an individual series a specimen bar was cut into 20 slices of 1.5 mm thickness. 614 M. Schmu¨cker et al. / Composites: Part A 34 (2003) 613–622