M. Schmiicker et al /Composites: Part A 34 (2003)613-622 617 For a three-dimensional analysis, faws clearly dis- 经势 tinguishable in consecutive slices were marked and the coordinates of their centers were determined. Although the accuracy of this method is limited it gives a clear impression of the spatial distribution of flaw areas. The results are shown in Fig. 8: faw types i and iii their position on the plane perpendicular to the winding direction (x-z-plane) in going through the material winding direction (y-direction). Closer inspection reveals a continuous change in x-direction but a constant z-position Type ii flaws(Fig. 8b), on the other hand, do not change their x-z-positions in going from one slice to the other. e The angle between faw alignment and the winding ection (y-axis) is determined by the faw centers Fig.6.Construction of fiber cell areas(after [0): Fiber cell x contains all x-displacement and the known distance from one slice to points closer to fiber x than to any other. the next which is about 1.5 mm the angles thus found for a idealized microstructure, all deviations from a homogeneous total number of 13 type i and type iii flaws range between 6 fiber distribution leading locally to matrix enrichments, are and 20 Considering the accuracy of the measurements, it considered as fabrication-induced 'flaws,. Such matrix can be assumed that type ii and type iii flaws spread through agglomerations typically contain large macropores[ll] the sample by the winding angle of 1 The flaws occurring in the investigated WhIPOX CMCs can be grouped into three general types that differ in size, 3.2. Origin offiaws shape, and spatial distribution(Fig. 7) Type i flaws. As the rovings are wound at specific angle, Type i: Relatively large matrix agglomerations with huge misalignment of adjacent rovings will occur at their crossing pores(Fig. 7a) points: Flattening and compressing in the moist stage either Type ii: Narrow, lense-shaped matrix accumulations produces distorted laminae or wedge-shaped breakoff arise existing throughout the entire height of samples and as sketched in Fig. 9. Voids formed in these break off dividing the individual laminae from each other. This regions can be partially filled by matrix slurry pressed out type of defect is especially observed in samples from the from the surrounding infiltrated fiber bundles. Since these middle of the WHIPOX plates kind of flaws are associated with the crossing points of the Type iii: Matrix agglomerations which, however, are not fiber bundles they move across the material at the same ompletely fiber free. Thereby, the number of individual angle as the rovings are wound. For this type of flaws, fibers dispersed within this flaw area corresponds to the therefore, one should expect a change of position of 15,as number of fibers in the fiber roving used for the cmc one moves through the sample from one slice to the next. fabrication This actually has been observed Fig. 7. Different types of faws identified in the investigated WHIPOX CMCs. Type i(a): bulky matrix agglomerations with macropores; type ii(b): interlaminate matrix accumulations of moderate thickness existing throughout the entire height(z-direction, see Fig. 5); type iii(c): spread out fiber roving with high amounts of interlaminate matrixidealized microstructure, all deviations from a homogeneous fiber distribution leading locally to matrix enrichments, are considered as fabrication-induced ‘flaws’. Such matrix agglomerations typically contain large macropores [11]. The flaws occurring in the investigated WHIPOX CMCs can be grouped into three general types that differ in size, shape, and spatial distribution (Fig. 7): Type i: Relatively large matrix agglomerations with huge pores (Fig. 7a). Type ii: Narrow, lense-shaped matrix accumulations existing throughout the entire height of samples and dividing the individual laminae from each other. This type of defect is especially observed in samples from the middle of the WHIPOX plates. Type iii: Matrix agglomerations which, however, are not completely fiber free. Thereby, the number of individual fibers dispersed within this flaw area corresponds to the number of fibers in the fiber roving used for the CMC fabrication. For a three-dimensional analysis, flaws clearly dis￾tinguishable in consecutive slices were marked and the coordinates of their centers were determined. Although the accuracy of this method is limited it gives a clear impression of the spatial distribution of flaw areas. The results are shown in Fig. 8: flaw types i and iii (Fig. 8a and c) change their position on the plane perpendicular to the winding direction (x–z-plane) in going through the material in winding direction (y-direction). Closer inspection reveals a continuous change in x-direction but a constant z-position. Type ii flaws (Fig. 8b), on the other hand, do not change their x–z-positions in going from one slice to the other. The angle between flaw alignment and the winding direction (y-axis) is determined by the flaw centers’ x-displacement and the known distance from one slice to the next which is about 1.5 mm. The angles thus found for a total number of 13 type i and type iii flaws range between 68 and 208 Considering the accuracy of the measurements, it can be assumed that type ii and type iii flaws spread through the sample by the winding angle of 158. 3.2. Origin of flaws Type i flaws. As the rovings are wound at specific angle, misalignment of adjacent rovings will occur at their crossing points: Flattening and compressing in the moist stage either produces distorted laminae or wedge-shaped breakoffs arise as sketched in Fig. 9. Voids formed in these break off regions can be partially filled by matrix slurry pressed out from the surrounding infiltrated fiber bundles. Since these kind of flaws are associated with the crossing points of the fiber bundles they move across the material at the same angle as the rovings are wound. For this type of flaws, therefore, one should expect a change of position of 158, as one moves through the sample from one slice to the next. This actually has been observed. Fig. 7. Different types of flaws identified in the investigated WHIPOX CMCs. Type i (a): bulky matrix agglomerations with macropores; type ii (b): interlaminate matrix accumulations of moderate thickness existing throughout the entire height (z-direction, see Fig. 5); type iii (c): spread out fiber roving with high amounts of interlaminate matrix. Fig. 6. Construction of fiber cell areas (after [10]): Fiber cell x contains all points closer to fiber x than to any other. M. Schmu¨cker et al. / Composites: Part A 34 (2003) 613–622 617