D. Hiilsenberg et al/ Composites: Part B 39(2008)362-373 369 TO FVC% Inm BN-40nm TO, FVC 12% 5-40nm BN-11Onm TO,, FVC 10% △a(FM)=0.pmK Fig10.Three-point-bending-test curves of differently coated Nextel 440-fibers and 756 glass matrix: AzF-M=0.5x10-K- Matrix BN Fig. Il. SEM-picture of a fracture surface of a composite Nextel 440) 40 nm BN, 40 nm TiO/756 glass Fiber broken composite shows where the Ti+ is located, cf. Fig. 13. On the left, the Ti portion on the surface of 30 nn double-coated fiber is given(arbitrary units). The figure Fig 12. TEM-picture of the interphases in a composite Nextel 440/40 nm in the middle shows the situation on the surface of a for- BN, 20 nm Tio) /756 glass (picture made at the TU Chemnitz) merly double-coated fiber after fiber pull-out. The EDX analysis revealed that the Ti had almost completely left the fiber. The TiOz layer, which had seemingly got lost, is glass is considerably higher than that of the Nextel 440 found in the valley of the matrix glass(channel where the fiber. From this fact, it may be concluded that the matrix iber was originally running) as can be seen from Fig 13, will clamp the fibers when the hot-pressed composite is on the right. Hence, one can draw the conclusion that the cooled, thus preventing the fiber pull-out even if they are sliding or fiber pull-out takes place between the BN- and coated with BN. In this case, the composite is not dam the TiOz-layer. The TiOz-layer reacts with the matrix age-tolerant. Nevertheless, a composite was prepared and (probably through diffusion), or the comparatively rough tested as the refractive indices of the fiber and the matrix anatase surface prevents each kind of relative movement correspond well with each other and N-SK 4 glass does between itself and the matri not contain any lead oxide. The tensile strength of the dif- ferently coated fibers is already illustrated in Fig. 2. Only 4.3. Mechanical properties of Nextel 440-fibers/N-SK 4 glass the fibers coated with TiO2 or BN-single layers present a Matrix coMposite significantly lower tensile strength, which could have an influence on the properties of the composite. The tensile Comparing Tables I and 2 with each other, one can strength of the double-coated fibers, whose layers present immediately see that the expansion coefficient of N-sk 4 different thicknesses, differs only slightly from that of thebroken composite shows where the Ti4+ is located, cf. Fig. 13. On the left, the Ti4+ portion on the surface of a double-coated fiber is given (arbitrary units). The figure in the middle shows the situation on the surface of a for￾merly double-coated fiber after fiber pull-out. The EDX analysis revealed that the Ti4+ had almost completely left the fiber. The TiO2 layer, which had seemingly got lost, is found in the valley of the matrix glass (channel where the fiber was originally running) as can be seen from Fig. 13, on the right. Hence, one can draw the conclusion that the sliding or fiber pull-out takes place between the BN- and the TiO2-layer. The TiO2-layer reacts with the matrix (probably through diffusion), or the comparatively rough anatase surface prevents each kind of relative movement between itself and the matrix. 4.3. Mechanical properties of Nextel 440-fibers/N-SK 4 glass matrix composites Comparing Tables 1 and 2 with each other, one can immediately see that the expansion coefficient of N-SK 4 glass is considerably higher than that of the Nextel 440 fiber. From this fact, it may be concluded that the matrix will clamp the fibers when the hot-pressed composite is cooled, thus preventing the fiber pull-out even if they are coated with BN. In this case, the composite is not dam￾age-tolerant. Nevertheless, a composite was prepared and tested as the refractive indices of the fiber and the matrix correspond well with each other and N-SK 4 glass does not contain any lead oxide. The tensile strength of the dif￾ferently coated fibers is already illustrated in Fig. 2. Only the fibers coated with TiO2- or BN-single layers present a significantly lower tensile strength, which could have an influence on the properties of the composite. The tensile strength of the double-coated fibers, whose layers present different thicknesses, differs only slightly from that of the Fig. 10. Three-point-bending-test curves of differently coated Nextel 440-fibers and 756 glass matrix; DaF–M = 0.5 · 106 K1 . Fig. 11. SEM-picture of a fracture surface of a composite Nextel 440/ 40 nm BN, 40 nm TiO2/756 glass. Fig. 12. TEM-picture of the interphases in a composite Nextel 440/40 nm BN, 20 nm TiO2/756 glass (picture made at the TU Chemnitz). D. Hu¨lsenberg et al. / Composites: Part B 39 (2008) 362–373 369