A.R. Boccaccini et al. Materials Characterization 54(2005)75-83 of fibres and softening of the glass matrix with consequent microstructural rearrangement [10]. This form of microstructural damage has been observed and discussed in other fibre-reinforced glass and glass-ceramic matrix composites aged at intermediate temperatures(in the range 400-800C)for different times(from a few hours to over 500 h)[7, 20 Fig. 8 confirms the same form of damage in the present composi observed by SEM on th sample thermally aged for 100 h at 700C. Despite 50um this extensive microstructural damage, the thermal expansion coefficient measured did not show a large difference with that of the as-received sample(see Fig. 6. SEM micrograph showing the fracture surface of a sample Fig. 3). This verifies theoretical results in the literature that had been subjected to thermal shock 20 times(A7-630"C), predicting that the thermal expansion coefficient of after impact test(4 J). Extensive fibre pull-out, similar to that bserved in the sample in the as-received state(Fig. 5), is observed materials is not affected by porosity [21] not exhibit a unique surface of fracture, and in a zone 4. Final remarks and conclusions that extends from the point of impact towards one of the sample edges, total debonding of the matrix (delamination) could be observed with only the fibre The thermal expansion coefficient(ac)was meas- bundles remaining on the fractured surface. Moreover, ured in Sic-Nicalon fibre reinforced glass matrix ome of these fibres have been fractured during the composite materials subjected to different mechanical impact test. Fig. 7 shows a macroscopic photograph of and thermal loads. The objective was to evaluate the the sample thermally aged(100 h, 700oC), which possibility to use this coefficient to monitor changes illustrates the morphology of fracture of the specimen in the material microstructure(microstructural dam- The degradation of the mechanical behaviour of this age) which occurred as result of the thermomechanical material as a result of the prolonged exposition to high mainly to the degradation of the interface, debonding Fig. 7. Macrograph showing the sample submitted to themal aging Fig. 8. SEM micrograph showing porosity induced in the glass (100 h, 700C), after impact test. Extensive macroscopic damage is matrix after thermal aging for 100 h at 700C, due to glass viscous observed and fracture by delamination along the fibres has occurred. deformation.not exhibit a unique surface of fracture, and in a zone that extends from the point of impact towards one of the sample edges, total debonding of the matrix (delamination) could be observed with only the fibre bundles remaining on the fractured surface. Moreover, some of these fibres have been fractured during the impact test. Fig. 7 shows a macroscopic photograph of the sample thermally aged (100 h, 700 8C), which illustrates the morphology of fracture of the specimen. The degradation of the mechanical behaviour of this material as a result of the prolonged exposition to high temperature in oxidant environments is attributed mainly to the degradation of the interface, debonding of fibres and softening of the glass matrix with consequent microstructural rearrangement [10]. This form of microstructural damage has been observed and discussed in other fibre-reinforced glass and glass-ceramic matrix composites aged at intermediate temperatures (in the range 400–800 8C) for different times (from a few hours to over 500 h) [7,20]. Fig. 8 confirms the same form of damage in the present composites, as observed by SEM on the sample thermally aged for 100 h at 700 8C. Despite this extensive microstructural damage, the thermal expansion coefficient measured did not show a large difference with that of the as-received sample (see Fig. 3). This verifies theoretical results in the literature predicting that the thermal expansion coefficient of materials is not affected by porosity [21]. 4. Final remarks and conclusions The thermal expansion coefficient (ac) was meas￾ured in SiC-NicalonR fibre reinforced glass matrix composite materials subjected to different mechanical and thermal loads. The objective was to evaluate the possibility to use this coefficient to monitor changes in the material microstructure (microstructural dam￾age) which occurred as result of the themomechanical Fig. 7. Macrograph showing the sample submitted to thermal aging (100 h, 700 8C), after impact test. Extensive macroscopic damage is observed and fracture by delamination along the fibres has occurred. Fig. 8. SEM micrograph showing porosity induced in the glass matrix after thermal aging for 100 h at 700 8C, due to glass viscous deformation. Fig. 6. SEM micrograph showing the fracture surface of a sample that had been subjected to thermal shock 20 times (DT=630 8C), after impact test (4 J). Extensive fibre pull-out, similar to that observed in the sample in the as-received state (Fig. 5), is observed. A.R. Boccaccini et al. / Materials Characterization 54 (2005) 75–83 81