A.R. Boccaccini et al. Joumal of Materials Processing Technology 169(2005)270-280 15KV 9 10 SEI 13 Z6 SE I Matrix 28kU X3, 008 Fig. 10. SEM micrographs of fracture surfaces of "sandwich structure" composites showing(a) impression left in the matrix by a fibre debonded during fracture,(b)very short"pull-out"length in these composites and (c)the relatively sharp interface between sapphire fibre and borosilicate glass, indicating strong fibre/matrix bonding. ished sample has better transmittance properties than the non- Fig. 12, can be analysed quantitatively by the following rela- polished sample; polishing the sample increases its optical tion, which was developed for optomechanical composites transmittance by 20%.The"sandwich structure"composites with regularly aligned fibres in a transparent matrix [24] exhibit an almost constant transmittance of about 60% before are in agreement with the images in Fig. 11, showing the Te=Tml_D polishing and of about 80% after polishing. These results (1) high transparency of the composites, and they confirm that e"optical window"concept is a convenient way to fabri- where Te and Tm are the light transmittance of the compos- cate optomechanical composites, as proposed in the literature ite and the monolithic matrix, respectively, and Dr and Lr [18, 24]. The present results are better in terms of transparency are the fibre diameter and fibre to fibre spacing, respectively than those obtained in our previous work [22], where only Incorporating the diameter of the sapphire fibre( 150 um) 60% transparency in Nextel fibre reinforced soda-lime glass and the fibre to fibre spacing(l mm)in Eq. (1), the light composites fabricated by the"sandwich structure"method transmittance of the polished"sandwich structure"compos- was achieved. The results are similar to those obtained ite relative to that of the monolithic matrix(Tc/Tm)is found recently by Dericioglu and Kagawa [44], who achieved 80% to be%. This value is in good agreement with the expe relative transparency in SiC fibre reinforced MgAl2O4 matrix imentally determined relative light transmittance value given optomechanical composites, in which the fibre diameter and in Fig. 12 for the polished composite that reads-80%.This fibre to fibre spacing were identical to those of the present result demonstrates the effectiveness of the optical window sandwich structure"composites. The light transmittance of concept in the present sapphire fibre/borosilicate glass com- the polished "sandwich structure"composite, which is given posites and its efficiency in providing optical transparency to relative to that of the monolithic borosilicate glass matrix in he resulting optomechanical composite278 A.R. Boccaccini et al. / Journal of Materials Processing Technology 169 (2005) 270–280 Fig. 10. SEM micrographs of fracture surfaces of “sandwich structure” composites showing (a) impression left in the matrix by a fibre debonded during fracture, (b) very short “pull-out” length in these composites and (c) the relatively sharp interface between sapphire fibre and borosilicate glass, indicating strong fibre/matrix bonding. ished sample has better transmittance properties than the non￾polished sample; polishing the sample increases its optical transmittance by 20%. The “sandwich structure” composites exhibit an almost constant transmittance of about 60% before polishing and of about 80% after polishing. These results are in agreement with the images in Fig. 11, showing the high transparency of the composites, and they confirm that the “optical window” concept is a convenient way to fabri￾cate optomechanical composites, as proposed in the literature [18,24]. The present results are better in terms of transparency than those obtained in our previous work [22], where only 60% transparency in Nextel® fibre reinforced soda-lime glass composites fabricated by the “sandwich structure” method was achieved. The results are similar to those obtained recently by Dericioglu and Kagawa [44], who achieved 80% relative transparency in SiC fibre reinforced MgAl2O4 matrix optomechanical composites, in which the fibre diameter and fibre to fibre spacing were identical to those of the present “sandwich structure” composites. The light transmittance of the polished “sandwich structure” composite, which is given relative to that of the monolithic borosilicate glass matrix in Fig. 12, can be analysed quantitatively by the following rela￾tion, which was developed for optomechanical composites with regularly aligned fibres in a transparent matrix [24]: Tc = Tm
1 − Df Lf (1) where Tc and Tm are the light transmittance of the compos￾ite and the monolithic matrix, respectively, and Df and Lf are the fibre diameter and fibre to fibre spacing, respectively. Incorporating the diameter of the sapphire fibre (∼150m) and the fibre to fibre spacing (∼1 mm) in Eq. (1), the light transmittance of the polished “sandwich structure” compos￾ite relative to that of the monolithic matrix (Tc/Tm) is found to be ∼85%. This value is in good agreement with the exper￾imentally determined relative light transmittance value given in Fig. 12 for the polished composite that reads ∼80%. This result demonstrates the effectiveness of the optical window concept in the present sapphire fibre/borosilicate glass com￾posites and its efficiency in providing optical transparency to the resulting optomechanical composite.