PSI - Issue 23

Zdeněk Chlup et al. / Procedia Structural Integrity 23 (2019) 505 – 510 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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c)

d)

Fig. 3 SEM micrographs of fracture surfaces for composites reinforced by a) E-Glass, b) R-Glass, and c-d) Carbon fibres.

Explanation of obtained results is connected with the fracture mechanism acting. In the case of basalt fibres, reinforced composite was predominately active fibre pull-out which was also reported in our previous work (Cerny, Glogar, Sucharda, Chlup, & Kotek, 2009). Similarly, in the case of E- and R-Glass reinforced composites the fibre pull out toughening mechanism was observed as is shown in Fig. 3a, b) but the fibre pull-out length was significantly shorter compared to basalt fibres (one order of magnitude). Therefore, less effective as corresponds with obtained mechanical characteristics (Chawla, 2012). The carbon fibres reinforced composite exhibited rarely the fibre pull-out as is demonstrated in Fig. 3c) and in detail in Fig. 3d). The obtained higher mechanical resistance of carbon fibres reinforced composite in comparison with composites reinforced by glass fibres can be ascribed to higher Young modulus which is approximately three times higher than glass fibre. Than suppressed pull-out is compensated by higher ability of load transfer trough elastic fibre deformation and strong fibre-matrix bonding given by high surface roughness. It is obvious that the composition of fibres plays a key role in the formation fibre matrix interface. One can deduce that the pull-out mechanism activity is closely connected with interfacial/deboning strength between matrix and fibres. The chemistry of the matrix is kept the same and the only change is on the fibres side. Two silicate glass fibres with similar chemical composition as basalt fibres, differing mainly in the presence of iron oxides (see Table 1), were used for comparison as well as pure carbon fibres. This finding indicates that iron oxide is responsible for an optimal fibre – matrix bonding what is in good agreement with the literature and our previous hypothesis (Subramanian & Austin, 1980; Černý, Sucharda, Strachota, Chlup, & Glogar, 2010) . The resulting mechanical properties are in all cases strongly in favour of basalt fibres. The partially pyrolysed SiOC based matrix composites reinforced with various fibres were successfully prepared using the same process parameters. It was clearly demonstrated that the fibres surface quality, their diameter as well as the chemical composition influences resulting properties when used in the same matrix. Results presented here suggested that the content of iron in the basalt fibres plays a significant role. This hypothesis is supported by the fact that silicate fibres reaching similar chemical composition as well as fibre diameter and surface quality (E-Glass) possess lower fracture toughness and flexural strength. No even other silicate fibres or carbon fibres reached the exceptional properties obtained when basalt fibres were used. Acknowledgements This research was supported by the Czech Science Foundation under the project GAP 17-12546S and the infrastructure was supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project CEITEC 2020 (LQ1601). 4. Conclusions