PSI - Issue 23

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

507

3

Specimens for flexural strength and fracture toughness tests with nominal dimensions 2.5  4  45 mm were prepared. The three-point bending configuration with the span of 40 mm for load application in the position controlled regime using the cross-head speed of 0.5mm/min at a universal testing machine Instron 8862 (Instron, USA) was used in both cases. The chevron notch technique for fracture toughness determination was employed. The same testing system was used but the span was set to 16 mm and the cross-head speed to 0.1 mm/min. At least 6 valid values for each experiment were obtained. The bulk density was determined from the weight and dimensions of each specimen. The microstructural and fractographical analysis was performed using an SEM Lyra 3 XMU (Tescan, Czech Republic). Image analysis of cross-section to estimate fibres diameter distributions (at least 1000 fibres) and the fibre volume fraction (at least 5 micrographs) was utilised.

3. Results and Discussion

The typical micrographs of polished cross-sections of all prepared composites can be seen in Fig. 1.

a)

b)

c)

d)

Fig. 1 Cross-section micrographs of composites reinforced by a) Basalt, b) E-Glass, c) R-Glass and d) Carbon fibres.

Obvious differences are visible especially defects in the microstructure of composite with R-Glass reinforcement when compared with others. Morphology of fibre cross-sections is noticeable in the case of carbon fibres where the irregular shape is present. Both the fibres average diameter D f,avg and the fibre volume fraction v f in the composite were determined from the polished cross-sections and are together with corresponding geometrical densities of composites summarised in Table 2.