PSI - Issue 13

Martina Drdlová et al. / Procedia Structural Integrity 13 (2018) 1731–1738 Drdlová and Čechmánek/ Structural Integrity Procedia 00 ( 2018) 000 – 000

1736

6

which is more than 4 times higher than the critical strain of specimen No. 4 (without fibres). High value of critical strain (1.7%) was achieved also in the case of polypropylene fibre reinforced specimen (No. 2), even though their tenacity is quite low (40 cN/tex compared to 240 cN/tex of used aramid fibres). The critical strain of No. 2 specimen was higher than this of carbon fibre reinforced specimen (1.3%), which could be attributed to the low elongation of carbon fibres. High-speed loading leads to the formation of high number of finer-disconnected cracks than low speed loading does; such increase in number of microcracks activates a greater number of fibres; the effective crack-bridging by fibres delays the failure localisation and therefore supports multiple cracking, which increases the ductility of the whole material. The higher critical strain achieved in the case of fibre reinforced specimens may be attributed to the fact that the incorporated fibres prevent the material from disintegration and reduce the lateral expansion of the specimens. Thus, a higher strain rate is required to start the change of the behaviour for fibre reinforced mixtures. Further research is planned to be performed on the fractured surfaces of all specimens using electron microscopy, when the surface and deformation of the fibres will be investigated. Also, other fibres with different mechanical properties are planned to be investigated. The influence of fibre amount and length will be also observed.

Fig. 3. Strain-time courses of aramid reinforced (left) and plain (right) specimens

Fig. 4. Strain-time courses of carbon (left) and polypropylene (right) reinforced specimens