PSI - Issue 13

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

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Fig. 5. Indirect tensile strength over loading rate (all specimens)

3. Concluding remarks The main objective of the presented investigation was to provide more information about the effects of various micro-fibre reinforcement on tensile behaviour of fine-grained cementitious composites at high strain rates, needed for the design of the suitable hybrid reinforcement for UHPC and SIFCON type composites. The following conclusions can be drawn: - The addition of fibres increases indirect tensile strength at quasi-static load, whereas dynamic indirect tensile strength was generally affected by fibres addition only in low extent, the calculated values were only up to 4% higher compared to plain specimen (aramid fibre), and even lower in the case of specimen reinforced with polypropylene fibre. - All tested specimens showed strain rate dependence. With the increase of strain rate, the peak stress increased significantly. The highest value (13.9) of DIF fct was observed in the case of plain specimen without fibres; fibre reinforced specimens showed lower strain rate effect (DIF fct 6.5-9.1). The fibre network formed by the presence of the fibres may slow crack velocities, which influences the DIF fct . - Quasi-ductile behavior of fibre reinforced specimens as observed under quasi-static loading remained and even improved with loading at high strain rates. Addition of any kind of fibre enhances the ductility of the material at both quasi-static and dynamic load, but the level of the enhancement is different and depends on the mechanical properties of the incorporated fibres. The highest critical strain (2.1) was obtained in the case of specimen reinforced with aramid fibres, followed by PP (1.7) and carbon (1.3) reinforced specimen. The same value for specimen without fibres was 0.5. It was observed, that high tenacity of the fibre is not the only relevant factor when good mechanical parameters at impact load need to be achieved; the value of tensile strength and critical strain at high stain rates seems to be related to both the strength and elongation of the incorporated fibre. Thus, mechanical parameters (including ductility) at high strain rate loading can be positively influenced by proper selection of the fibre. - From the mechanical parameters point of view, aramid fibres seems to be the most effective reinforcement, the achieved values of both indirect tensile strength and critical strain of the aramid fibre reinforced specimen outperformed the values obtained when using the other tested fibres (PP, carbon). Acknowledgement The authors wish to express their gratitude and sincere appreciation to the authority of Ministry of Industry of Czech Republic, project No. 10120, for financial support.