Issue 31

A. Abrishambaf et alii, Frattura ed Integrità Strutturale, 31 (2015) 38-53; DOI: 10.3221/IGF-ESIS.31.04 50 Series Parameter σ peak [MPa] σ 0.3 [MPa] σ 1 [MPa] σ 2 [MPa] G F1 [N/mm] G F2 [N/mm] θ = 0º (   ) NUM SPLT 4.50 4.10 2.60 1.25 3.91 6.35 EXP UTT 3.33 3.24 2.30 1.14 2.94 4.47 θ = 90º (   ) NUM SPLT 3.20 1.06 1.40 0.47 1.26 2.18 EXP UTT 2.72 1.05 1.02 0.56 1.09 1.86 Table 5 : Residual stress and toughness parameters obtained from different analysis. Fibre Concrete flow direction Figure 15 : Explanation for fibre alignment in flowing concrete of a panel casting from the centre. Fig. 16 depicts the relationships between the fibre distribution, f eff N , the fibre orientation factor ( η θ ) and the post-cracking parameters, as well as their projection for both series obtained from the uniaxial tensile test. Since post-cracking parameters were affected by not only the fibre distribution but also the fibre orientation, it is more logical to plot these parameters versus both factors. It was observed, as expected, that the post-cracking parameters, except σ peak , had a tendency to increase with the fibre orientation factor and the number of fibres bridging the fracture surface, being this effect more pronounced in the σ 0.3 and σ 1 . To investigate the influence of each factor ( f eff N or η θ ) on the post-cracking parameters, independently, in each figure, the projection of the results in the corresponding plane was executed. In all figures, θ= 0 ° specimens showed higher post-cracking parameters and also lower scattering. As it was proved from the image processing results in the previous section (Tab. 2), the CoVs of f eff N and η θ for the θ= 90 ° series were considerably higher than for the θ= 0 ° series. C ONCLUSIONS n this study, the influence of fibre dispersion/orientation on the tensile post-cracking parameters of steel fibre reinforced self-compacting concrete panel was investigated. The σ – w law was determined indirectly from inverse analysis of the splitting tensile test results, as well as directly derived from the uniaxial tensile test. According to the experimental and numerical investigation, the following conclusions could be derived out: 1. The tensile behaviour of the drilled specimens from the panel was influenced by the fibre dispersion and orientation significantly. Specimens with notch direction parallel to concrete flow ( θ= 0 ° ) have significantly higher post-cracking residual stresses than when the notch direction was perpendicular to the flow direction ( θ= 9 0 ° ). 2. Roughly, a linear relationship between number of the effective fibres, orientation factor and post-cracking parameters were observed. It was shown that by increasing the number of effective fibres as well as their orientation, fracture parameters tend to raise. This strong dependency could explain that in θ= 0 ° series due to the appearing higher number of effective fibres which were mainly perpendicular to the crack plane, the concrete represented a semi- hardening behaviour, while in the other series a high stress decay was achieved. 3. In the case of casting panels from the centre, fibres have a tendency to align perpendicular to the radial flow, mainly due to the uniform flow profile velocity that diffuses outwards radially from the centre of the panel. Consequently, the total number of the effective fibres was higher in crack planes parallel towards the concrete flow ( θ= 0 ° ) when compared to the other case of an orthogonal crack plane towards the concrete flow ( θ= 90 ° ). I