PSI - Issue 78

Antonella D’Alessandro et al. / Procedia Structural Integrity 78 (2026) 1887–1894

1891

= ∗ 4

(6)

where F is the applied load. The moment of inertia (I n ) for a rectangular cross-section is calculated as follows: = ∗ℎ 3 12 (7) With b corresponding to the width of the sample. The normal bending stress ( α ) at a given distance from the neutral axis can be determined using Equation 8: = ∗ (8) where c is the distance from the neutral axis to the outermost fiber. 2. Results Electrical conductivity measurements were performed under unloaded conditions using biphasic signal acquisition. The 3D-printed cement paste samples doped with CCMF showed conductivities of 2.006 S/m and 0.794 S/m when printed in the longitudinal and transverse directions, respectively. In comparison, the cement mortar sample with identical fiber doping levels and longitudinal printing direction exhibited a lower conductivity of 0.439 S/m. The higher conductivity observed in the longitudinally printed cement paste sample may be attributed to the alignment of carbon fibers along the conductive path between the electrodes. On the other hand, the lower conductivity observed in the mortar sample printed in the longitudinal direction is related to the presence of sand in the mixture, which disrupts the continuity of the conductive paths. A variation in FCR was observed at the rupture point for all specimens, indicating crack initiation. In Figure 4a, the FCR increased by up to 70% for the paste printed in the longitudinal direction. In Figure 4b, an increase of up to 3% was noted, significantly lower than the previous sample, likely due to the fiber orientation following the transverse printing path. In Figure 4c, a sharp drop to -10% in FCR was followed by an increase up to 20%. This initial drop may be attributed to fiber alignment (CCMF) between printed layers, enhancing the bridging effect, while the subsequent rise indicates the failure of this bridge and crack propagation. a) b)

10 20 30 40 50 60 70

0 0,02 0,04 0,06 0,08 0,1

10 20 30 40 50 60 70

0 0,02 0,04 0,06 0,08 0,1

FCR (%) Strain (mm/mm)

Crack initiation

Crack initiation

FCR (%)

FCR (%)

-10 0

-10 0

Strain (mm/mm)

Strain (mm/mm)

0 500 1000 1500 2000 2500 3000

0 500 1000 1500 2000 2500

Time (s)

Time (s)