## 3 Results and Discussion
### Experimental Results
This is because once a crack faces a fiber, it demands higher energy of the fracture to pull the fiber out and then propagate [15]. Figure 5: Strength vs. fiber content (black line: compression test; blue line: bending test; red line: splitting test): (**a**) yield strength; (**b**) ultimate strength. The fundamental role played by the fiber in the mechanical behavior of the material under examination can be further evidenced by examining Figure 6, where, for each mechanical test, the ratio between the ultimate strength and the yield strength is sketched. This ratio indicates the ability of the material to possess a hardening phase. As it is evident from Figure 6, in the case of compression, this ratio is almost independent from the fiber content, while in the case of the splitting test and three-point bending tests, this ratio shows an increment of about 40-60% (depending on the test) with the fiber content, confirming either its fundamental role in the tensile behavior of the material and the results reported in [44] and suggesting that, in this case, the fiber length does not greatly influence the results. To further evaluate the influence of the fiber content on the mechanical behavior of the material, in Figure 7, the strength ratios \(f_{cu}/f_{fu}\), \(f_{cu}/f_{tu}\) and \(f_{tu}/f_{fu}\) are sketched versus the fiber content. In all cases, the evolution of the curves is a decreasing one confirming, as reported in [46], that the fibers influence the flexural behavior more than the compressive and splitting ones and that this influence is greater in tensile behavior than in the compressive one. In Figure 8, the Young' modulus in the case of compression and bending tests is sketched vs. the fiber content. The obtained result confirms the remark already made for Figure 3, i.e., the dependency of the relevant mechanical parameter on the fiber content is higher in the case of the three-point bending test. Finally, to characterize the post-crack energy absorption ability induced by the fiber reinforcement and its dependency on the fiber content, in Figure 9a, the fracture energy determined from the experimental tests is sketched vs. the fiber content. The fracture energy \(G_{f}\) defined as the amount of energy absorbed to create a unit area of a crack, which was determined starting from the stress-displacement curves obtained through the experimental tests, assuming a linear interpolation of the post-peak behavior to calculate the displacement at null stress; \(G_{f}\) is calculated as the area under the post-peak behavior. It can be seen from the Figure that the role played by the fiber reinforcement is confirmed since, in all tests, \(G_{f}\) increases with the fiber content. To enhance the stitching effect of the fibers in Figure 9b, the ratio between \(G_{f}\) and its value in the absence of fibers (\(G_{f,0}\)) is sketched vs. the fiber content. Also, in this case, the obtained result confirms the role of the fiber content, since in the test where tension stress arises significantly (i.e., bending and splitting tests), this ratio increases by up to more than 60 times in the bending test and  
Figure 6: Ultimate strength/yield strength vs. fiber content (black line: compression test; blue line: bending test; red line: splitting test). more than 10 times in the splitting test, whereas in the compression test, this increment is around 5 times. Figure 8: Young’ modulus vs. fiber content (black line: compression test; blue line: bending test). Figure 7: Strength ratio vs. fiber content (black line: \(f_{cu}/f_{fu}\); blue line: \(f_{cu}/f_{tu}\); red line: \(f_{tu}/f_{fu}\)).