Issue 40

Z.S. Metaxa et al, Frattura ed Integrità Strutturale, 40 (2017) 61-73; DOI: 10.3221/IGF-ESIS.40.06 66 sensors) constant amplitude loadings - unloadings have been performed to assess the screening of the sensors. In total 11 different test categories were performed that can be seen in Tab. 3. Reference Coated PVA-CNT fiber Coated and annealed PVA-CNT fiber (-) P - - Attached surface strain gauge P M, P M, P FOBG and attached surface strain gauge M, P P P NOMENCLATURE: M: Monotonic four point bending (4pb) till fracture P: Progressive damage accumulation in 4pb (incremental loading-unloadings till fracture) Table 3 : List of the experimental tests. R ESULTS AND DISCUSSION he experimental bending test results will be presented and discussed in this section in order to establish a useful correlation of the readings of the embedded / attached sensors with the mechanical deformation of the specimen. Monotonic bending tests Monotonic tests have been performed on different specimens for the three investigated embedded sensors, (a) coated PVA-CNT fiber, (b) coated and annealed PVA-CNT fiber and (c) FOBG. Fig. 6 shows the comparison of the mechanical response of the each specimen during four-point bending testing. The specimens with the embedded PVA-CNT fiber seem to resolve identical maximum stress values along with axial deformation at the bottom level of the specimen. All four different cases seem to have approximately the same mechanical response and the average fracture stress is around 3 MPa. Figure 6 : Comparison of the monotonic mechanical response of the specimens with embedded sensors. Fig. 7 shows the mechanical response of the material along with the simultaneous electrical resistance response of the embedded PVA-CNT fiber for the monotonic loading of the specimen till the macroscopic fracture. Fig. 7a corresponds to the coated PVA-CNT fiber, while the respective results of the coated and annealed PVA-CNT fiber can be seen in Fig. 7b. By comparing the two diagrams, it can be clearly seen that linearity is evident in both types of fibers for the low applied loadings that corresponds to the elastic loading regime. This linearity is no longer evident with increasing the applied bending stresses. Additionally, for the case of the coated PVA-CNT fiber this linear stage ends at higher ERC values that allows for better screening of the results. This loss in linearity is probably due to the partial fracture of the 0 50 100 150 200 250 0 1 2 3 4 Maximum bending stress [MPa] Lower surface axial strain [με] Four point bending tests on prismatic mortar samples with embedded: no fiber coated PVA-CNT fiber coated and annealed PVA-CNT fiber FOBG fiber T