Issue 40

Z.S. Metaxa et al, Frattura ed Integrità Strutturale, 40 (2017) 61-73; DOI: 10.3221/IGF-ESIS.40.06 70 loads gives measurements that can be hardly be quantified and processed. To this end, this fiber seems to be more favorable for future research in case that proper interphase will be created with the surrounding matrix. Figure 12 : Incremental loading – unloading loops in type I specimen with embedded coated PVA-CNT fiber for applied loadings up till: (a) 40 Ν, (b) 160 Ν, (c) 200Ν, (d) 280 Ν, (e) 360 Ν and (f) 520 Ν (fracture). Fig. 14 shows the respective test results for the type II specimen with the surface attached fiber. Test results are more encouraging when compared with the respective constant amplitude results, as the screening of the ERC measurements is evident. Linearity between strain and ERC measurements can be justified for low strain values, while hysteresis loops are formed when unloading the specimens, e.g. [20, 21]. Definitely this kind of fiber can be used for sensing applications, provided that optimization on the attaching procedure and loading transfer methodology should be applied. C ONCLUSIONS • An experimental work has been performed to successfully accomplish the embedding procedure of the sensing fiber without damaging the sensor or the hosting medium. • Monotonic bending tests with in-situ electrical resistance change of the embedded fiber showed encouraging results. Linearity between bending strain at the bottom of the specimen and electrical resistance change of the embedded fiber for the low applied loading regime was evident. For higher applied monotonic stress, a sudden drop in ERC was noticed that was attributed to the loss of the interphase between the fiber and the specimen as well as micro- cracking formation at the sequence of the test up till fracture. • The embedded coated PVA-CNT fiber gave satisfactory results on the monotonic bending tests when compared against the coated and annealed PVA-CNT fiber. It enabled the linearity between applied strain and ERC at the low loading regime and generally gave higher ERC values when mechanically stressed that enables for the better screening of the test results. • For the case of constant amplitude tests, the embedded coated PVA-CNT fiber gave the best results, showing a trend of continuous increasing ERC measurements that can be justified with continuously increasing damage in the