Issue 31

M. Merlin et alii, Frattura ed Integrità Strutturale, 31 (2015) 127-137; DOI: 10.3221/IGF-ESIS.31.10 131 (a) (b) (c) Figure 2 : Pull-out curves for (a) VE_NT, VE_A and VE_AB samples, (b) PE_NT, PE_A and PE_AB samples, (c) VE_S and PE_S samples. Fig. 2 depicts the results obtained from the pull-out tests performed on the samples, in which the NiTi wires subjected to different surface treatments are embedded in the two PE and VE resins. In particular, Fig. 2a shows the curves related to the pull-out samples realised with VE resin and in the surface conditions of the NT, A and AB wires. Fig. 2b shows the results of the pull-out tests for the PE resin with embedded wires in the NT, A and AB surface conditions. The pull-out curves of the samples in VE and PE resin with wires functionalised with the silane coupling agent are compared in Fig. 2c. In Fig. 2 it should be noted that the cutting-off of the pull-out curves corresponding to the sudden drop to the quasi-zero load level is marked with a short vertical solid line. As can be seen, all curves present a small plateau of 0.2-0.3 mm in correspondence to an applied force of ≈15-20 N. This plateau should be compared with the one observed in Fig. 3, which reports the engineering stress-strain curve of the same free heated NiTi wire. Therefore, in this initial region of the pull-out test the curve reproduces only the stress-strain behaviour of the free length wire. Figure 3 : Engineering stress-strain curve for the heated NiTi wire.