Issue 27

T.V. Tretiakova et alii, Frattura ed Integrità Strutturale, 27 (2014) 83-97; DOI: 10.3221/IGF-ESIS.27.10 87 (a) (b) (c) Figure 5 : Axial strain (a) , (c) and axial strain rate (b) fields on the specimen’s surface (corresponding to point I, Fig. 4). Stage of Yield Plateau Forming The rapid jump of the axial strain level up to 0.93% yy   was registered on the specimen surface from the grip side at the moment of transition from the yield drop to the yield plateau or the lower yield point ( Н Т  ). At the same time, the load value declined to 2.40 kN. The experimental data depicted in Fig. 6 corresponds to point II of the load-displacement curve (Fig. 4). It is the moment when the front of the localized plastic strain nucleated and started to propagate along the specimen gauge. According to the scientific literature, this is the well-known example of the unstable plastic flow of the material, the so-called Lüders behavior [1, 2, 4, 14]. The strain rate at the top of the front swiftly increased to 2.66%/ yy s    . (a) (b) (c) Figure 6 : Axial strain (a) , (c) and axial strain rate (b) fields on the specimen’s surface (corresponding to point II, Fig. 4).