Issue 27

T.V. Tretiakova et alii, Frattura ed Integrità Strutturale, 27 (2014) 83-97; DOI: 10.3221/IGF-ESIS.27.10 88 (a) (b) (c) Figure 7 : Axial strain (a) , (c) and axial strain rate (b) fields on the specimen’s surface (corresponding to point III, Fig. 4). When the front reached the opposite side of the specimen, the configuration of the axial strain fields became almost homogeneous (Fig. 8). It is important to note that in the region where the front of the localized strain had passed, the material’s deformation processes stopped until the next deformation stage - the material hardening stage. (a) (b) (c) Figure 8 : Axial strain (a) , (c) and axial strain rate (b) fields on the specimen’s surface (corresponding to point IV, Fig. 4). To conduct numerical analysis and show regularities in the Lüders band motion, the diagrams of axial strain and the axial strain rate were calculated along the central line of specimen (in the line of loading). The curves I IV t t  , shown in Fig. 9, correspond to points I–VI of the P–u curve (Fig. 4). The velocity of the strain band propagation was about 7.7 mm/s or 462 mm/min and remained quite stable during the whole stage of the yield plateau forming. It is known that during the Lüders band motion the slope of the load-displacement curve is approximately zero, in other words the load remained at the level of 2.4 kN. The macroscopic increase of specimen was provided by the localized deformation in the region of the strain band.