Issue 18

G. Del Piero et alii, Frattura ed Integrità Strutturale, 18 (2011) 5-13; DOI: 10.3221/IGF-ESIS.18.01 11  Figure 2 : Response curves for a steel bar in numerical simulations with N = 3 and different values of l , and experimental response curve (the dotted line) for l = 80 mm.   Figure 3 : Force-elongation response curve for a steel bar in a numerical simulation with N = 6 and l = 80 mm, compared with the experimental response curve (the dotted line) (a). Detail of the plateau at the onset of the inelastic regime (b) For the concrete specimen, at present the simulations are still in progress. A first result is shown in Fig. 4. While the general trend of the response is well reproduced, just after the onset of the inelastic deformation a sharp change of the slope occurs in the simulation but not in the experiment. A larger N is probably necessary to eliminate this discrepancy. The distribution of the inelastic deformation  ( x ) along the bar’s axis is shown in Fig. 5 for different values of  . The resemblance with the measurements by Miklowitz made many decades ago [11], is impressive. Both diagrams show a progressive concentration of inelastic deformation at the central zone of the bar. If we imagine that, by a sort of Poisson effect, axial elongation is accompanied by a proportional transversal contraction, we have that a concentration of axial deformation is accompanied by the necking of the cross section. Therefore, the proposed model provides a good description of the phenomenon of necking observed in bars subjected to a tensile load.