Discontinuous Deformation of Tensile Steel Bars: Experimental Results

Marked differences have been observed between the global and local responses of tensile steel bars—the first traditionally defined by considering average strains (displacement of the bar's ends divided by its undistorted length), and the second obtained by local strain measures through high performance resistance strain gauges. This distinction highlights the peculiarities of various qualities of steel normally employed as reinforcement in concrete. In particular, the phenomenon of serrated deformation at yielding (the Portevin-Le Chatelier effect) and the peculiarities of this metastable state, when unloading sequences are performed, will be discussed. It will be shown how the presence of ribs can influence the local behavior and how this is reflected in the gross response. In the analysis, the importance of strain hardening in improving the ductility performance of steel bars is observed.