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#13908, The Influence of Specimen Thickness on the Lüders Effect in Mild Steel: Experimental Observations using DIC

At certain temperatures and strain rates, low carbon steels, as well as some aluminum and magnesium-based alloys, exhibit plastic flow instability at the onset of their respective yield points, known as the Lüders effect. Such effect is recognized by a distinct yield point and subsequent plateau on the stress-strain curve, and takes the form of a band when full-field tensile strain contours are observed experimentally. The work presented here investigates the specimen thickness dependence of the Lüders effect in mild steel. Uniaxial testing in conjunction with digital image correlation were employed to gain insight and capture the Lüders band formation, size, as well as rate of propagation during the extent of the plateau. More specifically, 1 mm, 2 mm, 3 mm, and 4 mm thick flat specimens of mild steel were tested under identical conditions, most notably strain rate, in order to isolate and understand the effect of specimen thickness. Preliminary findings demonstrated that the Lüders effect is greatly influenced by the specimen's thickness in mild steel, whereby an increase in specimen thickness results in a decrease in Lüders strain, and an increase in Lüders band velocity.

Joost van der Heijde   Rochester Institute of Technology
Wael Samad   Rochester Institute of Technology