Evolution of Localization Length during Postpeak Response of Steel in Tension: Experimental Study

Abstract

This paper presents an experimental study into the influence of localization length (Lc) and its evolution during the postpeak response of cylindrical low-carbon steel bars. A novel longitudinal strain method for the determination of the localization length is compared to the average strain method. Four specimen lengths [38.1 mm (1.5 in.), 76.2 mm (3 in.), 152.4 mm (6 in.), and 304.8 mm (12 in.)] with a diameter of 12.7 mm (0.5 in.) were tested according to ASTM A370 standards. A three-dimensional digital image correlation (3D DIC) measurement system was used to record the longitudinal and transverse deformations along the specimen length. The results indicate that the engineering stress-strain relation up to the peak load is almost identical for all tested specimens. However, the postpeak response shows a steeper softening response for longer specimens. Two methods were used to extract the localization length from the longitudinal engineering strain profile. The average strain method shows a length dependence for different specimen lengths, while the longitudinal strain method eliminates the length dependence. The consistency of the localization length obtained through the longitudinal strain method enables improved generalized analytical relationships. Linear and exponential curve fitting formulae are given to predict the localization length for a generic specimen.