Uncoupled fracture model for E250, E350, and E450 grades of structural steel under monotonic loading

Abstract

Forty-eight specimens with four notch specimen configurations have been extracted from three structural steel grades used in the Indian construction industry. The extracted specimen simulates stress states of ductile fracture initiation similar to the sacrificial element installed in seismic-resistant steel structures. All the specimens are monotonically tested under a displacement-controlled loading protocol. With the help of a universal testing machine and digital image correlation, the load versus notch elongation until the point of ductile fracture initiation has been captured for all the specimens. A validated numerical model is then developed to extract the ductile fracture initiation parameters, namely stress Triaxiality (T), Lode function (L - ξ or θ or Lp), and Equivalent Plastic Strain (PEEQ). The extracted T, L, and PEEQ are then used to construct a three-dimensional fracture locus for all three study grades. In addition, a new uncoupled ductile fracture model named the Exponential based Lode parameter Void Growth Model (ELVGM) is proposed to predict the point of ductile fracture initiation and is then compared with six well-established existing uncoupled ductile fracture models using eight error measures. The proposed ELVGM with two free parameters is observed to provide better prediction accuracy for both low and high-yield strength steel corresponding to the considered stress states.