Ductile Fracture Tests and Simulation of High-Strength Steel at Elevated Temperatures

This paper presents the experimental results of Q690 steel coupons tensioned to fracture at elevated temperatures, and the development of a finite element methodology for investigating the ductile fracture behavior. Smooth round bars, notched round bars, and flat shear sheets were tested and analyzed to cover the conditions of high-, intermediate-, and low-stress triaxialities, respectively. It was found that the fracture strain could either increase or decrease with increasing temperature within a given range, depending on the stress state. Finite-element models (FEMs) were developed using a newly proposed damage accumulation law. Compared to the traditional damage accumulation law, the new law is consistent with the constant stress state assumption and avoids error accumulation through successive increments. With the new law, the scaling factor used to account for mesh sizes can be determined without iteration. The developed FEMs closely traced the load-displacement paths of the smooth and notched round bar specimens including their postfracture paths at various elevated temperatures. The FEMs were less successful in tracing the postfracture paths of the flat shear sheets due to the existence of uniform stress–strain fields in the potential fracture section. In all cases, the fracture initiation points were accurately determined. The developed numerical procedure was also verified against bolted connections tested by independent researchers.