Ductile Fracture Simulation of Constructional Steels Based on Yield-to-Fracture Stress–Strain Relationship and Micromechanism-Based Fracture Criterion

Fracture is an important mode of failure in steel structures, whereas traditional fracture mechanics is difficult to apply in predicting ductile fracture in the presence of large-scale yielding or in flaw-free geometries. This study offers a means for numerical simulation of ductile fractures of constructional steels. Experimental investigations on the conventional smooth round bar specimens are carried out with special focus on the postnecking strain hardening and fracture properties, and a new experimental procedure is proposed to explicitly obtain the yield-to-fracture true stress–strain relationship, as well as the fracture strain and corresponding stress triaxiality. A fracture criterion is proposed by means of finite-element unit cell–based micromechanical studies, in which the most significant microscopic features of fracture including both void growth and coalescence are considered. To calibrate and validate the proposed fracture criterion, tests of notched round bar specimens representing high stress triaxiality are also carried out. The numerical method for material fracture simulation in implicit time integration analyses is addressed, and matters needing attention when using such a method are discussed, including the countermeasures of convergence difficulties caused by material softening and determination of mesh sizes.