Numerical simulation with an improved ductile fracture model for steel connections considering effect of element size

Crack initiation and propagation behaviors are the dominant characteristics of ductile fracture for structural steels. This study aims to predict the strength degradation of steel connections caused by ductile crack and the effect of element size in FE simulation. Tensile fracture tests were conducted on notched specimens to study the crack behavior of structural steel. An improved micromechanics-based fracture model which considers crack initiation and propagation was proposed, and the parameters involved in the model were calibrated. The micro void growth and coalescence inside the material were numerically investigated using the void-cell model. The fracture process of bolted connections under tension was studied with the aid of the proposed model. Results show that a higher stress triaxiality leads to an increase in the yield and ultimate strengths. The proposed fracture model is applicable to different element sizes of numerical models, and its effectiveness was verified by the experimental results. Stress triaxiality has a great influence on the micro void grow rate, and the void grows faster at a higher stress triaxiality state. The ductile fracture process of bolted connections can be predicted very well using the proposed model. For the multi-bolt connection, the load carrying capacity decreases as the load angle increases.