A Simple Calibrated Ductile Fracture Model and Its Application in Failure Analysis of Steel Connections

A new fracture model is developed to predict the ductile fracture of structural steel under multiaxial stress states. First, the Lee–Mear void growth theory is used to establish the quantitative relationship between the stress triaxiality and material’s ductility. A stress triaxiality dependence function, which accounts for the material’s strain hardening, is derived from modifying the dilatation rate of a spherical void in a typical unit cell. Subsequently, the Tresca failure model is used in conjunction with the Swift hardening law to establish a Lode dependence of fracture strain. Then, the theoretical formula of the new fracture model is obtained by combining both stress triaxiality and Lode angle dependence functions. The proposed fracture model has a unique advantage: i.e., this model has only two material parameters. These two parameters can be easily calibrated through a simple standard coupon test, which significantly reduces the difficulty of model calibration work and facilitates its application in practical engineering. In order to verify the new fracture model, the test results of five types of Q460 steel specimens were used to calibrate the model parameters. The prediction accuracy of the new model is then checked by calculating the average error between the test results and the predicted fracture strain envelope. Finally, the new fracture model was applied in the numerical analysis of two types of steel connections. The validation of the proposed fracture model is verified by comparing the load–displacement curve and failure modes of the steel connections obtained from both test and numerical analysis.

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