A unified damage factor model for ductile fracture of steels with different void growth and shrinkage rates

Abstract

Micromechanical fracture modelling is an effective method to predict ductile fracture in steel structures. This paper aims to establish a simplified and general fracture model for various loading conditions, which is convenient to calculate the instantaneous damage index. With the concept of the ductile damage factor, a unified ductile damage factor model considering the difference of rates between void growth and shrinkage has been proposed. Based on experiment results and finite element analysis, the model parameters for Q235B Chinese structural steel were calibrated. The ductile damage factor and equivalent plastic strain at fracture initiation were investigated. Comparison among the proposed model, experimental results, and the cyclic void growth model demonstrated the effectiveness and accuracy of the proposed model. A parametric study was conducted to investigate the influence of cyclic constitutive parameters on the accuracy of fracture prediction. The predicted results are acceptable while reducing those calibrated cyclic constitutive parameters by 20%.

Effects of the stress state on plastic deformation and ductile failure: Experiment and numerical simulation using a newly designed tension‐shear specimen

“…Stress triaxiality increases initially, followed by a decrease, then again increases with increasing the equivalent plastic strain. Similar sharp transitions in the beginning of the stress triaxiality versus the equivalent plastic strain curves were also reported for different types of specimens . The major reason for the sharp transition is believed to be that the local stress redistribution occurs in the beginning of yielding or hardening of materials (Figure S1).…”

“…Similar damage evolution models were also employed in other literature. [41][42][43][44][45][46] A damage parameter ω which keeps track of damage accumulation is defined. Incremental damage △ω is calculated by the ratio of the equivalent plastic strain increment, △ε p, and equivalent plastic strain at failure, ε f , at each Gauss point, determined by Equation ( 2)…”

Ductile tearing analyses of cracked TP304 pipes using the multiaxial fracture strain energy model and the Gurson–Tvergaard–Needleman model

“…Therefore, neither the initial value nor the final value of W f can be representative. In the process of determining the value of W f, in order to consider the impact of the loading history, it is reasonable to use the average value of stress triaxiality, of which the range can be obtain from an FE calculation, as described in the literature 20,31 :…”

A Simplified Ductile Fracture Model for Predicting Ultra-Low Cycle Fatigue of Structural Steels

“…Regardless of the fact the CVGM shows fairly accurate results in predicting ULCF, it is limited by some assumptions stated in the study. Myers et al [ 25 ] and Yin et al [ 26 ] modified the equivalent plastic strain accumulated in compressive loading as a new damage variable to extend its scope of application on unequal tensile and compressive loading cases, but the studies [ 27 , 28 , 29 ] show that a problem exists whereby the results predicted by CVGM may occur with large discreteness.…”