The Effects Of Pre-damage On The Later Fracture Behaviors Under Mixed Mode I/II

In this paper, the effects of pre-damage on the later damage evolution and fracture behaviors of a HSLA steel under mixed Mode I/II are investigated by FEM calculation and comparison with experimental results. The new results obtained are as follows:(1) Under the mixed Mode I/II loading, micro-voids located at the blunted side of the notch do not grow when the P/Pgy is less than 0.2, and the micro-voids grow slowly when the P/Pgy is in a range of 0.2< P/Pgy< 0.8, and micro-voids grow fast when the P/Pgy is larger than 0.8. The growing rate of micro-voids increases with increasing pre-load ratio P/Pgy. Micro-voids located at the sharpened side of the notch almost do not grow, and the increase of whole void area fraction with P/Pgy is due to the growth of the micro-voids located at the blunted side. The higher values ofσ_m/σ and ε_p at the blunted side is the main cause of the micro-void growth.(2) Under Mode I loading, the high values of σ_m/σ and ε_ p ahead ofnotch promote fast growth of micro-void and cause the fastest damage rate and the lowest toughness, and the fracture initiation location is located at notch center. When the specimens are loaded under mixed Mode I/II loading, the micro-void growth rate at the blunted side decreases, and the sizes of the micro-voids at the sharpening side change from slight growth to unchange and then to decrease with increasing the ratio of Mode II. This causes the decrease of the whole damage rate with increasing the ratio of mode II. The location of the column with the fastest growth rate of voids and the fracture initiation location move from notch center to side with increasing the ratio of mode II. These results arise from the change of thedistribution of σ_m/σ and ε_p ahead of notch with the change of the Mode IIratio. The voids at the location with higher values of σ_m/(σ|-) and ε_p havefast growth rate and early coalescence with other voids and notch, which determines ductile fracture initiation toughness and location.(3) The void area fraction fa of the three specimens with different initial damage does not increase with P/Pgy when the P/Pgy is less than 0.8, and it increases slowly with P/Pgy when the P/Pgy is in a range of 0.8