Abstract：To investigate the effect of plastic crystallographic slip on the evolution of micro-voids in P91 martensitic steels, the present paper proposes a micromechnical finite element model based on the crystal plasticity theory to quantify the effects of stress triaxiality, Lode parameter and crystallographic orientation. The results indicate that under relatively high stress triaxialities, with the increase of the stress triaxiality, the equivalent stress-strain response of the voided martensitic blocks exhibits a rapidly softening characteristic, and the void volume fraction increases rapidly with increasing the equivalent strain. For a given stress triaxiality and the three crystallographic orientations examined, the void coalescence strain of the martensitic block has the minimum value at the [111] orientation and the maximum value at the [110] orientation. At the beginning of the void coalescence, the void shape tends to be ellipsoidal under relatively low stress triaxialities, while the void shape becomes transversely bulge slightly under the relatively high stress triaxialities. Over a certain range of the stress triaxiality and the Lode parameter, there is, in the phase diagram for the failure, a banded transition state between the two failure states of the void coalescence and the void collapse. For the [100] orientation of interest, the band widths are different under different Lode parameters, and the largest width occurs at the Lode parameter L=0.
2023, Vol. 44 
