Simulation of stage I-short crack propagation in forged Ti6Al4V

Abstract

The propagation of stage I-cracks is simulated in a mill-annealed microstructure of forged Ti6Al4V, consisting of primary alpha grains and lamellar alpha/beta colonies. The crack growth mechanisms are investigated experimentally by means of fatigue tests yielding the following results: Within primary alpha grains cracks usually grow on the basal plane or a prismatic plane. In the lamellar colonies crack propagation often occurs parallel to the orientation of the lamellae. The misorientation between active slip bands in neighbouring grains is measured by electron backscatter diffraction. These findings have been implemented into a two-dimensional, mechanism-based short-crack model, which describes crack propagation as a partially irreversible dislocation glide on a crystallographic slip plane. The model is solved numerically using dislocation dipole boundary elements. The nonuniform propagation kinetics of short cracks is considered by defining grain boundaries as obstacles to plastic slip and crack propagation. The described model is used to simulate crack propagation in virtual microstructures, which are based on Voronoidiagrams. Statistical parameters such as grain size and volume fraction can be adjusted to agree with the real microstructure.