Heterogeneous random medium plasticity and fracture model of additively-manufactured Ti-6Al-4V

Abstract

The large deformation response of Ti-6Al-4V structures made through shaped metal deposition is heavily affected by the prior-beta grain structure induced by the manufacturing process. Based on more than 25 tension and shear experiments on individual prior-beta grains, the statistical distribution of the isotropic hardening response of prior-beta grains is identified. In close analogy with Crystal Plasticity Finite Element (CPFE) analysis, Voronoi tesselation is used to generate finite element models of additively-manufactured structures containing multiple prior-beta grains. For each prior-beta grain, a different hardening curve is assigned using a random pull from the truncated Gaussian distribution of Hockett-Sherby type of hardening curves. Similarly, the parameters of the Hosford-Coulomb fracture initiation model are assigned. The comparison of the CPFE simulation results with the experimental results on tension specimens containing multiple prior-beta grains, shows good qualitative and quantitative agreement with regards to the force-displacement response, the surface strain fields, and fracture occurrences. The results demonstrate that the failure of additively-manufactured Ti-6Al-4V components through ductile fracture requires a heterogeneous random medium modeling approach. While the present study focuses on strength and hardening variations, it is noted that further improvements are expected when considering the known texture mismatch between prior-beta grains along with detailed models of the prior-beta grain boundaries.