Probabilistic fracture of Ti-6Al-4V made through additive layer manufacturing

The large deformation response of Ti-6Al-4V parts made through additive layer manufacturing is investigated. A wire-feed process is chosen instead of a powder process in an attempt to reduce the oxide contaminations of the final part. The experimental program includes uniaxial tension experiments along different part directions and fracture experiments on flat specimens with cut-outs covering stress states ranging from pure shear to equi-biaxial tension. More than 100 experiments are performed in total to characterize the randomness in the material's fracture response. It is found that the stress-strain response of the ALM material is comparable to that of Ti-6Al-4V sheet stock, while its average ductility is substantially lower. For example, for pure shear loading, the average strain to fracture for the ALM material is 0.47, while the mill product of the same alloy failed at a strain of 0.65. A probabilistic extension of the stress state dependent Hosford-Coulomb fracture initiation model is proposed to account for the significant standard deviation in the identified strains to fracture. Microscopic and surface strain field analysis demonstrate that the initiation and propagation of ductile fracture in the ALM material is strongly affected by the presence of prior-beta grains.