The determination of residual stress in extruded Ti-6Al-4V by contour method and finite element analysis

The contour method has been used to assess the level of residual stress generated during the post extrusion air cool and water quenching of a Ti-6Al-4V extruded bar. A length of the extrudate was transversally sectioned using electrical discharge machining (EDM), resulting in minimal damage to the cut surface; the stress relieved profile present at the cut surface was then measured using a coordinate measuring machine (CMM). The cut section was recreated in an ABAQUS finite element (FE) model and the inverse of the stress relieved profile recorded by CMM was applied as a boundary condition; by forcing the model’s surface topology to match the measured cut surface, residual stresses normal, i.e. longitudinal stresses, to the cut surface of the extruded profile were then calculated. Results were compared to air cooling and quenching simulations performed in the DEFORM FE package. The distribution of tensile and compressive residual stresses observed via experimental and simulation work were found to be a good match with the distribution correlating with local variations of cooling rate during quenching.