On the Fracture Characterization in Double-Sided Incremental Forming of Ti6Al4V Sheets at Elevated Temperatures

In this paper, the characteristics of fracture arising in Ti6Al4V sheets deformed using the Double-Sided Incremental Forming (DSIF) strategy are investigated and related to the stress state characteristics of the process. Due to the limited material formability of Ti6Al4V at room temperature, Electrically-assisted Double-Sided Incremental Forming (E-DSIF) experiments were performed under different current intensities, and the resulting fracture surfaces were investigated by means of Scanning Electron Microscopy (SEM) observations. To classify the fracture characteristics and identify the corresponding stresses leading to failure in E-DSIF, tests characterized by simpler stress states, i.e., uni-axial tensile and pure shear, were also carried out at different temperatures. The comparison of the related fracture surfaces demonstrates the prominent contribution of the shear effect in E-DSIF. Furthermore, the mechanisms controlling fracture occurrence in E-DSIF were analysed, proving that Mode I (tearing) was responsible for the occurrence fracture and that cracks start from the outer surface of the sheet.