Identification of deformation mechanisms responsible for failure in incremental forming using a damage based fracture model

Single Point Incremental forming (SPIF) has generated significant interest recently due to its increased formability and greater process flexibility. However, the complicated deformation me chanisms involved in SPIF have prevented conclusive identification of the primary mechanisms responsible for failure. This work successfully predicts the forming forces and occurrence of failure in SPIF using explicit FEA with a damage based fracture model in which failure envelope depends on the hydrostatic pressure and the Lode angle. Furthermore it is shown that through-the-thickness shear is primarily responsible for failure in SPIF. Simulations are also performed to form the same component using SPIF and using a conventional punch and die, and a comparison is made between the dominant mechanisms of failure in the two processes. Furthermore, it is shown that reduction of tool-sheet friction can delay fracture in SPIF and the mechanism behind this effect is discussed as well.