Numerical simulation and experimental investigation of ductile fracture in SPIF using modified GTN model

Incremental sheet forming (ISF) is a relatively new flexible forming process with excellent adaptability to CNC milling machines due to the fact that it does not require any high capacity presses or dies of a specific shape and this makes the process cost-effective and easy to automate for various applications. The purpose of this work is to develop a modified Gurson–Tvergaard-Needleman (GTN) model that can be used to predict ductile fracture in the ISF process. The GTN damage constitutive model was implemented in Abaqus/Explicit via a VUMAT user subroutine. Tensile tests and a scanning electron microscope (SEM) were utilized to determine the parameters for the GTN model experimentally. The deformation on the surface of the tensile specimen was measured and observed by using a digital image correlation (DIC) system to evaluate necking and instability in the tensile specimens. Based on the results obtained by the SEM in the affected zone of tensile specimens, a modified GTN model was employed to predict the fracture of a pure titanium hyperbolic cone using the ISF process. A comparative study was carried out by using experimental testing and numerical simulation results of the ISF process to validate the modified GTN model