Abstract
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.
Highlights
IntroductionTo predict the occurrence of failure in the AA5052 sheet, Malhotra et al [5, 6] used explicit FEA with a damage-based fracture model, in which the failure envelope depends on the hydrostatic pressure and the lode angle
The results show that the shear modification model can have a significant influence on the fracture depth in the Incremental sheet forming (ISF) process
To evaluate the heterogeneity of deformation and measure the displacement on the surface of the tensile specimens, several tensile tests were conducted with the use of digital image correlation (DIC)
Summary
To predict the occurrence of failure in the AA5052 sheet, Malhotra et al [5, 6] used explicit FEA with a damage-based fracture model, in which the failure envelope depends on the hydrostatic pressure and the lode angle. W.B Lievers et al [8] presented a method to determine the void nucleation rate in the ISF process based on density changes using the GTN model. Three automotive aluminium sheet alloys, i.e. AA5754, AA5182 and AA6111, were used to calibrate the void nucleation behaviour. This technique provides a large homogenous deformation area and avoids the large strain and stress gradient associated with smooth or notched tensile specimens. The results show that the shear modification model can have a significant influence on the fracture depth in the ISF process
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