Abstract
Understanding the deformation and failure mechanisms in single point incremental forming (SPIF) is of great importance for achieving improved formability. Furthermore, there will be added benefits for more in depth evaluation of the effect of localised deformation to the fracture mechanism in SPIF. Although extensive research has been carried out in recent years, questions still remain on the shear and particularly its effect to the formability in SPIF processes. In this work, a modified Gurson–Tvergaard-Needleman (GTN) damage model was developed with the consideration of shear to predict ductile fracture in the SPIF process due to void nucleation and coalescence with results compared with original GTN model in SPIF. A combined approach of experimental testing and SPIF processing was used to validate finite element results of the shear modified Gurson–Tvergaard-Needleman damage model. The results showed that the shear modified GTN model improved the modelling accuracy of fracture over the original GTN model under shear loading conditions. Furthermore, the shear plays a role under meridional tensile stress to accelerate fracture propagation in SPIF processes.
Highlights
Single point incremental forming (SPIF) is a relatively new flexible forming process
Extensive research has been published on SPIF for improved understanding of material deformation and fracture mechanisms of SPIF to form a part without defects
A theoretical model for different modes of deformation in SPIF was built upon membrane analysis and ductile damage mechanics by Martins, Silva and co-workers [1,2]
Summary
Single point incremental forming (SPIF) is a relatively new flexible forming process. The main motivation of this study is to develop a GTN based model and to investigate its accuracy and effectiveness in predicting the ductile fracture in SPIF processing of typical truncated cone and pyramid shapes. Nahshon-Hutchinson type shear mechanism was incorporated in GTN model to take into account of the effect of shear in the increment of void volume fraction. When the space between two adjacent voids is small enough, the voids begin to coalesce and this leads to cracks and subsequent fractures of the material, as shown in Fig. 1 [18,19] This phenomenon can be analysed utilizing damage models taking into account the effect of microstructure defects by defining a relationship between particular failure stages and the strength of the material. Dfgrowth 1⁄4 ð1 À f Þdepii ð7Þ where depii is the trace of the plastic strain tensor
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