Establishment of a constitutive model for the solid granules medium and its application in sheet metal forming

The solid granules medium forming process is a new type of forming process that employs solid granules medium as the medium for force transfer. To effectively predict experimental results, establishing an appropriate simulation model for the SGMF process is paramount. However, due to the intricate contact and frictional relationships inherent within solid granules medium, the precise development of constitutive models for these materials remains a significant challenge. In this study, the mechanical properties of the solid granules medium were investigated by triaxial compression tests, and the results showed that these properties were similar to those of over-consolidated soil or dense sand. Then, based on the parameters of the triaxial compression test, four different mechanical models for the solid granules medium were constructed, including the Mohr-Coulomb model, Drucker-Prager model, Drucker-Prager Cap model and DEM-FEM model. These models are used to numerically simulate the pressure transfer performance within the solid granules medium. Comparison with experimental data shows that the Drucker-Prager Cap model can predict the pressure transfer performance of solid granules medium with greater precision. Finally, the solid granules medium is employed in conducting the deep drawing test of 08Al cylindrical parts with hemispherical bottom, and the results are compared with the finite element model. The accuracy of the Drucker-Prager Cap model in predicting the thickness distribution of formed parts is confirmed. Therefore, the model can be used as the constitutive model for solid granules medium forming in the simulation model.