Numerical Study Of Plastic Forming Process Of Sandwich Panels Based On Elastoplastic Equivalent Model

As a new type of composite material,metal sandwich panel is widely used in housing construction,aerospace,rail vehicles and ships because of its light weight,high specific strength,high specific stiffness,sound insulation,noise reduction,heat insulation and vibration damping and a series of other superior properties.In engineering applications,simplified analyses of sandwich panels and the establishment of an accurate and feasible equivalent model for sandwich panels can save time and economic costs in the calculation process.Therefore,the elastoplastic equivalent analyses of sandwich panels are of great significance.In this paper,three typical composite panels,honeycomb sandwich panel,aluminum foam sandwich panel and bi-directional trapezoidal sandwich panel,are studied,and a universal elastoplastic equivalent method for sandwich panels is proposed,and the macroscopic equivalent model of the three sandwich panels is established by equating the core layer and the sandwich panel as a whole.The accuracy of the equivalent model and its applicability in plastic forming analyses are investigated using a combination of numerical simulations and experiments.The main contents and conclusions are as follows:1.According to the composite panel theory,the honeycomb sandwich core,aluminum foam sandwich core and bi-directional trapezoidal sandwich core are equated to homogeneous thick anisotropic single-layer panels,and the macroscopic equivalent three-layer panel model of the three sandwich panels is established.The uniaxial tensile and shear numerical simulations of the mesoscopic models of the core layers of the three sandwich panels are carried out to obtain the elastic parameters and the anisotropic plastic parameters in Hill'48 yield criterion as well as the equivalent stress-strain curves of the equivalent core models.2.The finite element models of honeycomb sandwich panel,aluminum foam sandwich panel and bi-directional trapezoidal sandwich panel are established respectively,and the numerical simulation of curved multi-point forming is carried out using the mesoscopic model and the equivalent three-layer model.The stress distribution and forming accuracy of the equivalent three-layer model and the mesoscopic model are compared and analyzed to verify the accuracy of the equivalent three-layer model for sandwich panels,and to investigate the effect of mesh size on the numerical simulation results and calculation time.3.The honeycomb sandwich panel,aluminum foam sandwich panel and bi-directional trapezoidal sandwich panel as a whole are equivalent to single-layer panels,and the anisotropic or transverse isotropic single-layer panel equivalent models of the three sandwich panels are established.The elastic parameters,anisotropic plastic parameters and equivalent stress-strain curves of the equivalent models of the three sandwich panels are obtained through finite element analyses,and the numerical simulations of curved forming are carried out for the single-layer panel equivalent models of the three sandwich panels respectively,and the section bending moments and forming accuracy of the whole equivalent models and the mesoscopic models of the three sandwich panels are analyzed,and the influence of the mesh size on the numerical simulation results is studied.4.Multi-point forming experiments are conducted on three types of sandwich panels,and the experimental parts are measured by a 3D laser scanner PRO CMM to obtain the point cloud data of the experimental parts,and the shape error analyses are conducted between the equivalent model and the experimental parts of the sandwich panels to verify the accuracy and applicability of the equivalent model of the sandwich panels established by the elastoplastic equivalent method in plastic forming analyses.