Comparison of Shell and Solid Models for Corner Fill in Tube Hydroforming

Abstract

The tube hydroforming process has been analyzed numerically by finite element analyses. For production applications in the automotive industry, most analyses use shell element models. This is a natural extension from sheet metal forming. However, since it is well known that radial stress and shear distortion are common phenomena in tube hydroforming and shell elements are not formulated to include them, there is a question on how accurate those shell model results are. To answer the above question, a shell element model and a solid element model, with comparable finite element meshes, are used to analyze a corner fill benchmark test and their results are compared. It is found that shortly after plastic deformation occurs, deviations between the shell model and solid model results can be detected. The shell model is less flexible. When further pressurization reduces the corner radius to less than eight (8) times the original thickness, unusually high local stress and strain concentrations developed in one finite element in the shell model. The shell model results are considered less accurate given the formulation constraints in omitting shear distortion and radial stress and in predicting discontinuous results at higher pressures.