Influence of hydroforming on stress analysis of U-shaped metal bellows under axial compression

To enhance the accuracy of stress calculations for U-shaped bellows, a novel stress analysis method is proposed that incorporates the influence of hydroforming on both geometric structure and material properties. By simulating the hydroforming process of bellows and conducting uniaxial tensile tests with varying pre-strains, a finite element (FE) model is developed to analyse the stress in bellows under axial compression. The meridional and circumferential stresses under various compression levels are obtained and compared against results from an FE model that does not consider the hydroforming process, as well as with EJMA and GB/T 12777 standards and experimental data. The results demonstrate that the hydroforming process significantly influences the stress distribution in bellows under axial compression. Considering the changes in geometric structure and material properties markedly improves the accuracy of stress calculations. The stress formula provided by the EJMA and GB/T 12777 standards exhibits the largest calculation error, which increases with greater deformation.