Numerical modeling of riveting process on steam turbines blades

ABSTRACT The structural fragility due to the riveting process has been investigated in several components, such as in aeronautical structures. This process affects the reliability of the equipment when subjected to the operation loads. The high-pressure rotor under study operated about 3000 hours after re-pair maintenance of blades until the failure detected. This failure is related to the techniques used in the riveting process of the shroud in the blade, which ended up generating cracks in the radius of tenon blade. Thus, the present study numerically evaluates the mechanical behavior of the riveting process by means of a nonlinear analysis using the finite element method (FEM). For the geometry, under analysis (punch, tenon, and shroud) a 2D configuration with axisymmetric behavior was adopted, using the plane183 element for the components and the contac172 and targe169 elements for the contacts. It was adopted the elastoplastic behavior of the material in order to investigate the residual stresses after the riveting process. The results of the simulation presented good correlation with the blades failures, indicating a stress concentration in the radius of the tenon. The stresses on the tenon radius are about 1200 MPa and 180 MPa for the maximum principal stress and minimum principal stress, respectively. However, future studies using other models, such as fracture mechanics, would be applied in order to avoid failure of the joint when requested during the operating phase.