Investigation On Mechanism Of Plastic Deformation And Fracture Of Cylinders In Expanding Process

The analyzing method of cylinders in mechanical expanding process and engineering application is researched, which is based on the elastic-plasticity theory and metal forming theory by using the FEM.The comparative study of properties between classic the elastic-plasticity analysis and the FEM in mechanical expanding process is performed in this paper. The results of the study show that it is feasible and accurate to analy cylinders in expanding process by the FEM. The change of the expanding force in the whole forming process is reaearched by the FEM analysis of cylinders with isotropic hardening materials, and the result shows the friction coefficient and different taper angles have an important impact on the expanding force and the forming quality.According to damage and fracture theories and elastic mechanics, the singularity of stress around the crack tip is simulated by applying to isoparametric singular fracture finite element via FEM. The stress intensity factor(SIF) along the crack tip is obtained by the node displacement method. By comparing the analysis result with the theoretical result, it proves that this method is feasible. Because isoparametric singular finite element with 20 nodes is distinguishingly arranged near the crack front, the 3D fracture model of the crack in the axial direction is established from top to bottom by the separate block modeling. The stress intensity factor along the crack front is calculated by the FEM analysis and the influences of different taper angles in the forming process on the stress intensity factor are discussed, which provides a valid approach to keep cylinders from fracturing in the expanding process.