In gas cooled exchanger applications, the stress state at large plastic deformation of expanded tubes is critical to control tightness but at is the same time vulnerable to cracks and failure. Therefore, it is important to analyze the stress distribution in the tube when being subjected to expansion together with the residual stress after expansion. Unfortunately, there are few theoretical and experimental studies available in the literature that treats the stress distribution of the forming tube, especially for the expansion with spherical or elliptical dies.In this study, a 3/8 copper and stainless steel tube specimens are expanded experimentally in an MTS tensile/compression machine with an elliptic die in a specially designed holding fixture. The tangential and longitudinal strains were monitored during the expansion process. The results are compared to those obtained by a newly developed analytical model and those obtained numerically using nonlinear finite element analysis. The analytical model is based on the plastic deformation of a thin cylinder with a Ludwik strain hardening model to which the Von Mises yield criteria is applied. The numerical finite element model is an axisymmetric model with a multilinear kinematic hardening material behavior.&nbsp;&nbsp;The results show that the analytical model can predict accurately not only the stresses and strains but also the residual stresses and the push force of the die &nbsp;&nbsp;&nbsp;

Stress Analysis of Tubes During Die Expansion Process

Paper Proceedings: https://asmedigitalcollection.asme.org/PVP/PVP2021/volume/85314

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