On elastic and elastoplastic analysis of tube junction problems by coupling of the FEM to BEM technique

The tube junction structures have been widely adopted for nuclear engineering usages, so have been for many other technologies. In application of the finite element method to stress analysis for such a three dimensional complex structures, it is necessary to subdivide the regions of stress concentration into very refined meshes. In this paper, schemes for incoporating the finite element equation as a natural boundary condition into boundary integral equation have been employed. The relevant formulae and some of the details of treatments have been given. For the nozzle junction: The 3D isoparametric finite elements with 8-20 nodes containing additional internal degrees of freedom have been employed for the cylindrical shell parts which remain at elastic stage and with less stress gradients, while for the junction part with high stress gradients, the boundary integration technique of 8 nodes 2D isoparametric boundary elements has been used and the volumetric integral elements of 8 nodes have been used for the elastoplastic incremental computations. (orig./GL)