Geometrically nonlinear static analysis of sandwich plates and shells

Sandwich shells composed of three layers: two thin and very strong faces, and the soft and comparatively weaker core which is much thicker than their neighbouring layers covering it from up and down, are considered in the paper. The proposal of a finite element adequate to such a kind of structural members is presented. In the paper the finite element based principally on the Ahmad original element and on the author's adaptation of this very element to the nonlinear range is presented. It was assumed that in the faces and in the core the materials exhibit orthotropic properties, and only elastic deformations are taken into account. The static analysis is performed within fully geometrically nonlinear range. The ultimate purpose of the work is determination of the critical value of the load intensity factor in a quasi static stability analysis. All procedures related to tracing of nonlinear equilibrium paths are adopted from the codes prepared before for homogeneous shells. Two verification problems are inserted. They confirm correctness of the adopted approach.