ELASTIC-PLASTIC ORTHOTROPIC MULTILAYERED PIPE DEFORMATION UNDER EXTERNAL LOAD AND INTERNAL-PRESSURE

Elastic-plastic deformation of a thin-walled pipe, composed of layers with material orthotropic in the elastic and plastic domains, is analy zed, The first material direction for each layer is inclined for an an gle (+alpha and -alpha successively) with respect to the pipe axis. Th e yield condition of the material represents a generalization of Hill' s criterion to include material hardening. The pipe is loaded by inter nal pressure and other external loads, and it is supposed that the pip e cross section is free to expand or contract. The derived incremental relations for stress integration, which take into account the stress- strain conditions in the pipe wall, are based on the governing paramet er method, developed by the first author, where the problem of implici t integration of inelastic constitutive relations within a time (load) step is reduced to solution of one governing nonlinear equation. Also , the expressions for the tangent elastic-plastic constitutive matrix are derived. One solved simple numerical example demonstrates the main characteristics of the developed algorithm, especially suited for a g eneral elastic-plastic analysis of composite pipes (within the displac ement-based finite element method).