Abstract:
This thesis introduces a method for the coupling of the elastic Boundary Element
Method (BEM) and the elastoplastic Finite Element Method (FEM) and the extension
of this method to contact problems by using gap finite elements.
A method for the coupling of BEM subregions and FEM subregions is derived which
limits the transformation of nodal forces into nodal traction to the interface degrees of
freedom. This method is also capable of modelling body forces. Then the coupling
procedure is extended to allow for elastoplastic material models in the FEM parts of the
structure. Additionally contact conditions are included by defining an extra artificial
subregion which consists of gap finite elements. Incremental iterative algorithms are
used to overcome the present nonlinearities resulting from plasticity, non-conforming
contact and friction.
A computer program based on the developed methods and algorithms was coded in
FORTRAN77 and tested on PCs. Patch tests and case studies were run in order to
validate the developed package against known analytical solutions or the commercial
finite element package ABAQUS. It can be concluded that all the original ideas and
methods developed in this work are successful. The coupled FEM/BEM is as accurate
and reliable as the pure FEM for elastoplastic analysis, with FEM/BEM having the
advantage of ininimising the modelling effort. The use of gap elements in an artificial
subregion was found to be an ideal and accurate way of including contact conditions
into the environment of the elastoplastic coupled FEM/BEM.
