Three dimensional geometrical and material nonlinear finite element analysis of adhesively bonded joints for marine structures.
University of Southampton, School of Engineering Sciences,
The use of adhesive bonding as a structural joining method has been gaining recognition in
marine industry in recent years, though it has been widely adopted in other fields such as
aerospace, automobiles, trains and in civil constructions. The type of materials used and
design practices followed in marine structures are different from what is applied in other
disciplines. Therefore new research approaches are required and recent novel ideas are ex-
plored in the context of application of bonded joint configurations in marine environment.
The research is directed at developing analysis tools for predicting the displacement,
stress and strain fields in adhesively bonded joints between dissimilar adherends. In the
finite element formulation, the adherends may be isotropic or orthotropic layered materi-
als, which are assumed to behave linear elastically. The adhesive material is assumed to
behave as elasto-plastic continuum, where the nonlinear behaviour is modelled as either a
rigid or a semi-rigid adhesive solid that can be represented by the Ramberg-Osgood ma-
terial model. The yield behaviour of the polymeric adhesive is modelled using a modified
von Mises criterion, which accounts for the fact that plastic yielding of polymer materials
may occur under the action of hydrostatic as well as deviatoric stresses. The geometric
nonlinearity is based on the assumption of large displacement, large rotation but small
strain, and it is implemented in the code using the total Lagrangian approach.
The scheme is applied on three case studies viz.: a study of adherend imbalances in
a single lap joint, stress analysis of a butt-strap joint system and a hybrid joint are un-
dertaken. The influence of geometric and material nonlinearity on joint deformations and adhesive stresses, are studied for a single lap joint with dissimilar adherends, aluminium
and a Fibre Reinforced plastic composite material, with varying adhrend thickness ratios.
The adhesive stress-strain data obtained from the model are compared with the exper-
imental stress-strain curve and the numerical results are validated with the analytical
solution. Three dimensional effects like ’anticlastic’ and bending-twisting’ are shown in
the joint with a dissimilar adherends. Key results are obtained that explains the state of
nonlinear adhesive stress state in the joint.
Analysis of butt-strap joint focussed on nonlinear modelling of a semi-rigid adhesive ma-
terial that is used to bond two dissimilar adherends, steel and aluminium. The analysis
demonstrate that the influence of geometric and material nonlinearity on the joint de-
formations as well as the adhesive stresses is significant. Nonlinear adhesive stresses are
compared with the actual strength of the highly flexible adhesive, highlighting the need for
the consideration of material nonlinearity in the bonded joints. Failure modes for the joint
are inferred from the observations made on the adhesive stress state in the butt-strap joint.
Last study, deals with three dimensional analysis of a GRP-Steel hybrid joint carried
out to model the initiation and propagation of crack under a set of static loading cases.
Earlier studies were restricted only to two dimensional analysis. This three dimensional
analysis showed that the adhesive normal stress is not constant across the width of the
joint. Critical locations of stress concentrations are identified and the failure mechanisms
are compared with the experimental specimens.
The observations made from this research study using a three dimensional finite element
program, compliments the present knowledge in the field of adhesively bonded joints.
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