Three-dimensional stress analyses in composite laminates with an elastically pinned hole

We present a three-dimensional (3-D) stress analysis for composite laminates with an elastically pinned circular hole. The effects of friction, bearing force and bypass loading on the stress redistribution are studied in detail. The numerical approach is based on a multilayer boundary element method (MLBEM), a non-traditional BEM particularly designed for anisotropic composite laminates, coupled with the traditional BEM for the pin filling the hole. The unique characteristic of the MLBEM is that the fundamental solution employs Green's functions that satisfy the interfacial continuity conditions and top- and bottom-surface traction-free and symmetry conditions. This fundamental solution allows us to design a BE scheme without involving discretization on the interfaces and surfaces unless the laminates are imposed by different boundary conditions. Consequently, in this case of pinned joint, only the hole surface among the composite boundary and interfaces needs to be discretized. A Coulomb-type friction law is used to simulate the frictional contact interaction between the composite and pin. To solve the frictional contact problem, an iterative scheme of successive over-relaxation has been proposed where the contact location and frictional contact condition are determined at the same time in the iteration solution. By applying the MLBEM, stress analyses are performed for a laminate plate with the stacking sequence (0/ -/+ 45/(9) over bar(0) over bar)(delta). The issues of engineering interests, such as the loading-sequence and cycling dependencies of stress state due to the presence of friction, are addressed. The solutions, shown by complicated contact maps and stress states around the hole, suggested that a 3-D approach to pinned composite joints is necessary for the interpretation of the underlying physics. (C) 2002 Published by Elsevier Science Ltd.