Residual stresses in aircraft components: I. Nonlinear finite element modeling

Hole expansion is a cold working method used for fatigue life improvement of aircraft structures containing fastener holes. The insertion of an oversized mandrel through the hole induces inhomogeneous plastic deformation in the surrounding regions. The resulting unloading residual stresses play a major role in determining the fatigue life improvement of the structure. It is therefore the purpose of this investigation to conduct comprehensive 3D elasto- plastic finite element analysis to evaluate the development and growth of the plastic zone and unloading residual stress resulting from the cold expansion of two adjacent holes. In this study, we focus our attention to the sequential expansions of the two holes. The contact between the mandrel and the hole was modelled using special contact elements, which employ the combined penalty-Lagrange multipliers formulation using ANSYS. Some of the results contained in this paper are based on an article published in the International Journal of Mechanical Sciences, which is currently in press.