Bending behavior modeling of unbonded flexible pipes considering tangential compliance of interlayer contact interfaces and shear deformations

•The assumption is verified that wire slippage in its axial direction is only governed by the axial force and friction.•More rigorous analytical formulations are given to describe the gross slip initiation and progression of the armor wire.•Two mechanisms are thought to contribute to the decrease of layer stiffness before gross slip begins.•The first one introduces micro-slip of contact interfaces and the other considers shear deformations of the plastic layer.•Poisson's effect is found to have the influences of delaying the gross slip initiation and reducing the layer stiffness.

Rigorous analytical formulations are given to describe the gross slip initiation and progression in tensile armor layers of unbonded flexible pipes. Then two mechanisms are thought to contribute to the decrease of layer stiffness before gross slip begins. The first one considers the micro-slip occurred at the interlayer contact interfaces. The relative displacement between an armor wire and the underlying layer is determined according to the theory of contact mechanics. Shear deformations of the supporting plastic layer are taken into account in the other mechanism where plane sections no longer remain plane. The results of bending moment-curvature relationship from the presented models are compared with the available test data and good correlations are found. The shear model is seen to describe the slip transition better than other models do.