Fracture resistance of tubular composite joints under combined axial and in-plane bending
Abishek Baskar (TU Delft - Civil Engineering & Geosciences)
Mathieu Koetsier (TU Delft - Civil Engineering & Geosciences)
Gisele Goes Cintra (Universidade do Estado do Rio de Janeiro)
Clement Waltener (Tree Composites)
Marko Pavlovic (TU Delft - Civil Engineering & Geosciences)
Frans van der Meer (TU Delft - Civil Engineering & Geosciences)
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Abstract
Wrapped composite joints offer a promising alternative to welded tubular joints in fatigue-critical offshore structures by reducing stress concentrations, improving fatigue performance, and reducing material consumption. While their effectiveness under debonding-dominated failure modes has been demonstrated and characterized, the composite material cracking dominated failure mechanism remains unexplored. Tubular joints subjected to offshore loading conditions experience multiple loading directions, inducing complex stress states at the root of the composite wrap. This underscores the need to understand the influence of multiaxial loading on the composite's static fracture resistance. This paper presents an experimental and numerical investigation into the static fracture behaviour of tubular composite X90 joints, comprising six specimens subjected to monotonic axial tension, in-plane bending, and combined axial-in-plane bending, with two specimens per loading case. The load–deformation response, damage evolution, and governing failure modes are characterized using full-field strain measurements from three-dimensional digital image correlation and distributed fibre-optic sensing, enabling detailed monitoring of debonding and composite fracture initiation. The experimental results indicate an approximately linear interaction between the axial force and in-plane bending resistances from the limited set of specimens tested. A finite element modelling framework incorporating anisotropic plasticity, cohesive interface modelling, and damage-based fracture is developed. The model accurately captures the failure mode and ultimate resistance under uniaxial tensile loading. However, under bending-dominated and combined axial-in-plane bending conditions, numerical simulations increasingly overpredict experimental results, highlighting the limitations of modelling the composite material with nonlinear response using existing anisotropic plasticity models.
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