Influence of fracture toughness on multi-axial loading interaction criteria for wrapped composite X-joints

Wrapped composite joints arise as an innovative solution for joining circular non-welded hollow sections (CHS) in jacket support structures for offshore wind, intending to enhance fatigue performance and consequently reduce weight and costs when compared to traditional welded joints. Due to combined waves and wind loads, these joints are subjected to different multi-axial loading scenarios. Therefore, it becomes fundamental to establish an interaction criterion that accurately predicts the failure behavior provided by the superposition of different load conditions. In this context, this paper aims to present the results of a numerical investigation on the multi-axial load behavior of wrapped composite joints. Based on previous standards for welded tubular joints [1,2], a multi-axial loading interaction criterion is proposed for wrapped composite tubular joints, and a finite-element (FE) model is developed using the cohesive zone model approach. Eighteen loading cases, with different combinations of axial load and bending moments, were applied in a medium-scale X-shaped wrapped joint to derive the corresponding failure envelope. Three values of fracture toughness were considered to evaluate the influence of this fracture parameter on the interaction failure criteria exponents. It was concluded that the given exponents are not significantly affected by the change of interfacial strength and fracture toughness, which represents a valuable finding for the development of future design guidelines.