Combined High and Low Cycle Fatigue Assessment of Tubular K-Joints With Consideration of Plasticity Accumulation

Abstract Various types of marine engineering structures, such as offshore platforms, often use intersecting tubular joints and are prone to initiate fatigue crack under cyclic loadings. Considering that the actual service process may encounter extreme sea conditions, the fatigue of the tubular joints is often not a simple fatigue problem, but a more complex combined high and low cycle fatigue (CCF) one that should take plasticity accumulation into account. The traditional hot spot stress (HSS) method often fails to achieve satisfactory results when local stress exceeds yield strength. In this paper, a new CCF model considering the accumulation of plasticity is proposed. A nonlinear kinematic hardening material model of Chaboche was used to characterize the hardening behavior of materials under cyclic loadings. The damage under various loadings is calculated based on the new CCF model. And an assessment of a tubular K-joint was made under extreme loadings with the help of FEM. Compared with the traditional HSS method, this method takes into account the interaction between various loadings, reflects the material’s kinematic hardening behavior, and can predict the fatigue performance of tubular joints more accurately under potentially extreme sea conditions. This method is also applicable to other forms of marine engineering structures.