Fracture mechanics study of tubular joint weld toe defects with three-dimensional finite elements

Scope and method of study. A three-dimensional finite element post-processor based on a general displacement procedure for mixed mode stress intensity factors has been developed. The stress intensity factors (SIF) of weld toe cracks of T-, Y- and K-joints were calculated using the three-dimensional finite element method (FEM), which is a reliable method available for tubular joint cracks in engineering. The effects of crack position, crack shape, joint dimension, interaction of a surface crack on each saddle point, through-wall cracks, and finite element modeling have been investigated. The calculated SIF solutions were analyzed from the viewpoint of the tubular joint physical behavior to clarify some aspects of the tubular joint fracture mechanics problem, including the mixed mode behavior of tubular joint fatigue cracks.; Findings and conclusions. The trends of the SIF solutions from the three-dimensional finite element method (FEM) are consistent with the physical behavior of tubular joint weld toe cracks, as well as with the stress distributions of an uncracked tubular joint. The three-dimensional FEM is reliable and practical for the SIF calculations of tubular joint weld toe cracks, while a simplified method involves uncertainties. It is very efficient to use the superposition procedure to handle the multi-axial load and boundary condition effects on the SIF of tubular joint defects. Empirical SIF formulas of T-joint saddle defects have been developed through statistical design and three-dimensional FEM. These formulas are useful for fracture and fatigue assessment of tubular joint with weld toe defects. The mixed mode behavior is a possible mode of fatigue of tubular joint weld toe cracks. The mixed mode behavior is a possible mode of fatigue of tubular joint weld toe cracks. However, the modeling and practical aspects of the mixed mode behavior should be further studied through numerical and experimental investigations.