Evaluation of Crack Tip Constraint Effects on the Assessment of Pipes Subjected to Combined Loading Conditions

Abstract

Under certain conditions, pipelines may be submitted to biaxial loading situations. In these cases, questions arise about how biaxial loading influence the driving force (i.e.: CTOD, J-integral) of possible presented cracks and how affects the material fracture toughness. For further understanding of biaxial loading effects on fracture mechanics behavior of cracked pipelines, this work presents a numerical analysis of crack-tip constraint of circumferentially surface cracked pipes and SENT specimens using full 3D nonlinear computations. The objective is to examine combined loading effects on the correlation of fracture behavior for the analyzed cracked configurations. The constraint study using the J-Q methodology and the h parameter gives information about the fracture specimen that best represents the crack-tip conditions on circumferentially flawed pipes under combined loads. Additionally, simulations of ductile tearing in a surface cracked plate under biaxial loading using the computational cell methodology demonstrate the negligible effect of biaxial loadings on resistance curves.

Numerical study on the strain capacity of girth-welded X80 grade pipes

“…6(d)) was used to describe the shape of the crack tip, the radius of which was equal to the element size of the crack front. This kind of structure has been proven to have a good effect in simulating the blunting process of crack tips, and the simulation results are in good agreement with the test results (Cravero et al, 2008;Østby et al, 2008).…”

Numerical Study of the Crack-Front Constraint for SENT Specimens of X80 Pipeline Steel

“…Due to symmetry, the 1/4 of the specimen which meshed by eight-node reduced integration unit (C3D8R) was modeled. The element size in the crack growth zone in this paper is 0.125mm [7,8]. The transition from a coarse mesh away from the crack tip region to a fine mesh in the crack tip region is obtained by using a structured transitional mesh pattern.…”

Evaluation of CTOD resistance curves in clamped SE(T) specimens with weld centerline cracks

“…They showed that clamped SE(T) specimens having crack sizes in the range 0.2 ≤ a/W ≤ 0.4 provide fracture resistance curves in good agreement with the corresponding fracture behavior of circumferentially cracked pipes. Also a number of previous works[15,16,113,[115][116][117][118][119] have addressed effects of constraint on ductile crack growth in SE(T) fracture specimens and cracked pipelines to establish a more effective correlation of fracture behavior for these crack configurations. CTOD resistance curves derived from multiple methods were experimentally investigated for low and high strain hardening material to show the sensivity of the CTOD values on the deriving method, such J-CTOD relationships and DCG[120].…”