Finite Element Analysis For Elastic-plastic Deformation Field And Constraint Effect On The Crack Tip Fields

In recent years, the study of constraint effect on fracture resistances for pipeline steels has attracted more attention. Much theoretical and numerical work has been done to quantify fracture constraint at the crack tip in both two-dimension and three-dimension. The two-parameter J-A₂ formulation is precious to quantify constraint effect on the crack tip fields. It is fit for the elastic-plastic fracture analysis.For X60 and X80 steels are high ductile steels often used for oil and gas pipelines, some test specimens geometry and load configuration for the two kinds of steels are selected in this paper. Based on the J-A₂ method, the constraint effect on the crack tip fields for pipelines and fracture specimens with different variety and size is studied by using plane strain and nonlinear numerical calculation. The specimens which are choosed include single edge notched compact tension (CT) specimens and single edge notched tension (SENT) specimens. The pipelines contain the inner crack and the exterior crack. The constraint parameter A₂ is extracted by matching the J-A₂ solution with finite element results for a specific crack configuration. The J-A₂ and a/W-A₂ curves of specimens and pipelines are determined by numerical analysis. So the relativity of their constraint effect is discussed. From the experimental curves of specimens and the result of finite element analysis for pipelines, the fracture failure pressures of pipelines are predicted.In addition, the crack tip fields and three-dimensional stress constraint of finite-thickness planks are explored primarily. The out-of-plane stress constraint affects the crack tip fields and fracture toughness significantly. The constraint parameters and the corresponding curves of different test specimens have been attained.