Research on the constraint of SE(T) specimen based on crack tip plastic zone parameters

In this paper, X80 high-strength pipeline steel is taken as the research object. Combined with numerical and theoretical analysis, the constraint parameters $r_{p0}^{1/2}$、$r_{p\max }^{1/2}$、$A_{pz}^{1/4}$、${\chi _P}$ based on the geometric characteristics of the plastic zone at the crack tip are studied for the crack tip stress of different single edge notch tensile SE(T) specimens. The in-plane and out-of-plane constraint effects on the fracture toughness of SE(T) specimens of X80 pipeline steel were quantified by fracture toughness tests. The relationship between $r_{p0}^{1/2}$、$r_{p\max }^{1/2}$、$A_{pz}^{1/4}$、${\chi _P}$, the uniform of in-plane and out-of-plane constraint based on the plastic zone at the crack tip, and the stress intensity factor K were established. The analytical relationship between the constraint parameters and the T stress (T₁₁ and T₃₃) was determined, and the fracture toughness prediction methods under small-scale yield conditions were proposed through finite element simulation and theoretical analysis.