Material Behavior of Two High Grade Pipe Steels Under Different Triaxility Levels Available to Purchase

Particular geometries and loading conditions may have important effects on the stress fields of a given component promoting complex triaxial stress states and modifying the hydrostatic stress level. The yield condition of a ductile material is represented by the von Mises stress. However, the triaxial stress states have important effects on material toughness and ductility. This work presents a study of the effects of stress concentrators (different triaxial stress states) on material rupture. The aim is to determine the effects of hydrostatic stresses on the strain at failure in two low alloy high strength mill steels employed in field well and linepipe applications. Cylindrical specimens with different notch radius were tested to obtain different hydrostatic to von Mises stress ratios during tensile tests (h = σ_h/σ_VM). The considered notch radii were 2.0, 0.8, 0.4 and 0.25 mm. The notched specimens were loaded in tension and applied load vs. reduction of transversal area data were recorded during the tests. Numerical simulations of the tensile tests allow reproducing the test in the numerical model and calculating the stress and strains fields during each stage of the applied loading. Finally, tables of strain at failure vs. stress triaxiality are obtained for both steels that allow determining the most appropriate material for critical applications.