Plastic Collapse Analysis of Elbow With Circumferential Through-Wall Cracks Under Combined Loading Conditions

Abstract This study investigates the yield criterion of plastic collapse loads for pipe bends under combined loading conditions, including internal pressure, in-plane bending, and out-of-plane bending. The plastic collapse loads were determined using the Twice Elastic Slope (TES) method based on reaction moment-rotation curves obtained through finite element analysis (FEA). Both crack-free pipe bends and those with through-wall circumferential cracks were analyzed. To address the limitations of the circular interaction model in representing geometric nonlinearity effects, an elliptical interaction model was proposed. The variation in plastic collapse loads due to internal pressure were quantified as α for in-plane bending and β for out-of-plane bending, and these parameters were incorporated into the elliptical interaction model. The proposed yield criterion equations were validated through FEA, demonstrating accurate predictions of plastic collapse loads under various loading conditions. The results confirmed the applicability of the elliptical interaction model to both crack-free and cracked pipe bends. This study provides a reliable framework for structural integrity assessments of pipe bends under realistic operating conditions. Future research will extend the proposed model to surface cracks and explore the effects of crack geometry on yield criteria and load-carrying capacity.