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

• Ano de defesa: 2022
• Autor(a) principal: Afzalimir, Seyed Hamidreza
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Circumferential defects; Crack growth; Crescimento de trincas; CTOD; CTOD-R resistancecurves; Curvas de resistência CTODR; Defeitos circunferenciais; Ductile fracture; Dutos e tubulações; Fratura ductil; J-Integral; Pipes; SE(T) specimens
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/3/3135/tde-24052023-145700/

This work addresses the characterization of the crack tip opening displacement (CTOD or ) for extending cracks in clamped single edge notched tension, SE(T), fracture speci- mens based upon fracture toughness tests and numerical analyses of stable crack growth conducted on specimen geometries extracted from pipe girth welds with different material properties. The study covers fracture resistance tests and crack growth analysis of plane strain and 3-D models for clamped SE(T) specimens with a weld centerline crack, in which a computational cell methodology to model Mode I crack extension in ductile materials is utilized to describe the evolution of J and CTOD with increased loading for the extending crack. Laboratory testing of girth welds made of different materials provides the measured crack growth resistance curves from which the key microstructural parameters utilized in the growth analysis are calibrated. The present investigation shows that CTOD resistance curves based on the double clip-gage (DCG) procedure are consistently higher than the corresponding fracture resistance data based on J-CTOD relationships, thereby potentially yielding nonconservative fracture toughness estimates. To gain a deeper insight in cor- relation of SE(T) fracture specimen R-curves with actual circumferentially cracked pipe, DCG based R-curves are also derived in actual pipe. Using homogenization procedure to accurately consider the effect of V-groove girth weld and clad layer confirmed our initial conclusion regarding DCG nonconservative assessment. Next step, we tried to measure the CTOD using only one CMOD values, unlike DCG that requires CMOD at two point, to overcome the DCG setup difficulty (it is a little bit cumbersome process to mount two clip gauge on one fracture specimen). Plastic rotational factor (rP) is investigated to see if it can measure CTOD precisely or not. The results show that it provides R-curves more conservative than J based CTOD values and less conservative than that of DCG method.