Constraint effects in ductile fracture on J-resistance curve for full-scale cracked pipes and fracture toughness testing specimens

Fracture toughness is an important quantity in structural integrity assessment of pressurised vessels and piping. This paper reports J resistance (J-R) curves for toughness test specimens and full-scale pipes with a circumferential crack in a carbon steel. Full-scale pipes with a circumferential crack subjected to four-point bending are investigated with single edge-notched-tension specimens, SE(T), under fixed grip and pin-loaded conditions and compact tension, C(T), fracture toughness test specimens. Finite element (FE) damage analyses based on a stress-modified fracture strain model are used to simulate ductile fracture. An element-size-dependent critical damage model is introduced and applied to the large-scale components. Fracture parameter J values are calculated using both experimental data and FE analysis. In the first part of this paper, experimental results performed by Battelle Memorial Institute are compared with results from FE simulations to gain confidence in the ductile fracture simulation. Subsequently, different types of fracture toughness tests and thickness variations are considered to address the effect of in-plane and out-of plane constraint, respectively. Also, pipe geometries and crack depth are varied systematically. In conclusion, the transferability of J-R curves from toughness test specimens to full-scale cracked pipes is discussed.