As ships and offshore structures become larger than before the usage of high strength steel and ultra thick plate has been increased. However, the thick plates have disadvantages with respect to brittle fracture and fatigue strength. Elastic plastic fracture mechanics (EPFM) is the domain of fracture analysis which considers extensive plastic deformation at crack tip prior to fracture. The J integral and crack tip opening displacement (CTOD) have been commonly used as parameters for EPFM analysis. The relationship between these parameters has been studied by industry and academia. The plastic constraint factor can serve as a parameter to characterize constraint effects in fracture. Therefore, the characteristics of plastic constraint factor are important in EPFM analysis.

In this study, the relationship between J Integral and CTOD was investigated by conducting 3-point bending tests using single edge notched bend (SENB) specimens. Two types of specimens were fabricated. One is API 2W Gr.50 welded by means of flux cored arc welding (FCAW) with heat input 15kJ/cm, and the other is API 2W Gr.50 welded by means of submerged arc welding (SAW) with heat input 45kJ/cm. The plastic constraint factor was estimated considering heat input, temperatures at weldment and heat affected zone (HAZ).

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