Experimental Application of Methodologies to Quantify the Effect of Constraint onJc for a 3-D Flaw Geometry

摘要

In an effort to validate methodologies to quantify the effect of crack tipconstraint on cleavage fracture toughness, a series of experiments were conducted to measure the cleavage fracture toughness, Jc, of an ASTM A515 Grade 70 steel utilizing large plate bend specimens containing semi-elliptical surface cracks, SC(B), (3-D flaw geometry). Jc was estimated with modified EPRI and Turner design curve schemes from load and remote strains measured at initiation. The cleavage toughness of the A515 steel used for this testing was previously characterized using a series of through-cracked single edge notch bend specimens, SE(B), (2-D flaw geometry) with various initial crack-length to specimen-width ratios, a/W. The toughness values measured for the surface cracked plate specimens were consistent with the toughness ranges predicted from the SE(B) results using the toughness scaling and two parameter fracture mechanics (J-Q) methodologies to account for differences in crack tip constraint. This result verifies the applicability of small specimen, constraint adjusted, results to engineering structural integrity prediction for the case of cleavage fracture. Fracture mechanics, Cleavage, Constraint, Steel, Surface crack, Fracture toughness, J-Integral.