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Title:Constraint Effects on Fracture Initiation Loads in HSST Wide-Plate Tests
Author(s):Dodds, Robert H., Jr.
Subject(s):Fracture mechanics
finite elements
Abstract:During the period 1984-1987, researchers of the Heavy Section Steel Technology program at the Oak Ridge National Laboratory performed a unique series of fracture mechanics tests using exceptionally large, SECT) specimens (a/W = 0.2) fabricated from a reactor pressure vessel material, A533B Class 1 steel. These "wide-plate" specimens have test sections of width W = 1000 mm, thickness B = 100 mm and initial crack lengths of 200 mm. While the specimen design, instrumentation and pre, post-test analyses focused on the cleavage run-arrest events, a disturbing outcome of the program centered on the inability of fracture mechanics analyses at that time to predict the loads required to initiate the first cleavage event - required loads exceeded twice those estimated from 3-D finite element analyses. The source of the much larger than expected initiation loads remained unresolved at completion of the wideplate test program. This study re-examines fracture initiation loads in the wide-plate tests using two constraint assessment methodologies developed over the past five years: the J-Q toughness locus approach and the toughness scaling approach based on a local failure criterion for cleavage. Both approaches demonstrate a significant loss of constraint in the elastic-plastic fields ahead of the crack in the wide-plate specimens caused by the inherent negative T -stress of the shallow notch SECT) configuration. Moreover, the 25 mm wide machined notch required for specimen fabrication is shown to further reduce constraint by introducing a traction free surface very near the crack tip. Both of these factors combined to reduce near-tip stresses by 10% below those of the small-scale yielding, SSY CT= 0), fields. This reduction places fracture results for the wide-plate specimens within the J-Q toughness locus defined by fracture toughness tests on the A533B material and within the constraint corrected Jc values defined by the toughness scaling methodology.
Issue Date:1994-07
Publisher:University of Illinois Engineering Experiment Station. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Civil Engineering Studies SRS-591
Genre:Technical Report
Sponsor:Heavy-Section Steel Technology Program. Oak Ridge National Laboratory. Contract 19X-SM986V
Date Available in IDEALS:2009-11-12

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