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Title:Numerical Investigation of 3-D Constraint Effects on Brittle Fracture in SE(B) and C(T) Specimens
Author(s):Nevalaninen, M.; Dodds, Robert H., Jr.
Subject(s):Finite element analysis
J-Q theory
brittle fractures
Abstract:Specimen size and geometry effects on cleavage fracture of ferritic steels tested in the ductile-to-brittle transition region remain an important technological impediment in industrial applications of fracture mechanics and in the on-going development of consensus fracture testing standards. This investigation employs 3-D nonlinear finite element analyses to conduct an extensive parametric evaluation of crack front stress triaxiality for deep notch SE(B) and C(T) specimens and shallow notch SE(B) specimens, with and without side grooves. Crack front conditions are characterized in terms of J-Q trajectories and the constraint scaling model for cleavage fracture toughness proposed previously by Dodds and Anderson. An extension of the toughness scaling model suggested here combines a revised "in-plane" constraint correction with an explicit thickness correction derived from extreme value statistics. The 3-D analyses provide "effective" thicknesses for use in the statistical correction which reflect the interaction of material flow properties and specimen aspect ratios, a/Wand W /B, on the varying levels of stress triaxiality over the crack front. The 3-D computational results imply that a significantly less strict size/deformation limit, relative to the limits indicated by previous plane-strain computations, is needed to maintain small-scale yielding conditions at fracture by a stress-controlled, cleavage mechanism in deep notch SE(B) and C(T) specimens. Moreover, the analyses indicate that side grooves (20%) should have essentially no net effect on measured toughness values of such specimens. Additional new results made available from the 3-D analyses also include revised 1]-plastic factors for use in experimental studies to convert measured work quantities to thickness average and maximum (local) J-values over the crack front. To estimate CTOD values, new m-factors are included for use in the expression J = m atzow <5.
Issue Date:1995-02
Publisher:University of Illinois Engineering Experiment Station. College of Engineering. University of Illinois at Urbana-Champaign.
Series/Report:Civil Engineering Studies SRS-598
Genre:Technical Report
Sponsor:Naval Surface Warfare Center, Anapolis Detachment.
U.S. Nuclear Regulatory Commission. Office of Nuclear Regulatory Research. Division of Engineering.
Contract N61533-92-K-0030
Date Available in IDEALS:2009-11-13

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