Determination of constraint limits for cleavage initiated toughness data

Measurement of a high constraint T0 in bend specimens is shown to require Mlim > 200. As Mlim increases from 30 to 200 in bend specimens, the corresponding Tlim can increase by approximately 15 °C. Further increases in Mlim do not result in substantial increases in Tlim. This evolution buttresses previous numerical findings by Dodds and co-workers [Specimen size requirements for fracture toughness testing in the ductile-to-brittle transition regime, J Test Eval 1991;191:123-34; Size and deformation limits to maintain constraint in KIc and Jc testing of bend specimens. In: Kirk M, Ad Bakker, editors. Constraint effects in fracture theory and applications: second volume. ASTM STP 1244, 1995; Numerical investigation of 3-D constraint effects on brittle fracture in SE(B) and C(T) specimens, Int J Fract 1995;74:131-61] and provides a strong justification for changes to ASTM E1921-02 if a conservative, geometry insensitive, and transferable reference temperature, T0, is to be determined using this standard. Possible short-term changes to ASTM E1921-02 could include raising Mlim and requiring an upward shift of SE(B) T0 values. A more desirable solution is to adjust individual KJc toughness values before evaluation of T0 to eliminate specimen geometry bias.