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Volume 36, Issue 1 (January 2008)
A Revised Procedure for the Construction of a 3-Parameter Resistance Curve and the Determination of Initiation Toughness
(Received 24 February 2006; accepted 5 March 2007)
Published Online: 2007
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Fracture toughness testing procedures often advocate the use of a 3-parameter offset power law fit to define a resistance curve, and subsequently an estimate of initiation toughness (e.g., ). Experience has indicated that the fit coefficients A, α, and β are highly variable. What is required is a consistent method of estimating A and thus α and β to reflect physical sense. In this paper it is proposed that the offset A is defined using a J-elastic term given by . Experimental data are provided in support of the use of for a well characterized A533B-1 steel. Tests were made at ambient temperature using geometrically scaled plain-sided and side-grooved compact C(T) specimens of sizes . The fixing of A through the use of provides less variable α and β parameters. The exponent β is found to be independent of W, noting that , as is the α coefficient for side-grooved specimens . The α coefficient for plain-sided specimens may be related to specimen width and thus thickness (B) for geometrically-scaled specimens, noting that approximates to . . The results indicate that the curves and thus vary with specimen width W. For conventional laboratory-sized C(T) specimens (i.e., ) the variation in with a size over this range is of the same order as the general level of scatter observed in the measurement. However, for specimen sizes outside of this range size effects may be predicted.
Technical Director, Warhelle Consulting Ltd., Lowton, Cheshire
Stock #: JTE100328
Title A Revised Procedure for the Construction of a 3-Parameter Resistance Curve and the Determination of Initiation Toughness