Journal Published Online: 12 November 2007
Volume 36, Issue 1

A Revised Procedure for the Construction of a 3-Parameter Resistance Curve and the Determination of Initiation Toughness



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., J0.2 ). JR =A+α (Δa) β . 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 Je given by A= Je =W/2( σy2 E )f ( ao W) . Experimental data are provided in support of the use of Je 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 20<W<200 mm . The fixing of A through the use of Je provides less variable α and β parameters. The exponent β is found to be independent of W, noting that βSG < βplain , as is the α coefficient for side-grooved specimens ( αSG ) . The α coefficient for plain-sided specimens ( αplain ) may be related to specimen width and thus thickness (B) for geometrically-scaled specimens, noting that α approximates to αSG . αplain = α (1+1 B ) . The results indicate that the JR curves and thus J0.2 vary with specimen width W. For conventional laboratory-sized C(T) specimens (i.e., 25<W<100 mm ) the variation in J0.2 with a size over this range is of the same order as the general level of scatter observed in the J0.2 measurement. However, for specimen sizes outside of this range size effects may be predicted.

Author Information

Wardle, Graham
Warhelle Consulting Ltd., Lowton, Cheshire, UK
Pages: 9
Price: $25.00
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Stock #: JTE100328
ISSN: 0090-3973
DOI: 10.1520/JTE100328