scope:

THE PRESENT MANUAL IS WR1TTEN AS EDUCATIONAL MATERIAL FOR non-specialists in the field of fracture mechanics. The intention is to introduce a concept that can be understood and used by engineers who have had limited exposure to elastic-plastic fracture mechanics and/or advanced statistical methods. Such subjects are covered in detail in USNRC NUREG/CR-5504 [1].

Section 2 explains why the application of fracture mechanics to ordinary structural steels has been delayed for so long. Underlying the explanation is a problem with a technical subject matter that has become, to a degree, unnecessarily esoteric in nature. The Master Curve method, on the other hand, addresses the practical design related problem of defining the ductile to brittle fracture transition temperature of structural steels directly in terms of fracture mechanics data. Section 2 describes the evolution of the method from a discovery phase to the development of a technology that can be put to practical engineering use (see Note 1).

Note 1--Section 2 denotes stress intensity factors as K_ic or K_jc. The former implies linear elastic and the latter elastic-plastic stress intensity factor properties. K_Ic also implies that larger specimens had to be used.

Section 3 explains the data validity requirements imposed on test data and the number of data required to constitute a statistically useable data set for determining a reference temperature, T_o. The temperature, T_o, has a specific physical meaning with regard to the fracture mechanics properties of a material.

Section 4 describes the test specimens that can be used to develop valid K_jc data. The recommended specimen designs optimize the conditions of constraint, while at the same time they require the least amount of test material to produce a valid K_jc fracture toughness value. Care is taken to explain why certain other specimen types would be unsuitable for this type of work.

Section 5 presents, in simple terms, the fixturing and test equipment needs. Detailed descriptions are not necessary in the present manual, since The Annual Book of ASTM Standards, Volume 03.01, has several standard methods that present detailed information on fixtures that have been used successfully for the past 30 years. However, some of the lesser-known details relative to experience in the use of this equipment for transition temperature determination are presented herein.

Section 6 covers preparation of specimens for testing. The pre-cracking operation is an extremely important step, since, without sufficient care, it is possible to create false Kjc data, influenced more by the pre-cracking operations than by accurately representing the material fracture toughness property.

Section 7 deals with test machines, their mode of operation, and recommended specimen loading rates. The usual practice of measuring slow stable crack growth during loading of test specimens is not a requirement when testing to determine K_jc values. This greatly simplifies the procedure. Post-test visual measurement of the crack growth that has occurred up to the point of Kjc instability is required, however.

Section 8 presents all of the information needed to calculate values of Kj. Some K_jc data may have to be declared invalid due to failing the material performance requirements discussed in Section 3. Contrary to the implication in other ASTM Standards that invalid data are of no use, this method makes use of such data to contribute to the solution for the T_o reference temperature. The only data to be discarded as unusable are data from tests that have not been conducted properly.

Section 9 contains the statistical equations that produce the fracture toughness, "scale parameter," for the material tested. The only complexity involved is the determination of substitute (dummy) K_j0 values, which must replace invalid K_jc values to be substituted into the calculations. The "scale parameter" is calculated and used in expressions given in Section 10 to calculate the reference temperature, T_o, which indexes the Master Curve.

Section 10 includes a second option for calculating the T_o temperature that is useable when the K_jc data have been generated at varied test temperatures. In this case, test temperature becomes an added variable in the calculation.

Section 11 shows how the variability of K_jc values is handled using the threeparameter Weibull model. Tolerance bounds that will bracket the data scatter can be calculated with associated confidence percentages attached to the bounds. Also included is reality-check information that sets limits, or truncation points, outside of which the ductile to brittle-transition (Master Curve) characterization of a material may not be represented by the test data.

Section 12 presents information on work in progress. The pre-cracked Charpy specimen, if proven to be viable for the production of fracture mechanics data, would greatly expand the applications for the Master Curve procedure. This specimen, because of its small size, taxes the limit of specimen size requirements, so that a classification of work in progress is warranted at the present time. Another subject introduced is a proposal for dealing with macroscopic metallurgical inhomogeneity of the steel being tested. Some steel products, such as heavy-section steel plate, can have fracture toughness property variations that are a significant function of the throughthickness position. The Master Curve concept, unmodified, is not well suited for dealing with such macroscale inhomogeneity. In this particular case, the recommended approach that is suggested herein is only a subject for future evaluation.

Section 13 contains a brief discussion of important considerations involved in directly applying Master Curve fracture toughness data to the fracture-safety analysis of actual structures.

Appendices taken directly from standard E 1921-03 [ 19] have been added to the present document, since they contain example problem solutions for Sections 10.1, 10.2, 11.1, and 11.3 of the present manual. These problems can be used as self educational material to familiarize the user of the manual with the computational steps involved with the determination of the Master Curve reference temperature, T_o ,