Journal Published Online: 01 March 1991
Volume 19, Issue 2

Specimen Size Requirements for Fracture Toughness Testing in the Transition Region



The article utilizes plane strain elastic-plastic finite element analysis and a local criterion for cleavage fracture to establish specimen size requirements for the ductile-brittle transition region. Critical J and CTOD values, relative to the small-scale yielding value, were predicted as a function of specimen size, strain hardening exponent, and a/W. These analyses predict an increase in the apparent toughness with decreasing specimen size due to a loss in crack tip constraint; this effect is particularly pronounced in shallow notched specimens and low hardening materials. For deeply notched bend and compact specimens, the following size requirement must be met for critical J values for cleavage to be size independent: b,B,a>200JcσY where b is ligament length, B is thickness, a is crack length, and σγ is flow stress. This criterion is eight times more severe than the size requirements in ASTM E 813-87, but it is less stringent than the requirements of ASTM E 399-83. In order for a CTOD value to be nearly size independent, it must be less than 1/300 times the relevant specimen dimensions.

The constraint loss in shallow notched specimens is usually far too rapid to obtain J-controlled cleavage fracture, but the analyses presented in this article provide a means for correcting fracture toughness data for constraint loss. Predictions of the effect of a/W on toughness in the transition region agree favorably with experimental data.

Future work will consider the effects of specimen thickness and ductile tearing on transition region toughness.

Author Information

Anderson, TL
Texas A&M University, College Station, TX
Dodds, RH
University of Illinois, Champaign-Urbana, IL
Pages: 12
Price: $25.00
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Stock #: JTE12544J
ISSN: 0090-3973
DOI: 10.1520/JTE12544J