SYMPOSIA PAPER Published: 01 January 1993

Effect of Constraint on Specimen Dimensions Needed to Obtain Structurally Relevant Toughness Measures


This study examines the feasibility of predicting the fracture toughness for structurally relevant situations (shallow cracks in thick plates) based on toughness values measured with experimentally convenient specimen geometries (deep cracks in small specimens). The cleavage fracture toughness, Jc, of ASTM A515 Grade 70 steel plate was measured using single edge notch bend specimens. Specimen size and initial crack depth were varied to obtain Jc values over a range of constraint conditions. The results of these experiments indicate that crack depth and thickness cannot be traded off against each other to achieve the same constraint and thereby the same fracture toughness. The absence of this simple trade-off is due to the greater effect of crack depth than of specimen size on Jc and to the scatter in fracture toughness data characteristic of temperatures in the transition range. Alternative techniques for determining structurally relevant toughness measures from specimens based on recently proposed constraint parameters were therefore examined. These various parameters divide into two categories: those which index constraint and those which correct for constraint. Application of these constraint parameters to the A515 data indicate that all of the currently proposed techniques can account for the constraint-induced changes in cleavage fracture toughness. However, the feasibility of applying these techniques during a structural fracture safety assessment depends upon the experimental complexity and cost associated with fracture toughness determination and the ease with which the constraint parameter can be calculated for a structure.

Author Information

Kirk, MT
University of Illinois, Urbane, IL
Koppenhoefer, KC
University of Illinois, Urbane, IL
Shih, CF
Brown University, Providence, RI
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Developed by Committee: E08
Pages: 79–103
DOI: 10.1520/STP18024S
ISBN-EB: 978-0-8031-5229-8
ISBN-13: 978-0-8031-1481-4