An alternative method for small pop-in assessment

Fracture mechanics tests of welds and ferritic steels in the brittle to ductile region often show a phenomenon called pop-in, a process df trigger and arrest of a-brittle crack. Regarding pop-in initiation as a critical event results in too conservative values of fracture toughness. Different pop-in. treatment proposals taken from the literature are analyzed in this paper. The degree of conservatism of the pop-in assessment procedures issued in some fracture toughness test standards is also analyzed. An alternative proposal for the analysis of the pop-in significance in SENB CTOD tests is introduced. This method is based on the change in elastic compliance, and;it allows the evaluation of any pop-in, even those that are preceded by ductile crack growth or previously ignored pop-ins. The relaxation of the maximum pop-in crack extension implicit in both ASTM and BSI procedures (Delta a(p) < 2%b(0)) by the Willoughby criterion of Delta a(p) < 4%b(0) is also proposed. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.