The effect of crack blunting in liquid metal environments on KIEAC determined by the rising load test

Abstract

KIEAC is the threshold stress intensity below which environmentally assisted crack growth does not occur. This parameter is equivalent to Klscc for stress corrosion cracking, or KILME for crack growth in molten metal environments. Two techniques frequently employed in the determination of KIEAC are the constant load and constant displacement tests. Although these tests have been used extensively in the past [1], they require substantially long testing times before reliable KIEAC values can be obtained. By using environments significantly more aggressive than those encountered in practice, the testing times can be reduced. However, this approach introduces considerable difficulties and uncertainties in the interpretation of data. In order to overcome the limitations of the constant load and constant displacement tests, McIntyre and Priest [2] proposed the use of an accelerated testing method, now commonly referred to as the rising load K~scc test. This technique is essentially identical to the procedure used for Kic fracture toughness testing [3], except that slower loading rates are used. A monotonically increasing load is applied to a pre-cracked fracture mechanics type specimen exposed to the environment of interest. The stress intensity for crack initiation is calculated from the initiation load, as determined from the point of deviation from the linear load-displacement record, and the corresponding crack length (Fig. 1). This stress intensity value is assumed to be equivalent to KIEAC.