ISO 7539-9:2021

1.1  This document specifies procedures for designing, preparing and using pre-cracked specimens for investigating the susceptibility of metal to stress corrosion cracking (SCC) by means of tests conducted under rising load or rising displacement. Tests conducted under constant load or constant displacement are dealt with in ISO 7539-6. The term “metal” as used in this document includes alloys. 1.2  Because of the need to confine plasticity at the crack tip, pre-cracked specimens are not suitable for the evaluation of thin products such as sheet or wire and are generally used for thicker products including plate, bar, and forgings. They can also be used for parts joined by welding. 1.3  Pre-cracked specimens can be stressed quantitatively with equipment for application of a monotonically increasing load or displacement at the loading points. 1.4  A particular advantage of pre-cracked specimens is that they allow data to be acquired from which critical defect sizes, above which stress corrosion cracking can occur, can be estimated for components of known geometry subjected to known stresses. They also enable rates of stress corrosion crack propagation to be determined. 1.5  A principal advantage of the test is that it takes account of the potential impact of dynamic straining on the threshold for stress corrosion cracking. 1.6  At sufficiently low loading rates, the threshold stress intensity factor for susceptibility to stress corrosion cracking, KISCC, determined by this method can be less than or equal to that obtained by constant load or displacement methods and can be determined more rapidly.