An intraspecimen method for the statistical characterization of stress corrosion crack initiation behavior

Abstract

The life of a structural component susceptible to stress corrosion cracking (SCC) can be expressed as the sum of an initiation time and a propagation time. Because the SCC initiation time, in particular, has a large scatter, it is often described by a Weibull model. To produce a statistically significant number of data from limited tests, a specimen area with a uniform condition is divided into smaller intraspecimens. Requirements of minimum surface area for an intraspecimen are established by Monte Carlo simulation to ensure equivalent maximum normal grain boundary stress between intraspecimens. SCC tests have been conducted to test the viability of the intraspecimen method using a sensitized Alloy 600 loaded by the four-point bending method in 0.1 M sodium tetrathionate (Na2S4O6.2H2O) solution at 40°C. It is demonstrated that a Weibull model can be obtained from a single test using the intraspecimen method. Using the weakest link theory, a new area-dependent Weibull model is developed to characterize the increase of crack initiation probability with specimen size observed in measured data. It is recommended that a specimen be designed to minimize the effect of stress relaxation caused by significant crack growth in adjacent intraspecimens.