STATISTICAL MODELING FOR LOW CYCLE FATIGUE

Low cycle fatigue (LCF) is a common loading condition experienced by structural components. LCF is usually defined as the fatigue cycles to failure are less than 10(5). In order to certify and qualify a material for an application that requires high reliability for operation and safety, fundamental material properties must be experimentally investigated and validated. The well documented strain-life approach serves as the underlying experimental method for the investigation herein. The purpose of this paper is to investigate the statistical variability and appropriately model that variability for life in LCF. Specifically, the variability associated with the median behavior in a strain-life graph for data is examined. The ensuing analyses are based on data for a cold-rolled, low carbon, extra deep drawing steel; ASTM A969. ASTM A969 is intended for applications where extremely severe drawing or forming is envisioned. The probability distribution functions considered for characterizing the LCF life are taken from a generalized Weibull distribution function that empirically incorporates load history and damage accumulation. The strain-life computation employs the standard Coffin-Manson relationship.