An investigation of the scatter in constant amplitude fatigue test results of aluminium alloys 2024 and 7075

Abstract

A brief review of some of the investigations that have been conducted in the past into the form of the distribution of constant amplitude fatigue test results is presented and is followed by an analysis of a large amount of constant amplitude data for 2024 and 7075 materials collected from a variety of sources. This analysis, in terms of a log-normal distribution of life, confirms that the amount of scatter obtained in fatigue results increases with a decrease in the alternating stress amplitude. Further, a comparison of the scatter for the two materials is made and the effects on the scatter of such parameters as notch acuity and mean stress are investigated. The discussion is in terms of a simplified model of the fatigue mechanism and indicates a possible correlation between the amount of scatter and the number of crack nuclei present in a specimen.