Application of optical and electron microscopic techniques in the fractographic determination of fatigue crack growth rates

Abstract

To be presented as an overview paper on 'Fracture Surface Ana1ysis Techniques' at the Specialists Meeting on 'Fatigue Crack Topography', AGARD SMP, Siena, Ita1y 1-6 April 1984. The fractographic derivation of fatigue crack growth information is entirely dependent on the fractographer's ability to correlate accurately the striated fracture surface topography with the applied test or service loads. This paper will review some of the techniques that have been developed to acquire this type of quantitative information through the application of optical and electron microscopy. Fractographic analyses of fatigue specimens and components that have failed during laboratory and full-scale aircraft fatigue tests will be presented. These analyses will show how the identification and correlation of various fatigue load application formats, i.e. constant amplitude, programmed block, flight-by-flight and random loading, can be utilized to derive this type of experimental crack growth data.