Existing exact knowledge on fatigue crack growth parameters and characteristics is an essential condition for an application of Damage Tolerance design philosophy in dynamically loaded structures. Measurement of fatigue crack growth (FCG) rates in an Al 7175-T7351 alloy of a particularly high homogeneity was carried out as a part of the Proficiency Test Programme organised by Exova in France. Results were evaluated in terms of parameters C and m of the Paris dependence in the stable growth region. To pass the test programme successfully, a particular attention was paid to improve and verify DCPD (direct current potential drop) method being used for the crack length measurement. The attention paid to the experimental methodology bored fruit - the results obtained were close to the average of results measured at different accredited worldwide aircraft laboratories. Additionally, the results of the FCG measurements generated by different participating laboratories were further analyzed. A distinct correlation between C and m values, so called “coupling”, was found and demonstrated. Some paradoxes of the assessment of laboratories were addressed, namely the fact that a laboratory assessed as unacceptable concerning one of the parameters generated much more accurate and useful data than another laboratory with a better assessment. Eventually, the results including their scatter were used to provide an example of probabilistic assessment of a simple beam residual life to show practical actual impacts of the scatter on the life assessment.Keywords: Fatigue crack growth, Proficiency Test Programme, Al 7175 alloy, probability assessment
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