The Fatigue Crack Growth under Variable Amplitude Loading in Built-up Structures

摘要

Seventy-four specimens, made of 2024-T3 aluminum alloy, were tested both at constant and variable amplitude loading. The specimens were both simple sheets and riveted stiffened panels. The constant amplitude tests on simple sheet specimens were conducted in order to obtain the average K-rate relationship and the relevant scatter of the batch of sheets. The constant amplitude tests of stiffened panels aimed at obtaining information on the overall junction flexibility. Variable amplitude tests were performed utilizing three standard fatigue spectra, like FALSTAFF, MINITWIST, and Gaussian random. The data from sheet specimens was used to assess the reliability of prediction methods such as those devised by Wheeler and Willenborg, and the stiffened panels test data to evaluate how these methods work in the case of built-up structures. Some general conclusions on the reliability of the crack growth prediction methods have been obtained treating on statistical basis the data collected in the current year, as well as in the previous year's research activity. To this end, data from variable amplitude tests, irrespective of the type of spectrum and of the material, has been collected and analyzed in order to evaluate in this respect the methods proposed by Willenborg and by Wheeler. The results are quite interesting, because they allow to evaluate the scatter associated with most of the parameters involved in crack growth predictions.