Nesterov, Alexey (2006) The effects of corrosion, cold expansion and interference fit on the fatigue of aluminium alloy specimens containing fastener holes. (PhD thesis), Kingston University, .
Abstract
One of the most vulnerable areas for the initiation and propagation of fatigue cracks in aircraft structures is in the region of fastener holes. To reduce the incidence of fatigue cracking a number of methods have been developed which introduce residual stresses or induced stress fields at the fastener holes. Of these methods, two of the most widely used in the aerospace industry involve the use of interference-fit fasteners or a procedure for cold working the fastener holes. This investigation studies the effect of these two technologies on the fatigue performance of specimens manufactured from 2024-T351 aluminium alloy. The effect of exposure of the specimens to corrosion damage was also investigated. Fatigue tests were carried out on flat plate specimens containing open plain holes and open cold worked holes as well as on plain hole and cold worked hole specimens containing interference fit pins. The fatigue crack growth in the specimens was investigated under constant amplitude sinusoidal loading at a stress ratio of R=0.1 and a frequency of 10Hz. A proportion of the specimens were subjected to controlled corrosion exposure prior to testing. Crack Growth Rate (CGR) diagrams were constructed from these experimental results and an analysis made of crack initiation, crack propagation rate and total life. Crack Growth Rate models were developed based on the assumption that the dependence of CGR vs effective Stress Intensity Factor (SIF) for this material are not affected by residual stresses in the material. Crack opening stress distributions were derived from experimental crack growth rate data which were also confirmed by experimental data obtained by other investigators previously. The beneficial effects of cold expansion and interference fit on fatigue performance were confirmed in plain and corroded specimens. Cold expansion treatment combined with the use of an interference fit fastener gave the greatest benefits in fatigue performance for the specimens tested including improvements in both crack initiation and propagation stages and in the total fatigue life. The effect of corrosion was found to be detrimental for both cold worked and plain specimens but was less severe for cold worked samples in comparison with plain untreated specimens.
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