Improving the fatigue life of fastener holes by using cold expansion technique

Othman Ahmed, Talal Mahmood (2018) Improving the fatigue life of fastener holes by using cold expansion technique. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

Fatigue can be defined as the behavior in which the failure takes place in a material due to repetitive applications of loads subjected to that material. Fatigue constitutes a serious concern for engineers as it happens suddenly and cannot be predicted accurately. Cracks are the leading cause of the fatigue failure which happens in many engineering structures and components. Cold expansion technique is one of the techniques that has been used in the last forty years to retard the crack initiation and propagation. As a result of using this technique, the strength of material and fatigue life are improved. In this thesis, Aluminum alloy 6061 is used as the tested material. A total of 15 specimens of dog-bone shaped with centralized hole to act as the stress concentration zone are prepared based on ASTM standards to study the fatigue life before and after applying the cold expansion technique. High carbon steel is the material that was used to produce the cold expansion tools. A set of machining process need to be done in order to prepare the specimens for both tensile and fatigue tests. Three different amount of interferences, which are 1.5% , 2.2% and 2.9%, are generated to study the impact of cold expansion process. The fatigue tests are conducted by using INSTRON 8802 universal testing machine and the test is run at 0.1 stress ratio and 10Hz resonant frequency. The results obtained from this study are shown in tables and plotted in the form of S-N curve. The findings indicated a remarkable improvement in the fatigue life when the interference is 2.2%. In contrast, there is a decrease in the fatigue life when the interferences are 1.5% and 2.9% respectively.

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