Fatigue behaviours in aluminum and 2024-T 3 aluminum alloy were investigated. The fatigue test was carried out with a sheet specimen loaded repeatedly at various stress levels. It has been found that the direcrional change in mechanical properties of the tested sheet materials and the change in size of a fatigue specimen have no appreciable effects on the S-N curves. It has been observed that fatigue cracks propagate along the principal stress plane in 2024-T 3 aluminum alloy, but along the principal shear stress plane in pure aluminum. In the case of repeated stress cycle test at tension levels, a single crack was nucleated and grew to fracture, however, in the case of reversed cycle test a number of small cracks were nucleated, and then a single crack was formed linking them. The length of propagating fatigue crack was related exponentially to the number of stress cycles in the repeated stress cycle test, but no simple relationship was found in the reversed stress cycle test. Metallographic observations also have been made to investigate the inception of fatieue cracks.
航空機用アルミニウム合金の疲労によるクラックの発生と伝ぱ(1)
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