Existence of the coaxing effect and effects of small artificial holes on fatigue strength of an aluminum alloy and 70-30 brass

In order to study the existence of the coaxing effect and the effects of small defects on the fatigue strength of an aluminum alloy and 70-30 brass, plain specimens and special holed specimens containing one or more very small drilled holes with diameters of 40,50,100,200, and 500 ώm were prepared. Contrary to commonly accepted knowledge, the existence of a distinct coaxing effect was confirmed in the fatigue test on 2017-T4 aluminum alloy. However, the coaxing effect was not confirmed in the fatigue test on 70-30 brass, though specimens with small artificial holes could contain non-propagating cracks at the fatigue limit. It was found that the appearance of the coaxing effect depends on the endurance at a higher stress level of small cracks initiated at a lower stress level. The very small drilled holes with diameters of 40 and 50 ώm had no harmful effect on the fatigue strength of both the aluminum alloy and 70-30 brass; that is, the fatigue limits of specimens containing one or more drilled holes with diameters of 40 and 50 ώm were identical with those of the plain specimens.