Axial-load fatigue tests at a stress ratio of zero were performed on notched and unnotched sheet specimens of 61S-T6 aluminum alloy and 347 and 403 stainless steels. Special emphasis was placed on tests at high stress levels which produce failures in small numbers of cycles. The stress-concentration factors effective in fatigue of notched specimens were found to be somewhat less than the theoretical elastic values at low stresses and were approximately equal to one at the ultimate strength. The minimum life to failure at stresses near the ultimate strength was drastically reduced with increasing stress-concentration factor.
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