NACA-TN-2324

Abstract

This report presents information on the axial-load fatigue behavior of unnotched specimens of each of three sheet materials: 24S-T3 and 75S-T6 aluminum alloys and normalized SAE 4130 steel. <br>The experimental investigation of these materials included the following items: <br>1. Determination of fatigue strengths, in tests at a speed of about 1100 cycles per minute, covering a range of mean loads from zero to a high tensile value and, for each loading condition, lifetimes from 10,000 to 10,000,000 cycles <br>2. Determination of fatigue strengths in tests at a slower speed of about 90 cycles per minute <br>3. Several measurements of damage or strengthening at one stress level due to previous loading at another stress level; these tests included interchanging the order of application of high stress level and low stress level <br>In several respects, fatigue test data are extended beyond those previously available. However, results are in general agreement with such previously reported data as are available for comparison, The main observation unpredictable from previous work is that fatigue strengths at 90 cycles per minute appear, in some ranges of loading, appreciably lower (up to 10 percent) than corresponding strengths at 1100 cycles per minute.