Fatigue Under Random and Programed Loads
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION HAMPTON VA LANGLEY RESEARCH CENTER
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An investigation has been conducted to determine which combination of method counting and type of load programing best retains the essential fatigue-inducing characteristics of a random time history of stress. In an earlier investigation several time histories were numerically generated and counted by various methods. The data obtained in the earlier investigation were used in this investigation to conduct axial load fatigue tests of 2024-T3 aluminum-alloy sheet specimens with not d edges. The fatigue life obtained from tests using the random peak history was used as a basis of comparison. The elimination of various sized fluctuations, due to the different counting methods, had little, if any, effect on fatigue life in tests using a random sequence of loads. Tests conducted by using ordered loading produced lives greater than the random fatigue life. The value of life in the ordered tests varied with the counting method, with statistical properties of the time history, and probably with the assumptions made in reducing the data to block form.
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