A recent proposal by Prot suggests that both the expense and the duration of fatigue tests may be lessened by a progressive load method which consists of subjecting a test specimen to a completely reversed stress whose amplitude increases regularly with time until the specimen fails. By assuming (A) that the ordinary S-N curve, when plotted on a linear scale, becomes an approximate hyperbola which is asymptotic to the vertical axis and to the endurance limit, and (b) that the material is not affected by the completely reversed stress until the amplitude of the stress 1s greater than the endurance limit, Prot shows that the stress at failure,SR, may be expressed as
where Eis the endurance limit, K is a constant for a particular material and a is the loading rate usually in psi/cycle. Plotting SR as a function of ao.so, a straight line results; the intersection of this line with the stress axis indicates the value of the endurance 11m1t. A logical modification of the above formula proposed by Henry is 1 SR= E + Ka m+l
where m 1a a constant dependent on the material. In this paper the validity of the above equations has been investigated for two materials, ingot-iron and 75S-T aluminum alloy. Conventional fatigue test data were also obtained for comparison wi~h the values of E predicted by the progressive loading tests. In general, it was found that the exponent of a that gave the best approximation to a linear plot of the experimental data was not 0.50 but approximately 0.371 and 0.1786 for the ingot-iron and 75S-T aluminum alloy, respectively. Further, the value of the endurance limit for these materials as determined by the above equations was affected by completely reversed stresses whose amplitudes were smaller than the endurance limit. Nevertheless, the method has certain inherent advantages of correlating the data for every specimen tested to determine the most probable endurance limit. FUrther studies are therefore being made of the method that will be reported at a later date.
Publisher
Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report Name or Number
TAM R 34
1967-0332
ISSN
0073-5264
Type of Resource
text
Language
eng
Permalink
http://hdl.handle.net/2142/112051
Sponsor(s)/Grant Number(s)
Office of Naval Research, U.S. Navy, Contract N6-ori-71, T.O. IV; Project NR-031-005
Copyright and License Information
Copyright 1953 Board of Trustees of the University of Illinois
TAM technical reports include manuscripts intended for publication, theses judged to have general interest, notes prepared for short courses, symposia compiled from outstanding undergraduate projects, and reports prepared for research-sponsoring agencies.
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