Fatigue tests were performed on low carbon steel at a rate of 2,600 load cycles per minute and at temperatures up to 700° F. All tests were conducted at a constant stress amplitude of 35,000 lb. per sq. inch. A number of specimens, usually 10, were tested at each selected temperature, and the results were analysed statistically. It was found that a peak occurred in fatigue life in the region of 450° F. There was a pronounced tendency for the scatter in life to increase as the mean life increased. Subsequent tests established that the magnitude of the observed peak depended on the amount of carbon and nitrogen in solid solution so that the effect could logically be classified as one of strain aging which takes place during the course of the test. When both carbon and nitrogen were present the peaking temperature was somewhat higher than when nitrogen alone was present, which seemed to indicate an interaction between the two types of interstitial atoms. A recently developed theory of strain aging has been applied in which carbon and nitrogen atoms are presumed to strengthen the metal by diffusing to dislocations in the crystal lattice. To apply this theory to fatigue conditions, the following assumptions were made: (1) The time available for aging was of the same order as the time of one loading cycle. (2) The distance to be travelled by the carbon and nitrogen atoms, in order to re-anchor dislocations in fatigue affected zones. was 2 x 10-6 cm. (This corresponds to the distance they travel under tensile conditions and approximates to the closest
approach of dislocations in a heavily cold worked metal.) Utilizing these assumptions. the calculated peaking temperature agreed well with the observed value. A curve was constructed of the predicted temperature for peak life over a wide range of cyclic rates.
Publisher
Department of Theoretical and Applied Mechanics. College of Engineering. University of Illinois at Urbana-Champaign
Series/Report Name or Number
TAM R 39
1967-0336
ISSN
0073-5264
Type of Resource
text
Genre of Resource
technical report
Language
eng
Permalink
http://hdl.handle.net/2142/112106
Sponsor(s)/Grant Number(s)
Office of Naval Research 54/08 Contract N6 ORI 71 04 54/08 TR 39
Copyright and License Information
Copyright 1954 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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