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Some Studies in the Fundamental Parameters of Fatigue


Valluri, Sitaram Rao (1954) Some Studies in the Fundamental Parameters of Fatigue. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/5Y4Z-CW45.


A torsional fatigue testing machine of the resonant vibrator type has been designed in order to investigate the fatigue and internal friction properties of 3S-O aluminum. This machine uses an elastic restraint on an a-c motor to create resonant conditions and uses a photocell electronic system for the measurement of internal friction by the method of measuring the logarithmic decrement of free oscillations. It has been established that for 3S-O aluminum at torsion stress levels below 112 psi, the stress history does not affect damping and that, for an annealed specimen, the material exhibits a maximum value of internal friction at 375[degrees]F. "Temporary mobility" aspects of the slip bands have been investigated and in addition, variation of internal friction as a function of stress amplitude in repeated torsional loading, temperature, and number of reversals has been obtained. At room temperature (75[degrees]F) the internal friction increases with the number of stress reversals in the 0 to 10[superscript 5] range. This increment in general increases with increasing amplitude of stress. At test temperatures of 225[degrees] and 525[degrees]F it was found that this increment does not show any regular variation with stress. In addition, however, it was found that at 375[degrees]F the internal friction decreases with stress reversals in the 0 to 10[superscript 5] range for all stresses. The variation of internal friction with stress history after a large number of stress reversals of the order 10[superscript 6] cycles, is quite complex, giving rise to random patterns of increase and decrease. This work is exploratory in nature and suggestions for further work are indicated.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:(Aeronautics and Mathematics)
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Minor Option:Mathematics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Sechler, Ernest Edwin (advisor)
  • Fung, Yuan-cheng (advisor)
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1954
Additional Information:Title varies in 1954 Caltech commencement program: Studies of the Fundamental Parameters of Fatigue
Record Number:CaltechETD:etd-01292004-104442
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:401
Deposited By: Imported from ETD-db
Deposited On:29 Jan 2004
Last Modified:13 Jun 2023 23:25

Thesis Files

PDF (Valluri_sr_1954.pdf) - Final Version
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