Valluri, S. R. (1954) Some studies in the fundamental parameters of fatigue. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-01292004-104442
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.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Engineering and Applied Science|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||1 January 1954|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||29 Jan 2004|
|Last Modified:||26 Dec 2012 02:29|
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